Utilizing pomegranate extracts for enhancing yogurt quality and preservation

Abstract

As consumers become increasingly conscious of synthetic preservatives, the demand for natural antioxidant and antibacterial agents is rising. This study investigates the potential of pomegranate (Punica granatum) extracts to control yogurt spoilage. Methanolic and ethanolic extracts of pomegranate peel, seed, and leaf were analyzed for total phenolic content (TPC), antioxidant activity, and inhibitory effects on ‘yogurt starter strains’ and selected food-related bacteria (Bacillus cereus, Staphylococcus aureus, Staphylococcus sciuri, Escherichia coli, Salmonella enterica subsp. enterica serovar Typhi, and Shigella flexneri). Yogurt samples treated with pomegranate extracts were stored at 4 °C for 28 days. Sensory evaluation was performed on fresh yogurt samples. Physicochemical properties (pH, titratable acidity (TTA), and antioxidant activity) and microbiological changes (aerobic plate count (APC), coliform count, lactic acid bacteria (LAB) count, and total yeast and mold count (TYMC)) were examined weekly. Among the extracts tested, methanolic and ethanolic extracts of peel had the highest TPC (603 and 576.9 mg GAE/g) and the strongest antioxidant activity with the lowest IC50 (141.8 and 183.43 µg/mL). Overall, pomegranate peel, seed, and leaf extracts inhibited foodborne bacteria more effectively than probiotic strains, indicating significant antibacterial potential against spoilage microorganisms. Based on a minimum inhibitory concentration (MIC) test, ethanolic pomegranate extracts were incorporated into lab-made yogurt at 8 mg/mL. Throughout the storage period, all yogurt samples maintained a standard pH (≤ 4.6) and TTA (> 0.5 %). Yogurt fortified with pomegranate peel and leaf extracts exhibited greater antioxidant activity and a significantly lower aerobic plate count while retaining LAB probiotic levels (≥ 106 CFU/g), ensuring safety for consumption (TYMC ≤ 102 CFU/g) and acceptability in terms of five selected quality attributes. Consequently, pomegranate peel and leaf extracts present a promising natural alternative to potassium sorbate in yogurt preservation, maintaining probiotic properties without compromising quality.