Effect of fermentation by Lactobacillus acidophilus CH-2 on the enzymatic browning of pear juice

The main purpose of this work was to clarify the underlying mechanism of Lactobacillus acidophilus CH-2 on the improvement of enzymatic browning of pear juice. L. acidophilus CH-2 was cultured in browned pear juice and in simulated browning model for 24 h. The colour index was analysed by browning degree and colour difference. The underlying mechanism was speculated by changing pH value, setting organic acid metabolites treatments, evaluating antioxidant activity, measuring the growth of viable counts and differential metabolites during fermentation. We observed that the browning was greatly reduced in both of the two models after fermentation by L. acidophilus CH-2. The browning degree of the medium containing variable concentrations of browning products decreased from 1.11-2.13 to 0.48-1.64 after fermentation, and the colour difference decreased from 2.25-4.59 to 0.62-3.74. Fermentation supernatant of L. acidophilus CH-2 showed high free radical scavenging activity. Moreover, differential metabolites during fermentation are mainly involved in the glutathione metabolism, D-Glutamine and D-glutamate metabolism and so on. Overall, it is extrapolated that the improvement of browning can be probably attributed to two-pronged approach 1) the production of metabolites with strong antioxidant activity via the fermentation by L. acidophilus CH-2, 2) the degradation of browning products by fermentation.