Anthocyanins from black glutinous rice bran: process efficiency and characterization of anthocyanins

Black glutinous rice bran (BGRB) serves as a plentiful natural pigment source. However, limited research has been conducted on the extraction, purification, and characterization of the anthocyanins present in BGRB. This work aims to provide an eco-friendly process for industrial anthocyanin extraction and purification. Following green chemistry principles, safe solvents and recyclable purification materials were used in the experiment. And waste production and energy consumption were limited. Optimal extraction conditions: ethanol-water ratio 40:60 (v/v, pH 2.5), solvent-feed ratio 80:1 (mL/g), 50 °C, and 40 min yielded 19.79 ± 0.14 mg/g anthocyanin, and 32 anthocyanins were identified in the BGRB anthocyanin extract. Optimal purification conditions: employing a D101/AB-8 mixed resin (7:3 w/w), the volume, pH value, and flow rate of BGRB anthocyanin extract were 1.5 Bed Volumes (BV), pH 3.0, and 0.5 BV/hr, respectively; desorption was performed successively with 40:60 (v/v, pH 2.5) ethanol-water of 6 BV, 0.5 BV/hr. Purification achieved 65.97% anthocyanin recovery. After purification, total anthocyanins (67.70 ± 5.43 mg/g to 171.27 ± 7.99 mg/g) and color value (33.48 ± 2.91 to 84.58 ± 1.41) were both 2.5 times higher than in the extract. The metabolite expression of purified anthocyanins showed 4.2 times increase by liquid chromatography-mass spectrometry (LC-MS).