Quantitative antifungal activity of reuterin against food isolates of yeasts and moulds and its potential application in yogurt

Reuterin is an antimicrobial agent produced by conversion of glycerol and excreted by several bacterial species including the food grade lactic acid bacterium Lactobacilli's reuteri. Several inhibitory activities have been reported to reuterin against a broad range of Gram-positive and Gram-negative bacteria, bacterial spores, moulds, yeasts and protozoa. However, the antifungal and anti-yeast activity of reuterin is poorly documented. The aim of the current work was:1) To quantify the minimum inhibitory activity (MIC) and the minimum fungicidal activity (MFC) of reuterin against a representative panel of the most abundant fungi and yeast species associated with food contamination; 2) To investigate the application of reuterin as antifungal agent for bio-preservation of yogurt. Reuterin was produced by L. reuteri ATCC 53608 in MRS and glycerol solution then purified before using. Our data showed that purified reuterin inhibited the growth of tested microorganisms at a concentration of 11 mM or less. Moreover, reuterin showed a fungicidal activity (killed 99.9% of all tested microorganisms) at concentrations equal or below 15.6 mM as indicated by MFC. Values of MFC were comprised between 1.0 and 4.8 of the MIC values, suggesting a potent fungicidal mechanism on both yeasts and filamentous moulds with one exception only. In yogurt, reuterin showed a fungistatic effect at a concentration of 1.38 mM while a fungicidal effect was obtained at 6.9 mM. Therefore, reuterin has a high potential as a food preservative, particularly owing to its biochemical properties and antibacterial and antifungal activities.