Fundamental study on the improvement of the antifungal activity of Lactobacillus reuteri R29 through increased production of phenyllactic acid and reuterin

Lactic acid bacteria have shown great potential as bio-preservative agents to maintain high food quality and safety. The strain Lactobacillus reuteri R29 is reported to have a broad spectrum of antifungal activity and suitability for application in food systems. Its antifungal activity is predominantly based on phenyllactic acid (PLA). Furthermore, it is potentially a producer of reuterin, a potent antimicrobial agent. This study focused on increasing the antifungal activity in vitro by supplementation of the growth medium with phenylalanine and glycerol to increase the yield of PLA and reuterin, respectively. For PLA, the addition of 1.5% phenylalanine (w/v) to MRS, resulted in significantly increased accumulation of PLA and antifungal performance against Fusarium culmorum. Supplementation of MRS with 500mM glycerol combined with a reduced glucose content (1.5%) showed the highest reuterin accumulation combined with fungal inhibition. To investigate the antifungal performance in situ, these cell-free supernatants (cfs) were applied in a bread system. The application of PLA-enriched cfs resulted in significantly extended (4 days) microbial shelf life compared to the control. The reuterin-enriched medium did not lead to significant shelf life extension. In conclusion, Lactobacillus reuteri R29 and its PLA-enriched cfs were found to be very promising alternatives for food bio-preservation.