Probiotic properties and antioxidant activity of selected lactic acid bacteria in fermented milk

This study was conducted to determine the probiotic properties of selected lactic acid bacteria and their ability to produce antioxidative metabolites in milk. Ten Lactobacillus strains (L. acidophilus BIOTECH 1900, L. brevis BIOTECH 1766, L. casei BIOTECH 1064, L. delbrueckii BIOTECH 1010, L. paracasei BIOTECH 10363, L. paracasei BIOTECH 10371, L. paracasei BIOTECH 10372, L. paracasei paracasei BIOTECH 10363, L. plantarum 1074, and L. plantarum 1160) were evaluated in vitro for their desirable probiotic properties. Seven isolates (1900, 1064, 10363, 10371, 10372, 10369, and 1074) were considered acid tolerant at pH 3. All strains displayed resistance to 0.3% bile, high auto-aggregation activity, and strong antagonistic activity against Escherichia coli and Staphylococcus aureus BIOTECH 1350. Eight strains (1766, 1064, 10363, 10371, 10372, 10369, 1074 and 1160) exhibited high cell surface hydrophobicity. Nine isolates were tolerant to 9% sodium chloride with the exemption of 1074. None of the strains exhibited betha-hemolytic activity. All strains were susceptible/moderately susceptible to amoxicillin, ampicillin, augmentin, penicillin G, erythromycin, clindamycin, and tetracycline. Resistance to kanamycin was observed in all strains, whereas four isolates were resistant to streptomycin (1900, 1766, 1064, and 1160), and cefaclor (1900, 1010, 10371, and 1074). The cumulative probiotic potential (CPP) of the selected LAB ranged from 75 to 100% indicating that all isolates can be labeled as potential probiotics with high prospective for commercial applications. Six strains (1064, 10363, 10371, 10372, 10369, and 1074) were adjudged very high, i.e. CPP of 100%. The six potential probiotic LAB with 100% CPP value exhibited high antioxidant activity in cow's, buffalo's and goat's milk. The highest antioxidant activity was observed in cow's milk fermented by L. paracasei BIOTECH 10363 (79.07%). Based on the result, cow's milk x L. paracasei BIOTECH 10363 combination was selected for the partial optimization of the incubation conditions for the maximum antioxidant activity. The results illustrate that L. paracasei BIOTECH 10363 had the highest antioxidant activity (84.23%), lactic acid content (1.08%) and viable count (10.31 log fu/mL) at 37 deg C for 72 hours. Therefore, the optimum incubation condition for L. paracasei BIOTECH 10363 for maximum antioxidant activity in cow's milk is at 37 deg C for 72 hours. The findings indicate that L. paracasei BIOTECH 10363 could be used as a starter or adjunct culture for the production of a fermented dairy product with antioxidative properties.