Plant cell culture in the production of flavour compounds.

Plants are an important source of natural flavourings for food. Plant-derived food flavours may be based on endogenous flavour compounds or be derived from flavour precursors following enzyme action when the tissue is disrupted or during a postharvest treatment. Such flavours are usually based either on a single compound or a small group of compounds with closely related chemical structure. However, many of the plant-derived flavours which are of most significance in the food industry are complex mixtures of compounds which each contribute to the overall flavour; these include fruit flavours and the essential oils. The present paper will describe experiments aimed at developing tissue-culture systems in which to study these more complex flavours. A variety of plant tissue-culture systems are now available for study of flavour compound production. These include callus and cell-suspension cultures which have been used in studies of simple flavours such as capsaicin formation in Capsicum [l] and vanillin formation in VaniZZa [2]. In the case of Capsicum, capsaicin production is enhanced significantly if the cells are immobilized in polyurethane foam particles [ 31. However such systems have generally proved unsuccessful with more complex fruit flavours, where frequently only a small part of the spectrum of flavour compounds is formed in culture [4]. Disorganized plant cell cultures are often genetically heterogeneous and although they are totipotent in that single cells can be induced to regenerate whole plants, it is frequently not possible to induce selective expression of the pathways leading to the formation of the desired flavour compounds. In the intact plant, these pathways are expressed in a co-ordinated fashion within the patterns of differentiation of plant organs, in particular tissues at defined stages in organ development. Although some genes involved in the co-ordination of expression of plant pathways, such as the Zc genes involved in the pathway of formation of anthocyanin pigments, have been identi-