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ADDIS ABABA UNIVERSITY SCHOOL OF GRADUATE STUDIES
INSTITUTE OF TECHNOLOGY DEPARTMENT OF CHEMICAL ENGINEERING
EEFFFFEECCTT OOFF PPRROOCCEESSSSIINNGG OONN SSOOMMEE QQUUAALLIITTYY AATTTTRRIIBBUUTTEESS OOFF MMAANNGGOO ((MMaannggiiffeerraa iinnddiiccaa)) FFRRUUIITT
LLEEAATTHHEERR
By
BINYAM TESHOME
A Thesis submitted to the school of Graduate Studies of Addis Ababa University in partial fulfillment of the Requirements for the Degree of
Master of Science in Chemical Engineering (Food Engineering)
Advisor: Mr. Adamu Zegeye
May, 2010
Addis Ababa
Ethiopia
i
ADDIS ABABA UNIVERSITY SCHOOL OF GRADUATE STUDIES
INSTITUTE OF TECHNOLOGY DEPARTMENT OF CHEMICAL ENGINEERING
EEFFFFEECCTT OOFF PPRROOCCEESSSSIINNGG OONN SSOOMMEE QQUUAALLIITTYY AATTTTRRIIBBUUTTEESS OOFF MMAANNGGOO ((MMaannggiiffeerraa iinnddiiccaa)) FFRRUUIITT
LLEEAATTHHEERR
By
Binyam Teshome
Approved by the Examining Board: _____________________ ___________________
Chairman, Departments Graduate Committee
Mr. Adamu Zegeye ___________________
Advisor
Dr. Cherinet Abuye ___________________
External Examiner
Dr. Eng. Shimelis Admassu ___________________ Internal Examiner
ii
Acknowledgment
I would like to forward my deepest gratitude to my advisor Mr. Adamu Zegeye for his keen interest
in my thesis work, follow up of my progress, encouragement and support.
I acknowledge Addis Ababa Institute of Technology for the financial support. I am also grateful to
the academic staff of the Department of Chemical Engineering for imparting tremendous
knowledge to me. I appreciate Dr. Eng. Shimelis Admassu for his constant supervision and
recommendation during my project work. Thanks to the Ethiopian Health and Nutrition Research
Institute (EHNRI) for letting me use their food analysis laboratory and facilitating my research,
especially Dr. Cherinet, Ato Adamu and Israel. Ethiopian Et-Fruit Company is also appreciated for
providing the mango varieties used in this research. I thank all the technical staff of my
Departments laboratory, particularly, Ato Hintsasilase Seifu and also Yeshihareg Nesibu for
providing me all the necessary support during the research.
Equally and importantly, I would like to acknowledge all family members particularly Girum
Teshome and my dearest wife Hayley Teshome, who contributed towards my success with their
financial support and encouragement in the course of this research, and also honor my friends who
shared my idea when I was in need.
iii
Table of Contents
CHAPTER Title Page
Title Page i
Acknowledgment ii
Table of Contents iii
List of Tables vi
List of Figures viii
List of Abbreviations ix
Abstract x
1 INTRODUCTION 1
1.1. Background 1
1.2. Statement of the problem 3
1.3. Objectives 4
1.4. Structure of the thesis 5
2 LITERATURE REVIEW 6
2.1. Production and marketing of Mango fruits in Ethiopia
2.1.1 Exporting Mango fruits
6
7
2.1.2 Mango value chain analysis in Ethiopia 8
2.1.3 Asossa market 9
2.1.4 Addis Ababa market 9
2.2 Processing of Mango fruits in Ethiopia 12
2.3 Selected Mango varieties for processing 13
2.4 Medicinal uses and by-products of Mango 14
2.5 Mango processing technologies 14
2.5.1 Ripe Mango processing 16
2.6 Fruit leather processing 17
2.6.1 Preparation of fruits 17
2.6.2 Heating, drying and packaging 18
2.7 Mango fruit leather recipes and processing procedures 19
iv
2.7.1 Adding sweeteners and flavoring to fruit leather
2.8 Quality control
2.9 Effect of processing on food quality attributes
2.9.1 Physicochemical properties
2.9.2 Changes on Vitamins
2.9.3 Flavor and pigment components
2.9.4 Sensory attributes
2.9.5 Influence of drying process
2.10 Food safety
20
20
22
23
24
26
29
30
31
3 MATERIALS AND METHODS
32
3.1 Raw material source and equipment 32
3.2 Approach for selection and preparation of Mango fruits 32
3.3 Development of Mango fruit leather 33
3.3.1 Raw material preparation and formulation of the puree mix 33
3.3.2 Heating and drying the puree mix 34
3.4 Methods for studying the effect of processing 37
3.4.1 Effect of processing on drying time 37
3.5 Quality parameters for studying the effect of processing 38
3.5.1 Proximate analysis methods for the puree and leather 38
3.5.2 Physicochemical analysis 41
3.5.3 Texture analysis of the Mango leather 42
3.5.4 Microbiological analysis 43
3.5.5 Sensory evaluation 44
3.6 Experimental design and data analysis 44
4 RESULTS AND DISCUSSION 45
4.1 Physicochemical properties of Mango puree 45
4.2 Proximate analysis results of the Mango puree and puree mix 46
4.2.1 Keitt Mango variety 47
4.2.2 Tommy Atkins Mango variety 47
v
4.3 Effect of heating temperature on viscosity of Mango puree mix 48
4.3.1 Keitt Mango variety 49
4.3.2 Tommy Atkins Mango variety 50
4.4 pH of the puree mix 51
4.5 Effect of drying on the proximate and Vitamin C content of fruit
leather
51
4.6 Effect of temperature and puree load on drying time 52
4.6.1 Drying characteristics of Mango puree mix 52
4.6.2 Analysis of moisture loss during drying process 53
4.7 Texture analysis of the Mango leather 54
4.8 Proximate analysis of Mango fruit leather 55
4.8.1 Moisture content 56
4.8.2 Protein content 57
4.8.3 Fat content 57
4.8.4 Crude fiber content 58
4.8.5 Ash content 58
4.8.6 Carbohydrate content 59
4.8.7 Effect of processing on Vitamin C content of Mango leather 59
4.9 Microbiological analysis of Mango fruit leather 60
4.10 Sensory analysis of Mango fruit leather 61
4.10.1 Effect of drying temperature, puree load and fruit varieties
on the sensory qualities
61
5 SUGGESTED TYECHNOLOGY FOR MANGO LEATHER
PROCESSING
66
5.1 Process description 66
6 CONCLUSIONS AND RECOMMENDATION 94
6.1 Conclusion 94
6.2 Recommendation 96
REFERENCES 97
ANNEXES 102
vi
List of Tables
Chapter Table Title Page
2 2.1 Estimate of area, production and yield of Mango fruits 6
4 4.1 Physico-chemical properties of fruit pulp for the mango varieties 45
4.2 Proximate analysis result for Keitt and Tommy Atkins varieties of
Mango puree and puree mix 46
4.3 Results of viscosities for Keitt and Tommy Atkins variety mango
puree mixes measured at different heating temperature 48
4.4 Proximate analysis result for Mango fruit leathers 51
4.5 Designed sample codes for both varieties of mangos with drying
temperature and puree load 52
4.6 Effect of drying air temperature and puree load on drying time of
Keitt Mango fruit leather 53
4.7 Weights and moisture loss of Keitt variety mango leather 53
4.8 Results of compression test using Texture Analyzer to different
number of Mango leather sheets (layers) 54
4.9 Effect of temperature on proximate composition of mango leather 55
4.10 Effect of puree load on proximate composition of mango leather 55
4.11 Effect of fruit variety on proximate composition of mango leather 56
4.12 Effect of drying temperature, puree load and fruit variety on
vitamin C content 59
4.13 Result of microbiological analysis of mango fruit leather 60
4.14 Effect of drying temperature on sensory qualities 61
4.15 Effect of puree load on sensory qualities 61
4.16 Effect of fruit variety on sensory qualities 62
4.17 Proximate and physicochemical composition of Mango and puree 68
4.18 Specific heat relationships for food product components 73
4.19 Recipes, calculations and amount of ingredients for making
Mango leather 85
4.20 Typical losses during processing of fruits and vegetables 86
vii
4.21 Machinery and equipment required for mango leather production 88
4.22 Manpower requirement for Mango leather production 89
4.23 Raw material costs for Mango leather production 89
4.24 Cost of utilities for Mango leather production 90
4.25 Fixed capital cost estimation for Mango leather production 91
4.26 Estimation of total product cost for Mango leather 92
viii
List of Figures
Chapter Figure Title Page
1 1.1 Structure of the thesis 5
2 2.1 Wholesale Mango market in Addis Ababa Market share by region 10
3 3.1 Process flowchart for Mango leather processing 36
4 4.1 Viscosity verses temperature of Keitt variety puree mix 49
4.2 Viscosity verses temperature of Tommy Atkins variety puree mix 50
4.3 Qualitative flow diagram for Mango leather processing 67
4.4 Quantitative flow diagram for mango leather processing 78
4.5 Quantitative flow diagram for daily production of mango leather 80
4.6 Equipment layout for mango leather processing 81
ix
List of Abbreviations
AAU Addis Ababa University
AMARI Awash Melkasa Agricultural Research Institute
AOAC Association of Official Analytical Chemists
BAM Bacteriological Analytical Manual
CIA Central Intelligence Agency
CSA Central Statistical Authority
EHNRI Ethiopian Health and Nutrition Research Institute
ETB Ethiopian Birr
Et-Fruit A state owned Ethiopian Fruit Marketing Agency
FAO Food and Agriculture Organization
FDA Food and Drugs Administration
GTZ Gesellschaft fr Technische Zusammenarbeit
LSD List Significance Difference
MC Moisture Content
ppm parts per million
RH Relative Humidity
SPSS Statistical Package for Social Scientists
TCA Trichloro Acetic Acid
TSS Total Soluble Solid
UAE United Arab Emirates
USD United States Dollar
USDA United States Drug Administration
x
Abstract
The seasonal production of mango fruit in Ethiopia has to be considered as an opportunity for the
utilization of the fruit. The objective of this research was to study the influence of processing on
some quality attributes of mango fruit leather developed from two fruit varieties namely, Keitt
(local mango) and Tommy Atkins (export standard mango). First, 3.2 kg of mango fruit from both
varieties were allocated for the process to be peeled, cut, sliced into pieces and stones removed.
Mango puree was made using a food processor to obtain 1.65 kg puree. It was put in a beaker and
covered with aluminum foil and then inserted into a water bath fitted with thermostat to control the
temperature. Additional ingredients of Honey, Ginger and Lemon Juice were added and mixed. In
order to cook and shorten the drying time, the mixture was heated at three different temperatures,
600C, 700C and 800C whilst being continuously stirred. The puree mixture was poured onto the
trays to an approximate thickness of 0.64 cm. The trays containing the puree were placed in a
drying oven. Oven drying was conducted for 8 h and finally 0.52 kg of mango leather was obtained.
Drying experiment was also undertaken using convective hot air dryer to minimize the drying time
of the fruit leather using a similar procedure. A minimum drying time of 4 h was achieved in a
convective hot air dryer for Keitt mango fruit leather at 800C with 0.4 g/cm2 puree load. The major
factors considered to have an effect on the leather quality were drying temperatures of 600C, 700C
and 800C, puree load of 0.4 g/cm2 and 0.6 g/cm2 and fruit variety. The developed leather underwent
physico-chemical, textural, microbiological and sensory analysis. The data obtained was analyzed
using SPSS version 17 statistical software. The result indicated that 70.3 % of moisture loss
resulted in the drying process. The viscosity of the mango puree was found to be dependent on
heating temperature. As the temperature increased, the viscosity of the puree first decreased and
then increased within the range of temperature 25.1 to 70.0 0C. The texture analysis result of the
final mango leather showed that 4 sheets and 5 sheets of leather with 5mm and 6mm thickness,
respectively, were found to be suitable for a single bite. The results of the proximate analysis for
both varieties of mango fruit leather indicated that the processing affected the nutritional
composition of the fruit leather. The vitamin C content was also found to be dependent on all
drying temperature, puree load and fruit variety. The vitamin C content of the Keitt mango leather
(26.93%) is greater than that of Tommy Atkins mango leather (22.71%). When compared to the
fresh puree mix, the Keitt mango leather is decreased by 39.66% and that of the Tommy Atkins
mango leather is decreased by 57.82%. The result of microbiological analysis for yeast, coliform,
xi
fecal coliform, E.coli, and Shigella species was found to be safe (
1
CHAPTER 1
INTRODUCTION
1.1 Background
Mango (Mangifera indica L) is a highly seasonal tropical fruit, very popular among millions of
people in the tropics. It also occupies a prominent place among the best fruits of the world.
However, it is in constant demand, there is a pre-harvest scarcity and at times a post-harvest glut
for this fruit. To increase the availability of this fruit throughout the year, the surplus production
must be processed into a variety of value-added products (Saxena and Arora, 1997; Srinivasan et
al., 2000; Singh et al., 2005). Dried mango products could successfully serve this purpose.
Mangos can be processed into a number of unique products such as dried mango pieces, chutney
and mango leathers (Azeredo, et al., 2006). Processing of mangos enables exporters to serve their
markets even during off season periods for fresh fruits. Mangos are a highly nutritious fruits
containing carbohydrates, proteins, fats, minerals, and vitamins, in particular vitamin A (beta
carotene), vitamin B1, vitamin B2, and vitamin C (ascorbic acid). As the fruit ripens, concentrations
of vitamin C decrease and glucose, fructose, and sucrose concentrations increase (Bally, 2006).
Drying of agricultural products is the oldest and widely used preservation method. It involves
reduction as much water as possible from foods to arrest enzyme and microbial activities hence
stopping deterioration. Moisture left in the dried foods varies between 2-30% depending on the
type of food. In tropical countries, solar dryers can be used to dry fresh produce when average
relative humidity is below 50% during drying period. Drying lowers weights and volume of the
product hence lowers costs in transportation and storage. However, drying allows some lowering in
nutritional value of the product e.g. loss of vitamin C, and changes of color and appearance that
might not be desirable (GTZ, 2009).
Fruit leathers are dried sheets of fruit pulp which have a soft, rubbery texture and a sweet taste.
They can be made from most fruits, although mango, apricot, banana and tamarind leathers are
amongst the most popular. Leathers can also be made from a mixture of fruits. Fruit leathers are
made by drying a very thin layer of fruit puree and other ingredients to produce a leathery sheet of
dried fruit with a texture similar to soft leather (Andress & Harrison, 1999). They may be eaten as
snack foods as a healthy alternative to boiled sweets and also used as ingredients in the
2
manufacture of cookies, cakes and ice cream. Fruit leathers are often targeted at the health food
market, using marketing images such as pure, sun dried, and rich in vitamins.
Mango leather is a traditional product prepared from sound ripe mango. Traditionally, sun drying is
the process employed for preparing mango leather from ripe fruit pulp. However the sun-dried
product is discolored and the process is unhygienic and lengthy. Cabinet drying has been carried
out for making mango leather (Heikal et al., 1972; Mir and Nath, 1995) resulting into a product
with improved color and flavor.
The preservation of fruit leathers depends on their low moisture content (15-25%), the natural
acidity of the fruit and the high sugar content. When properly dried and packaged, fruit leathers
have a shelf life of up to 9 months (FPT, 2009). Although fruit leather is a relatively well
established product overseas, few studies have been published about this kind of product. Most of
the studies utilize not only fruit purees in the fruit leather, but also other ingredients (especially
sugars) and additives. For instance, Chan and Cavaletto (1978) prepared papaya leathers with
sucrose and SO2. They observed that SO2 reduced changes in the colour of papaya leathers during
both processing and storage. Che Man, et al., (1992) prepared sapota leathers from sapota puree,
sucrose, rice flour, sorbic acid, and sodium metabisulphite; the leathers were shelf-stable for 3
months. Jackfruit leathers with added sucrose and sorbic acid were produced by Che Man and
Taufik (1995); the product remained stable for 2 months. Irwandi, et al., (1998) produced 12-week
stable durian leathers from a formulation including sucrose and sorbic acid. Vijayanand, et al.,
(2000) produced 3-month shelf-stable guava leathers with sucrose and metabisulphite. Mango
leather products have very low protein content (12%). Therefore several studies have increased
protein content in the mango leather by adding shrimp flour and rice flour, whey protein isolate and
soy protein isolate (Exama & Lacroix, 1989; Payumo, et al., 1981; Chauhan, et al., 1998). All the
above-mentioned studies reported good consumer acceptance of the fruit leather product.
3
1.2 Statement of the problem
Mango puree and leather products are largely unknown in Ethiopia, but may have good potential
for a number of reasons. According to Kadir (2009) the current postharvest loss of mango fruits in
Ethiopia is more than 26.3%. However, there is a growing international demand for dried mango
fruits and mango fruit leathers. Consequently the abundant supply of mango fruit in Ethiopia could
be utilized to create new products (including organic fruit leathers) for this overseas market.
The expansion of the bakery industry has created a demand for new ingredients, for cake
production, which are imported and are relatively expensive. Mango fruit leather, produced locally,
could be utilized as a cheaper alternative ingredient. There is also a growing consciousness over the
negative effects of sugar confectionery on dental health and at present there are few alternatives for
concerned parents to give to their children. Therefore, fruit leather products would be a more
acceptable healthy alternative. The current drying method used widely for making fruit leathers is
use of electrical oven and convective hot air drying. The drawback of hot air drying method is a
long drying time and the controlling of drying conditions (including increasing drying temperature,
decreasing initial moisture content of the puree and so on) will result in the quality of the mango
fruit leather. The technology of electrical oven drying method had long been employed to extend
the shelf life of foods. However, there is an urgent need to conduct basic studies to investigate the
effects of processing on the total drying time and some qualities of the mango fruit leather to
optimize the process and set up the processing industry.
The quality of mango fruit leather and the total drying time is directly affected by the drying
method, type of dryer, oven design and operating parameters. These parameters must be well
established and controlled for each type of fruit leathers. In the production of mango fruit leathers,
the puree making process and mixing with other ingredients, the drying temperature, and the puree
load on each tray during drying, the total drying time, packaging of the product and appropriate
storage conditions should be well established for high quality product. In this study, the effects of
processing on some qualities of mango fruit leathers and the total drying time taken are
investigated.
4
1.3 Objectives
The general objective of the thesis work is to study the influence of processing on some quality
attributes of mango fruit leathers.
The specific objectives of the thesis are to:
Produce fruit leather from locally grown mangos
Conduct physico-chemical analysis of both raw and processed product
Study the effect of processing on the qualities of the fruit leather
Suggest a manufacturing process for mango leather production
Significance:
The study is believed to be significant in that it will:
Reduce postharvest loss of mango fruit in Ethiopia
Produce the best quality mango leather products
Reassure the consumer that the mango leather product is safe for consumption
Optimize the processes for production of good quality mango leather products
Scope:
The study generally covers:
The processing method for production of mango fruit leather
Development of mango leather
Laboratory analysis majorly on: Physico-Chemical Analysis, Proximate Analysis (Nutritional Composition Analysis), Microbiological Analysis
Sensory Evaluation
Suggestion of technology and economic analysis
5
1.4 Structure of the thesis
Fig. 1.1 Structure of the thesis
6
CHAPTER 2
LITERATURE REVIEW
2.1 Production and marketing of Mango fruits in Ethiopia
The Ethiopian government has a plan to expand mango production by distributing high yielding
varieties for small scale farmers, especially in the Southern and Oromia region, by grafting mangos
of known and high yielding varieties. In July 2006, it was announced that the Oromia Government
distributed 14,000 improved seeds of mango. The production of mango fruits for the past six years
in Ethiopia was considered for the study which was found from CSA (2009), and is summarized
and presented below in Table 2.1. With an increase in Ethiopian mango crop production and
considering the current postharvest loss of mango fruits is at 26.3%, there is not only a need but
also a potential for the fruit to be processed into various product types, consequently increasing the
market potential of the mango fruit (Kader and Truneh, 2009). Industrial processing opportunities,
to increase the market value of the initial fruit, may lead to the potential development of the
following products:- Food (mango juice and fizzy drinks, canned fruits and pulp, fruit leather, dried
pieces, jam and chutney), domestic (mango detergent and cleaning agents), beauty (as an applied
product in skin creams products).
Table 2.1 Estimate of area, production and yield of Mango fruits, Meher season
Year Number of
holders
Area in
hectare
Production in
quintal
Yield
(qt/ha)
2003/04 (1996) E.C 350,067 4,964.00 292,283.00 58.88
2004/05 (1997) E.C 414,574 5,814.00 301,715.00 51.89
2005/06 (1998) E.C 463,868 5,400.31 547,291.24 104.06
2006/07 (1999) E.C 558,976 6,796.10 626,111.83 94.08
2007/08 (2000) E.C 695,030 6,730.83 484,360.97 71.96
2008/09 (2001) E.C 716,447 6,051.00 441,582.00 72.97
7
2.1.1 Exporting Mango fruits
At present, very little mango is exported from Ethiopia with only 4 tonnes exported in 2006 at a
value of less than US$1000 according to FAO. This represents a significant decline since 2002
when 811 tonnes were exported at a value of US$675,000 (US$832 per tonne). This appears to
have been a particularly high value year however, as the longer term average price for mango
exports has been approximately US$323 per tonne. Anecdotal information from key informants
suggested that one of the main reasons for the drop in mango exports has been the variable quality
of Ethiopian mango exports on arrival in overseas countries. It was reported that Et-Fruit (the state
owned Ethiopian Fruit marketing agency) had been exporting mangoes to countries such as
Djibouti, Saudi Arabia and UAE but had lost some of those contracts due to the poor quality of the
shipments on arrival. This situation highlights the key challenges faced in trying to develop the
export market for Ethiopian mangoes: Under-developed packaging and cold chain for exporting,
High cost of freight to overseas countries, Competing product from Egypt and South Africa and
Minimal production of commercial varieties
In order to begin considering export markets as a viable opportunity, it is essential to consider the
nature of demand in export markets. It is very clear that overseas markets are increasingly
demanding higher quality, commercial varieties of mangoes, and are also becoming more
sophisticated in their preferences for products that are organic. In Asossa then, the first step to even
consider export markets would be to begin growing more commercial varieties such as Kent, Keitt
and Tommy Atkins. Even if the export market was not a viable option in the short term, these
commercial varieties would present a better alternative to the domestic market with less fiber and
higher levels of sweetness than existing hybrid varieties (FAO, 2009).
In Ethiopia, the domestic market, consumption is largely in its fresh form due to the fact that the
cost increment for processing and packaging would make it beyond the purchasing power of the
vast majority of the Ethiopian consumer group (low-income). However, since 1997 the demand for
canned fruits in Ethiopia has increased by 7% suggesting there is a sufficient domestic market for
canned mangoes to be produced. The mango export markets are where the greatest growth
potentials exist for mango producers. The global mango markets are supplied by countries that are
strategically positioned to be preferred suppliers. For example, West Africa is a key supplier to
Europe due to its proximity to Europe and direct sea-links (Truneh, 2009).
8
2.1.2 Mango value chain analysis in Ethiopia
Ethiopia is a country that is often associated with famine and food shortage. Whilst this perception
is the reality for much of the country at certain times, there are also regions within Ethiopia that are
well suited to producing a surplus for particular agricultural commodities. One such location is the
Asossa Homosha region in western Ethiopia, which is particularly suitable to the production of
mangoes. In a 2006 study, it was estimated that as much as 28% of the mangoes sold in the capital
Addis Ababa, were grown in the Asossa region (WAFC, 2006).
Though the immediate market is small, there is a short and established value chain to Addis Ababa
via a 700 km trip. Typically, Asossa exports between 150-300 (10-ton) truckloads of fruit per
season to various regions, principally Addis Ababa. In spite of the high cost of imported fruit,
nationally the volume has risen by 100% in the last seven years, while that of imported juices has
more than doubled in the last four years, evidence of an up-scaling market. The farm-gate price of
mangoes in Asossa ranges from 0.25 to 1.15 Birr/kg while the retail price is approximately 5 Birr
per kg in Addis, compared to 10 Birr per kg of other imported whole fruits. Farmers typically
achieve approximately 5 to 8% of the final retail price (at lower levels) giving them about
1,400Birr in annual income, while wholesalers get about 30% of it but meet the high transport
costs. Analysis reveals a reasonably resilient subsector with a favored market position of the
Assosa mango regional brand. Also, the region appears to have a comparative advantage with
ideal growing conditions for mangoes and high yielding trees. At the production level however, the
value chain is quite rudimentary with mainly subsistence level cultivation, harvesting and post-
handling techniques that limit the quality of the fruit. Upstream there are also issues with most
grading and packaging being undertaken following a long road journey to the capital, undermining
not only the quality of fruit but also the potential value generated at the farmer level. At the
wholesale level in Addis Ababa, market traders dominate the landscape and operate in ways that
make it difficult for new entrants to enter the market. Addis wholesalers have strong relationships
with the traders based in Asossa and these two levels of the value chain account for most of the
final retail price. Given the roles they play, it appears that there is not a proportionate addition of
value in the chain, and that is where opportunities lie for improving farmer level value capture in
the chain (James et al., 2009).
9
2.1.3 Asossa market
Within the market in Asossa, there are three main channels for selling mangoes: Farm gate that
mainly sell to traders (who sell on to Addis), consumers and small retailers; Asossa Town Market
that mainly sell to local consumers and Small Retailers that mainly sell to local consumers. The
market is dominated by the open town market where many farmers bring their produce for sale.
During peak mango season, this market is saturated with mangoes to the point that prices fall
dramatically and many farmers do not even bother to carry their produce home at the end of the
day. As well as the open Asossa market, there are a number of kiosk-style small retailers in Asossa
which suffer from similar problems at peak supply times. A significant point to note is that much of
the mango being supplied at the regional market is not the top grade being produced, but is actually
the remaining produce from what has been already sold to traders at farm gate. In this way, traders
are siphoning the best quality mangoes to sell in the Addis market, but also provide very little
choice to disorganized farmers about where to sell. This study found that farmers on average sell
between 0.4 and 1.15 birr depending on quality, and also customer. The lower price tended to be
achieved in the Asossa market, with the higher price being received at farm gate from traders
purchasing only the higher quality mangoes (Aithal and Wangila, 2006).
2.1.4 Addis Ababa market
The market is dominated by two large wholesale markets, being the Mercato and the Piazza. These
markets are the main destination for agricultural produce arriving from around the country. These
markets serve not only consumers, but are also where supermarkets, large retailers, hotels and
thousands of small kiosk-like retailers source their mangoes. Actual data on the volume of mangoes
sold in these markets is very unreliable, however a number of interview sources have identified that
in the past five years there has been significant growth in market size and increasing consumer
demand. This is largely to do with a steadily increasing population (3.2% p.a.), more sophisticated
consumer preferences for exotic and tropical fruits, and growing incomes amongst emerging
middle and upper class consumers. The average price on the wholesale markets in Addis Ababa
was approximately 3.5 birr per kg, or 3,500 birr per tonne, whereas the final retail price in Addis
could reach as high as 5 birr per kg (5,000 birr per tonne). By analyzing the price differentials
throughout the value chain, it is clear to see that farmers only capture a small portion (8%) of the
final retail price. There is no reliable data on the number of small retailers in Addis, but it is
estimated there are thousands of street level small retailers/kiosks - some of them dealing
10
exclusively in fruit, whilst others sell a range of consumable goods. These are a major channel for
selling mangoes on to final consumers and are particularly convenient as a street level channel in
places of high traffic, with high turnover of goods (CIA, 2008).
Fig. 2.1 Wholesale Mango market in Addis Ababa Market share by region
Source: (Aithal and Wangila, 2006)
The Mercato and Piazza markets are largely controlled by approximately ten major wholesalers,
who deal in fruits and vegetables from all over the country. Industry sources mentioned that the
Addis wholesalers are organised under groups that have strong ethnic ties and tend to operate in
ways that have been described as cartels. Similar to the upstream nature of the value chain, the
wholesalers in Addis operate in a heavily crowded, poorly structured, and underdeveloped market
infrastructure. There is no known refrigerated storage facilities in the market as the cost of this
investment has always been seen as too high. The typical wholesale price in Addis is approximately
3,500 birr per tonne and means that Addis wholesalers achieve between 20-40% of the final retail
price. This is a considerable portion of the final price and reflects the risk that Addis wholesalers
take in ordering mangoes from Asossa. Other value add activities that wholesalers undertake is re-
packaging and grading the fruit on arrival in Addis, as produce most often arrives in bulk having
11
not yet undergone any systematic grading or packaging. These are functions that are possible at the
farm level and may be areas where farmers can extract a greater price and generate more value in
the chain (Aithal and Wangila, 2006).
According to a recent update from the mango value chain analysis by James et al., (2009), it has
been indicated that within the first six months of the project implementation, the following have
been achieved:
19 farmers cooperatives have been set up and linked to an umbrella cooperative union. Out
of these, 100 Cooperative members have been trained on Mango Processing especially in
producing jam, juice, compote, vinegar, wine etc. This processing is under taken on site in
Asossa.
Farm gate Price of Mango increased from 25 Birr/100kg to 175 and the farmers have started
using weighing scales to measure quantities rather than counting pieces or heaps.
Between March and June 2009, 357 tonnes of mangoes were sold at the price of 569,084
Birr (roughly USD 46,000) to the most reputable fruit dealer- Et-Fruit for the first time.
With World Vision supervision, the income was equitably shared among the farmers.
4,000 bottles of various processed mango products like jam, juice, wine and compote have
been packed and sold to a number of super markets in Addis Ababa.
The farmers have entered into partnership with the Ecological Products of Ethiopia,
(Ecopia) to process and market mango products.
12
2.2 Processing of Mango fruits in Ethiopia
The mango processing industry in Ethiopia is in its infant stage. However, mango is grown in many
parts, especially in the Rift Valley, western and south-western parts of the country. The national
research system has developed a number of varieties but they are not widely spread. Experiences
from other countries in growing this crop will therefore contribute to the success and distribution of
this fruit. The mango industry in Kenya has expanded considerably over recent years, not only in
size but also in the geographical location of commercial and homestead plantings. No longer is
commercial mango cultivation restricted to the Coast Province, as significant plantings of improved
cultivars now also exist in the Eastern and Central provinces, among other regions (EAP, 2009).
The fruit processing industry in Ethiopia is very weak, considering the substantial amount of fruit
that is grown in the country. No doubt, one of the reasons for this is the highly developed
processing industries in other countries which are able to export into countries like Ethiopia and
sell the final product at low cost. Indeed, there were a number of imported, long-life mango juice
brands available throughout Ethiopia and is certain to act as a competitive entry barrier for
domestically produced juice. Investigations of local processors found only one significant player,
who actually imported frozen mango flesh from India for processing juice in Ethiopia. The main
considerations for purchasing Indian imports were the variety, quality, consistency, and price of the
imports. When asked about replacing imports with Ethiopian produced mango, the informant
indicated that would be his preference, however so far, Ethiopian fruit was not able to compare on
the key criteria identified, particularly on price. The informant did however predict that juice
processing would begin to emerge as a more viable sector, as mango juice is clearly the most
favored juice product by consumers. He indicated that demand for the juice as a category was
seeing strong growth, with mango leading this growth. The other key challenges for developing a
fruit processing sector in Ethiopia include: lack of technical knowledge in processing, low level of
technical support for maintenance, low capital base from which to invest, and many low priced
mango juice imports (James et al., 2009).
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2.3 Selected Mango varieties for processing
Tommy Atkins Mango variety
It is one of the most popular mangos in the world and cultivated in Florida early 1920's. The
Mango cultivar was developed and grown for commercial export. The fruit is a regular oval,
medium to large sized, 12 to 24 ounces, yellowish-orange with deep red to purple blush, thicker
skinned, juicy but firm with medium fiber.
Pic. 2.1 Tommy Atkins (LFI, 2003)
Keitt Mango variety
Indian strain thought to have originated, like the Haden, from a seedling of Mulgoba 1945,
Homestead, Florida. The fruit is a large (20-26 oz.) ovate tapering with slight nose-like
protuberance above its tip. Green to orange-yellow as it ripens; firm flesh with a piney sweetness
and minimal fiber surrounding the seed area. It is a late fruiting mango, often available into fall.
Pic. 2.2 Keitt (LFI, 2003)
Kent Mango variety
Kent mango was first cultivated in Florida in 1944. It is a direct descendant of the Brooks cultivar,
derived from the Sandersha seedling. The fruit is a regular oval shape, large 20 - 26 ounces, with
plump cheeks, greenish-yellow color with red shoulder. Very rich and sweet with fiber-free flesh
(slices clean to the pit - like butter when ripe!) It is a softer mango that really should not be put to
the squeeze test.
14
Pic. 2.3 Kent (LFI, 2003)
2.4 Medicinal uses and by-products of Mango
Mangos are an excellent source of Vitamins A and C, as well as Potassium, Beta-carotene,
enzymes and anti-oxidants. Mangoes are high in fibre, but low in calories (approximately 110 per
average sized mango) fat (only 1 g) and sodium. Mangoes are a good staple for your daily diet. It
has a reputation (not necessarily scientifically proven) as an alternative or complementary medicine
for a wide range of illnesses including beriberi, bronchial diseases, anxiety, insomnia, fatigue,
depression, digestive problems heartburn, constipation, kidney stones.
Mango kernel contains high amounts of fat and starch. The oil extracted from kernel is of good
quality and could be used in cosmetic and soap industries. The kernel flour (starch) after mixing
with wheat or maize flour is used in chapattis in India. About ten percent alcohol could be obtained
from mango kernel by co-culture fermentation (Truneh, 2009).
2.5 Mango processing technologies
The processing of fruits has two objectives. Firstly, to preserve by slowing down the natural
processes of decay caused by microorganisms, enzymes in the food, or other factors such as heat,
moisture and sunlight. The second objective is to convert them into different foods which are
attractive and in demand by consumers Food Processors should utilize their skills to develop
recipes and create attractive products that consumers want to eat. Thereby successful Food
Processors increase product sales and generate profits. Food Processors must select their products
with caution. It is not enough to assume that processing can be a successful business simply
because there a large quantities of cheap fruit available in the marketplace. There must be a good
demand for the end product and this must be clearly identified before designing and investing in the
business. The best types of products for small-scale production are those that have a high added-
value as well as a good demand. A high added value means that cheap raw materials can be
processed into relatively expensive products. It also means that this can be done at a small scale of
processing, using equipment that is affordable (Fellows and Quaouich, 2004).
15
Fruits like mangos, pawpaw, guavas and bananas, can easily be dried. However, they should be
harvested at the right stage and ripeness. Hard ripe stage in mangoes, pawpaw and bananas gives
best results. Avoid overripe, under mature fruits in order to obtain good products. To prepare the
fruits for drying, wash them thoroughly with clean water. Scrubbing with a brush might be
necessary like in case of mango fruit with a lot of latex cover. The fruits are peeled if necessary and
cut into smaller uniform pieces to ensure faster drying. Stainless steel knives are recommended for
peeling and cutting of the slices or pieces. To avoid discoloration and excessive vitamin losses,
treatment with anti-oxidants like citrus (lemon) juice is done. Fruits like pineapples may require
pre-cooking to soften fibrous tissue hence hasten drying. Drying is done on trays, which should be
made of wood, fabric, plastic or sisal material. This is because metal materials may affect the
drying product negatively e.g. copper destroys vitamin C, iron rusts, aluminum discolors fruits and
corrodes. Most fruits have natural acids and sugars which are preservatives therefore moisture
contents of about 20% i.e. leathery and springy dry (not brittle) is good for storage. This is however
dependent on the fruit or vegetable. After the correct stage of dryness is achieved the product
should be removed from the dryer parked, and stored in a dry, dark store to avoid loss of vitamin A
(GTZ, 2009).
Mangos are processed at two stages of maturity. Green fruit is used to make chutney, pickles,
curries and dehydrated products. The green fruit should be freshly picked from the tree. Fruit that is
bruised, damaged, or that has prematurely fallen to the ground should not be used. Ripe mangoes
are processed as canned and frozen slices, puree, juices, nectar and various dried products. Mango
processing within the home and cottage industries converts the fruit into many other products.
Mango processing presents many problems as far as industrialization and market expansion is
concerned. The trees are alternate bearing and the fruit has a short storage life; these factors make it
difficult to process the crop in a continuous and regular way. The large number of varieties with
their various attributes and deficiencies affects the quality and uniformity of processed products.
Additionally, the lack of simple, reliable methods for determining the stage of maturity of varieties
for processing also affects the quality of the finished products. Many of the processed products
require peeled or peeled and sliced fruit. Within Ethiopia the lack of mechanized equipment for the
peeling of ripe mangoes is a serious bottleneck for increasing the production of these products. A
significant problem in developing mechanized equipment is the large number of varieties available
and their different sizes and shapes. The cost of processed mango products is also too expensive for
the general population in the areas where most mangoes are grown. However, there is a
16
considerable export potential to developed countries but in these countries the processed mango
products must compete with established processed fruits of high quality and relatively low cost
(Dauthy, 1995).
2.5.1 Ripe Mango processing
Mango Puree
Mangoes are processed into puree for re-manufacturing into products such as nectar, juice, squash,
jam, jelly, dehydrated products such as fruit leathers. The puree can be preserved by chemical
means, or frozen, or canned and stored in barrels. This allows a supply of raw materials during the
remainder of the year when fresh mangoes are not available. It also provides a more economical
means of storage compared with the cost of storing the finished products, except for those which
are dehydrated, and provides for more orderly processing during peak availability of fresh
mangoes. Mangoes can be processed into puree from whole or peeled fruit. Because of the time and
cost of peeling, this step is best avoided but with some varieties it may be necessary to avoid off-
flavors which may be present in the skin. The most common way of removing the skin is hand-
peeling with knives but this is time-consuming and expensive. Steam and lye peeling have been
accomplished for some varieties. Several methods have been devised to remove the pulp from the
fresh ripe mangoes without hand-peeling. A simplified method is as follows: the whole mangoes
were exposed to atmospheric steam for 2 to 2 and 1/2 min in a loosely covered chamber, and then
transferred to a stainless steel tank. The steam-softened skins allowed the fruit to be pulped by a
power stirrer fitted with a saw-toothed propeller blade mounted 12.7 to 15.2 cm below a regular
propeller blade. The pulp is removed from the seeds by a continuous centrifuge designed for use in
passion fruit extraction. The pulp material is then passed through a paddle pulper fitted with a
0.084 cm screen to remove fiber and small pieces of pulp.
Mango puree can be frozen, canned or stored in barrels for later processing. In all these cases,
heating is necessary to preserve the quality of the mango puree. In one process, puree is pumped
through a plate heat exchanger and heated to 90C for 1 min and cooled to 35 C before being
filled into 30 lb tins with polyethylene liners and frozen at -23.50 C. In another process, pulp is
acidified to pH 3.5, pasteurized at 90C, and hot-filled into 6 kg high-density bulk polyethylene
containers that have been previously sterilized with boiling water. The containers are then sealed
and cooled in water. This makes it possible to avoid the high cost of cans. Wooden barrels may be
used to store mango pulp in the manufacture of jams and squashes. The pulp is acidified with 0.5 to
17
1.0% citric acid, heated to boiling, cooled, and SO2 is added at a level of 1000 to 1500 ppm in the
pulp. The pulp is then filled into barrels for future use.
Dried/dehydrated Mango
Ripe mangoes are dried in the form of pieces, powders and flakes. Drying procedures such as sun-
drying, tunnel dehydration, vacuum-drying, osmotic dehydration may be used. Packaged and stored
properly, dried mango products are stable and nutritious. One described process involves as pre-
treatment dipping mango slices for 18 hr (ratio 1:1) in a solution containing 40 Brix sugar, 3000
ppm SO2, 0.2% ascorbic acid and 1% citric acid; this method is described as producing the best
dehydrated product. Drying is described using an electric cabinet through flow dryer operated at
60 C. The product showed no browning after 1 year of storage (Dauthy, 1995). Mango fruits can
also be dried in the form of leathers or bars.
2.6 Fruit leather processing
Fruit leathers are dried sheets of fruit pulp which have a soft, rubbery texture and a sweet taste.
They can be made from most fruits, although mango, apricot, banana and tamarind leathers are
amongst the most popular. Leathers can also be made from a mixture of fruits. Fruit leathers are
eaten as snack foods instead of boiled sweets. They are also used as ingredients in the manufacture
of cookies, cakes and ice cream. The preservation of fruit leathers depends on their low moisture
content (15-25%), the natural acidity of the fruit and the high sugar content. When properly dried
and packaged, fruit leathers have a shelf life of up to 9 months (FPT, 2009).
2.6.1 Preparation of fruits
Fruit should be washed in clean water, peeled and the stones removed. Washing water can be
chlorinated by adding 1 teaspoon of bleach to 4.5 liters of water. All fruit should be ripe and free
from bruising. Any rotten or bruised fruit should be thrown away as this will spoil the color and
flavor of the leather. The puree must be heated to a higher temperature for a longer time to destroy
the enzyme (it must be boiled for 20 minutes). Only stainless steel knives should be used to chop
the fruit. Other metals will discolor the fruit flesh. At the simplest level, fruit is made into a puree
by hand using a food mill. If electricity is available, a liquidizer or blender can be used to increase
the production output. The liquidized fruit is strained or sieved to remove the fibers, seeds, etc to
make a smooth puree. Fruit puree can be semi-processed and stored in sealed drums for further
processing later in the season. Sulphur dioxide (SO2) (600ppm) is added to the drums to prevent the
18
growth of micro-organisms. The semi-processed fruit can be stored for several months. Chemical
preservatives may be added to the fruit puree to maintain a bright color in the leather. Preservatives
are also added if the puree is to be stored before processing. A variety of ingredients can be added
to the fruit puree - sugar to increase the sweetness, citric acid to increase the acidity and chopped
nuts, coconut or spices to vary the taste and flavor.
2.6.2 Heating, drying and packaging
The puree must be heated to 900 C to inactivate the enzymes and reduce the level of
microbiological contamination. A double pan boiler is recommended for heating to avoid burning
the puree. The fruit puree is poured in a thin layer (3-6mm thick) on plastic trays or wooden trays
lined with greaseproof paper. The puree can be poured into a square which is later cut into small
pieces, or into small circles which are rolled up when dry. The leathers should not be dried in direct
sunlight as this will cause the color to fade and reduce the levels of vitamins A and C. Indirect solar
dryers or mechanical dryers should be used. The leather should be dried overnight in a solar dryer
or for about 5 hours in a mechanical dryer. After this time it is turned over and dried on the other
side. The leather is dried until it has a final moisture content of 15-25%. After drying, the leather
pieces should be dusted lightly with starch to prevent them sticking together. All equipment must
be thoroughly cleaned each day to prevent contamination by insects and micro-organisms.
In developing countries fruit leather is usually packaged cheaply with easily sourced materials. The
fruit leather is sold as a roll that is interleaved with greaseproof paper to prevent it from sticking
together. Strips of the leather are weighed, laid on a piece of greaseproof paper and rolled with the
paper. The rolls or discs of leather are packed in polythene or polypropylene heat-sealed bags. The
bags should be placed in boxes to protect them from the light. Fruit leather products in Europe are
packaged as a bar or as mini sweets, within a sealed plastic/foil case. The fruit leather bars within
their plastic/foil case may be packaged and sold as a multipack within a cardboard box made from
recycled paper products. The attractive, modern design of the packaging is specifically aimed at the
health conscious, luxury product niche within the consumer market (FPT, 2009).
19
2.7 Mango fruit leather recipes and processing procedures
The following basic recipes are only guidelines since they depend on the composition of fruit
(which varies between different types) and the different consumer tastes for sweetness. The recipes
needed for mango leather preparation are: fully ripe mango, Sugar (10-15% the pulp weight
according to the variety used and consumer taste), lemon juice or citric acid 2 spoons per kg pulp),
Sodium of potassium metabisulphite (2g per kg pulp), and Glycerin for foods.
The general procedure for making mango fruit leather is as follows:
1. Wash the mangoes in clean water. Drain, Sort and remove any unripe or over-ripe fruit.
2. Peel the fruit with a stainless steel knife and cut the flesh into small pieces.
3. Extract the pulp using a pulper.
4. Weigh the pulp and mix with the sugar, lemon juice and metabisulphite in the ratios
above.
5. Heat at 70-80 0C.
6. Remove the foam from the top of the mixture. Grease the surface of trays with glycerin
to prevent the leather from sticking.
7. Pour the hot puree onto the trays at a ratio of 15kg per square meter of tray area.
8. Place the trays in a dryer. Leave to dry until a final moisture content of 15%. The
product will have a soft, leather-like consistency.
9. Place three sheets of leather on top of each other and cut into small 4x4cm squares.
Wrap each square in cellophane. It may be necessary to dust the squares with corn flour
to prevent excess stickiness.
10. Pack in plastic bags, label and store in a cool dry place (FPT, 2009).
Mango fruit leather can also be made using electric dehydrator or drying oven. Andress (2004)
formulated mango fruit leather with different recipes and methods as described below.
Recipes: include; 4 cups mango puree (from about 4 large, unripe mangoes), 1 cup clover
honey, teaspoon ground cinnamon, teaspoon ground nutmeg, and teaspoon ground cloves.
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Yield: about 2 dryer trays (14 inches in diameter); 8 fruit rolls.
2.7.1 Adding sweeteners and flavoring to fruit leather
Once you have the basics of making fruit leathers it is fun to try some new flavoring, toppings, or
fillings. Below are some new ideas.
Sweetening - If the puree needs some sweetening, add up to cup sugar for each 2 cups of fruit.
Sugar substitutes may be used. Aspartame sweeteners however may lose sweetness during drying.
Spices Add spices to the puree. Add until the taste is acceptable. Begin by adding 1/8-teaspoon
for each 2 cups of puree. Try: cinnamon, cloves, ginger, mint, nutmeg, allspice.
Flavorings Add flavorings to the puree using only 1/8-teaspoon person 2 cups of puree to start.
Try almond extract, lemon peel, orange extract, vanilla or peppermint.
Toppings After spreading the puree on the drying sheet and before drying, sprinkle a topping
over the puree. Try not to cover entire puree, but just lightly sprinkle the topping. Try coconut,
dried fruits, granola, and sunflower seeds.
Fillings After the fruit leather is dried and cool, spread a thin layer of these fillings. Then roll, cut
and serve. If not served immediately, store in the refrigerator or wait to spread filling until just
before serving. Try melted chocolate, softened cream cheese, peanut butter, marshmallow cream,
jam or jelly. Here is an idea for adding dairy foods and calcium to your diet in a fun tasty way.
Yogurt Drops - 18-ounce vanilla yogurt, 13-oz package of sugar free gelatin powder (any flavor)
and mix the gelatin powder with the yogurt. Using a spoon drop the mixture onto a fruit leather
drying tray. They can be done in small rounds or as leather. Dry until sticky and store in the
refrigerator or freezer. This makes great healthy snack and provides another way to get dairy
products and calcium in the diet (Brown, 2009).
2.8 Quality control
Quality control begins with the acquisition of high-quality fruit concentrate. Many purees are
supplied by well-known fruit processors. Other quality control methods include careful calibration
of all additives, particularly of those additives that affect hardening/malleability (malto-dextrin in
particular). Also, cooking and drying temperatures are monitored closely to ensure moisture
content. Scales are carefully calibrated so that each roll contains just the right amount of extruded
21
product; similarly, the packaging machine is checked and re-checked so that each cardboard
package includes the correct number of fruit leathers. Sample testing is performed periodically as
well (Nancy, 2009).
One of the most important concerns of the food manufacturer is to produce a final product that
consistently has the same overall properties, i.e. appearance, texture, flavor and shelf life. When we
purchase a particular food product we expect its properties to be the same (or very similar) to
previous times, and not to vary from purchase-to-purchase. Ideally, a food manufacture wants to
take the raw ingredients, process them in a certain way and produce a product with specific
desirable properties. Unfortunately, the properties of the raw ingredients and the processing
conditions vary from time to time which causes the properties of the final product to vary, often in
an unpredictable way. How can food manufacturers control these variations? Firstly, they can
understand the role that different food ingredients and processing operations play in determining
the final properties of foods, so that they can rationally control the manufacturing process to
produce a final product with consistent properties. This type of information can be established
through research and development work (see later). Secondly, they can monitor the properties of
foods during production to ensure that they are meeting the specified requirements, and if a
problem is detected during the production process, appropriate actions can be taken to maintain
final product quality (McClements, 1999).
Quality control points:
Use only ripe fruits without bruising or damage. Over-ripe ones can easily become
damaged and bruised. Under-ripe fruits will not have the full flavor.
Use a double boiling pan to avoid burning which can occur if direct heating is used.
Weigh all ingredients to the correct formulation.
Do not dry the leather in direct sunlight as there will be loss of color and vitamins A and
C.
Dust the leather lightly with starch before packing to reduce their stickiness.
Seal the leather packed in the form of a roll interleaved with greaseproof paper to avoid it
sticking together.
22
Check the correct fill-weight before sealing the bags.
If available, use 400 gauge polypropylene bags as they provide greater protection against
moisture (Nancy, 2009).
Manufacturers measure the properties of incoming raw materials to ensure that they meet certain
minimum standards of quality that have previously been defined by the manufacturer. If these
standards are not met the manufacturer rejects the material. Even when a batch of raw materials has
been accepted, variations in its properties might lead to changes in the properties of the final
product. By analyzing the raw materials it is often possible to predict their subsequent behavior
during processing so that the processing conditions can be altered to produce a final product with
the desired properties. Monitoring of food properties during processing is advantageous for food
manufacturers to be able to measure the properties of foods during processing. Thus, if any
problem develops, then it can be quickly detected, and the process adjusted to compensate for it.
This helps to improve the overall quality of a food and to reduce the amount of material and time
wasted. Traditionally, samples are removed from the process and tested in a quality assurance
laboratory. This procedure is often fairly time-consuming and means that some of the product is
usually wasted before a particular problem becomes apparent. For this reason, there is an increasing
tendency in the food industry to use analytical techniques which are capable of rapidly measuring
the properties of foods on-line, without having to remove a sample from the process. These
techniques allow problems to be determined much more quickly and therefore lead to improved
product quality and less waste. The ideal criteria for an on-line technique is that it be capable of
rapid and precise measurements, it is non-intrusive, it is nondestructive and that it can be
automated. Once the product has been made it is important to analyze its properties to ensure that it
meets the appropriate legal and labeling requirements, that it is safe, and that it is of high quality. It
is also important to ensure that it retains its desirable properties up to the time when it is consumed
(McClements, 1999).
2.9 Effect of processing on food quality attributes
Foods undergo changes as a result of processing; such changes may be physical, chemical,
enzymatic, or microbiological (Singh & Heldman, 2001). Food processing is any and all processes
to which food is subjected after harvesting for the purposes of improving its appearance, texture,
palatability, nutritive value, keeping properties and ease of preparation, and for eliminating
microorganisms, toxins and other undesirable constituents (David & Arnold,1999).
23
The composition of a food largely determines its safety, nutrition, physicochemical properties,
quality attributes and sensory characteristics. Most foods are compositionally complex materials
made up of a wide variety of different chemical constituents. Their composition can be specified in
a number of different ways depending on the property that is of interest to the analyst and the type
of analytical procedure used: specific atoms (e.g., Carbon, Hydrogen, Oxygen, Nitrogen, Sulfur,
Sodium, etc.); specific molecules (e.g., water, sucrose, tristearin, b-lactoglobulin), types of
molecules (e.g., fats, proteins, carbohydrates, fiber, minerals), or specific substances (e.g., peas,
flour, milk, peanuts, butter). Government regulations state that the concentration of certain food
components must be stipulated on the nutritional label of most food products, and are usually
reported as specific molecules (e.g., vitamin A) or types of molecules (e.g., proteins) (McClements,
1999).
Many unit operations, especially those that do not involve heat, have little or no effect on the
nutritional quality of foods. Examples include mixing, cleaning, sorting, freeze drying and
pasteurization. Unit operations that intentionally separate the components of foods alter the
nutritional quality of each fraction compared with the raw material. Unintentional separation of
water-soluble nutrients (minerals, water-soluble vitamins and sugars) also occurs in some unit
operations (for example blanching, and in drip losses from roast or frozen foods.
Processing using heat is a major cause of changes to nutritional properties of foods. For example
gelatinization of starches and coagulation of proteins improve their digestibility, and anti-
nutritional compounds (for example a trypsin inhibitor in legumes) are destroyed. However, heat
also destroys some types of heat-labile vitamin, reduces the biological value of proteins (owing to
destruction of amino acids or Maillard browning reactions) and promotes lipid oxidation. Therefore
a continuing aim of food manufacturers should be to find improvements in processing technology
which retain or create desirable sensory qualities and nutritional properties or reduce the damage to
food caused by processing (Fellows, 2000).
2.9.1 Physicochemical properties
The physiochemical properties of foods (rheological, optical, stability, flavor) ultimately
determine their perceived quality, sensory attributes and behavior during production, storage and
consumption. The optical properties of foods are determined by the way that they interact with
electromagnetic radiation in the visible region of the spectrum, e.g., absorption, scattering,
transmission and reflection of light. For example, full fat milk has a whiter appearance than skim
24
milk because a greater fraction of the light incident upon the surface of full fat milk is scattered due
to the presence of the fat droplets.
The rheological properties of foods are determined by the way that the shape of the food changes,
or the way that the food flows, in response to some applied force. For example, margarine should
be spread able when it comes out of a refrigerator, but it must not be so soft that it collapses under
its own weight when it is left on a table. The stability of a food is a measure of its ability to resist
changes in its properties over time. These changes may be chemical, physical or biological in
origin. Chemical stability refers to the change in the type of molecules present in a food with time
due to chemical or biochemical reactions, e.g., fat rancidity or non-enzymatic browning. Physical
stability refers to the change in the spatial distribution of the molecules present in a food with time
due to movement of molecules from one location to another, e.g., droplet creaming in milk.
Biological stability refers to the change in the number of microorganisms present in a food with
time, e.g., bacterial or fungal growth. Foods must therefore be carefully designed so that they have
the required physicochemical properties over the range of environmental conditions that they will
experience during processing, storage and consumption, e.g., variations in temperature or
mechanical stress. Consequently, analytical techniques are needed to test foods to ensure that they
have the appropriate physicochemical properties (McClements, 1999).
2.9.2 Changes on Vitamins
Vitamins are minor components of foods which play an essential role in human nutrition. They are
organic compounds that are necessary in small amounts for proper growth. In general human
beings and animals can not be in a healthy state without vitamins, carbohydrates, fats, proteins,
minerals and water. Very small quantities of vitamins are necessary for health, but a lack of them
may upset the normal metabolism, resulting in deficiency diseases. Many of the vitamins are
unstable under certain conditions of processing and storage and their levels in processed foods,
therefore, may be considerably reduced. Most of the vitamins are also heat sensitive. The
occurrence of the vitamins in the various food groups is related to their water or fat solubility.
Vitamins are classified into two main groups: water soluble vitamins and Fat soluble vitamins
(Deman, 1980).
25
2.9.2.1 Effects of preliminary treatments: trimming and washing on Vitamins
The peeling and trimming of fruits and vegetables can cause losses of vitamins to the extent that
they are concentrated in the discarded stem, skin, or peel fractions. Although this can be a source of
significant loss relative to the intact fruit or vegetable, in most cases this must be considered to be
an inevitable loss regardless of whether it occurs in industrial processing or home preparation.
Alkaline treatments to enhance peeling can cause increased losses of labile vitamins such as float,
ascorbic acid, and thiamin at the surface of the product. However, losses of this kind tend to be
small compared to the total vitamin content of the product. Any exposure of cut or otherwise
damaged tissues of plant or animal products to water or aqueous solutions causes the loss of water-
soluble vitamins by extraction (leaching). This can occur during washing, transportation via
flumes, and exposures to brines during cooking. The extent of such losses depends on factors that
influence the diffusion and solubility of the vitamin, including pH (can affect solubility and
dissociation of vitamins from binding sites within the tissue), ionic strength of the extract,
temperature, the volume ratio of food to aqueous solution, and the surface-to-volume ratio of the
food particles (Fennema, 1996).
2.9.2.2 Effects of blanching and thermal processing on Vitamins
Blanching, a mild heat treatment is an essential step in the processing of fruits and vegetables. The
primary purposes are to inactivate potentially deleterious enzymes, reduce microbial loads, and
decrease interstitial gasses prior to further processing. Inactivation of enzymes often has a
beneficial effect on the stability of many vitamins during subsequent food storage. Blanching can
be accomplished in hot water, flowing steam, hot air, or with microwaves. Losses of vitamins occur
primarily by oxidation and aqueous extraction (leaching), with heat being a factor of secondary
importance. Blanching in hot water can cause large losses of water-soluble vitamins by leaching. It
has been well documented that high-temperature, short-time treatments improve retention of labile
nutrients during blanching and other thermal processes. The elevated temperature of thermal
processing accelerates reactions that would otherwise occur more slowly at ambient temperature.
Thermally induced losses of vitamins depend on the chemical nature of the food, its chemical
environment (pH, relative humidity, transition metals, other reactive compounds, concentration of
dissolved oxygen, etc.), the stabilities of the individual forms of vitamins present, and the
opportunity for leaching. The nutritional significance of such losses depends on the degree of loss
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and the importance of the food as a source of the vitamin in typical diets (Da-Silva and Williams,
1991).
2.9.2.3 Effect of processing on Vitamin C
Vitamin C (L-ascorbic acid) is the least stable of all vitamins and will easily be destroyed during
processing and storage. The rate of destruction of vitamin C is increased by the action of metals,
especially copper and iron, and also by the action of enzymes. Exposure to oxygen and light and
prolonged heating in the presence of oxygen during processing will decrease the vitamin C content
of foods. Factors that affect vitamin C destruction during processing include heat treatment and
leaching. The severity of processing conditions can often be judged by the percentage of ascorbic
acid that has been lost. The extent of loss depends on the amount of water used. Vegetables during
blanching covered with water may lose 80% half covered 40% and quarter covered 40% of the
ascorbic acid. Particle size affects the loss, for example in blanching of small pieces of carrots,
losses may range from 32-50% and losses from large pieces only 22-33%. Blanching of cabbage
may result in 20% loss of ascorbic acid and subsequent dehydration may increase this to a total of
50%. In the processing of milk losses may occur at various stages. From an initial level of about
22mg/l in raw milk the content in the product reaching the consumer may be well below 10mg per
liter. Ascorbic acid is oxidized in the presence of air under neutral and alkaline conditions. At acid
pH the vitamin is more stable for example in citrus juice. Since oxygen is required for the
breakdown, removal of oxygen should have a stabilizing effect. For the production of fruit drinks
it is recommended to de-aerate the water to minimize the vitamin C loss. The type of container may
also affect the extent of ascorbic acid destruction. Use of tin cans for fruit juices result in rapid
depletion of oxygen by the electrochemical process of corrosion. In bottles all of the residual
oxygen is available for ascorbic acid oxidation. To account for processing and storage losses it is
common to allow for a loss of 7-14mg of ascorbic acid per 100ml of fruit juice (Fennema, 1996).
2.9.3 Flavor and pigment components
The flavor of a food is determined by the way that certain molecules in the food interact with
receptors in the mouth (taste) and nose (smell) of human beings. The perceived flavor of a food
product depends on the type and concentration of flavor constituents within it, the nature of the
food matrix, as well as how quickly the flavor molecules can move from the food to the sensors in
the mouth and nose. Analytically, the flavor of a food is often characterized by measuring the
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concentration, type and release of flavor molecules within a food or in the headspace above the
food (McClements, 1999).
Fresh foods contain complex mixtures of volatile compounds, which give characteristic flavors and
aromas, some of which are detectable at extremely low concentrations (Fellows, 2000). These
compounds may be lost during processing, which reduces the intensity of flavor or reveals other
flavor/aroma compounds. Volatile aroma compounds are also produced by the action of heat,
ionizing radiation, and oxidation or enzyme activity on proteins, fats and carbohydrates. Examples
include the Maillard reaction between amino acids and reducing sugars or carbonyl groups and the
products of lipid degradation or hydrolysis of lipids to fatty acids and subsequent conversion to
aldehydes, esters and alcohols. The perceived aroma of foods arises from complex combinations of
many hundreds of compounds, some of which act synergistically (Maruniak and MacKay-Sim,
1984). In addition, the perceived flavor of foods is influenced by the rate at which flavor
compounds are released during chewing, and hence is closely associated with the texture of foods
and the rate of breakdown of food structure during mastication (Clark, 1990).
The colors of foods are the result of the presence of natural pigments or of added dyes. Pigments
are a group of natural colorants found in animal and vegetable products (Deman, 1980). These
pigments are organic in their nature and generally considered to embrace the pigments already
formed in the foods as well as those which can be formed on heating, storage or processing. Many
naturally occurring pigments are destroyed by heat processing, chemically altered by changes in pH
or oxidized during storage. As a result the processed food may lose its characteristic color and
hence its value. Maillard browning is an important cause of both desirable changes in food color
(for example in baking or frying and in the development of off-colors (for example during canning
and drying. Major food processing activities such as ambient temperature processing, processing by
the application of heat and processing by the removal of heat will affect the flavor, aroma and
pigment of food stuffs (Fellows, 2000).
2.9.3.1 Heat induced processing effects on flavor and color
Most foods have no significant changes to flavor or aroma when correctly blanched, but under-
blanching can lead to the development of off-flavors during storage of dried or frozen foods. In
fruit juices the main cause of color deterioration is enzymatic browning by polyphenoloxidase. This
is promoted by the presence of oxygen, and fruit juices are therefore routinely de-aerated prior to
pasteurization. In fruits and vegetables, chlorophyll is converted to pheophytin, carotenoids are
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isomerized from 5, 6-epoxides to less intensely colored 5, 8-epoxides, and anthocyanins are
degraded to brown pigments. Changes are due to complex reactions which involve the degradation,
recombination and volatilization of aldehydes, ketones, sugars, lactones, amino acids and organic
acids. In aseptically sterilized foods the changes are again less severe, and the natural flavors of
milk, fruit juices and vegetables are better retained. Aroma compounds that are more volatile than
water can be lost during evaporation. This reduces the sensory characteristics of most concentrates;
in fruit juices this results in loss of flavor, although in some foods the loss of unpleasant volatiles
improves the product quality, for example in cocoa (Anon, 1981).
Heat not only vaporizes water during drying but also causes loss of volatile components from the
food and as a result most dried foods have less flavour than the original material. The extent of
volatile loss depends on the temperature and moisture content of the food and on the vapor pressure
of the volatiles and their solubility in water vapor. Volatiles which have a high relative volatility
and diffusivity are lost at an early stage in drying. Foods that have a high economic value due to
their characteristic flavors (for example herbs and spices) are dried at low temperatures (Mazza and
LeMaguer, 1980).
The open porous structure of dried food allows access of oxygen, which is a second important
cause of aroma loss due to oxidation of volatile components and lipids during storage. Most fruits
and vegetables contain only small quantities of lipid, but oxidation of unsaturated fatty acids to
produce hydro peroxides, which react further by polymerization, dehydration or oxidation to
produce aldehydes, ketones and acids, causes rancid and objectionable odours. Some foods (for
example carrot) may develop an odour of violets produced by the oxidation of carotenes to -
ionone (Rolls and Porter, 1973). Evaporation darkens the color of foods, partly because of the
increase in concentration of solids, but also because the reduction in water activity promotes
chemical changes, (for example Maillard browning). As these changes are time and temperature
dependent, short residence times and low boiling temperatures produce concentrates which have a
good retention of sensory and nutritional qualities (Anon, 1981). Blanching brightens the color of
some foods by removing air and dust on the surface and thus altering the wavelength of reflected
light. The time and temperature of blanching also influence the change in food pigments according
to their D value (Fellows, 2000).
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2.9.4 Sensory attributes
The quality and desirability of a food product is determined by its interaction with the sensory
organs of human beings, e.g., vision, taste, smell, feel and hearing. For this reason the sensory
properties of new or improved foods are usually tested by human beings to ensure that they have
acceptable and desirable properties before they are launched onto the market. Even so, individuals'
perceptions of sensory attributes are often fairly subjective, being influenced by such factors as
current trends, nutritional education, climate, age, health, and social, cultural and religious patterns.
To minimize the effects of such factors a number of procedures have been developed to obtain
statistically relevant information. For example, foods are often tested on statistically large groups
of untrained consumers to determine their reaction to a new or improved product before full-scale
marketing or further development. Alternatively, selected individuals may be trained so that they
can reliably detect small differences in specific qualities of particular food products, e.g., the mint
flavor of a chewing gum Although sensory analysis is often the ultimate test for the acceptance or
rejection of a particular food product, there are a number of disadvantages: it is time consuming
and expensive to carry out, tests are not objective, it cannot be used on materials that contain
poisons or toxins, and it cannot be used to provide information about the safety, composition or
nutritional value of a food. For these reasons objective analytical tests, which can be performed in
laboratory using standardized equipment and procedures, are often preferred for testing food
product properties that are related to specific sensory attributes. For this reason, many attempts
have been made to correlate sensory attributes (such as chewiness, tenderness, or stickiness) to
quantities that can be measured using objective analytical techniques, with varying degrees of
success (McClements, 1999).
Many types of food processing techniques have been employed throughout human history, mainly
to ensure microbiological and chemical safety of foods and to improve palatability. Growing
consumer demand for healthy, nutritious and convenient food is a key driver for improvements and
new developments in food processing. New processes or newly recognized compounds, often
identified due to improved analytical capabilities, require careful evaluation of potential human
health impact. The most important quality attributes of a food to the consumer, are its sensory
characteristics (texture, flavor, aroma, shape and color). These determine an individuals preference
for specific products, and small differences between brands of similar products can have a
substantial influence on acceptability. So during processing great care must be taken to retain or
enhance these properties (Fellows, 2000).
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2.9.5 Influence of drying process
Drying of agricultural products is the oldest and widely used preservation method. It involves
reduction as much water as possible from foods to arrest enzyme and microbial activities hence
stopping deterioration. Moisture left in the dried foods varies between 2-30% depending on the
type of food. In tropical countries, solar dryers can be used to dry fresh produce when average
relative humidity is below 50% during drying period. Drying lowers weights and volume of the
product hence lowers costs in transportation and storage. However, drying allows some lowering in
nutritional value of the product e.g. loss of vitamin C, and changes of color and appearance that
might not be desirable (GTZ, 2009).
Fruits like mangoes, pawpaw, guavas and bananas, can easily be dried. However, they should be
harvested at the right stage and ripeness. Hard ripe stage in mangoes, pawpaw and bananas gives
best results. Avoid overripe, under mature fruits in order to obtain good products. To prepare the
fruits for drying, wash them thoroughly with clean water. Scrubbing with a brush might be
necessary like in case of mango fruit with a lot of latex cover. The fruits are peeled if necessary and
cut into smaller uniform pieces to ensure faster drying. Stainless steel knives are recommended for
peeling and cutting of the slices or pieces. Drum-drying of mango puree is described as an efficient,
economical process for producing dried mango powder and flakes. Its major drawback is that the
severity of heat preprocessing can produce undesirable cooked flavors and aromas in the dried
product. The drum-dried products are also extremely hydroscopic and the use of in-package
desiccant is recommended during storage (Dauthy, 1995).
To avoid discoloration and excessive vitamin losses, treatment with anti-oxidants like citrus
(lemon) juice is done. Fruits like pineapples may require pre-cooking to soften fibrous tissue hence
hasten drying. Drying is done on trays, which should be made of wood, fabric, plastic or sisal
material. This is because metal materials may affect the drying product negatively e.g. copper
destroys vitamin C, iron rusts, aluminum discolors fruits and corrodes. Most fruits have natural
acids and sugars which are preservatives therefore moisture contents of about 20% i.e. leathery and
springy dry (not brittle) is good for storage. This is however dependent