Abstract:
The objective of this research was to study the effect of adding hydroxypropylmethyl cellulose (HPMC) and carboxymethyl cellulose (CMC) on staling and keeping quality of white wheat bread. The effect of storage temperature on bread quality was also investigated. HPMC and CMC were added at the levels of 0.5, 1.0 and 1.5% of wheat flour and the bread samples were stored at either ambient (25±2 oC) or refrigerated temperature (4±2 oC). Freshly baked HPMC- and CMC-added samples contained significantly higher moisture and freezable water as compared to the all-wheat control (p≤0.05). A decrease in moisture and freezable water contents with increasing storage time was observed in all samples. Among the samples stored at the same temperature, the control exhibited greatest degree of amylopectin recrystallization. Between the two storage temperatures studied, higher degree of amylopectin recrystallization was observed in refrigerated samples. Amylopectin recrystallizaton was found to increase sharply during the first few days of storage. Changes in soluble starch content were well correlated to the degree of amylopectin recrystallization. A decrease in soluble starch content was found to be lower in HPMC- and CMC-containing breads. Bread samples stored at refrigerated temperature were lower in soluble starch content than those stored at ambient temperature. Both freshly baked and stored HPMC- and CMC-containing breads were lower in hardness as compared to the control. HPMC and CMC addition also helped increase crumb springiness. An investigation using a stereomicroscope revealed that HPMC- and CMC-containing breads had smaller air cells than the control. The crust of all samples had hue angle of approximately 62o, representing orange-yellow color, with similar chroma and lightness. The crumb of all samples had hue angle of approximately 95o, representing yellow color, with similar chroma, whiteness index and lightness. Refrigerated breads were lower in staling flavor than those stored at ambient temperature. From sensory evaluation, HPMC- and CMC-containing breads stored for 1 day or longer obtained significantly higher overall preference score than the control did (p≤0.05)