WORK PACKAGE 6

COATING FORMULATION

• 10 % Kaffirin • Ethanol as solvent• Plasticiser mixture (1:1:1)

–Polyethylene Glycol –Lactic Acid–Glycerol

• Relaxation Time –16 hrs

OBJECTIVES OF THE STUDY

To determine the effect of 10 % Kaffirin coating:

• On the sensory acceptability of litchi

• On the post-harvest response & shelf-life of litchi over the distribution chain

COATING PROCEDURECleaned, freshly harvested litchi

Dipped with stalk in coating for 10 secs

Allowed to air dry for 1 hour

Stalk clipped off and litchi placed on trays or plastic bag

EXPERIMENTAL CONDITIONS

• AMBIENT (25-30 OC, RH 70-77 %)• 13 OC, RH 85 %• 4 OC, RH 45 %

• Packaging was included as trials as UEM, CSIR showed that packaging can reduce whitening.

PACKING

Primary objective of Packing was to reduce the white deposit on coated litchi

However Packing:• did not prevent whitening- may decrease it to some

extent )• Favoured mould growth and reduced the shelf life• Gave the impression that the litchis were mouldy

Thus data for packing was not further processed

Day 6, Day 6, Ambient Ambient TempTemp

Day 9, Day 9, Ambient Ambient TempTemp

Packing favoured mould growth

Day 6, Ambient TempDay 6, Ambient Temp

Uncoated, PackedUncoated, Unpacked

Coated,UnpackedCoated, packed

White deposit still present

Day 6, Day 6, 1313ooCC

• In practical terms, coating does not have a major effect on pH, TSS, TA

Weight loss IV

Coating does not seem to act as a barrier to water loss

Possible explanations: No proper film formation on the litchi as

depicted by white deposit Kaffirin coating (as other protein coatings) is

permeable to water (SIK )

RESPIRATION IV

Litchi, being a non-climacteric fruit, will exhibit a decreasing respiration rate

The coating does not seem to affect the respiratory pattern significantly

Possible explanations:Kaffirin has very good gas barrier properties

(SIK study but experience from Pears) In litchi, it would seem that a perfect film was

not formed on the litchi

COLOUR I

Litchi LightnessL*

Rednessa*

Yellownessb*

Hue angleh

Fresh,uncoated

40 31 21 34

Freshly coated

36 27 19 34

Uncoated, brown, 3 days

38 20 16 40

Coated, brown,3 days

48 10 11 48

COLOUR IV

Main observations:

•Coating significantly changed the colour characteristics of the peel

•Darkening of the peel + white deposit

•Mechanisms underlying the darkening different from browning of uncoated peel

MICROBIOLOGY

Main observations:

Coliforms, TVC, yeasts & moulds:

Coating tends to decrease the load for these flora

Lower values recorded for 4°C

Moulds identified: Torula, Scopulariosis, Cladosporium, Aspergillus, Geotrichum, Rhizopus

Properties of ideal coating for litchi

• To reduce water loss

• To maintain red colour and hence slow down browning

UNDERSTANDING THE MECHANISM I

• Darkening of pericarp (distinct from natural browning process)

• Last meeting, one hypothesis was ethanol may have killed the pericarp

• Import of litchi from Reunion, Trial with • water only, • ethanol only, • ethanol+plasticiser• Observation• Combination of ethanol + plasticiser brought this

darkening very early as from day 2

UNDERSTANDING THE MECHANISM II

• WhiteningIn the absence of the protein, darkening occurs but no white deposit appears

• One probable explanation for white deposit may be some form of precipitation of the protein on the peel

• It can have some relationship with RH as in packed containers, it is less (as drying occurs, water coming out of the peel may cause it)

• Probably, no proper film is formed on the surface of the peel, thus it does not act as a barrier to gas and water

• Can the rough spikes on the pericarp account for failure of film formation?

• Or is it some properties of the litchi pericarp that makes the coating incompatible?

Bozdemir and Tutas (2003) studied the barrier properties of edible films prepared from polysaccharide polymer (locust bean gum) and various plasticisers (glycerol, propylene glycol, sorbitol, and polyethylene glycol 200) together with hydrophobic modifiers (stearopten and beeswax). They too observed the presence of a white residue and reported that the appearance of a white residue on edible films containing plasticisers has been referred to as “blooming" or blushing" -this occurs when the plasticiser concentration exceeds its compatibility limit in the polymer causing phase separation and physical exclusion of the plasticiser. A similar phenomenon of blooming can have occurred in this study

• Consumers preferred uncoated litchi to coated litchi

APPLICATIONS OF COATINGS TO FRUITS AND NUTS INTRODUCTION The main aim of the ENVIROPAK project was to improve the quality of southern African export fruits and nuts by extending their shelf-life through application of edible coatings made from sorghum protein, kafirin. These coatings can potentially provide a semi-permeable barrier to gases and water vapour, thereby reducing respiration rate and water loss. Studies have therefore been carried out to determine the effect of selected kafirin coatings on the post-harvest response and shelf-life of litchis, pears and cashew nuts.

 EXTENDING THE SHELF-LIFE OF EXPORT QUALITY LITCHIS Daya GoburdhunUniversity of MauritiusFaculty of AgricultureReduitMauritiusE mail number: daya@uom.ac.mu From a baseline study conducted, the major post harvest problems associated with litchis were identified as rapid peel (pericarp) browning resulting in a loss of the favourable red colour as well as water loss. The effect of a kafirin coating on the post-harvest response and shelf-life of litchis stored under conditions simulating domestic, retail and export

conditions were investigated.

Immediately after coating, the litchis appeared red in colour and were glossier than the uncoated litchis (Figure 1). However, after only one day of storage, an unacceptable darkening of the whole peel (pericarp) surface occurred as well as the formation of a white powdery deposit on the peel (Figure 2). It was therefore not surprising that the external colour of the uncoated litchis were preferred to that of the coated litchis by the majority of panelists in a consumer sensory evaluation test.

Although the kafirin coating did not affect the pH, titratable

acidity or total solids content of the litchis during storage, it

decreased the respiration rate of the litchis stored at 4 °C. .

Compared with the uncoated litchis, slight decreases were

observed in microbial counts for the coated litchis in terms of

aerobic bacteria, coliforms and moulds. However, the kafirin

coating did not provide a suitable water vapour barrier, since the

use of the coating did not reduce water losses