Screening and Enhancement of Hyaluronic Acid Production in Yogurt via Modification of Temperature and Nutrient Composition

Background: Hyaluronic acid (HA) is a valuable bioactive polysaccharide produced by lactic acid bacteria (LAB) that plays a role in tissue hydration, joint lubrication, and tissue repair. Methods: Twenty yogurt samples (15 traditional, T1–T15; 5 commercial, C1–C5) were collected from Zanjan Province, Iran, between May and September 2023. LAB were isolated using De Man, Rogosa and Sharpe (MRS) agar and M17 media and identified via Gram staining, cellular morphology, and catalase/oxidase tests. The four samples with the highest HA production (C1, T2, T14, T15) were selected. HA was extracted using trichloroacetic acid (TCA) precipitation and quantified via the carbazole assay. The effects of fermentation temperature, carbon source, and nitrogen source on HA production were evaluated using a One-Factor-at-a-Time (OFAT) approach. Yogurts were assessed for syneresis and sensory characteristics over 21 days of refrigerated storage. Data were analyzed using one-way Analysis of Variance (ANOVA) and Tukey’s HSD post-hoc test in IBM SPSS Statistics software (version 20; IBM Corporation, Armonk, NY, USA). Results: Among the 20 samples, T15 showed the highest initial HA production (0.71 g/L). Optimization identified 37°C, 15 g/L glucose, and 20 g/L yeast extract as the most favorable conditions, increasing HA production by T15 1.75-fold. The optimized yogurt exhibited a 37.2% reduction in syneresis compared with T14 on day 21 and significantly higher sensory scores at several time points (p < 0.05). Conclusion: Optimizing fermentation temperature and nutrient composition significantly enhanced HA production in yogurt while improving water-holding capacity and sensory quality. These findings confirm the feasibility of in situ HA production by LAB for functional dairy products.