Impact of hydrocolloid and foaming agent on the physicochemical, microstructural and bioactive characteristics of foam-mat freeze-dried tapai (fermented black glutinous rice) powder

The aim of this study was to obtain fermented black glutinous rice (FBGR) powder using the foam-mat freeze-drying method and to evaluate the physicochemical, microstructural, and bioactive characteristics of FBGR powder. To obtain FBGR foams, maltodextrin (MD; 0%–40% w/w) and whey protein isolate (WPI; 7.5% w/w) were used. The results showed that MD concentration had a significant effect (p ≤ .05) on powder recovery and bulk density which increased from 68.9% to 80.5% and 0.46% to 0.63 g/ml, respectively. The lowest moisture content (2.17%) and water activity (0.48) were found in powders produced with 20% MD. The solubility of FBGR powders ranged from 74% to 75% and increasing MD concentration gave higher lightness (L*) and yellowness (b*) readings in color properties of powders. Although the addition of the carrier agent caused reductions in total phenolic content and anthocyanins, the retention of these bioactive compounds rose with increasing MD content from 67% to 76% and 78% to 84%, respectively. FBGR produced with 40% MD had the most superior physical and technological properties, and foam-mat freeze-drying is a promising technology for retaining the bioactive compounds in FBGR.