Physicochemical and antioxidant properties of a fermented beverage based on buttermilk, Lactobacillus gasseri LG08 and curcumin

Buttermilk is a by-product of butter production. It has technological and functional properties but remains underutilized in the dairy industry due to its classification as a low-value by-product. Reducing food losses throughout the production chain is one of the Sustainable Development Goals (SDG). Fermenting buttermilk can improve its flavor, texture, and nutritional profile, while adding probiotic and postbiotic benefits. Functional beverages with probiotics and antioxidants, such as curcumin—a phenolic compound with antioxidant and prebiotic effects—offer higher market value, better sensory qualities, and potential health benefits. We aimed to develop a functional dairy beverage with high antioxidant potential by fermenting buttermilk and adding curcumin, and to evaluate its technological and antioxidant properties. Four formulations were prepared: 1: Pasteurized Buttermilk (BM); 2: Pasteurized Buttermilk + Curcumin (CUR); 3: Pasteurized Fermented (Lactobacillus gasseri LG08) Buttermilk (FBM) and 4: Pasteurized Fermented (Lactobacillus gasseri LG08) Buttermilk + Curcumin (FCUR). To fermented beverages, L. gasseri LG08 was added in a proportion of 1 mg of probiotic (2.1 x 108 CFU/mg): 1mL of BM and kept at 44 ºC, for 24 hours. Curcumin was added to BM (CUR) and to the FBM (FCUR) considering a dosage of 15 mg/mL. Physicochemical properties (pH, titratable acidity and water holding capacity) were analyzed and the total phenolics and antioxidant capacity were determined. Data were compared using ANOVA with Tukey’s test or Kruskal–Wallis with Dunn’s test. As expected, the fermented beverages showed lower pH values and higher lactic acid content than non-fermented ones, which is typical of fermented or acidified products. The fermented beverages showed a higher water-holding capacity (WHC) compared to the non-fermented ones, indicating improved protein network stability and water retention. Beverages containing curcumin presented the highest levels of phenolic compounds among all formulations. Additionally, BM presented a higher concentration than FBM and a similar pattern was observed when comparing CUR and FCUR, with the fermented beverage containing less phenolic compounds. This fact may be due to the use of phenolic compounds as a substrate for the growth of microorganisms, justifying the reduction after the fermentation. The ABTS and DPPH methods showed no differences in free radical scavenging capacity between BM and FBM. However, CUR has a higher antioxidante capacity compared to FCUR. Beverages added with curcumin had the antioxidant capacity improved when compared to BM. Curcumin enhanced bioactivity profile of buttermilk beverages. Utilizing underused by-products reduces waste and supports sustainability.