ECHNOLOGY OF CEREALS most cereals, they fall into two groups depending Proteolysis increases access by amylases to upon their isoelectic points. The Triticeae cereals starch granules as well as producing nitrogenous contain two groups while sorghum, millet, maize, nutrients, for the growing embryo in nature oats and rice have only one(Kruger and reed, and for yeast during fermentation for beer 1988 production Even the combined action of alpr. solubilized starch. Neither of them can catalyze hydrolysis of Lipid modifying enzymes a-(1-6)-bonds and hence branch points remain Enzymes of two types are important in catalyz intact. Also, those a-(1-4)bonds close to branch ing breakdown of lipids: lipase and lipoxidase points resist hydrolysis. Hence only about 85% Both are capable of causing rancidity in cereals of starch is converted to sugars. In order to thus both hydrolytic and oxidative rancidity increase yield of sugars in commercial processes, are recognized. Lipoxidase can only catalyze debranching enzymes may be used. Amylogluco- degradation of free fatty acids and monoglyce- sidase from fungal sources is a popular expedient, rides and therefore follows lipolysis. Lipolysis it catalyzes hydrolysis of both a-(1-4) -and a- proceeds slowly in the dry state; enzymic oxidation (1-6)-bonds leaving glucose as the ultimate occurs rapidly on wetting product. Some brewing processes permit the The problem of rancidity is potentially greatest of this enzyme and sake(see Ch. 9)production in oats which have a high oil content(4-1l average 7%). Maize also has a relatively high oil content because of its large embryo(about 4. 4%) B-Glucanases brown rice contains about 3% but other cereals contain only 1.5-2%. Problems caused by hydro- These enzymes assume greatest importance in lysis catalyzed by lipase are prevented in the case processing of barley in which B-glucans contri- of processed oats by stabilization,, a steaming bute 70% of cell walls. There are two endo-B- process which inactivates the enzyme(cf Ch 6) glucanases in barley malt, both synthesized In other cereals that are milled potential storage during germination. Each catalyzes hydrolysis of problems can be avoided in starchy endosperm -(1-4) linkages adjacent to B-(1-3)links, ulti- if it is separated from other grain parts where mately producing a mixture of oligosaccharides enzyme and substrate are concentrated. This is containing three or four glucosyl units ( Woodward common practice in the cases of sorghum and and Fincher, 1982). The two isoenzymes are maize grits, in which the embryo presents the and II in the aleurone. before being susceptible the aleurone layer also has a high lipid content. In to these enzymes it is thought that another wheat, lipase activities in the embryo and aleurone enzyme,B-glucan solubilase renders the substrate layer are 10-20-fold that of the endosperm(Kruger soluble(Bamforth and Quain, 1989 and Reed, 1988). The storage lives of bran, germ and wholemeal flour are considerably less than Proteolytic enzymes that of white four for this reason(see Ch. 7) As well as true lipases, esterases are also present Although proteolytic enzymes may be import- in cereals and in most studies the two classes have nt technologically in baking, their significance not been distinguished. Like other hydrolases is usually masked by the greater effects of alpha- they are synthesized during the early stages of amylase. In brewing their role is better under- germination, although oats are exceptional in stood. Both endo- peptidases and exo-enzymes having a high lipase activity in resting grain (the carboxypeptidases which catalyze cleavage Lipases catalyze hydrolysis of triglycerides to of single amino acids from the carboxyl terminus) produce diglycerides and free fatty acids, diglyce are present rides to give monoglycerides and free fatty acids68 TECHNOLOGY OF CEREALS most cereals, they fall into two groups depending Proteolysis increases access by amylases to upon their isoelectic points. The Triticeae cereals starch granules as well as producing nitrogenous contain two groups while sorghum, millet, maize, nutrients, for the growing embryo in nature oats and rice have only one (Kruger and Reed, and for yeast during fermentation for beer 1988). production. Even the combined action of alpha- and beta￾amylases cannot completely digest solubilized Lip jd modifyjng enzymes starch. Neither of them can catalyze hydrolysis of a-( 1+6)-bonds and hence branch points remain Enzymes of two types are important in catalyz￾intact. Also, those a-( 1-4) bonds close to branch ing breakdown of lipids: lipase and lipoxidase. points resist hydrolysis. Hence only about 85% Both are capable of causing rancidity in cereals; of starch is converted to sugars. In order to thus both hydrolytic and oxidative rancidity increase yield of sugars in commercial processes, are recognized. Lipoxidase can only catalyze debranching enzymes may be used. Amylogluco- degradation of free fatty acids and monoglyce￾sidase from fungal sources is a popular expedient, rides and therefore follows lipolysis. Lipolysis it catalyzes hydrolysis of both a-( 1-4)- and a- proceeds slowly in the dry state; enzymic oxidation (1+6)-bonds leaving glucose as the ultimate occurs rapidly on wetting. product. Some brewing processes permit the use The problem of rancidity is potentially greatest of this enzyme and sake (see Ch. 9) production in oats which have a high oil content (4-1l0h, is dependent upon it. average 7%). Maize also has a relatively high oil content because of its large embryo (about 4.4%), brown rice contains about 3% but other cereals contain only 1.5-2%. Problems caused by hydro- p- Glucanases These enzymes assume greatest importance in lysis catalyzed by lipase are prevented in the case processing of barley in which p-glucans contri- of processed oats by ‘stabilization’, a steaming bute 70% of cell walls. There are two endo-0- process which inactivates the enzyme (cf. Ch. 6). glucanases in barley malt, both synthesized In other cereals that are milled, potential storage during germination. Each catalyzes hydrolysis of problems can be avoided in starchy endosperm, p-( 1-4) linkages adjacent to p-( 1-3) links, ulti- if it is separated from other grain parts where mately producing a mixture of oligosaccharides enzyme and substrate are concentrated. This is containing three or four glucosyl units (Woodward common practice in the cases of sorghum and and Fincher, 1982). The two isoenzymes are maize grits, in which the embryo presents the synthesized in different sites, I in the scutellum greatest hazard, and in wheat and rice, in which and I1 in the aleurone. Before being susceptible the aleurone layer also has a high lipid content. In to these enzymes it is thought that another wheat, lipase activities in the embryo and aleurone enzyme, 0-glucan solubilase renders the substrate layer are 10-20-fold that of the endosperm (Kruger soluble (Bamforth and Quain, 1989). and Reed, 1988). The storage lives of bran, germ and wholemeal flour are considerably less than that of white flour for this reason (see Ch. 7). As well as true lipases, esterases are also present Proteolytic enzymes Although proteolytic enzymes may be import- in cereals and in most studies the two classes have ant technologically in baking, their significance not been distinguished. Like other hydrolases, is usually masked by the greater effects of alpha- they are synthesized during the early stages of amylase. In brewing their role is better under- germination, although oats are exceptional in stood. Both endo-peptidases and exo-enzymes having a high lipase activity in resting grain. (the carboxypeptidases which catalyze cleavage Lipases catalyze hydrolysis of triglycerides to of single amino acids from the carboxyl terminus) produce diglycerides and free fatty acids, diglyce￾are present. rides to give monoglycerides and free fatty acids;