Extraction of anthocyanins from the byproduct and wastes of black rice production by ecofriendly method

A green and sustainable method has been developed to extract anthocyanins from broken black rice (BBR) using aqueous solutions of poly(ethylene glycol) (PEG). The effects of time, PEG concentration, temperature, BBR mass, and PEG molar mass were investigated using multivariate experimental designs. Time and temperature were not significant in the studied range and PEG 1500 was the most suitable. Under the optimized conditions, the anthocyanin concentration was 130.7 mg 100 g−1. The stability of the extract was higher at 25 °C and pH 5.0, with a reduction in absorbance (λmax = 455 nm) of only 7.14% after 60 days. The extract was applied in a colorless soap, and the color remained stable for 60 days (greater reduction in absorbance of 15.5% at 40 °C, λmax = 497 nm), indicating its potential for direct application in products of industrial interest. The method was also effective to extract anthocyanins from the husk and bran of black rice, with concentrations of 148.1 and 883.2 mg 100 g−1, respectively. In comparison with conventional methods for extracting anthocyanins, the proposed new technique offers the advantages of efficiency, simplicity and low cost, with the difference in extract concentration being obtained with methanol acidified with HCl of only 11%.