CHANGES IN SUGARS AND AMINO ACIDS DURING PARBOILING OF RICE

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Changes in reducing sugars (RS), sucrose (SUC) and free amino acids (FAA) in rice as a result of parboiling (soaking and steaming), or just soaking (at a number of different temp.), were studied; effect of milling was also studied. RS contents (%) were in raw brown rice 0.08, raw milled rice 0.08, parboiled brown rice 0.22 and parboiled milled rice 0.19; corresponding SUC contents (%) were 0.93, 0.02, 0.66 and 0.65; corresponding FAA contents (mol/100 g) were 0.80, 0.23, 0.83 and 0.80. Changes in RS, SUC and FAA after soaking raw rice at 37 degree , 60 degree and 80 degree C are presented graphically. There were considerable increases in RS (max. at 60 degree C) and larger decreases in SUC, leading to overall lower sugar content after soaking. Steaming affected rice contents much less than soaking. Time courses of effect of incubation of brown rice, degermed rice, rice germ and rice flour at 37 degree , 55 degree and 80 degree C on RS, SUC and FAA contents are presented graphically. It is concluded that rice contents are subject to enzymic action during the soaking stage, RS being produced from SUC and other sources, and some FAA being produced. A considerable part of the sugars is leached out during soaking (0.5% of grain wt. after 24 h at 37 degree C).