Changes in the Physical and Chemical Properties of Thai Brown Rice Caused by High-Temperature Treatment

Abstract

The market for healthy food in Thailand is increasing rapidly due to growing recognition that food ingredients can causes diseases such as cancer and type 2 diabetes. Healthy food from natural products, and especially from whole grains such as brown rice, has become a priority for Thai consumers. Brown rice is rich in nutrients such as fiber and vitamins. However, brown rice has a high glycemic index and is therefore not suitable for patients with type 2 diabetes, since blood sugar and insulin levels increase rapidly after ingestion of this rice. The Khao Dok Mali 105 cultivar of brown rice has a low amylose content (12% to 17% by weight), and is popular in Thailand because of its flavor, aroma, and soft texture. However, cultivars such as Phisanurok 3 and Suphan Buri 1 with high starch amylose contents (23% to 26% by weight) are also in demand. Thai rice varieties normally contain degrees of crystallinity of A-type amylose, with a medium to fast digestion rate. Recently, researchers found that hig-temperature treatment (130 to 150°C) influenced the glycemic index of brown rice. Gelatinization was produced during the processing, and affected physical and chemical properties such as texture and starch digestibility. The processing decreased the degree of crystallinity (i.e., increased the proportion of V-type amylose) and produced amylose-lipid complexes in the brown rice, which slow digestion of the starch. Our study is the first to confirm these previous results for three popular Thai rice cultivars.