CHIANG MAI UNIVERSITY JOURNAL OF NATURAL SCIENCES

Volume 18, No. 04, Month OCTOBER, Year 2019, Pages 534 - 552

Changes of anthocyanins in black rice flours prepared by cooking and pregelatinization

Sudarat Jiamyangyuen, Nitra Nuengchamnong, and Paradorn Ngamdee

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Black rice is considered healthier than white rice as it contains anthocyanins which have been claimed to have multiple health benefits. The wide application of black rice is limited due to the limiting properties of native rice flour. The Thai black rice cultivar, Niew Dam (ND; glutinous type) and Hom Nil (HN; non-glutinous type), were pregelatinized through conventional cooking (C) followed by drum-drying (D). The effects of the heat treatments on physical and chemical properties, anthocyanin content, and antioxidant activity were determined. Rice flour with no heat treatment (native: N) showed lower hydration values compared to those of cooked and drum dried samples. Total anthocyanin contents (TAC) of ND-N, ND-C, and ND-D (4,099, 452, and 358 mg/100 g dw, respectively) were significantly higher than those of HN-N, HN-C, HN-D (305, 95, and 23 mg/100 g dw, respectively). After cooking and drum-drying processes, the retention percentage of TAC in ND-D and HN-D were 9 % and 8%, respectively. Specific anthocyanin compounds, namely cyanidin-3-glucoside and peonidin-3-glucoside, were significantly decreased in both rice cultivars after cooking and the drum-drying processes. The LC-ESI-QTOF was able to identify cyanidin-3-sambubioside for the first time in black rice. Compared to untreated grains, the antioxidant activity of the drum dried samples was decreased by approximately 20% indicating reasonable preservation of the antioxidant benefits. The improvement of physical properties and the remaining anthocyanin content of the pre-gelatinized black rice flour indicates that it has a potential application as an ingredient in healthier food products.

Keywords

Anthocyanin, Black rice, Drum-drying, Pregelatinization

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