Cereal Chem 66:305-309 | VIEW
Differential Scanning Calorimetry, Water Activity, and Moisture Contents in Crumb Center and Near-Crust Zones of Bread During Storage.
Z. Czuchajowska and Y. Pomeranz. Copyright 1989 by the American Association of Cereal Chemists, Inc.
Water content, water activity, and enthalpy changes (by differential scanning calorimetry [DSC]) were determined in the center of the crumb and near-crust area of polyethylene-wrapped bread stored for up to 168 hr at 21 +/- 2 C. Moisture content and water activity decreased little in the center of the crumb. In the near-crust area there was a large decrease in moisture content and in water activity during the first 24 hr after baking. For thermograms of melting amylopectin crystallites, at about 50-60 C, samples were tested by DSC after adding water to obtain ratio of 1.5:1.0 of water to dry bread crumb. Mean temperatures of onset and maximum enthalpy changes were, respectively, 7.7 and 5.8 C higher for the center crumb than for the near-crust zone. The peak area of amylopectin crystallite melting increased during 168 hr of bread storage much more rapidly in the near crust than in the center crumb. The difference reached a maximum at about 48 hr after baking. In the crumb center and near crust, respectively, enthalpy changes were 0.27 and 0.66, 0.53 and 1.19, and 1.35 and 1.82 J/g after 24, 48, and 168 hr. Without added water (as-is basis), the mean onset and maximum peak temperatures for dissociation of the amylose-lipid complex (110-140 C) were, respectively, 10.1 and 17.0 C higher in the near crust than in the crumb center zones. Enthalpy values in the center averaged 0.52 J/g and changed little during storage; in the near-crust area, they averaged 1.04 J/g. When DSC thermograms were run with a 1.5:1.0 ratio of water to dry bread crumb, there were no significant differences in mean onset and maximum peak temperatures and enthalpy between crumb samples from the bread center and area near the crust zone. No consistent changes in enthalpy at 100-110 C were recorded as a result of bread staling.