Comparative Kinetics of Single- and Multiple-Strain Buckwheat Fermentation: Microbial Growth, Sucrose Hydrolysis and pH Dynamics

This study investigated lactic fermentation of green buckwheat beverages formulated at 8% (A, AA) and 10% (B, BB) solids using single- and multiple-strain cultures of Lactiplantibacillus plantarum, Lactobacillus acidophilus, Lacticaseibacillus paracasei and Lacticaseibacillus rhamnosus. Fermentation at 37 °C rapidly reduced pH from slightly alkaline values (7.44–7.57) to approximately 4.2–4.5 within 3–8 h, while viable counts increased from near-zero to 8–9 log10CFU mL−1, confirming efficient lactic acid bacteria (LAB) proliferation in all substrates. A general trend was observed in the sugar consumption strategy of studied LAB: sucrose (after hydrolysis) and glucose were almost completely depleted within 6–8 h, fructose was consumed more slowly, and raffinose remained largely unchanged, with the 10% substrate mainly accelerating early sugar turnover without altering final cell densities or the qualitative utilisation pattern. Dry matter changed little during fermentation, whereas total phenolic content (TPC) and total tannin content (TTC) were strongly affected in a matrix- and strain-dependent manner. At 8% solids, fermentation promoted substantial TTC reduction and, for several cultures, a net decrease in extractable phenolics. In contrast, 10% formulations, particularly those inoculated with L. acidophilus and L. paracasei (alone or in combination), partially preserved or increased TPC while achieving more moderate tannin losses. Overall, green buckwheat proved to be a promising substrate for developing fermented beverages in which solids level and starter composition can be tuned to combine rapid acidification and high LAB viability with tailored sugar depletion and favourable modulation of phenolic and tannin fractions.