Microbial carboxylic ester hydrolases (EC 3.1.1) in food biotechnology

Abstract

Ester linkages between carboxylic acid groups and hydroxyl groups are basic to the structure of carboxyesters and lipids, and occur commonly as modifications of polysaccharide molecules. Microorganisms produce enzymes which hydrolyse the carboxylic ester linkages in substrates which are being utilized for growth. Such esterase reactions are frequently easily reversible, depending on the concentration of reactants or availability of water. The importance of esters as flavour compounds has resulted in the selection of yeast strains which produce esters in beverage fermentation. The synthetic potential of triacylglycerol lipases (EC 3.1.1.3) has been exploited by use of the purified enzymes in environments of low water activity. The techniques of molecular biology facilitate analysis of the homology between carboxylesterase enzymes and a detailed knowledge of structure and specificity provides the opportunity to modify enzymes to suit particular applications in biotechnology. Esterase activity can be assayed conveniently by using synthetic chromogenic esters of naphthol or nitrophenol. Naphthyl and nitrophenyl acetates are readily hydrolysed by a wide range of enzymes including lipases (Hofelmann et al. 1985; Brahimi-Horn et al. 1990; Gilbert et al. 1991), serine protease (Klapper et al. 1973) and acetylxylan esterase (Lee et al. 1987). Electrophoretic separation followed by detection using chromogenic esters has demonstrated polymorphism of esterase enzymes and has been used to type strains of bacteria (Goullet & Picard 1990, 1991; Picard & Goullet 1990) but was less discriminating with yeasts (Campbell et al. 1972) and edible mushrooms (Itavaara 1988).