Kombucha tea as a natural coagulant in legume-based milk systems: Optimization and characterization of fermented...

This study investigated the potential of kombucha tea as a natural coagulant for developing sustainable legume-based curds from chickpea, mung bean, kenaf seed and red kidney bean milks. A Box-Behnken response surface design was employed to assess the combined effects of sugar concentration (5-15%), kombucha-to-milk ratio (20-60%) and fermentation time (4-8 h) on pH, moisture content, total soluble solids (TSS) and textural attributes. The models showed strong predictive power (R² > 0.80) and non-significant lack of fit (p > 0.05), confirming the adequacy of the response surface methodology. Despite differing optimum conditions, all legume-based formulations produced curds with desirable acidity (pH ≈ 4.5), enhanced cohesiveness and springiness, and high composite desirability. Extended fermentation (7-14 days) led to substrate-dependent variations in physicochemical, antioxidant and microbial properties. Chickpea curd exhibited the most active microbial proliferation, while red kidney bean curd showed higher hardness and cohesiveness due to its fiber-rich matrix. Lactic acid bacteria count increased markedly (up to 4.2 × 10⁶ CFU/mL in chickpea and 3.2 × 10⁶ CFU/mL in red kidney bean curds), whereas yeast and total plate counts declined, indicating microbial stabilization. Although DPPH activity decreased, total phenolic content and ferric-reducing power increased significantly, reflecting enhanced phenolic release and redox potential. Overall, kombucha served as a potential natural coagulant, improving texture and promoting microbial stabilization of plant-based curds. The findings highlight kombucha fermentation as a promising strategy for investigating potential plant-based dairy-like structures aligned with natural ingredient innovation.