Acta Scientiarum Polonorum Technologia Alimentaria

Background. This study aimed to determine the optimal bacterial cell density in the initial starter culture for fermentation of plant-based yogurt produced from purple brown rice supplemented with soy milk.
Material and methods. The relationship between bacterial density and the quality of the final product was examined in terms of both physicochemical and sensory properties. The initial starter cultures had bacterial densities of 107, 2×107, 4×107, 6×107, 8×107, and 108 cfu/mL, which were used for fermentation.
Results and discussion. The optimal bacterial density was found to be 6×107 cfu/mL. Yogurt produced at this density exhibited the highest water-holding capacity (96.60%) and firmness (3.88 g-force), resulting in a soft texture with minimal syneresis. The brightness L and a redness value in the CIELAB scales were 43.49 and 1.65, respectively, corresponding to the peak sensory scores. The viable cell count reached at least 2.14×108 cfu/mL; °Brix, lactic acid, protein, total sugar, and reducing sugar contents were 11.64, 0.63, 9.26, 19.98, and 16.28 g/100 g dry matter, respectively – values consistent with the requirements for mar­ketable yogurt products. Although bioactive components such as anthocyanins and phenolics were present in relatively low concentrations (0.07 g and 1.08 g TAE per 100 g dry matter, respectively), their presence indicates the product’s antioxidant potential.
Conclusion. The study demonstrated that an initial microbial density of 6×107 cfu/mL in the starter culture yields a product with the most desirable balance of fermentation efficiency and yogurt quality.