Effects of baking on protein and aqueous ethanol-extractable carbohydrate in white bread fractions
1989
Westerlund, E. | Theander, O. | Aman, P.
The contents of protein and of 80% (v/v) aqueous ethanol-extractable carbohydrate were investigated in the crumb and crust of white bread baked at 210 degrees C for 22 or 35 min. The original protein content decreased on baking and this was associated in particular with losses of lysine and arginine. The amount of 80% ethanol-extractable protein was substantially higher in crust than in crumb, presumably as a result of different degrees of thermal degradation, but the contents were lower in both crust and crumb than in dough, presumably due to denaturation and formation of Maillard reaction products during baking. Predominant sugars in bread were, in decreasing order, maltose, fructose and glucose/maltulose. Maltulose is an epimerisation product of maltose and was found mainly in the crust. Oligosaccharides with beta-1,6-anhydro-D-glucopyranose as end units were formed by thermal depolymerisation of starch. Trace amounts of these glucosaccharides were detected as maltosan after enzymic hydrolysis of aqueous ethanolic extracts, obtained from a thin outer layer of crust. The content of glucosaccharides that could not be degraded by amylolytic enzymes was significantly higher in crust than in crumb, indicating occurrence of reversion and/or transglycosidation reactions among the oligosaccharides originally present in flour or dough and those produced by thermal starch depolymerisation.
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