Chapter 20
Effect of Enzyme Treatment on the Quality of Processed Fruit and Vegetables
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W. Pilnik and A. G. J. Voragen Department of Food Science, Agricultural University, P.O. Box 8129, 6700 EV Wageningen, Netherlands
Pectinases, cellulases and hemicellulases are used f o r clarification of f r u i t juices, juice extraction, improvement of cloud s t a b i l i t y of vegetable and f r u i t juices and nectars, liquefaction and maceration of fruits and vegetables, reduction of cooking time of pulses and improvement of rehydration c h a r a c t e r i s t i c s of dried vegetables. The chemical basis of these treatments and of the consequential changes i n sensory and n u t r i t i o n a l quality are discussed.
In the processing of f r u i t and vegetables exogenous enzymes are used as processing aids to improve or maintain the quality c h a r a c t e r i s t i c s of t r a d i t i o n a l products. The use of enzymes further provides p o s s i b i l i t i e s f o r product and process development ( 1 ) . Table I summarizes present uses and Table II shows the quality aspects involved. Table I. Commercial p e c t o l y t i c enzymes i n f r u i t and vegetable technology
Clarification of fruit juices,
e.g. apple j u i c e ; depectinised juices can also be concentrated without g e l l i n g and without developing t u r b i d i t y . Enzyme treatment of pulp of soft f r u i t , red grapes, c i t r u s and apples, for better release of juice and colour pigments.
Maceration of
fruits
and
vegetables
(disintegration
by c e l l
separation) to obtain nectar bases and baby foods. Liquefaction of fruits and vegetables, to obtain products with increased soluble solids content (pectolytic and c e l l u l o l y t i c enzymes combined). Special applications. Treatments to improve rehydration and cooking c h a r a c t e r i s t i c s of pulses and dried products.
0097-6156/89/0405-O250$06.00/0 ο 1989 American Chemical Society
In Quality Factors of Fruits and Vegetables; Jen, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.
20.
PILNIK & VORAGEN
251
Enzyme Treatment and Quality
Table I I . Quality aspects of use of exogenous enzymes C l a r i t y or cloud s t a b i l i t y of j u i c e s . Acid taste, aroma, mouth f e e l (changes). N u t r i t i o n a l compounds. Undesirable compounds. Rehydration / cooking time of dried vegetables, pulses, potatoes.
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Pectinases Because pectic substances are important f o r the firmness ( c e l l walls) and cohesiveness (middle lamella) of parenchymatic plant tissue (2j_3) and for the properties of products derived from f r u i t s and vegetables (4) p e c t o l y t i c enzymes are mainly used. Commercial preparation are usually c a l l e d pectinases and are derived mainly from Aspergillus niger. Table III (5) shows the s p e c i f i c a c t i v i t i e s of three different commercial preparations determined on polysaccharide substrates. The points of attack of the p e c t o l y t i c a c t i v i t i e s are i l l u s t r a t e d on a pectin model i n Figure 1. Pectin lyase (PL) depolymerizes highly e s t e r i f i e d pectin by s p l i t t i n g g l y c o s i d i c linkages next to methyl e s t e r i f i e d carboxyl groups through a β-elimination mechanism (Figure 2). Another depolymerization pathway i s by the combined action of pectinesterase (PE) and polygalacturonase (PG). PE s p l i t s off methanol from highly e s t e r i f i e d pectin transforming i t into low ester pectin which i s hydrolyzed by PG attacking glycosidic linkages next to a free carboxyl group. PG and PE occur also as technologically important endogenous enzymes of f r u i t s and vegetables ( 6 ^ ) . Pectate lyase (PAL; Figure 2) also attacks g l y c o s i d i c linkages next to a free carboxyl group so that PE also prepares a substrate for this enzyme. PAL was not found i n the pectinases analyzed i n Table I I I , because i t i s a b a c t e r i a l rather than a fungal enzyme. Table I I I . S p e c i f i c enzyme a c t i v i t i e s of multi-enzyme complexes in technical fungal pectinase preparations expressed as International Units per g of Enzyme Preparation Enzyme a c t i v i t y Polygalacturonase Pectin lyase Pectin esterase Combined p e c t o l y t i c Cx-cellulase Ci-cellulase Arabanase: linear arabinan Arabanase: branched arabinan a-L-Arabinofuranosidase Galactomannanase Mannanase Galactanase Xylanase
A 1982 43 548 198 998 99 9 14 35 3 7 11 4
Β 3314 53 448 290 180 1 10 14 37 4 0 58 0
Source: Reproduced with permission from r e f . 5. Copyright 1986 International Federation of F r u i t Juice Producers.
In Quality Factors of Fruits and Vegetables; Jen, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.
c 1878 74 227 274 1228 22 16 16 333 9 0 91 2
252
QUALITY FACTORS OF FRUITS AND VEGETABLES ^ COOCH3
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pectin lyase pectînesterase
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