KERNEL EXPOSURE AND MICROBIAL SPOILAGE IN PARBOILED RICE

Abstract

Kernel exposure due to husk opening in parboiling predisposes the parboiled paddy to microbial spoilage, heat development, breakage and loss in rice outturn during slow yard drying in humid rainy weather. When soaked paddy was steamed after addition of salt at 0.8 per cent (W/W) rice kernels were not exposed because the salt rendered closed grains to stay closed in parboiling. Salt treated closed grains offered protection to the rice kernel from mould invasion and withstood non-drying for seven days with superficial infection of moulds compared to the deeper infection in grains with exposed kernels. In a period of seven days of non-drying, parboiled paddy with exposed kernels sustained 51.2 per cent grain infection, yielded 57.8 per cent rice outturn with 55.2 per cent breakage, 18.6 per cent oil bran with a free fatty acid content of 34.9 per cent compared to 5.9 per cent grain infection, 67.5 per cent rice outturn with 11.4 per cent breakage, 28.9 per cent oil with 22.0 per cent free fatty acid in closed grains. Salt treatment to the opened grains at 0.6 per cent (W/W) level equivalent to the present in grains treated with 0.8 per cent salt offered only a slight protection indicating that it is the intactness of husk and non- exposure of kernels in closed grains that protect the rice kernel from spoilage than the protective action of salt.