REVIEW PAPER

TEXTURE OF TABLE OLIVES AND PIMENTOS

MATIAS J. F E R N ~ N D E Z D ~ E Z Instituto de la Grasa y sus Derivados

Sevilla, Spain

(Manuscript received June 7, 1978; in final form October 11, 1978)

ABSTRACT

Mechanical and chemical methods applied to quantifying the texture o f table olives and pimientos are reviewed, and examples are given o f studies on factors affecting the texture o f these products (such as fruit maturity and processing) in which these methods have been used. The four instruments found applicable to olives are: Christel Texturometer, FFL Penetrometer, IC Texturometer and Krumer Shear Press (com- pression and shearlcompression cells). The latter has also been used with pimientos. Advantages and disadvantages o f each are discussed. Additional work is needed on correlating the mechanical tests with sensory evaluation. The chemical methods involve quantification o f pectic su bstunces and their degradation products.

INTRODUCTION

The table olive is utilized widely for human consumption throughout the world. Either as an appetizer, accompanying alcoholic and non- alcoholic beverages, or as a food of high nutritive value its use is exten- sive in all markets, especially in Europe and the USA.

T h e annual product ion reaches values oscillating between 550,000and660,000 tons within the last 10 years and shows a definite, although relatively slow, upward trend. The annual production in the previous decade averaged about 450,000 tons.

The most important production zones are located in the Mediter- ranean area which accounts for about 85% of the total production, the rest being produced mainly in the USA and Argentina; Australia, Chile, Peru and other countries account for a lower proportion of the crop.

The producing countries may be listed in the following decreasing order of importance: Spain, Turkey, Greece, Italy, USA, Morocco, Argentina, Peru and Portugal. This order changes slightly from year to year, except for the first two countries where the annual production is

Journal o f Texture Studies 10 (1979) 103-116. All Rights Reserved. @Copyright 1979 by Food & Nutrition Press, Inc., Westport, Connecticut 103

104 MATIAS J. F E R N ~ N D E Z D ~ E Z

close to or above 20% of the world crop each. Fruits are picked at different stages of maturity which, according to

the color of the skin, ranges from green to black or purple black. After harvesting, olives are processed to eliminate the characteristic bitterness caused by the presence of a glucoside, oleuropein. Afterwards, either a fermentation period or a thermal treatment give to the final product the special flavor, color, and texture which are so appreciated by the consumers.

The specific processing conditions vary according to the customs of the producing country, the selected degree of fruit maturity during harvest and the consumer preference. As a result, different types of olives are marketed to meet specific consumer demands. The important commercial types in the international market are:

(a) Spanish style pickled green olives (b) California style black ripe olives (c) Greek naturally ripe olives. For the Spanish style pickled green olives, fruits are harvested when

the skin achieves a green or a yellowish-green color. Bitterness is elimin- ated by treatment with a dilute NaOH aqueous solution. The fruits are then washed with water and placed into a diluted NaCl brine to under- go a lactic acid fermentation. The final fermented product is frequently pitted and stuffed with different products, the most popular among which is the pimiento (sweet red pepper). This item represents 60-70% of the Spanish export olives.

California style black ripe olives are prepared from fruits which are picked when the skin color is changing from yellowish-green to red or purplish-red. The fresh olives are also treated with a dilute NaOH solu- tion to eliminate oleuropein, and are then subjected to an air oxidation process to obtain the black color. The fruits are canned in dilute brine and thermally processed.

Greek naturally ripe olives are prepared from quite ripe fruits, with either purple or black skin and flesh. They are placed directly into a dilute NaCl brine and fermented. The elimination of oleuropein is very slow and incomplete. Thus, the final product is slightly bitter, very tasty and different from the other two. It is also highly valued in international markets.

A detailed description of olive processing and of the fruit varieties used for thel different pro,cessed olive types has been published by Fern’andez Diez (1971). This publication also reviews the research on that subject during the last thirty years.

The international market for table olives is regulated by standards prepared through the International Olive Oil Council (1975) and the consumer is protected by standards elaborated by the combined com-

TEXTURE OF TABLE OLIVES AND PIMIENTOS 105

mission of the International Olive Oil Council and the Codex Alimen- tarius through F A 0 and WHO (1974). Independently, all import and export countries have their own national standards to regulate and control the quality of the product.

In the final product, texture is one of the sensory quality attributes of greatest importance to the consumer. Subjective impression to touch and chewing (finger feel and mouthfeel) have a definite influence on consumer acceptance of the product. Hence, there is much interest in identifying objective quality control procedures which would simulate the subjective impression as much as possible.

The literature contains much work related to fruit texture in general and to specific fruit types in particular. Recently, Calzada and Peleg (1976) have prepared an extensive and interesting review of 218 such papers which represent all of the main research conducted up to 1976.

However, research on the texture of table olives and pimientos is sketchy and not very complete. It will be summarized in this paper with the hope of stimulating the research workers to increase the investiga- tive efforts within so interesting an area.

OBJECTIVE TEXTURE TESTING METHODOLOGY

Purpose

An objective method constitutes a very useful tool to replace the subjective' evaluation if it is possible to establish a good correlation between the two measurements. In this way, both the manufacturer and the seller may have a clearer understanding of how to control buyer and consumer reactions. However, obtaining such a correlation is diffi- cult and research towards that point is always long and tedious.

The first step in this work, studying the accuracy and precision of an objective method, may supply a useful tool to research workers, permit- ting them either to control the process at the factory or to compare processing methods at the laboratory. Even so, correlations with sensory evaluation have not been well determined.

Important parameters determining the quality of the final product, such as fresh fruit maturity, composition, treatments during different stages of the process, and even different manufacturing procedures, may be controlled with an objective method, although such a method reflects the subjective impression of the consumer only in a partial or approximate way.

Thus, the purpose of research on the texture of olives may be sum- marized as follows:

106 MATIAS J. FERNANDEZ DIEZ

(a) study of factors which may have an influence on the final product texture

(b) comparison among processing and storage methods in rela- tion to the effect on texture

(c) correlation between objective and subjective evaluation. It could be said that, for table olives and pimientos used for stuffing

the Spanish style green olives, research along the first two objectives has progressed at a moderate speed. Investigations against the third objec- tive are still in the beginning stage.

Classification of the Studied Methods

Objective methods for texture determination which have been applied to olives and pimientos may be classified within two main groups: (1) instrumental, or direct methods, based on a physical measurement (force or pressure) related to texture; (2) chemical, or indirect methods, based on the analysis of certain components of the fruit related to cell structure and to the mechanism of its degradation. These data can be correlated with texture changes.

INSTRUMENTAL OR DIRECT METHODS

Research workers of the California Olive Association (1956, 1959, 1960, 1961) made the first texture measurements on processed olives using the Christel Texturometer, described by Kramer and Twigg (1962). The action of the instrument is based on a combined measurement of compression and shear force. Although these evaluations allowed to es- tablish a tentative texture scale for olives and certain correlations with the taste panel, the method could not be standardized because of large deviations in values obtained with different units.

The Kramer Shear Press (presently called the Texture Test System and manufactured by Food Technology Corp., Rockville, MD 20852, USA) measures compression and shear-compression forces and is also described in detail by Kramer and Twigg (1962). Its action is mechanical and hence it shows a precision and accuracy greater than the Christel Texturometer which is hand operated. For those reasons it seemed to have good possibilities as a control tool for olive proyessing. Fernhndez Diez and Cordon Casanueva (1966 ), and Fern'andez Diez and Vidal Sigler (1968) established the test conditions for determining the texture of olives (fresh, processed, pitted and unpitted) using two stan- dard cells: compression and shear-compression. These authors studied statistically different factors such as the sample type, piston speed,

TEXTURE OF TABLE OLIVES AND PIMIENTOS 107

number of replicates, significance of readings, and the manner of expressing the results. Kramer Shear Press conditions selected for olives are given in Table 1.

Table 1. Selected Kramer Shear Press conditions for olives

Compression Test Shear-compression Test

Type of Sample Size graded Pitted fruits Unpitted fruits

1-4 fruits placed in a single layer

Constant (24.3 s)

Size of Sample 100 g randomly placed into the cell

Constant (24.3 s Piston Speed

Number of Replicates

Reading 10 10

First stop of dynamometer; or first relative maximum when using electronic recorder recorder

Maximum point reached by dynamometer or

Results Kg per 100 g unpitted h i t s pitted fruits

Kg per 100 g

Source: Fernhndez Dkez and Cordbn Casanueva (1966) and Fernhndez Diez and Vidal Sigler (1968)

The Shear Press was studied t o determine its capabilities in measuring the effect on the texture of the final product of (1) different processing treatments, and (2) fruit maturity. Table 2 shows a typical example of texture variations with maturity for Manzanilla variety fresh olives.

The results showed a good possibility of correlating the compression test with the finger feel. A correlation significant at the 1% level was obtained between Kramer Shear Press readings on olives of 3 degrees of texture and 20 sensory tests ,made with 10 trained panelists.

Afterwards, Fernandez Diez et al. (1968) adapted with good results the shear-compression test to study the texture of pimientos used for stuffing Spanish-style green olives. Whole pimientos were divided into quarters and 100 g samples were used for the measurements. The piston speed and the number of replicates were the same as used for olives

108 MATIAS J. FERNXNDEZ D ~ E Z

Table 2. Typical texture variations with maturity for Manzanilla variety

Shear-Corn pression Test Harvesting Date kg/100 g Fruit

July 20 Sept. 3 Nov. 5

388 340 195

Source: Fernbdez Diez and Vide1 Sigler (1968)

(‘hble 1). Texture values ranking from 183 to 116 kg/100 g fruits were obtained for different samples depending upon the degree of quality.

Professor Etchells of North Carolina State University designed an experimental FFL Penetrometer similar in certain aspects to the Magness Taylor Pressure Tester (Magness and Taylor 1925). Etchells et al. (1966) used that apparatus to determine the texture of Spanish style green olives and to study the influence of several factors, such as fruit variety, acidity of the fermented product, thermal treatment, etc. They also established a scale to classify the fruits according to their texture. That scale, expressed as grams of pressure per fruit, ranged from 175 and below for soft olives to 326 and above for hard olives. However, those values must be considered only as relative to the test conditions.

The FFL Penetrometer was also used by Blasco Frois et al. (1973) to determine the texture of Greek naturally ripe olives in brine and by Mhrquez Gonzhlez et al. (1975) and Etchells et al. (1975) on Spanish style green olives.

Although the apparatus presents a high degree of subjectivity because of the influence of the operator, it permits one to study the different texture-influencing factors if it is always used by the same person. The Penetrometer has the advantage of using smaller samples as compared to the Shear Press and correlates well with the compression cell (r = 0.9971; P < 0.001). A lower correlation was obtained between the Penetrometer data and the shear-compression cell (r = 0.8049; P = 0.02 - 0.05 ).

Garrido Fernhdez et al. (1975) designed the IG Texturometer which works by air pressure and measures the pressure necessary to move a shear-compression cell. The results correlated perfectly with the Kramer Shear Press measurements (r = 0.9512, P < 0.001 ) and with panel tests (P < 0.01). This apparatus has the advantages of low cost and reduced size sample (10 g of pitted fruits) and is easy to construct. The details are fully described in the referred paper.

TEXTURE OF TABLE OLIVES AND PIMIENTOS 109

Table 3 summarizes the principal characteristics of the different devices mentioned above and used in recent years as direct methods for determining the texture of olives and pimientos.

CHEMICAL OR INDIRECT METHODS

I t is known that pectic substances and their degradation by the action of enzymes either naturally present in the fruits or produced by microorganisms are important factors influencing texture.

Femhndez D!ez et al. (1974) have recently initiated research along these lines on olives and pimientos adapting the existing methodology. They have determined the total pectins, the degree of esterification and the diacetyl content, and have proved the presence of pectinesterase in olives. Later on, Castillo Gomez et al. (1978) studied the presence and action of polygalacturonase in the same products.

All these analyses may be correlated with textural changes in the fruits at different stages of maturity and due to processing and storage before and after treatment. They may represent an efficient way to monitor the textural quality of olives.

APPLICATIONS OF OBJECTIVE TEXTURE TESTING METHOD0 LOGY

Spanishstyle Pickled Green Olives

Fernhndez Diez and Cordbn Casanueva (1966) applied the technique of Shear Press to fresh fruits in order to see the effect of harvesting time on texture. They studied four different varieties of olives: Gordal, Manzanilla, Rapazalla and Zorzalena. The effect of lye penetration during the NaOH treatment needed to eliminate the bitterness, and the action of further water washings was also investigated. Using the second reading obtained with the compression cell, these authors determined the pit texture and its variation with maturity. Typical data are shown in Table 4.

Using the same apparatus, Fernhndez Diez and Vidal Sigler (1968) studied the correlation between the fruit size and the compression force, and the effect on the pickled product of storage time, salt con- centration and harvesting time. They also analyzed the correlation be- tween the compression test and the finger feel and found it to be highly significant.

Femhndez Villasante and Fernhndez Diez (1968) also used the shear- compression test with good results to control the different stages of

Tab

le 3

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TEXTURE OF TABLE OLIVES AND PIMIENTOS 111

salting the fresh fruits. The better the texture of the fruits, the higher was the salt concentration necessary to float the olives (Table 5).

Table 4. Effect of maturity on texture of flesh and pit in fresh olives

Stage of Compression Test (kg/100 g fruit) Variety Maturity 1st Reading (flesh) 2nd Reading (pit)

Manzanilla unripe ripe

Zorzaleiia unripe ripe

4 8 3 9

51 45

180 144

137 114

Source: Femandez Diez and Cordon Casanueva (1966)

Table 5. Effect of olive texture o n floating condi- tions of the fruit

Shear Compression Test (kg/100 g fruit)

306 Water 315 1" Bb NaCl brine 325 2" B'e NaCl brine 332 3" Bk NaCl brine 335

Liquid t o Float Olives

Over 3" Bb NaCl brine

Source: Fernhdez Villasente and Fernhndez Diez (1968)

Both tests, compression and shear-compression, were applied by Rodriguez de la Bordolla et al. (1969) to control the effect of lye con- centration on the pickling process and the effect of a previous pasteriza- tion on the final product.

Montero Marin and Fernhndez Diez (1976) studied in detail the be- havior of the Gordal variety in relation to the following factors: fresh fruit maturity and growth, size and pickling process. They used both tests with the Shear Press and expressed the results as the ratio between compression and shearlcompression forces which they called the texture index, a parameter previously utilized by Fern'andez Diez et al. (1972) for other olive varieties (Table 6).

Marquez Gonzalez et al. (1975) and Etchells et al. (1966, 1975) applied the FFL Penetrometer to studying the effect on texture of different factors such as fruit size, variety and treatments.

112 MATIAS J. F E R N ~ N D E Z D ~ E Z

Table 6. Typical variation of the texture index (compression testlshear compression test) with maturity for Gordal variety olives

Harvesting Time Texture Index

August 26 0.77 September 5 0.70 September 14 0.66 October 4 0.65 October 16 0.64

Source: Montero Marin and Fernkdez Diez (1976)

California Style Black Ripe Olives and Greek Naturally Ripe Olives

California style black ripe olives were studied by Garrido Fernhdez e t al. (1975) who used the IG Texturometer to determine the effect on texture of different treatments applied during the pickling process.

With Greek naturally ripe olives, textural changes in fresh fruit during growth and maturation were folfowed with the Shear Press by Garripo Femhdez and Femhdez Diez (1972) on three varieties, Lechn, Hojiblanca and Verdial.

Blasco Frois et al. (1973) undertook a comparative texture study on processed olives of 4 varieties (the 3 mentioned above plus Pic0 Limbn) with 2 devices, the Shear Press and the FFL Penetrometer. They found a highly significant correlation between the compression test and the penetrometer values. However, the correlation between the shear- compression values and the penetrometer results was only fair.

The relationship between the texture of fresh fruits and that of the processed product all along the fermentation period has been studied in Greek naturally ripe olives by Ganido Fem'andez e ta l . (1972), Durhn Quintana e t al. (1973) and Gonzkilez Cancho et al. (1975) using the two Shear Press standard cells.

The shear-compression cell has been utilized by Femhdez Diez e t al. (1975) to control the effect of calcium salts treatments on the same type of olives.

Indirect methods, using determinations of pectic composition and pectinolytic enzymes essays, have been applied to Greek naturally ripe olives by Femhdez Diez e t al. (1974), Minguez Mosquera e t al. (1976) and Castillo Gbmez e t al. (1978). When the texture decreased, a parallel decrease in pectin content was always found, as well as a decrease in the degree of esterification. Pectinesterase and polygalacturonase activity always accompanied changes in texture (Tables 7 and 8).

TEXTURE OF TABLE OLIVES AND PIMIENTOS 113

Table 7. Pectinesterase activity in the extracts of fresh olives, Hojiblanca variety, with different stages of maturity

Stage of Maturity Date (u. PE) g

Green Nov. 20 0.02 Turning color Dec. 21 0.12 Black Jan. 26 1.40 Black Feb. 3 2.47 Black Feb. 20 1.06 Black (overripe) March 16 0.57

Table 8. Polygalacturonase activ- ity in the extracts of Hojiblanca variety olives with different stages of maturity (pH = 4.0)

Decrease in Stage of Maturity Viscosity (%)

Green 0.0 Turning color 0.0 Ripe 16.4 Overripe 39.4

Hmien t 0 s

In the case of the pimiento, the shear-compression cell of the Shear Press is the only device which hasI been used to meyure texture. Re- search conducted by Femhndez [Diez e t aZi (1968), Minguez Mosquera e t al. (1970,1973), Femhndez Diez and Minquez Mosquera (1975) and Gonzhlez Cancho et al. (1975) has allowed to study the textural effects of different processing stages and methods of peeling, storage and fermentation, to establish a tentative textural scale (Table 9), and to determine the action of salt concentration and acidity,

Indirect methods used on black olives were also successfully applied to pimientos. Ahin changes in pectic composition with texture variation were similar to those found in black olives.

SUMMARY

During the last 12 years 3 different instrumental devices and some

114 MATIAS J. FERNXNDEZ D ~ E Z

Table 9. Classification of processed pimientos according to texture (tentative scale)

Shear Compression Test Subjective Commercial (kg/100 g fruit) Evaluation Category

above 190 Very hard 1 90-1 7 1 Hard 1st 170-1 51 Medium 2nd 1 50-1 31 Soft 3rd 130 and below Very soft

chemical methods, based on pectin analysis and pectic enzymes deter- minations, were used to measure the texture of 2 important items of the Spanish pickling industry: table olives and pimientos.

Only partially positive results were obtained, and several interesting avenues remain open for the continuation of these investigations and for the identification of better quality control methods to be applied to the textural parameters of these products.

REFERENCES

BLASCO FROIS, J. J., GARRIDO FERNANDEZ, A., and FERNhNDEZ DiEZ, M. J. 1973. Applicacibn de un penetrbmetro experimental a la detenninacibn de textura en las aceitunas negras maduras en salmuera. G r a m y Aceites 24, 280-286.

California Olive Association. Proceedings 1956. California Olive Association. Proceedings 1959. California Olive Association. Proceedings 1960. California Olive Association. Proceedings 1961. CALZADA, J. F. and PELEG, M. 1976, Evaluacibn de la te3tura en frutas. Revision

bibliogrbfica, Revista de Agroqdmica y Technologla de Alimentos, 16, 459-472.

CASTILLO GbMEZ, J., d N G U E Z MOSQUERA, M. I. and FERNANDEZ DiEZ, M. J. 1978. Presencia de poligalacturonasa y su relacion con el ablandamiento en algunos productos empleados en la industria del aderezo (pimientos y acei- tuyas), Grasas y Aceites, 29, 97-101.

CANCHO, F. and FERNANDEZ DfEZ, M. J. 1973. Aceitunas negras maduras en salmuera. 111. Estudio fisico-quimico y microbiologico de la ferrnentacion, Grasas y Aceites 24, 149-159.

ETCHELLS, J. L., BERG, A. F., KITTEL, I. D., BELL, T. A. and FLEMING, H. P. 1966. Pure culture fermentation of green olives, Appl. Microbiol. 14, 1027-104 1.

ETCHELLS, J. L., KITTEL, D. I., KELLING, R. E., BELL, T. A , MONROE, R. J., and FLEMING, H. P. 1975. El texturbmetro FFL: Un aparato para medir la firmeza de las aceitunas verdes tip0 espanol, Grasas y Aceites 26, 139-146.

D U R A N QUINTANA, M. c., GARRIDO F E R N ~ N D E Z , A., GONZALEZ

TEXTURE OF TABLE OLIVES AND PIMENTOS 115

FERNANDEZ DiEZ, M. J. “The Olive” In The Biochemistry of Fruits and Their Pro@cts. Vol. 2 1971 (A.C. Hulme e,d.) pp. 255-279, Academic Press, London.

FERNANDEZ DiEZ, M. J. and CORDON CASANEUVA, J. L. 1966. Determina- ciorfes de textura en aceitunas, G p a s y Aceites 17, 8 8 4 4 .

FERNANDEZ D’IEZ, M. J., FERNANDEZ VILLASANTE, J. and GONZhLEZ PELLISSb, F. 1968. Textura de pimientos empleados en el relleno de aceitunas. Efeyto de la acidez y del tiempo de conservacion, Grasas y Aceites 19, 16-18.

F., DURAN QUINTANA, M. C. and CORDbN CASANEUVA, J. L. 1972. Elaboracion de aceitunas negras de mesa, Instituto de la Grasa y sus Derivados, Sevjlla, pp. 104-112.

FERNANDEZ DiEZ, M. J. and MfNGUEZ MOSQUERA, M. I. 1975. Efecto de la concentracibn de sal sobre las deterrninaciones de textura en pimientos y su

ALVAREZ, M. 1975. Efecto del cloruro chlcico sobre la textura y color de aceitunas negras. Anales de Bromatologih XXVII-3 209-222.

FERNhNDEZ DiEZ, M. J., IdNGUEZ MOSQUERO, M. I., and CASTILLO GbMEZ, J. 1974. Composicibn pectica y presencia de pectinesterasa en algunas py luc tos del aderezo. Grasas y Aceites, 25, 331-340.

FERNANDEZ DfEZ, M. J. and VIDAL SIGLER, A. 1968. Determinaciones de textura en aceitunas, 11. Las pruebas de compresion-cizallamiento. Grasas y Aceites 19, 199-204.

FERNXNDEZ VILLASANTE, J. and FERNhNDEZ D!EZ, M. J. 1968. Classifica- tion des olives vertes d’apr8s leur degre de maturite par flottage en summure, Informations Oleicoles Internationales 42, 59-63.

GA RID0 FERNANDEZ, A., CORDbN CASANEUYA, J. L. and FERNhNDEZ

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GARRIDO FERNXNDEZ, A. and FERNXNDEZ DiEZ, M. J. 1972. Aceitunas negras de mesa. Evolucion de las principales caracteristicas del fruto durante el desarrollo y maduracion. Grasas y Aceites 23, 309-318.

CANCHO, F. and FERNANDEZ DfEZ, M. J. 1972. Aceitunas negras maduras en sa lmuera . 11. Estudio fisico-quimico y microbiolbgico de la fermenta- cion. G r a m y Aceites 23, 22-31.

GARRIDO FERNANDEZ, A. and FERNANDEZ DfEZ, M. J. 1975. El proceso de fermentacibn en las aceitunas negras maduras en salmuera. Grasas y Aceites 26, 1297-309.

FERNANDEZ D’IEZ, M. J., GARRIDO FERNANDEZ, A., GONZALEZ CANCHO,

Grasa y Aceites 26, 313-315. J., MfNGUEZ MOSQUERO, M. I., and CARVAJAL

D 7 EZ, M. J. 1975. DiseTo y estudio de un texturometro experimental para su

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GONZALEZ CANCHO, F. NOST. VEGA, M., D U R ~ N QUINTANA, M. c.,

0, F., NOSTI VEGA, M., MfNGUEZ MOSQUERA, M. I. and M. J. 1975. Estudio de las fases de la ferrnentacion del

pimiento ernpleado en el relleno de aceitunas. Grasas y Aceites, 26, 63-72. International Olive Oil Council 1975. Document 1, 12th Meeting of the Table

Olives Committee, Madrid. KRAMER, A. and TWIGG, B. A. 1962. Fundamentals of Quality Control f o r the

Food Industry, pp. 87-93, The Avi Publishing Co., Inc., Westport, Conn. MAGNESS, J. R. and TAYLOR, G. F. 1925. An improved type of pressure tester

for the determiantion of fruit maturity. USDA Circ. 350.

116 MATIAS J. FERN~NDEZ D ~ E Z

MARQUEZ GONZALEZ, J., MONFALVEZ CORThS, J. and FERNhNDEZ DiEZ, M. J. 1975. Empleo del penetrometro FFL para determinar la textura de acei- tunas verdes estilo espanol. Grasas y Aceites 26, 221-232.

MtNGUEZ MOSQUERO, M. I., CASTILLO GbMEZ, J. and FERNhNDEZ DfEZ, M. J. 1976. Variaciones en la composicion pectica durante la elaboracibn, fer- mentacibn y conservacibn de productos aderezados (pimientos y acei- tunas), Grasas y Aceites 27, 27-32.

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