Caproic Acid-Producing Bacteria in Chinese Baijiu Brewing

Abstract

Caproic acid can be used as spices, preservatives, animal feed additives, and biofuels. At the same time, caproic acid plays an important role in Chinese Baijiu. It is the precursor substance for the synthesis of ethyl caproate, which directly affects the quality of Chinese Baijiu. Caproic acid-producing bacteria are the main microorganisms that synthesize caproic acid in Chinese Baijiu, and the most common strain is Clostridium kluyveri. Caproic acid-producing bacteria synthesize n-caproic acid through reverse β-oxidation to extend the carboxylic acid chain. This method mainly uses ethanol and lactic acid as substrates. Ethanol and lactic acid are converted into acetyl-CoA, and acetyl-CoA undergoes a series of condensation, dehydrogenation, dehydration, and reduction to extend the carboxylic acid chain. This review addresses the important issues of caproic acid-producing bacteria in the brewing process of Baijiu: the common caproic acid-producing bacteria that have been reported metabolic pathways, factors affecting acid production, biological competition pathways, and the effect of mixed bacteria fermentation on acid production. It is hoped that this will provide new ideas for the study of caproic acid-producing bacteria in Chinese Baijiu.