INTERNATIONAL JOURNAL OF AGRICULTURAL TECHNOLOGY

Volume 14, No. 07, Month DECEMBER, Year 2018, Pages 1399 - 1412

Effect of oil addition on in vitro starch digestibility and physicochemical properties of instant rice

Luangsakul, N. and Ritudomphol, O.

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The most varieties of rice have high starch digestibility and glycemic index (GI), which is unsuitable for diabetics. The processes involved in the production of instant rice, not only make it more convenient for the consumer, but can also lower its starch digestibility and GI through the decrease in enzymatic accessibility to rice kernels. One way to control the enzymatic digestion of rice was increasing the amylose-lipid complex formation. The effect of oil addition during rice cooking on in vitro starch digestibility, GI and some physicochemical properties (thermal properties, X-ray diffraction patterns and pasting properties) of instant rice wasc studied. During rice cooking, 2 type of cooking oil, including coconut oil (C) and rice bran oil (R) at 2.5, 5 and 7.5% (w/w, on the basis of uncooked rice) were added to Sao Hai rice (SH), which had amylose content of 21.35 g/100g (dry weight basis, db). Thermal properties showed amylose-lipid complex dissociation peaks when rice was cooked with oil, and the highest enthalpy was found in the addition of oil at 2.5%. In X-ray diffraction patterns, cooked rice with oil which showed A+V type crystalline structure and the addition of rice bran oil at 2.5% exhibited the highest relative crystallinity (19.98%). The formation of amylose-lipid complex of cooked rice with oil reduced in vitro starch digestibility and eGI compared to cooked rice without oil. The addition of rice bran oil at 2.5% had the highest slowly digestible starch (SDS) and resistant starch (RS) contents, which were consistent with their lowest estimated glycemic index (eGI). The addition of oil to rice resulted in a lower peak viscosity (PV) and setback (SB), as compared to instant rice without oil.

Keywords

instant rice, amylose-lipid complex, starch digestibility and glycemic index

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