Melatonin has recently been detected in fermented beverages and foods, in which microorganism metabolism is highly important. The existing literature knowledge discusses the direction for future studies in this review. Evidence shows that many species of microorganisms could synthesize melatonin. However, the actual concentrations of melatonin in fermented foods and beverages range from picograms per milliliter to nanograms per milliliter. 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 difference of melatonin levels. Thus 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 significant to discuss whether all species of microorganisms have the capacity to synthesize melatonin and what the biological functions of melatonin are in microorganisms. Melatonin plays a lot of 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.

The methanol content is an important indicator in determining the quality of wine. The effects of material quality, fermentation conditions and storage containers on the formation of methanol and other substances in winemaking process were studied. The methanol content in spine grape wine was observed to increase as the fermentation temperature increased. Extending maceration time and the increasing addition of pectinase also increased the methanol content. No significant change in methanol content was observed with various yeasts added. The methanol content in wine that is stored in oak barrels was the lowest compared to that in other containers. The optimal conditions to control the methanol content in spine grape wine should be as follows: ferment wine with highquality materials under 25-26°C for 3-6 d, with a pectinase of 15-20 mg/L and yeast added; and store the wine in oak barrels.

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