Soaking Induced Changes in Chemical Composition, Glycemic Index and Starch Characteristics of Basmati Rice

Abstract

An attempt was made to determine the qualitative changes in basmati rice (Pusa Basmati 1121, PB1121) during soaking at 40 °C to 80 °C. Soaking temperature had significant effect (α = 0.01) on chemical composition, glycemic index and starch characteristics of rice. Starch content, apparent amylose content, crude protein content and crude fat content in un-soaked rice were found to be 73.24%, 27.26%, 8.79% and 2.56%, respectively, but differences in these traits were observed after soaking. Amylose to amylopectin ratio (Am/Ap) decreased from 0.59 to 0.52 (soaked at 80 °C). Crude fibre and crude ash contents increased after soaking. The mineral composition (K, P, S, Ca, Mg, Mn, Fe, Cu and Zn) in soaked rice was found to be 16.46% higher than un-soaked rice at the same degree of polishing. Glycemic index of un-soaked rice was found to be 58.41, but decreased to 54.31 after soaking at 80 °C. Pasting properties, scanning electron microscope images, and X-ray diffractograms suggested partial gelatinization of starch in the temperature range of 60 °C to 80 °C. Based on qualitative changes in rice (apparent amylose content, Am/Ap ratio and crystallinity rate), it was concluded that intermediate soaking temperatures (60 °C to 70 °C) would be useful for soaking of PB1121.