Effect of hydrothermal treatment varying in time and pressure on the properties of parboiled rices with different amylose content

摘要

Effects of mild, moderate and severe hydrothermal treatments at open and under steam pressure on four rice varieties differing in amylose content were studied. Degree of gelatinization was markedly high in the severely pressure parboiled samples. Pressure parboiled waxy samples showed extensive fall of gelatinization temperature and increased hydration at lower temperatures. Formation of short amylopectin fine structures in these samples was indicated by sediment volume and viscosity patterns. The pattern of change in the infrared spectroscopic bands may be due to shift in stretching mode. Wide angle X-ray diffractographs of raw samples showed peaks at 2 θ values near 20 which indicated 'in situ' points for amorphous amylose complex formation. A, B and V-type polymorphs were seen in pressure parboiled samples and only A and V-type poly-morphs were observed in open steamed samples. Loss in crystallinity with simultaneous increase in water uptake can be attributed to the amorphous fractions in parboiled rice.