Cereal beta-amylases

Cereal beta-amylases are perhaps best known in terms of the vital role they play in releasing easily fermentable sugars from cereal grain starch to fu el the production of alcohol by yeast in brewing. The extent to which they have been investigated is indeed largely due to their significance in this economically important industry. However, cereal beta-amylases are also, or could be, employed in many other aspects of the food industry and the anal ysis of starch, and they constitute valuable markers in cereal assessment a nd breeding studies. Quite apart from their practical significance, they ar e rewarding objects of biochemical and physiological research. They are int eresting models for the study of enzyme polymorphism, post-translational mo dification and the differential expression of isoenzymes. In spite of their often high activities in situ and all that is known about their generation , they are an enigma in that their physiological function, or even necessit y, remains unclear. It has been recently recognised that there are two diff erent categories of cereal beta-amylases which exhibit different tissue and taxonomic specificities and physiological developmental patterns. The 'cla ssical' beta-amylases present at high activities in cereal seeds appear to be limited to the endosperm of the species of the Triticeae tribe of the Fe stucoideae subfamily of the Gramineae (wheat, barley and rye), whereas all cereals exhibit a different, tissue-'ubiquitous' form of the enzyme which i s present at much lower activity levels. The physiological phenomenology an d the usage of cereal beta-amylases are discussed in relation to these two categories of enzyme. (C) 1999 Academic Press.