Abstract
ABSTRACTThe effect of various soaking mediums, viz. water (control), 3% NaCl and 0.2% acetic acid, and without soaking on the physicochemical properties of parboiled selected glutinous (TDK8 and TDK11) and non-glutinous (Doongara) was investigated in the present study. Results showed that the chemistry of soaking had a significant effect on the head rice yield (HRY), grain hardness, crystallinity, color, pasting and thermal properties, textural attributes, and glycemic index of these rice varieties. Soaking with NaCl and acetic acid significantly increased the grain hardness and HRY than control and without soaking treatments. Acetic acid and NaCl soaking significantly affected crystalline regions of starch resulting in reduced crystallinity in X-ray diffraction analysis and thermal endotherms in DSC analysis. NaCl soaking induced swelling of starch granules resulting in high peak and final viscosities. However, acetic acid restricted swelling resulting in reduced peak and final viscosities. NaCl and acetic acid soakings also resulted in increased hardness and adhesiveness of cooked grains than normal water soaked and un-soaked parboiled rice samples. Interestingly, change in textural attributes was prominent in parboiled glutinous rice. The color difference value for fresh parboiled samples was significantly lower for acetic acid soaked samples compared to NaCl soaked and un-soaked samples probably due to bleaching effect of acetic acid. Moreover, parboiling also resulted in significant reduction in glycemic index of glutinous rice. These findings revealed the potential application of parboiling with modified soaking techniques to improve the grain quality.
Highlights
Parboiling is hydrothermal processing of paddy and/or brown rice to improve the head rice yield, nutritional and organoleptic properties by using a three-stage process, viz. soaking, steaming, and drying.[1,2,3] According to the recent statistics, 130 million tons of paddy is parboiled annually around the globe with about 3–4 million tons high-value parboiled milled rice being moved in world trade.[4]
Results showed that the parboiling and subsequent drying of paddy resulted in significant (p < 0.05) increase in grain hardness as compared to the fresh non-parboiled grains (Fig. 1)
These results are in agreement with the findings of previous researches, which reported that the increased grain hardness is due to less internal fissures in parboiled rice grain because of the gelatinization and fusion of starch granules during parboiling process.[14,17,33]
Summary
Parboiling is hydrothermal processing of paddy and/or brown rice to improve the head rice yield, nutritional and organoleptic properties by using a three-stage process, viz. soaking, steaming, and drying.[1,2,3] According to the recent statistics, 130 million tons of paddy is parboiled annually around the globe with about 3–4 million tons high-value parboiled milled rice being moved in world trade.[4]. Parboiling is hydrothermal processing of paddy and/or brown rice to improve the head rice yield, nutritional and organoleptic properties by using a three-stage process, viz. Parboiling results in profound changes in the physicochemical and functional properties of rice.[13] Starch granules are swelled due to gelatinization, protein bodies are disrupted due to denaturation and disulfide cross-linking, and lipid–amylose complex formation takes place.[14] parboiling results in inward diffusion of water-soluble vitamins and minerals from bran to endosperm improving the nutritional quality.[15,16] These changes in physicochemical
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