Extraction, foam-mat drying, and physicochemical analysis of Indonesian black glutinous rice (Oryza sativa L. var glutinosa) anthocyanins

Anthocyanins are water-soluble flavonoid that gives a purplish-blue colour to black glutinous rice. Anthocyanins can be degraded by high temperature (>65ᵒC), oxygen, and light during storage. Foam-mat drying is expected to maintain anthocyanins from degradation and prolong their shelf life. This research aimed to obtain the optimum condition for anthocyanins extraction and foam-mat drying with the physicochemical evaluation of anthocyanins extract. The extraction process was done by the maceration method using food-grade solvents, water+citric acid and water, at four different times (6, 18, 24, and 48 hrs). Ethanol+citric acid were used as a control. The results showed that extraction using water+citric acid solvent for 48 hrs yielded higher total anthocyanins content (2.15±0.03 mg/g rice) than using water solvent (0.70±0.01 mg/g rice). Production of anthocyanins powder was carried out using the foam-mat drying method with the variation of maltodextrin (10 and 20%) and egg white (7.5, 10, and 20%) as the encapsulant and foaming agent. The highest anthocyanins content (0.45±0.06 mg/g powder) was obtained from water+citric acid extract mixed with 10% maltodextrin and 7.5% egg white. The solubility of its powder was acceptable (96.23±0.67%), and the water activity fulfilled the water activity standard of the powder drinks (0.33±0.00). In conclusion, the most optimum condition for anthocyanins extraction was using water+citric acid for 48 hrs and foam-mat drying using 10% maltodextrin and 7.5% egg white.