EFFECTS OF PARBOILING STEPS ON STARCH CHARACTERISTICS AND GLYCEMIC INDEX OF BASMATI (PB1121) RICE

Abstract

Effects of soaking and steaming steps, individually on selected starch characteristics and GI of Pusa Basmati 1121 rice was evaluated. Rough rice was soaked at seven different temperatures (40-80°C) and soaking effect on starch content, Am/Ap ratio, pasting properties, starch crystallinity, degree of gelatinization, grain transparency and GI of rice was determined. Similarly, rough rice was soaked at 65°C for 345 min and subsequently steamed at different steaming conditions to determine the steaming effect on these quality parameters. Starch content, Am/Ap ratio, crystallinity, DG and GI of raw rice was determined as 73.24%, 0.59, 28.49%, 5.59% and 58.41, respectively. Soaking reduced the crystallinity up 14.08% whereas steaming reduced it up to 5.72%. Similar trend was observed for other parameters also. Both soaking and steaming decreased the pasting viscosities, converted crystalline form of starch into amorphous one, imparted translucency to the grains, and decreased the GI. However, soaking step achieved partial gelatinization whereas steaming step achieved complete gelatinization of starch. Soaking step absorbed the moisture to swallow the starch granules whereas steaming step ruptured the crystalline polyhedral structure to yield compact, amorphous and translucent rice.