422 Novel food packaging techniques 115 Air0°C AC5%C02+5%O2-0°C -AC5%CO2+5%02-5°C Initial 14 days Fig 20.2 Colou ges ( Hue)of celery sticks stored for 14 days in air and in ontrolled atmosphere (5%CO2+ 5%O2) free of ethy lene at 0 and 5C(Artes et al, hand, antioxidants are related to chlorophyll retention in leafy products. Two antioxidants commonly present in fruits and vegetables are ascorbic acid and B- carotene, which protect chlorophyll by inhibiting the reactions that degrade it, retarding yellowing(Schwartz and von Elbe, 1983) 20.4.1 Anthocyanin degradation Anthocyanins are very unstable pigments, particularly once removed from their natural environment and the protection provided by co-pigmentation, leading to unattractive yellowish and brownish pigments. This is particularly evident when minimal fresh processed products are prepared. When conditioning fruit and vegetables by techniques like peeling, cutting, slicing, etc, cell membranes are disrupted, allowing the mixing of phenolic substrates located in the vacuole and pecific polyphenol oxidases enzymes(PPO; EC 1. 14. 18. 1)associated to cell membranes, (mainly in the plastids) Washing the product immediately after cutting removes sugars and other substrates at the cut surfaces minimising It is well known that colour due to anthocyanins is particularly degraded by the nzymic hydrolysis in harvested products as recently reviewed (artes et al., 2002c) Anthocyanins are oxidised in the vacuole of the plant cells in the presence of molecular O2 and under appropriate conditions of pH, temperature and water activity, by the action of the enzyme tyrosinase(EC 1.10.3. 1)or polyphenol oxidasehand, antioxidants are related to chlorophyll retention in leafy products. Two antioxidants commonly present in fruits and vegetables are ascorbic acid and - carotene, which protect chlorophyll by inhibiting the reactions that degrade it, retarding yellowing (Schwartz and von Elbe, 1983). 20.4.1 Anthocyanin degradation Anthocyanins are very unstable pigments, particularly once removed from their natural environment and the protection provided by co-pigmentation, leading to unattractive yellowish and brownish pigments. This is particularly evident when minimal fresh processed products are prepared. When conditioning fruit and vegetables by techniques like peeling, cutting, slicing, etc., cell membranes are disrupted, allowing the mixing of phenolic substrates located in the vacuole and specific polyphenol oxidases enzymes (PPO; EC 1.14.18.1) associated to cell membranes, (mainly in the plastids). Washing the product immediately after cutting removes sugars and other substrates at the cut surfaces minimising reactions responsible for changes in colour and nutritional quality. It is well known that colour due to anthocyanins is particularly degraded by the enzymic hydrolysis in harvested products as recently reviewed (Arte´s et al., 2002c). Anthocyanins are oxidised in the vacuole of the plant cells in the presence of molecular O2 and under appropriate conditions of pH, temperature and water activity, by the action of the enzyme tyrosinase (EC 1.10.3.1) or polyphenol oxidase Fig. 20.2 Colour changes (ºHue) of celery sticks stored for 14 days in air and in controlled atmosphere (5% CO2 + 5% O2) free of ethylene at 0 and 5ºC (Arte´s et al,. 2002b). 422 Novel food packaging techniques