Natural food-derived antimicrobials against beer spoilage microorganisms

The spoilage of beer significantly threatens the quality and safety of products in the beverage industry. Certain natural foods contain beneficial bioactive components that are considered to be safer than chemical additives. This study aimed to identify extracts of natural foods as potential alternatives to chemical preservatives for controlling beer spoilage microorganisms. Among the two extraction methods applied to 176 natural foods, the extracts of clove alone effectively inhibited the growth of representative beer spoilage microorganisms, specifically Levilactobacillus brevis, Sporolactobacillus vineae, Pectinatus frisingensis, and Saccharomyces cerevisiae var. diastaticus. High-performance liquid chromatography and half-maximal inhibitory concentration analysis revealed that gallic acid and eugenol in cloves were active compounds with antimicrobial properties in vitro that were of a similar order of magnitude to those of commercial preservatives (potassium sorbate and sodium benzoate) under the tested conditions. Scanning electron microscopy observations and a fluorescence leakage assay using 3,3'-dipropylthiadicarbocyanine iodide indicated morphological alterations and membrane perturbation in treated microorganisms, except for the limited effect of gallic acid on S. cerevisiae var. diastaticus. These findings provide insight into the potential role of natural food-derived antimicrobials in controlling beer spoilage microorganisms, pending further validation in real beverage systems.