Effect of probiotic bacterial species on the bioactivity of a fermented spelt-based beverage

Background: Spelt grain, due to its valuable chemical composition, can serve as a promising substrate for functional beverages. Probiotic microorganisms are capable of hydrolyzing bound phenolics and synthesizing new phenolic compounds during fermentation. Fermentation of spelt with probiotic bacteria increases the concentration of free phenolic compounds and organic acids, thereby enhancing the bioactivity of the beverage.  Objective: The aim of this study was to evaluate the ability of the strains B. adolescentis, P. freudenreichii, L. casei, L. plantarum, and L. fermentum to accumulate phenolic compounds and organic acids during fermentation and to ensure high antioxidant activity in a spelt-based beverage. Methods: The spelt substrate was obtained by enzymatic hydrolysis of flour derived from Triticum dicoccum grains and subsequently fermented using the probiotic strains B. adolescentis AC1531, P. freudenreichii B9654, L. casei B32, L. plantarum B4, and L. fermentum B28. The content of proteins, sugars, starch, and free amino nitrogen in the spelt substrate was determined using the Kjeldahl method, high-performance liquid chromatography (HPLC), polarimetry, and spectrophotometry. The number of probiotic bacteria was monitored by plating on MRS agar and corn–lactose medium. Total phenolic content was determined using the Folin–Ciocalteu method, while organic acids were analyzed by HPLC. Antioxidant activity was evaluated by measuring the ability of the samples to scavenge the DPPH radical; results were expressed as mg ascorbic acid equivalents (AAE) and as percentage inhibition of DPPH. Results: The study demonstrated that, for all tested bacterial strains, the highest levels of total phenolic compounds and antioxidant activity (AOA) were observed at pH 4.5 ± 0.1. The greatest accumulation of phenolic compounds was observed during fermentation with L. fermentum B28 and L. plantarum B4 (115.5 and 104.5 mg GAE/L, respectively). The highest antioxidant activity was recorded in samples fermented with L. fermentum B28, L. plantarum B4, and B. adolescentis AC1531 (69.4, 67.4, and 66.1% DPPH inhibition; 122.3, 110.8, and 106.9 mg AAE/L, respectively). The most intensive accumulation of organic acids occurred during the period of pH reduction to 4.5 ± 0.1. Fermentation with B. adolescentis AC1531 resulted in high concentrations of acetic, citric, and succinic acids. Fermentation with L. plantarum B4 and L. fermentum B28 resulted in simultaneously high concentrations of lactic, acetic, propionic, succinic, formic, and citric acids. Changes in antioxidant activity across all samples correlated with phenolic compound accumulation and were not associated with acid production. Conclusion: L. plantarum B4, L. fermentum B28, and B. adolescentis AC1531 demonstrated the highest levels of phenolic compounds, physiologically valuable organic acids, and antioxidant activity during fermentation. These strains can therefore be recommended as promising starter cultures to produce a bioactive spelt-based beverage.  Novelty of the Study:  This study evaluates the bioactivity of a spelt-based beverage after fermentation with probiotic bacteria and demonstrates quantitative improvements in the levels of bioavailable phenolic compounds and physiologically valuable organic acids (propionic, acetic, succinic, and formic acids) when specific strains were used (L. plantarum B4, L. fermentum B28, and B. adolescentis AC 1531). Keywords: spelt; bioactive spelt beverage; fermented cereal beverage; Bifidobacterium adolescentis AC1531; Propionibacterium freudenreichii B9654; Lacticaseibacillus casei B32; Lactiplantibacillus plantarum B4; Limosilactobacillus fermentum B28, phenolic compounds, antioxidant activity, short-chain fatty acids