Isolation of an exopolysaccharide-producing Weissella confusa strain from lettuce and exploring its application as a texture modifying adjunct culture in a soy milk alternative.

Consumers often seek healthier options but still desire the familiar eating experience of traditional dairy. Incorporating exopolysaccharide (EPS)-producing cultures into fermented plant-based milk alternatives (PBMAs) offers a promising approach to improving the textural quality of these products. For this, it is essential that the EPS-producing cultures are able to produce EPS in the plant-based substrate. The present study screened 593 plant-derived lactic acid bacteria (LAB) for their ability to produce EPS on a soy milk agar medium. Fifteen LAB isolates (eight Weissella spp. and seven Leuconostoc spp.) exhibited high EPS production. One of the strongest EPS producers was a Weissella confusa strain, and genome sequencing revealed the presence of two potential related EPS genes. To identify the key gene responsible for EPS production in soy milk, 70,000 colonies were screened on soy milk agar and a spontaneous EPS-defective mutant was isolated. The mutant (W. confusa dsr1) had a mutation in a putative dextransucrase gene, which could encode the enzyme catalysing the transfer of glucose from sucrose into a growing chain of dextran. The mutation introduced a premature stop codon, disrupting the enzyme production. Another mutant (W. confusa sac) found during this screen had impaired acidification and growth in soy milk, which was linked to a mutation in the sucrose metabolism gene cluster. Soy milk fermentations using the W. confusa wild-type or sac mutant, significantly increased water holding capacity and viscosity. This suggests their potential to enhance EPS production in fermented PBMAs, bringing their texture closer to that of traditional dairy.