Optimization of process parameters for foam mat drying of black rice bran anthocyanin and comparison with spray- and freeze-dried powders

The foaming conditions and air-drying temperature for producing instant powder from black rice bran anthocyanin extracts were studied. The conditions required for forming a foam to possess the maximum overrun, foam density, and foam stability, which contributed to boost the efficiency of drying foams using a hot-air dryer, were optimized using response surface methodology (RSM). Two independent variables were studied: the foaming agent concentrations (0.02-0.10%, w/w) and the whipping times (7.93-22.1 min). The optimal foaming conditions from RSM were 0.06% (w/w) foaming agent and 16.1 min whipping time, providing foams with the highest overrun (218%), foam density (0.31 g/mL), and foam stability (79.3%). The foams were dried at different temperatures (60, 70, and 80 degrees C). The best qualities of foam mat-dried powders were observed at 80 degrees C. Compared to spray- and freeze-dried anthocyanin powders, the total anthocyanin content and encapsulation efficiency of the foam mat-dried powders were comparable and higher to those of the spray- and freeze-dried powders, respectively. However, the solubility and dispersibility of the foam mat-dried powders were lower. The morphology of the foam mat-dried powder showed a smooth, flat shape, with a larger size than the spray- and freeze-dried powders.

Automated summary

The foaming conditions for producing instant powder from black rice bran anthocyanin extracts were optimized using response surface methodology (RSM). The foam with the highest overrun, foam density, and foam stability was obtained with a foaming agent concentration of 0.06% (w/w) and a whipping time of 16.1 min. The foam was then dried at different temperatures, with the best results observed at 80 degrees C. The foam mat-dried powders showed comparable or higher total anthocyanin content and encapsulation efficiency compared to spray- and freeze-dried powders, but had lower solubility and dispersibility.