Bioactive Compounds and Antioxidant Properties of Sheep’s Milk Yogurt Enriched with a Postbiotic Extract from <i>Lactiplantibacillus plantarum</i> UCLM56: Effects of <i>In Vitro</i> Digestion and Fermentation

Lactic acid bacteria present in yogurts produce bioactive compounds, such as gamma-aminobutyric acid (GABA) and short-chain fatty acids (SCFAs). Sheep's milk yogurt is an excellent medium to enhance their bioactive properties. In this study, the impact of adding an extract derived from the GABA-producing strain <i>Lactiplantibacillus plantarum</i> UCLM56 to sheep's milk yogurt was evaluated in terms of its bioactive and antioxidant properties. Samples were subjected to <i>in vitro</i> digestion and fermentation to simulate the effects of the gastrointestinal tract. GABA, SCFAs, amino acids, biogenic amines, antioxidant capacity, and organic acid levels were analyzed. Yogurt enriched with UCLM56 postbiotic extract showed higher levels of GABA and propionic acid, with increases of more than 360 and 260%, respectively, along with an improved antioxidant capacity (FRAP and DPPH methods) compared to conventional yogurt. After <i>in vitro</i> fermentation, the levels of lactic and propionic acids were significantly higher in the enriched yogurt (50 and 41% increases, respectively), as well as the antioxidant capacity (more than 200% improvement). In conclusion, the use of <i>Lactiplantibacillus plantarum</i> UCLM56 extract enhances the bioactive properties of sheep's milk yogurt, making it a promising option for developing functional dairy products with added value.