Mixed-Culture Anaerobic Acidogenic Fermentation of Cabbage

Abstract

Dating back to 10,000 B.C.E., fermentation has served as a vital tool primarily for food preservation. In the nineteenth century, Louis Pasteur put forth the proposition that the occurrence of fermentation is predominantly facilitated by the presence of microorganisms. Pasteur’s discovery spurred comprehensive studies on microorganisms, revealing their strategic roles in fermentation and microbial ecosystems. However, in striving for stable processes and consistent products, researchers largely focus on simple substrates and pure cultures, yet practical applications of fermentation face obstacles due to substrate complexity and culture maintenance.

This research aims to provide insights into the intricate relationship between the microbial community and the complex substrate. It primarily focuses on the anaerobic acidogenic fermentation of cabbage, with the aim of identifying and understanding the key influences on microbial behavior and fermentation patterns. Cabbage was chosen as the feedstock for this investigation due to its historical and robust use as a substrate, specifically for the generation of lactic acid. This byproduct not only holds economic value but also presents intriguing scientific implications, such as serving as a promising raw material in biodegradable plastic manufacturing. The initial segment of our research endeavors to investigate the fermentation process and characterize the microbial community dynamics observed during the fermentation of chopped cabbage. Interestingly, our analysis of chopped cabbage fermentation revealed a triphasic progression, wherein the Bacilli class—predominant in the initial stages—facilitated lactic acid production, succeeded by Clostridia and Actinobacteria driving butyrate and propionate generation, respectively.

Despite the principles of thermodynamics and ATP yield suggesting that the transformation of sugars into alternative end products, such as short-chain fatty acids, is more favourable, the production of lactic acid is frequently observed, notably in fermentations involving vegetables. State-of-the art flux balance analysis models suggest that these microorganisms achieve dominance when sugar concentration exceeds a certain threshold, leading to enhanced (Lactic Acid Bacteria) LAB growth rates. We hypothesize that by employing a novel water solubilization method to separate the cabbage into soluble and ”insoluble” fractions, it would enable us to manipulate the initial soluble organic load, under the assumption that the substrate composition maintains similarity. This, in turn, could potentially influence the growth rates of LAB. Remarkably, the data revealed Clostridia class dominating the “insoluble” cabbage, while Bacilli class predominated in the soluble cabbage fermentation at the early stages.

The majority of LAB are documented to necessitate specific amino acids for their growth. A crucial aspect of our research was to elucidate whether LAB engaged in cabbage fermentation exhibits a similar dependency on the substrate. To elucidate this, we used the inoculum from cabbage fermentation to ferment solely cabbage sugars in the absence of the cabbage. The objective was to determine if the microbial community could produce similar fermentation patterns without the non-monosaccharide constituents of cabbage, thus investigating their role in LAB growth. Noteworthy, in the absence of cabbage, a divergent pattern with minimal lactic acid and lack of LAB was observed, highlighting their dependence on non-monosaccharide cabbage components.

This research provided critical insights into the interactions between substrates and microbial communities, with potential applications in optimizing fermentation processes in the food industry and biochemical production. It may also lead to a better understanding of microbial behavior in different substrate conditions, providing a foundation for more efficient and sustainable fermentation.