PHYSICOCHEMICAL CHARACTERISTICS AS INDICATORS OF STARCH AVAILABILITY FROM MILLED RICE

The hypothesis was tested that certain physico-chemical characteristic s might be used as indicators of total starch availability and rate of starch availability of milled rice. Milled unparboiled (uPB) and parb oiled (PB) rice samples (n=93) were characterized using standardized m ethods of physical tests and chemical analyses and an in vitro method was used for measuring the rate of starch digestion on a subsample of rice (n = 26). The rice varieties were dominated by medium long, bold rice grain with high amylose rice and intermediate gelatinization temp erature (GT), but a wide range in all characteristics was measured. Sm all amounts of resistant starch (RS) were measured in the cooked rice, indicating virtually complete starch availability. The RS of PB rice (0.4g/100g rice as eaten) was significantly (P<0.004) higher than the RS of uPB rice (0.1 g/100g) however. The rate of starch digestion was significantly affected by both variety and parboiling. The starch dige stion index (SDI) values of the PB samples (mean value 73.7) were sign ificantly (P<0.001) lower than those of the uPB samples (mean value 79 .0). The apparent amylose content (AC) was the strongest determinant f or SDI in both uPB and PB rice. The widths and shapes of the raw grain s and the elongation after cooking were correlated significantly with SDI values for the uPB rice, while the relatively mild parboiling proc edure followed in this study eliminated this correlation. The minimum cooking times were correlated significantly with the SDI values in the uPB samples. (C) 1997 Academic Press Limited.