Plant-based food products are generating a growing interest as part of the ongoing transition to a primarily plant-based diet, which makes demands to the quality, functionality, and health properties of plant proteins. Microbes used for traditional food fermentations such as lactic acid bacteria (LAB) and fungi (yeasts and molds) carry out enzymatic changes on their protein substrates by which technological and sensorial characteristics can be improved. The literature on extracellular proteases targeting plant proteins, on the other hand, is scattered with only a narrow representation of plants even for traditionally plant-based products. Therefore, this review aims to explore the current state of knowledge regarding the application potential of microbial extracellular proteases targeting plant proteins, with a focus on traditional applied food microbes. Plant proteins are targeted by proteolytic microbes of both animal and plant origins, and their proteases show a wide range of activities. Extracellular microbial proteases can hydrolyze specific protein-based allergens and even reduce the toxicity of plant proteins. Additionally, microbial assisted proteolysis can improve plant protein digestibility by increasing availability of peptides and amino acids. This catabolic process will change the organoleptic characteristics of fermented plant proteins, and the release of bioactive peptides can provide additional functionalities to the plant matrix. The proteolytic activity is determined by the microbial strain, and it can be quite substrate selective, which is why proteases may be overlooked by the prevalent use of casein as substrate in proteolytic screenings. The synergetic effects of LAB and fungal species consortia can facilitate and steer plant protein hydrolysis by which co-fermentation may increase or change the properties of plant protein hydrolysates. Microbes do not necessarily require extracellular proteases because endogenous proteases in a plant-matrix may meet the microbial amino acid requirements. However, extracellular proteases have the potential to provide central properties to diverse food-matrixes by which the full proteolytic potential of food microbes needs to be explored in order to facilitate the development of high-quality plant-based food products.

Multiple sensorial, technological, and nutritional challenges must be overcome when developing plant‐based fermented dairy alternatives (PBFDA) to mimic their dairy counterparts. The elimination of plant‐derived off‐flavors (green, earthy, bitter, astringent) and the degradation of antinutrients are crucial quality factors highlighted by the industry for their effect on consumer acceptance. The adaptation of plant‐derived lactic acid bacteria (LAB) species into plant niches is relevant when developing starter cultures for PBFDA products due to their evolutionary acquired ability to degrade plant‐based undesirable compounds (off‐flavors and antinutrients). Some plant‐isolated species, such as Lactiplantibacillus plantarum and Limosilactobacillus fermentum , have been associated with the degradation of phytates, phenolic compounds, oxalates, and raffinose‐family oligosaccharides (RFOs), whereas some animal‐isolated species, such as Lactobacillus acidophilus strains, can metabolize phytates, RFOs, saponins, phenolic compounds, and oxalates. Some proteolytic LAB strains, such as Lacticaseibacillus paracasei and Lacticaseibacillus rhamnosus , have been characterized to degrade phytates, protease inhibitors, and oxalates. Other species have also been described regarding their abilities to biotransform phytic acid, RFOs, saponins, phenolic compounds, protease inhibitors, oxalates, and volatile off‐flavor compounds (hexanal, nonanal, pentanal, and benzaldehyde). In addition, we performed a blast analysis considering antinutrient metabolic genes (42 genes) to up to 5 strains of all qualified presumption of safety‐listed LAB species (55 species, 240 strains), finding out potential genotypical capabilities of LAB species that have not conventionally been used as starter cultures such as Lactiplantibacillus pentosus, Lactiplantibacillus paraplantarum , and Lactobacillus diolivorans for plant‐based fermentations. This review provides a detailed understanding of genes and enzymes from LAB that target specific compounds in plant‐based materials for plant‐based fermented food applications.

With increasing awareness of the impact of food on the climate, consumers are gradually changing their dietary habits towards a more plant-based diet. While acceptable products have been developed in meat analogues and non-fermented dairy products, alternative fermented dairy products such as yogurt and particularly ripened hard and semi-soft cheese products are not yet satisfactory. Since the cheese category has such a broad range of flavors and applications, it has proven complicated to find plant-based sources able to mimic them in terms of texture, meltability, ripening and flavor. Moreover, plant-based dairy alternatives do not provide the same nutritional supply. New technological approaches are needed to make cheese production more sustainable, which should be integrated in the already existing conventional cheese production to ensure a fast and cost-efficient transition. This can be tackled by incorporating plant-based components into the milk matrix, creating so-called “hybrid cheeses”. This review will discuss the challenges of both animal- and plant-based cheese products and highlight how the combination of both matrices can associate the best properties of these two worlds in a hybrid product, reviewing current knowledge and development on the matter. Emphasis will be drawn to the selection and pre-processing of raw materials. Furthermore, the key challenges of removing the off-flavors and creating a desirable cheese flavor through fermentation will be discussed.

With consumers becoming more aware of sustainability, healthier lifestyles and animal welfare, plant-based food products as alternatives to dairy products have become a fast-growing industry in the last decade, and an increasing number of plant-based products are showing up on the markets. With over 88 million tons of food wasted in Europe annually, a sustainable alternative to dairy could be to use side streams for new products. Here, we tried to develop a plant-based yogurt alternative based on three ingredients: commercial soy drink and a liquid fraction of brewers’ spent grain fermented with plant-adapted lactic acid bacteria. Analysis of the content and properties of the fermented product were compared to a commercial plant-based yoghurt-like product and a commercial dairy yoghurt. Results from the project show that fermentation of a commercial soy drink containing 20% of the liquid fraction of brewers’ spent grain results in a product with texture and sensory characteristics that mimics a dairy yogurt.

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.