Gap Analysis of Metabolic Conversions of Off-Flavors and Antinutrients in Plant-Based Substrates

To drastically reduce the carbon footprint of the food production chain, a major shift towards alternatives to conventional meat and dairy products is required. The use of plant-based proteins is a promising route, but it also comes with challenges: Plant-based proteins often contain antinutritional factors and off-flavors, which can negatively impact consumer acceptance. Fermentation is broadly used to improve the quality of these products. However, how these unwanted molecules are synthesized and degraded is poorly understood, but this knowledge is essential for fermentation-based strategies to improve the sensory and nutritional value of plant-based products. This review provides a comprehensive overview of synthesis and degradation pathways of key antinutritional factors and off-flavor compounds in plant-based substrates, including aldehydes, furans, sulfur compounds, pyrazines, glycoalkaloids (GAs), pyrimidine glycosides, polyphenols, saponins, glucosinolates (GSLs), phytic acid (PA), oxalates, lectins, and protease and amylase inhibitors. With this we identified the research gaps in the field, which can be divided into three types: (i) degradation pathways that are unknown (furans, alkyl-methoxypyrazines, and dimethyl trisulfide), (ii) well-characterized pathways but typically not found in food-grade organisms (dimethyl sulfide, dimethyl disulfide, and isothiocyanates derived from GSLs), and (iii) pathways that are only described partially (GAs, saponins, polyphenols, PA, and pyrimidine glycosides). Other molecule classes, like aldehydes, alcohols, and oxalate, have well-characterized degradation pathways in food-grade organisms. Focusing future research on compounds with poorly understood degradation pathways will help to accelerate the development of more rationally designed cultures for producing healthy and sustainable plant-based foods.