## 2 Characteristics of Plant-Based Food Matrices as Carriers of Probiotics  
In functional food manufacturing, the mandatory issue is the fact that the food matrix, as a carrier material of probiotic microorganisms, should be a hospitable environment for their growth and survival [12]. The food matrix should also protect viable probiotic cells to ensure survival during passage through the gastrointestinal (GI) tract, thus allowing the appropriate gut colonization. In these ways, the functional food probiotic health benefits on the host can be achieved [23].  
Plant-based food matrices are abundant in nutrients essential for the growth of probiotics (i.e., complex carbohydrates, simple sugars, plant proteins). It also comprises non-nutritive bioactive compounds, such as fibers, vitamins, minerals, and phytochemicals, including carotenoids, phenols, alkaloids, flavonoids, tannins, terpenoids, glycosides, and saponins [24, 25]. Some of them are secondary plant metabolites. These plant-derived food components exert antioxidant activity, have antimicrobial properties against pathogens, reduce the occurrence of dysbiosis, and fortify the intestinal barrier [26]. Many bioactive elements are involved in direct impact on gut microbiota, contributing to the maintenance of gut microbiome balance, and plausibly improving overall host health. Therefore, most of them are classified as prebiotics or candidates for prebiotics [12, 14]. According to the ISAAP, a prebiotic is defined as a substrate that is selectively utilized by host microorganisms, conferring a health benefit [27]. Health bioefficacy of prebiotics includes alleviation of versatile gastrointestinal symptoms and diseases, immunostimulation, prevention of metabolic disease (diabetes, obesity, hyperlipidemia), and enhanced absorption of minerals and vitamins [28]. The combination of probiotics and prebiotics is called synbiotics. It is an effective combination of synergistically acting constituents delivered by plant-based food [29]. Prebiotics of plant-based matrices are a source of mandatory nutrients and, therefore, can support probiotic survival in food environments as well as in the digestive tract. They also would moderate probiotic bioactivity [30]. Moreover, plant matrices comprise antibacterial, antioxidative, and antifungal peptides (i.e., defensins, 2S albumins, napins, cyclotides, thionins) [31].  
There is a worldwide growing number of vegan consumers demanding well-balanced, high-nutritional (protein-rich bioresources) pro-health plant foodstuff of good quality. Nowadays, a variety of products are available, from raw fruits, vegetables, cereals, and algae to processed products such as dairy analogues and meat analogues. In addition, this nutritional trend contributes to the innovations and development of novel plant-food products, creating new market niches [32]. However, the digestibility of plant proteins is inferior to animal-derived proteins. In this context, searching for new functional foods rich in digestible proteins and prebiotics, additionally fortified with probiotics, is of great importance. Fermentation is an appropriate natural preservation method that increasesthe bioaccessibility and bioavailability of plant proteins along with the enhancement of the functional properties of plant-derived food [33].