Abstract
The purpose of this study is to investigate the effect of fungi on kimchi metabolites during fermentation. A gas chromatography-mass spectrometry (GC-MS) based metabolite profiling approach in combination with principal component analysis (PCA) is performed to differentiate metabolites produced by fungi or bacteria. To avoid bacterial growth, kimchi is treated with 100 μg/mL of ampicillin every three days from 30 to 50 days of fermentation. The relative content of the major fungi at 50 days of fermentation, between the control group and the ampicillin treatment group, was not significantly different. The administration of ampicillin changed the metabolites in kimchi by affecting the growth of kimchi bacteria. Based on the pattern of change of each metabolite, the changed metabolites are grouped into four categories: (1) metabolites produced or consumed by fungi, (2) metabolites involving both fungi and bacteria, (3) metabolites produced or consumed by bacteria, and (4) metabolites of undetermined origin. Alanine, thymine, galacturonic acid, and malonic acid can be regarded as the metabolites produced by fungi between 30 and 50 days of fermentation. In contrast, malic acid, oxaloacetic acid, galactitol, glucose, and mannitol are presumed to be the metabolites mainly consumed by fungi. This study is meaningful as the first study conducted by inhibiting growth of bacteria to identify the metabolites contributed by fungi or bacteria in the kimchi fermentation process. These results could be used to make customized kimchi that controls the production of desired metabolites by selectively controlling the formation of microbial communities in the kimchi industry.
Highlights
Kimchi is a traditional Korean cuisine made from kimchi cabbage and various seasonings including ginger, garlic, red pepper, spring onion, jeotgal, and salts [1]
The organic acids or antimicrobial compounds produced by lactic acid bacteria (LAB) inhibit yeast growth, making it difficult for yeast to grow during kimchi fermentation [24,25,26]
Many kimchi studies report changes in metabolites during fermentation, they are interpreted in relation to bacteria, such as LAB
Summary
Kimchi is a traditional Korean cuisine made from kimchi cabbage and various seasonings including ginger, garlic, red pepper, spring onion, jeotgal (salted seafood), and salts [1]. There are many types of kimchi in Korea made with various vegetables as the main ingredients. In order to eat fresh vegetables that are not available in winter, there is a culture called ‘gimjang’ in Korea, which manufactures kimchi that can be consumed for a long time (more than a year) [2]. Kimchi made in early winter is stored at low temperatures and is consumed until the year. Spontaneous fermentation in kimchi leads to the formation of various microorganisms, affecting the sensory qualities of kimchi [3]. It is well known that the composition of metabolites important to kimchi taste and flavor, such as organic acids (lactic acid and acetic acid) and other flavoring compounds (mannitol and amino acids), are directly affected by the kimchi microbial community [4]
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