Discoloration in fruits and vegetables is reviewed in relation to the chemical and biochemical causes of black, brown, red, yellow, and green discolorations. In raw materials, only a limited understanding has so far been achieved of the internal black and brown discolorations. The biochemical signaling pathways triggered by wounding or chilling-storage, the nature of the enzymes and reactive oxygen species involved, and the identity of the phenolic compounds oxidized are areas where further information is desirable. In processed materials, a greater comprehension is needed of the role of ascorbic acid reactions in the browning of fruits and "pinking" of Brassicaceous vegetables, and more information is desirable on the structure and properties of the discoloring pigments in many products. It is concluded that a greater knowledge of these areas, and of the naturally-occurring constituents that can accelerate or inhibit the causative reactions, would lead to the development of more efficient methods of controlling fruit and vegetable discolorations.

Enzyme inactivation during heat processing is reviewed with regard to fundamental aspects (structure, thermodynamics and kinetics), mathematical models and the relationship between enzyme activity and food quality. Enzyme stability is related to enzyme structure and to factors in the microenvironment. Kinetics of inactivation are categorized with respect to reaction order and two models are briefly discussed which describe the variation of inactivation rates with temperature. The determination of accurate kinetic parameters is emphasized where the objective is to develop mathematical models of enzyme inactivation in real foods. The value of modelling inactivation is assessed. Enzymes having effects on sensory quality are reviewed with particular emphasis on those enzymes wiiich influence flavour, through lipid degradation, and those which affect texture by catalysing the breakdown of starch, pectin or protein.

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