Changes in flour thiols during storage, and improver action

Abstract

Measurements of total and accessible thiols in three wheat flours, kept at room temperature for up to six months or so after milling, showed that there was a slow loss of total thiol. The rate of loss varied with the flour. The accessible thiol fell more rapidly than the total thiol but this was partly because some became inaccessible. When a flour was treated at room temperature or at 44°C with five common additives at 10 5 ppm, no significant differences could be found by amino acid analysis compared with controls. Electrophoresis and dough tests produced no evidence for peptide chain scission caused by the improvers ammonium persulphate (APS), azodicarbonamide, potassium bromate or the bleaching agent benzoyl peroxide (BP). APS and BP caused slight crosslinking, presumably by free radicals. l-Ascorbic acid produced unexplained minor changes in electrophoretic pattern, notably an extra doublet of high molecular weight. It is very unlikely that any of these changes would be significant at the levels used commercially and the results support the idea that loss of thiol groups is the reason for both the improving effect noticed during the first few months of storage and the action of improvers.