Functional characterization of indigenous Lacticaseibacillus casei RVSRI-4 and Lactobacillus acidophilus RVSRI-6 from traditional dairy and their antioxidant effects in STZ–induced diabetic rats

Oxidative stress plays a key role in the development of diabetes and its complications, and probiotics from traditional fermented foods may help modulate host antioxidant defenses. This study screened lactic acid bacteria isolated from traditional dairy products for probiotic-related properties and evaluated the antioxidant effects of selected strains in a streptozotocin (STZ)–induced diabetic rat model. Among the isolates, strains S3 and S8 showed the most favorable characteristics, including tolerance to acidic and bile conditions, high hydrophobicity, strong aggregation ability, antimicrobial activity against selected pathogens, and absence of hemolytic activity. Based on 16S rRNA gene sequencing, the strains were identified as Lacticaseibacillus casei RVSRI-4 and Lactobacillus acidophilus RVSRI-6. The combined formulation of the selected strains was orally administered to STZ–induced diabetic male Wistar rats for six weeks. Probiotic supplementation significantly reduced serum malondialdehyde (MDA) levels and enhanced antioxidant defense markers, including catalase (CAT), superoxide dismutase (SOD), glutathione peroxidase (GPx), and total antioxidant capacity (TAC), compared with untreated diabetic rats ( p < 0.05). These findings indicate that the combined probiotic formulation containing the selected indigenous strains can improve antioxidant status in an experimental diabetic model, supporting the potential application of this formulation as a functional food ingredient for managing oxidative stress under diabetic conditions. However, the individual contribution of each strain cannot be determined because only the combined formulation was evaluated in vivo .