## 1 Introduction  
Global food production is striving to become more material-, labor- and energy-efficient. Hence, research is focusing on the design and production of consumer-acceptable plant-based foods, which have been shown to require fewer natural resources and to be less taxing on the environment [1, 2]. Increasing the amount of plant-based foods globally is not an easy task, though, since meat often serves as the main protein source in many diets. Nutritional value, texture, taste and cultural practices pose substantial hurdles to shifting dietstowards a predominately plant-based one [3,4]. To increase the approval of plant-based foods, protein-rich plant-based meat analogs (PBMAs) with organoleptic properties similar to those of their animal counterparts have been researched and developed, with a variety of products now being available in supermarkets. PBMAs that imitate processed meat products such as sausages are especially popular [5] and typically consist of insoluble textured plant proteins bound together via a first sticky, later solidifying binding system [6,7]. These binders usually require a heating step for solidification, and examples thereof include plant proteins heated to 65-85 \({}^{\circ}\)C to induce denaturation and crosslinking [8], modified starches heated to 52-100 \({}^{\circ}\)C to induce gelation [9], and hydrocolloids such as agar-agar, locust bean gum and xanthan heated to 50-90 \({}^{\circ}\)C to promote chain interactions and network formation [10]. While enzymes such as transglutaminase do not require heating to create crosslinks, a thermal treatment at 65-85 \({}^{\circ}\)C is typically needed to render them inactive in the final product. However, creating PBMAs with appealing quality attributes remains a challenge [11,12], and often a large number of additives (e.g., flavoring and preserving agents, stabilizers, and antioxidants) are required in their manufacture, which is detrimental to consumer acceptance [13]. Improvements could come from using novel processing approaches [12], amongst which microbial fermentation has been shown to be particularly promising, especially if specialized starter cultures are used. Implementation of fermentation therefore has the potential to replace many of these additives, since many fermentatively formed substances can take on tasks that are currently still performed by additives. For instance, fermentation has been shown to be able to improve the shelf life and quality of PBMAs [14, 15, 16], allowing for a reduction in preservatives and stabilizers; fermentation of pea protein with lactic acid bacteria also decreased the extent of protein oxidation [17], enabling a reduction in antioxidant insertion. The same also applies to the fermentative reduction of unwanted structures in products, like the reduction and masking of undesired flavor compounds inherent in many plant proteins [18,19], which in turn ensures the usage of fewer flavorings to mask off-flavors in these products. Moreover, fermentation may not only reduce the amount of undesirable flavor compounds in PBMAs, but also lead to the generation of new, desirable compounds. In dry fermented meat sausages, over 80 aroma active compounds were identified, most of them derived from the conversion of spices (60.5%), lipid oxidation (18.9%) and amino acid catabolism (11.8%) during ripening [20]. Similarly, the fermentation of some cereals has been shown to produce volatile compounds not unlike those found in fermented meat products [18]. Initial studies on the fermentation of protein extrudates made by high-moisture extrusion cooking have also demonstrated that suitable starter cultures, like those used in the production of dry fermented meat sausages, cleave plant proteins to produce bioactive peptides and amino acids and generate lactic acid without incurring negative effects on texture attributes like springiness and cohesiveness [21].