Effect of Parboiling on Minerals and Heavy Metal contents of Selected Sri Lankan Traditional Rice Varieties Grown under Organic Farming

Abstract

This study was conducted to evaluate the effects of parboiling treatment on the minerals and heavy metal contents of six Sri Lankan traditional rice varieties (TRV); Kalu heenati, Pokkali, Gurusinghe wee, Kahawanu, Sudu murunga and Unakola samba. Paddy was soaked (60°C, 3 % hours-for short grained rice or 4 hours-for long grained rice), steamed (100°C, 20 minutes) and dried (50°C, 12 hours) during parboiling. Metal contents were determined using ICP-AES for each variety in triplicates. Pokkali rice recorded the highest iron content (29.5 mg/100 g). This amount was further increased by 66.7% after parboiling. Iron content of the rest of the TRV decreased due to parboiling and ranged from 2.1 ± 0.1 to 3.5 ± 0.3 mg/100 g for un-parboiled rice and from 1.3±0.1 to 3.3±0.7 mg/100 g for parboiled rice. Parboiling slightly reduced the zinc content of these TRV except for Pokkali. Parboiled Pokkali contained the highest zinc content of 4.7±0.4 mg/100 g among all TRV irrespective of parboiled or not. Zinc content of the selected TRV ranged from 2.3±0.14 - 3.8±0.1 mg/100 g for un-parboiled rice and 2.1 ± 0.7- 4.7 ± 0.4 mg/100 g for parboiled rice. Parboiling did not have significant effect on the levels of potassium, magnesium, calcium and manganese contents except for Kahawanu. For Kahawanu, parboiling increased the potassium (12.3%), magnesium (64 %) and manganese (50%) contents. Heavy metals such as, Cd, Pb and Cu were not detected in the tested TRV varieties.