Effects of Dry Heat Treatment on Starch Crystalline Structure and Oil-binding Ability in Whole Pinto Bean Cells
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Abstract:
In this study, intact pinto bean cells were isolated as a research model of whole pinto bean flour, and subjected to dry-heat treatments. The effects of dry-heat temperature (80~160 ℃) on the crystalline structure and oil-binding ability of the starch were investigated. The results showed that pinto bean cells still remained intact with surface becoming wrinkled after the dry heat treatment. At lower dry heat temperatures (80~120 ℃), the relative crystallinity of the starch in the cells decreased slightly (ca. 3%) with increasing temperature. The thermodynamic analysis revealed the occurrence of two endothermic peaks: The first peak belonged to starch gelatinization, and the second one was the denaturation peak of pinto bean protein. The enthalpy values for both peaks decreased with increasing dry heat temperature. At higher dry heat temperatures (140~160 ℃), no change in the relative crystallinity of the starch in the cells was observed along with the disappearance of the protein denaturation peak, as compared with the cells treated at lower temperatures (80~120 ℃). It was found that as the dry-heat temperature rose, the oil-binding ability of the starch and the three-phase contact angle of pinto bean cells (122.0°~145.4°) increased gradually, but the volume of free oleic acid decreased (0.60~0.05 mL). The oil-binding stability was poor at higher dry heat temperatures (140~160 ℃). The results obtained in this research provided a theoretical basis for the utilization of the oil-binding properties of whole pinto bean flour in food formulations.
