Microorganisms: producers of melatonin in fermented foods and beverages.

Melatonin, has recently been detected in fermented beverages and foods, in which microorganism metabolism is highly important. The existing literature knowledge and discuss the direction for future researches in this review. Evidences show that many species of microorganisms could synthesize melatonin. However, the actual concentrations of melatonin in fermented foods and beverages range from pg/mL to ng/mL. Different types of microorganisms, different raw materials, different culture environments, the presence or absence of precursors, high or low alcohol content, and different detection methods are all possible reasons for the huge different of melatonin levels. So far, there have been relatively few studies on the melatonin synthesis pathway microorganisms. Thus, referring to the synthetic pathway of plants and animals, the putative melatonin biosynthesis pathway of microorganisms is presented. It will be significative to discuss whether all species of microorganism have the capacity to synthesize melatonin, what the biological functions of melatonin in microorganisms are. Melatonin plays a lot important roles in microorganisms, particularly in enhancing the tolerance of environment stress. Also, the loss of melatonin concentration in commercially available fermented foods and beverages is a ubiquitous trend, and how to solve this problem is a new field to be further explored.