Investigation on <scp>L</scp> -rhamnose metabolism of <i>Loigolactobacillus coryniformis</i> subsp. <i>coryniformis</i> DSM 20001 and its propionate-containing fermentates

Propionate is an important short-chain carboxylic acid (SCCA) that serves as an effective antimicrobial agent for food preservation. Previous research has highlighted that few <i>Lactobacillaceae</i> can synthesize propionate by metabolizing deoxyhexoses via the fermentation intermediate 1,2-propanediol (1,2-PD). In this study, we investigated propionate production by <i>Loigolactobacillus coryniformis</i> subsp. <i>coryniformis</i> DSM 20001 while utilizing L-rhamnose as the primary carbon source. We cultivated <i>L. coryniformis</i> in small-scale anaerobic bioreactors at 30°C and pH 6.5 for 72 h and monitored the expression of key genes associated with deoxyhexose metabolism using quantitative PCR. In addition, we assessed the contribution of individual SCCA to the antimicrobial activity of the fermentate against common foodborne pathogens, including <i>Escherichia coli</i>, <i>Salmonella enterica</i>, <i>Klebsiella oxytoca</i>, <i>Staphylococcus aureus</i>, <i>Candida albicans</i>, <i>Aspergillus niger</i>, <i>Penicillium roqueforti</i>, and <i>Penicillium purpurogenum</i> using broth dilution assays. During cultivation, we observed the production of up to 16 mM propionate, alongside other metabolites such as lactate (26 mM), formate (2 mM), and acetate (4 mM), derived from 32 mM L-rhamnose. Genes related to L-rhamnose utilization were upregulated within the initial 48 h, while genes involved in 1,2-PD utilization remained highly transcribed throughout fermentation. Comparing the antimicrobial efficacy of the fermentates to synthetic SCCA mixtures, bacterial indicator strains were more sensitive than molds and yeast. Propionate was the primary SCCA responsible for inhibitory activity; inhibition was reduced if indicator strains were able to use lactate.IMPORTANCEWorldwide, approximately 30% of food produced is lost. Despite the application of complementary treatment methods, microbial food spoilage can occur along the entire value chain. The rising concern about food waste has led to increasing interest in natural preservation approaches. <i>Lactobacillaceae</i> fermentative systems produce a variety of short-chain carboxylic acid (SCCA) with antimicrobial potential, and we present here fundamental insight into the only recently discovered deoxyhexose metabolism of <i>Loigolactobacillus coryniformis</i> producing the antimicrobial SCCA propionate. We developed a bioprocess to produce propionate from L-rhamnose under controlled conditions as a first step toward the exploitation of L-rhamnose metabolism in the production of antimicrobial fermentates for use in the food industry, potentially replacing chemical alternatives. Our investigations highlight the major contribution of propionate in antimicrobial activity but also indicate the issue of co-occurring fermentable metabolites, which can affect the efficiency of fermentates.