Antioxidant and Antiglycation Activities of Pigmented Thai Rice Husk Extracts

Abstract

Diabetes is one of the non-communicable diseases (NCDs) group which are the leading cause of death worldwide. High levels of blood glucose may induce the glycation of sugars and proteins both inside and outside the cell, leading to the formation of advanced glycosylation end products (AGEs), thereby reducing the elasticity of blood vessels and promoting more oxidation in the cells. Nowadays, there is growing interest in natural health care and more research has begun on rice, an important economic crop in Thailand, in the treatment of diabetes and its complications. However the study of the rice husks is still not very extensive. This work aimed to study the antioxidant activity by 2,2-diphenyl-1- picrylhydrazyl (DPPH) assay and the antiglycation property by in vitro BSA-glucose assay in crude extracts from 4 types of Thai rice husks containing pigments: Khao Dawk Mali Rice, Sangyod Rice, Riceberry Rice, and Black Sticky Rice. The rice husks were extracted by 2 methods: extraction with 70% ethanol (maceration) and extraction by decoction. The results showed that the anti-oxidant and antiglycation activities were significantly higher in ethanolic extracts than in the decoction extracts (p < 0.05). Black Sticky Rice husk extract had the highest anti-oxidant activity with IC₅₀ = 139.76 ± 52.07 µg/mL, when compared to the standard substance butylated hydroxytoluene (BHT) (IC₅₀ = 161.38 ± 33.75 µg/mL). Moreover, it also had the highest antiglycation effect, with IC₅₀ = 234.69 ± 29.02 µg/mL, when compared to aminoguanidine (AG) (IC₅₀ = 430.23 ± 6.03 µg/mL), which is used as AGE formation inhibitor. These may correspond to the highest amount of the total phenolic compounds content (60.60 ± 3.57 mg GAE/g) and the total anthocyanin content (2.064 ± 0.2 mg/L) in Black Sticky Rice husk extract. This study may provide information for the development of drugs and dietary supplements for diabetic patients.