Hydrolytic rancidity in whole wheat flour proceeds through the action of lipase (O’Connor et al.,1992). Lipase (EC 3.1.1.3) hydrolyzes triacylglycerols to non-esterified fatty acids and diglycerides, monoglycerides, and eventually glycerol; thus the release of nonesterified fatty acids in whole wheat flour is related to lipase activity. Wheat lipase activity is mostly located in the bran fraction of the grain (Galliard, 1986a). There is an enzyme termed ‘wheat germ lipase’ that catalyzes deesterification of triacetin and other artificial water-soluble substrates (O’Connor et al.,1992) and thus is technically an esterase. True lipase activity (i.e., activity on waterinsoluble substrates) of wheat germ lipase is likely a result of contamination with lipase from wheat bran (Galliard, 1994). Lipase exhibits maximum activity in wheat at about 17% moisture content; however, at moisture contents commonly observed in flour during storage (10e14%), lipase activity continues at about 50% of maximum (Fig. 3). This property makes lipase unique among hydrolytic enzymes, i.e., lipase only requires a catalytic amount of water to act, whereas excessive amounts of water protect the lipid from being exposed to the catalytic site of the enzyme and reduce activity (Galliard, 1994).
