Bioactivity and anthocyanin content of microwave-assisted subcritical water extracts of Manipur black rice (Chakhao) bran and straw

Kamaljit Moirangthem,Priya Ramakrishna,Mahetab H Amer,Gregory A Tucker

doi:10.1016/j.fufo.2021.100030

Abstract

Chakhao, the Geographical Indication (GI) tagged aromatic black rice of Manipur, India, is a rich source of bioactive compounds such as anthocyanins. However, there is limited work available on Chakhao and research has focused on its grain. No reports on the anthocyanin, antioxidant properties or in vitro bioactivities of its straw are available. Anthocyanins content of its different fractions displayed a positive correlation with their antioxidant potentials (r = 0.90). In this study, microwave-assisted sub-critical water extraction, at 90 °C for 5 min, from the straw gave an anthocyanins extraction efficiency of 85.8%. Furthermore, this microwave extract displayed higher antioxidant activity than an equivalent conventional methanol extract. In vitro studies on the microwave extracts of both straw and bran showed no apparent cytotoxicity on Jurkat cells and dose-dependent inhibition of colony growth in colorectal cancer cells. Black rice bran and straw are valuable by-products of the food industry that are rich in phytochemicals. This study reports the extraction of anthocyanins from black rice straw and presents evidence that the straw, in addition to the bran, contains important bioactive compounds; the extracts of which could further be explored as a natural antioxidant and/or functional ingredients.

Highlights

With a global production of over 758 million tons, rice provides more than 20% of calories for more than half of the human population (FAO, 2018)
Anthocyanins were extracted from the paddy and straw fractions using methanol and quantified using the pH differential method (Fig. 1)
The present study provides strong evidence that through microwaveassisted subcritical water extraction (MA-SWE), efficient anthocyanins extraction with an antioxidant capacity comparable or even better than conventional solvent extraction can be achieved

Summary

Introduction

With a global production of over 758 million tons, rice provides more than 20% of calories for more than half of the human population (FAO, 2018). Anthocyanins are natural colorants that can impart vibrant red, purple, and blue colours to foods and are approved as clean label alternatives to synthetic colorants in the EU, Australia and New Zealand with the E number E163 (EFSA, 2013; Wallace and Giusti, 2015) They have been reported as chemo-preventative and anticancer agents (Hou, 2003; Li et al, 2015; Tsai et al, 2014), exhibiting a dose-dependent decrease in cell proliferation and growth of human oral, breast, colon, and prostate cancer cell lines (Kang et al, 2003) with different sensitivity between cell lines (Li et al, 2015). Exploring potential non-food, natural plant sources rich in anthocyanins, which can be extracted with high efficiency at low cost would be of great interest

Methods

Results

Conclusion