Phenolic compounds and related enzymes as determinants of quality in fruits and vegetables

Phenolic secondary metabolites play an important role in plant-derived food quality, as they affect quality characteristics such as appearance, flavou r and health-promoting properties. Their content in foods is affected by ma ny factors that influence phenolic stability, biosynthesis and degradation. In terms of their biosynthesis the key enzyme phenylalanine ammonia-lyase (PAL) is especially relevant, as it can be induced by different stress (env ironmental) conditions. In addition, polyphenol oxidases (PPO) and peroxida ses (POD) are the main enzymes responsible for quality loss due to phenolic degradation. The different factors affecting phenolic-related food quality are reviewed. These include internal (genetic) and environmental (agronomi c) factors, technological treatments applied during postharvest storage of fruits and vegetables, as well as processing and storage of the processed p roducts. The different strategies that are required to either maintain or e nhance the phenolic-related quality of foods are critically reviewed. Genet ic modification designed to decrease polyphenol oxidases or peroxidases is not always a feasible method, owing to side problems related to the growth and defence of the plant. Agronomic treatments can be used to enhance the p henolic content and pigmentation of fruits and vegetables, although the inf ormation available on this topic is very scarce and even contradictory. Som e postharvest treatments (cold storage, controlled or modified atmospheres, etc) can also improve phenolic-related quality, as well as new processing methods such as irradiation (gamma, W), high-field electric pulses, high hy drostatic pressures and microwaves. (C) 2001 Society of Chemical Industry.