Evaluation of the fermentation potential of lactic acid bacteria isolated from herbs, fruits and vegetables as starter cultures in nut-based milk alternatives

Fermentation of plant-based milk alternatives (PBMAs), including nut-based products, has the potential to generate new foods with improved sensorial properties. In this study, we screened 593 lactic acid bacteria (LAB) isolates from herbs, fruits and vegetables for their ability to acidify an almond-based milk alternative. The majority of the strongest acidifying plant-based isolates were identified as Lactococcus lactis, which were found to lower the pH of almond milk faster than dairy yoghurt cultures. Whole genome sequencing (WGS) of 18 plant-based Lc. lactis isolates revealed the presence of sucrose utilisation genes (sacR, sacA, sacB and sacK) in the strongly acidifying strains (n = 17), which were absent in one non-acidifying strain. To confirm the importance of Lc. lactis sucrose metabolism in efficient acidification of nut-based milk alternatives, we obtained spontaneous mutants defective in sucrose utilisation and confirmed their mutations by WGS. One mutant containing a sucrose-6-phosphate hydrolase gene (sacA) frameshift mutation was unable to efficiently acidify almond, cashew and macadamia nut milk alternatives. Plant-based Lc. lactis isolates were heterogeneous in their possession of the nisin gene operon near the sucrose gene cluster. The results of this work show that sucrose-utilising plant-based Lc. lactis have potential as starter cultures for nut-based milk alternatives.