Screening of lactic acid bacteria to improve the techno-functional value of plant-based products

The global human population is projected to reach approximately 9.7 billion by the year 2050 (FAO, 2018), and this is moving the global interest to a more sustainable diet. In this optic, the attention towards plant-based foods is growing as alternatives to animal-derived products. Plant-based products are optimal for they clear environmental advantages, but many plant matrices present notable limitations, including undesirable flavors, the presence of antinutritional compounds, and scarce technological properties. As a valid tool to overcome these problems, lactic acid bacteria (LAB) have gained attention as an effective and natural approach to plant-based food production. Through their diverse metabolic activities, LAB can acidify plant substrates, enhance safety and shelf life, release bioactive molecules, and generate pleasant flavor compounds while breaking down unwanted ones. This PhD thesis wants to evaluate and utilize dairy isolated LAB to ferment and use their metabolism to enhance the plant-based matrices. The potentiality of LAB was explored with a systematic review based on 77 studies on single-strain LAB fermentation. The review explores the applications of lactic acid bacteria in various plant-based matrices, summarizing the main advantages and disadvantages identified from a techno-functional, nutritional, and organoleptic point of view. Within the pool of LAB genus, Lactiplantibacillus stood out for its versatility and adaptability, resulting in being the most effective and the most studied across several plant substrates, confirming its role in plant fermentation. Further work on different plant matrices proposed LAB as both natural preservatives and flavor enhancers. Their beneficial effects were also found in eight plant-based protein extracts: pea, faba, soy, potato, pumpkin, hazelnut, rice, were some of the LAB strains used were found to reduce off-flavor compounds, meanwhile acting as biopreservative agent. These results underline the potential of LAB fermentation not only to preserve but also to refine the sensory qualities of plant-based foods. On a more starch-oriented matrix like sorghum flour, LAB fermentation activity can help to modify the matrix structure. As an example, fermentation with L. delbrueckii subsp. bulgaricus, Leuconostoc spp., and Lacticaseibacillus casei led to a modification in starch and fiber, increasing water–biopolymer interactions, and improving gelatinization and viscosity. All of these modifications contribute to better processing and texture properties. A similar approach was used on batters prepared with chickpea flour, where LAB fermentation improved rheological behavior, water-holding capacity, and antioxidant properties, while reducing spoilage microorganisms. In the case of pea-based fermented beverages, Streptococcus thermophilus and L. delbrueckii subsp. bulgaricus used in a mixed cultures achieved faster growth and gelation and minimized the characteristic off-flavors of legumes. L. delbrueckii subsp. bulgaricus 2214, when used to ferment soybeans, showed strong substrate adaptation, good acidification, as well as good biopreservation effect. When various concentrations of sugar were tested, a diverse proteolytic effect was observed and also the composition of the volatile profile fraction was found to be different depending on the amount of added sugar. Taken together, those findings highlight the multifunctional role of LAB fermentation and underline the importance of carefully selecting strains tailored to each specific application. This is necessary to unlock the full potential of these bacteria in challenging, and underutilize, substrates as plant-based formulated can be. In this context, LAB can serve as a natural tool to improve product quality, extend shelf life, and increase consumer acceptance of novel plant-based foods. Future research should focus on the optimization of strain-matrix combinations merged with the tuning of fermentation parameters to support the feasibility on the industrial level, helping to develop the next generation plant-based food.