CHARACTERIZATION OF SELECTED VARIETIES OF RICE (ORYZA SATIVA) AND ITS BY-PRODUCT (RICE BRAN) FOR VALUABLE NUTRIENTS AND ANTIOXIDANTS

Abstract

Rice is one of the most important staple foods on which more than half of the global population de- pends as a source of their calories. Pakistan being one of the world’s major rice producing countries produces rice not only for its domestic needs but also for export to earn foreign exchange. With the current trends for functional foods and nutraceuticals, growing need exists to explore local rice cul- tivars for biochemical composition and nutrient specificity to enhance the share of rice in trade mar- ket and to benefit consumer’s health. The primary objective of the present research was to character- ize selected varieties of rice (Oryza sativa L.) and its by-product (rice bran) for the important nutri- ents, high value-components and antioxidant attributes. The rice varieties most commonly cultivated in Pakistan were analyzed for the quality- oriented physiochemical and nutritive attributes such as moisture, ash, crude fiber, carbohydrates, lipids, proteins and minerals etc. Proximate analysis re- vealed that Pakistani varieties, especially, Basmati rice, contain appreciable amounts of important nutrients such as carbohydrates, protein, fat, crude fiber and minerals. Extraction for antioxidant components from rice and rice bran was carried out by employing six solvents; methanol (100%,80%), ethanol (100%,80%) and isopropanol (80%,100%) and two extraction techniques; or- bital shaker and sonication-assisted orbital shaker. Overall, best extraction yields of antioxidant components were obtained with 80% isopropanol and 80% methanol using sonication-assisted or- bital shaker. The antioxidant activity of the tested varieties of rice and rice bran was assessed using various in vitro antioxidant essays e.g. estimation of total phenolic contents (TPC), 2,2-diphenyl-1- picrylhdrazyl (DPPH) free radical-scavenging capacity, reducing power and ferrous ion-chelating activity. Present study revealed that tested Pakistani rice varieties have considerable potential for total phenolics and radical scavenging activity. The profiles of carbohydrates, fatty acids, sterols, amino acids, tocopherols and γ-oryzanol compounds were studied by using state-of-the-art spectro- scopic and chromatographic techniques such as UV/Vis spectrophotometer, HPLC, GC, GC-MS etc., where applicable. Among rice varieties tested sixteen amino acids were detected with glutamic acid, arginine, leucine and aspartic acid as the major components. GC analysis of the fatty acids composition depicted C18:1 and C18:2 as the major fatty acids of rice varieties. GC and GC-MS analysis revealed the presence of β-sitosterol, stigmastenol and campesterol as the main phytosterol components. HPLC analysis of the tocopherols and γ-oryzanol showed the distribution of α- tocopherol (41.2-76.1 mg/kg), γ-tocopherol (20.5-27.5 mg/kg) and δ-tocopherol (6.5-14.2 mg/kg) and 24-methylcycloartenyl ferulate (140.2-183.1 mg/kg), cycloartenyl ferulate (65.5-103.6 mg/kg) and campesteryl ferulate (29.8-45.5 mg/kg) as the principal components. Overall, Basmati Pak, Basmati 198 and Basmati 2000 were found good nutritive varieties in respect of antioxidants poten- tial and valuable nutrients. In view of investigations of valuable phytochemicals and bioactives it is revealed that the rice has great potential for functional food and nutraceuticals applications. Efforts should be made to highlight the nutritive potential/quality of local aromatic rice varieties for enhanc- ing their commercialization at global level.