Adaptation of bacterial starter cultures from dairy to plant-based substrates: challenges and opportunities

The global market for plant-based milk alternatives (PBMA) is expanding with an increasing demand for sustainable plant-based products which offer similar nutritional and organoleptic properties to that of their dairy counterparts. These PBMAs are largely derived from legumes, seeds, nuts, cereals and pseudocereals. Lactic Acid Bacteria (LAB) are central to food fermentations wherein their metabolic activities contribute to the preservation, safety and organoleptic properties of a product. The biological pathways which underpin dairy fermentations have long been elucidated and exploited. However, it is now evident that many of the biotechnological traits which drive dairy fermentations, in particular casein hydrolysis and lactose utilisation, are not directly transferable to PMBA-substrates. Therefore, knowledge of the carbohydrate and protein composition and their metabolism by the applied starter cultures is required for the development of high quality fermented PBMA dairy analogues. Here, we review the fundamental traits that lactic acid bacteria should possess for the fermentation of varied PBMA substrates, with a particular focus on carbohydrate utilisation and protease activity. Firstly, we consider the genetic limitations of those dairy-adapted and industrialised starter strains which may prevent their successful application to PBMA fermentations. Secondly, we consider the genetic and bio-functional activities of both plant-associated and non-starter LAB and reveal their potential as starter cultures for the emerging PBMA fermentation industry. By understanding the genetic and metabolic requirements food producers will be afforded the opportunity to design the next generation of defined, rotational starter sets, which harbour the bio-specific traits required for the fermentation of PBMA substrates.