Artificial yellowing of rice at 60 deg C
1989
Yap, A.B. | Perez, C.M. | Juliano, B.O. (International Rice Rsearch Inst., Los Banos, Laguna (Philippines))
Recent studies have shown that rice yellowing or stack burning is due to the heating of relatively moist grains, and that microbial growth assists in raising grain temperature. Yellow milled rice is harder than white milled rice, has lesser lysine, and shows lower net protein utilization in growing rats. The effect of moisture content, incubation period, and variety on the yellowing of surface-sterilized rough, brown, and milled rice was studied at 60 deg C to better understand the yellowing phenomenon. After four days at 60 deg C, the Lab yellow b values of brown rice and milled rice increased progressively with moisture content (12, 14, 16, 18 and 20%) of stored rough rice but levelled off at 16% moisture content for stored brown rice and milled rice. The b values of milled rice were higher in samples stored as brown and rough rice than in stored milled rice. The extent and rate of yellowing were similar among rices differing in amylose content, gelatinization temperature, and gel consistency, and were not significantly correlated with initial levels of free amino acids and reducing sugars in brown rice. Significant increases in b values were observed after 24 hours in IR64 brown rice with 12% moisture content and after six hours in four brown rices with 14.2% moisture content.
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