Physicochemical, Antioxidant, and Antimicrobial Properties of Pasteurized Buffalo Milk Fortified with Roselle (Hibiscus sabdariffa L.) Extract

This study aimed to evaluate the effects of roselle (Hibiscus sabdariffa L.) extract fortification on the physicochemical properties, nutritional composition, and functional activities of pasteurized buffalo milk. The study employed a 2 × 2 factorial Completely Randomized Design (CRD) with three technical replicates. The treatment factors were buffalo milk type (River and Toraja Belang) and roselle extract concentration (0% and 5%, v/v). Fortification with 5% roselle extract decreased the pH to 5.60 ± 0.07 and 5.51 ± 0.06 and the viscosity to 2.76 ± 0.75 and 2.42 ± 0.41 mPa·s, respectively, but did not affect water activity. River buffalo milk had higher protein contents (4.86 ± 0.32 and 4.76 ± 0.15%) and lactose contents (7.33 ± 0.47 and 6.36 ± 0.55%) than Toraja Belang buffalo milk. Antioxidant activity, expressed as DPPH radical inhibition, increased to 67.93 ± 1.09% and 69.52 ± 0.95%. Inhibition zones also increased against Escherichia coli (11.50–11.83 mm), Staphylococcus aureus (12.10–19.03 mm), and Salmonella sp. (11.10–11.36 mm). The interaction between the two factors had a significant effect (p < 0.05) on pH, viscosity, lactose content, and the inhibition zones against E. coli and S. aureus, but had no significant effect (p > 0.05) on the other parameters. Roselle-fortified buffalo milk has potential for further development as a functional beverage based on its in vitro antioxidant and antimicrobial activities.