Probiotic Properties and Cellular Antioxidant Activity of Lactobacillus plantarum MA2 Isolated from Tibetan Kefir Grains

Lactobacillus plantarum MA2 was isolated from traditional Chinese Tibetan kefir grains. Its antioxidant properties had been demonstrated in vitro and in vivo previously. In the present study, the probiotic characteristics of this strain were further evaluated by investigating its acid and bile salt tolerances, cell surface hydrophobicity, and autoaggregation, respectively. In addition, the cellular antioxidant activity (CAA) assay was applied to test the antioxidant capacity of the isolate in different growth phases. Same method was also used to evaluate the antioxidant capacity of its fermentation supernatant, cell-free extract, and intact cell quantitatively. The results of probiotic characteristic tests showed that MA2 could survive at pH 2.5 and 0.3% bile salt. Meanwhile, the measurements of cell surface hydrophobicity and autoaggregation were 45.29 +/- 2.15 and 6.30 +/- 0.34%, respectively. The results of cellular antioxidant activity tests indicated that MA2 had high antioxidant potential. The CAAvalue of logarithmic phase cell-free extract of MA2 (39,450.00 +/- 424.05 mu mol quercetin equivalents/100 g sample) was significantly higher than that in stationary phase cell-free extract (3395.98 +/- 126.06 mu mol quercetin equivalents/100 g sample) and that of fermentation supernatant in logarithmic phase (2174.41 +/- 224.47 mu mol quercetin equivalents/100 g sample) (p < 0.05). The CAA method was successively applied to evaluate the antioxidant capacity of MA2 in this study, which suggests that it could be used as a useful method for lactic acid bacteria antioxidant potential evaluation.