Studies on the mechanism of the ascorbic acid improver effect on breed using flour fractionation and reconstitution methods

The roles of glutathione (GSH), glutathione dehydrogenase (GSH-DH), and other constituents of flour in the improving mechanism of ascorbic acid (AA) were analysed by fractionating flour into various parts, reconstituting flour with combinations of fractions, and testing the reconstituted flour for AA improvements on bread volume and crumb grain. Bread made from the water insoluble fraction of flour (mainly starch and gluten) had poor loaf volume, which was not improved by addition of AA. Two high M-r (>10 k) water soluble fractions, a GSH-DH containing fraction and a fi action rr ee of GSH-DH activity (X-Fraction), were necessary for restoration of the stereospecific L-AA improvement of loaf volume. The low M-r (<10 k) water soluble components of flour increased loaf volume, but were not involved in the AA improver effect. Without the GSH-DH fraction and L-AA in the reconstituted system, the X-Fraction caused a decrease in loaf volume. To explain this result, it is suggested that X-Fraction causes the cleavage of disulphide bonds in gluten, and possible mechanisms for the reaction are discussed. Mechanisms are also discussed to explain how addition of AA and the fraction containing GSH-DH either prevents the cleavage of disulphide bonds or restores the bonds necessary for improved loaf volume. Other flour reconstitution experiments indicated that GSH and cysteine are involved in a GSH-DH dependent L-AA improvement of crumb grain. (C) 1999 Academic Press.