Pre-selection on skim milk of dairy lactic acid bacteria to improve antioxidant activity and shelf life of cheeses

It has been shown that some lactic acid bacteria possess antioxidant activity [1]. The using of lactic acid bacteria to increase the antioxidant activity in cheese [2] is a good way to improve its shelf life. Consequently, the aim of this work was to perform the clonal isolation, identification and selection of lactic acid bacteria to produce compounds with the property to improve the antioxidant activity and the shelf life of cheeses. Seventy-three strains of lactic acid bacteria, belonging to the strain collection of the Unit of Microbiology of the Department AGRARIA of Reggio Calabria and isolated from dairy products during different years, were tested on skim milk for their pH and antioxidant activity. Each strain was first precultured in MRS broth (lactobacilli) or in M17 broth (coccal-shaped) at 37°C for 24 h. These cultures were then used in inoculation (1%, v/v) of 15 ml of skim milk treated at 121°C for 5’. Each strain was inoculated in triplicate for 44 h at 37°C. Then the pH was determined and the antioxidant activity was measured by analysing the radical scavenging activity using a spectrophotometric decolourization assay (ABTS) according to Virtanen et al. [3]. In addition, also DPPH assay was performed. The pH values were distributed in 34 homogeneous groups showing a mean value of 4.88, with a minimum of 3.49 and a maximum of 5.89. The ABTS values (expressed as % of inhibition) were distributed in 32 homogeneous groups showing a mean value of 51.56, with a minimum of 24.40 and a maximum of 71.52. These results confirm that the development of antioxidant activity is a strain-specific characteristic. In detail, the tested strains exhibit a high degree of biodiversity. Six strains [3 Lactobacillus, 2 Enterococcus, and 1 Lactococcus], exhibiting the highest radical scavenging activity, were selected for further investigation. Research will go on testing the best strains in cheese-making, in order to validate these results. References [1] Kaizu H, Sasaki M, Nakajima H, Suzuki Y (1993) Effect of antioxidative lactic acid bacteria on rats fed a diet deficient in vitamin E. Journal of Dairy Science 76: 2493-2499. [2] Osuntoki A, Korie I (2010) Antioxidant activity of whey from milk fermented with Lactobacillus species isolated from Nigerian fermented foods. Food Technology and Biotechnology 48: 505-511. [3] Virtanen T, Pihlanto A, Akkanen S, Korhonen H (2007) Development of antioxidant activity in milk whey during fermentation with lactic acid bacteria. Journal of Applied Microbiology 102: 106-115.