Optimization of paddy parboiling process for higher starch crystallinity by response surface methodology

Paddy parboiling has received considerable attention as far as nutritional and milling improvement is concerned. Parboiling is also advantageous as it renders enhanced head rice yield and insect resistance. However, lower starch crystallinity of parboiled rice invites easy fungal infestation under favourable moisture and temperature conditions during storage. Additionally, parboiled rice is expected to possess higher resistant starch. Unfortunately, conventional processing conditions lead to either very less or moderate resistant starch content. Thus, improving starch crystallinity in parboiled rice is desirable to make a portion of starch, less accessible to amylolytic enzymes and to impart slow digestible behaviour. The four independent factors selected were pH of soaking solution (3–7), steaming time (10–30 min), cooling temperature (5–25 °C) and cooling time (0–6 h). The experimental data were fitted to quadratic second-order polynomial models to study the relationship between independent and dependent variables. The controlled cooling of parboiled paddy exhibit a higher crystallinity%, along with better starch reorganization, as evaluated by XRD, FTIR and Visible spectrum. Further equilibrium moisture content on soaking (ambient temperature) and sediment value of optimally processed parboiled paddy showed reduced water absorption as compared to conventionally parboiled paddy sample, which is indicative about enhanced crystallinity parboiled rice.