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Water absorption and gelatinization kinetics of non-issuable rice and its characterization

Purohit, Soumya Ranjan, Rao, Pavuluri Srinivasa
Journal of food measurement & characterization 2017 v.11 no.4 pp. 2110-2118
Fourier transform infrared spectroscopy, X-ray diffraction, absorption, activation energy, ambient temperature, diffusivity, digestion, equilibrium moisture content, fungi, gelatinization, humans, parboiling, rice, seeds, soaking, starch
Fungal infestation or fungal damage in parboiled rice is one of the major issues, caused by poor storage practices and uncontrolled environmental factors. The fungal damaged rice is generally considered to be unfit for human consumption, if the extent of infested/fungal damaged kernel (FDK) exceeds the limit of 5% (w/w). Such rice bulk is also termed as non-issuable rice, though it contains around 95% of sound kernel (SK). Present study was focused to explore the effect of FDK content on water absorption and gelatinization behaviour of non-issuable rice and its characterization. The sample with higher percentage of FDK was observed to be lagging in both water absorption and gelatinization process. Kinetics study of gelatinization process also revealed lowest reaction rate constant, higher shape factor and activation energy of gelatinization (Eₐ) for sample with higher FDK%. Subsequently, moisture diffusion analysis also revealed lowest diffusivity and highest activation energy of diffusion (ED) (79.27 kJ kmol⁻¹) for the sample. Supportively, equilibrium moisture content on soaking (EMC-S) and sedimentation values (SV) (86.3% db and 4.06 mL) of FDK were higher than SK (79.1 and 3.16). FTIR spectrum and X-ray diffractogram confirmed relatively high order of starch organization and crystalline nature in SK. Additionally, amylolytic susceptibility for FDK was also found higher as compared to SK. Thus, high moisture absorption behaviour in ambient temperature and lower crystalline ordered starch with higher susceptibility to amylolytic digestion could be contributing to the fungal infestation in parboiled rice.