## 2 Characteristics of Plant-Based Food Matrices as Carriers of Probiotics
### Plant-Based Matrix Structure in Relation to Probiotic Incorporation  
According to [PERSON], a food matrix is a part of the microstructure of foods, usually corresponding to a physical and spatial domain, that contains, directly interacts, and/or gives a particular functionality to a constituent (e.g., a nutrient) or element of the food (e.g., starch granules, microorganisms) [49]. The structure of plant tissues (\"skeleton\") is sophisticated and consists of cells not tightly packed with intercellular spaces, capillaries, and pores [50]. Therefore, the plant-food microstructure matrix can protect probiotics during GI passage. On the other hand, factors leading to matrix disintegration (i.e., technological food processing, homogenization, fermentation, digestion) facilitate the degradation of cell walls, contributing to the release of dietary fibers and cellular organelles, allowing the liberation of phytochemicals. This phenomenon of bioavailability is called the \"food matrix effect\" [51]. Peeling and cutting can liberate sugars, nutrients, minerals, and vitamins, promoting the growth of probiotics [52]. Another phenomenon of food component interactions is called the \"plant effect\". An example is the study of [PERSON] et al. They analyzed the interaction between food components in pig nutrition and reported that dietary proteins can significantly reduce the bioavailability of polyphenols [53]. Due to the variety of diet ingredients and multiple possible interactions, the implication of this food phenomenon is difficult to assess or confirm in human nutrition.  
In general, plant-food matrices are considered to be suitable vehicles for probiotic delivery; however, they are demanding for probiotic microorganisms. However, due to the short shelf life of fruits and vegetables, the preferable form of plant food as probiotic carriers appears to be fermented foodstuff. Within the food matrix, there are different interplaying factors affecting probiotic growth and survival. Some of the plant foods constitute a harsh environment characterized by high acidity, limited availability of nutrients (including non-standard energy sources such as fructose and mannose), presence of oxygen or oxygen access (i.e., fragmentation of the matrix-aeration), and presence of antimicrobial compounds (bacteriocins, non-fermentable carbohydrates, phenols, different chemicals). Among factors of plant matrices that can inhibit probiotic growth, disadvantageous osmotic pressure, salinity, and temperature should also be listed [25].  
Examples of innovative functional probiotic non-dairy products are juices, frozen desserts, pickled vegetables, fermented beverages based on plant milk, jellies, etc. The examples of innovative probiotic and/or symbiotic plant-based products are shown in Table 1.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Product** & **Applied Probiotic** & **Applied Prebiotic** & **Research Issue** & **Reference** \\ \hline \multirow{4}{*}{Pumpkin frozen desserts} & \multirow{4}{*}{\(L\)_rhamnosus_ Lock 0900} & \multirow{4}{*}{Inulin} & Pumpkin and pumpkin–pineapple & \multirow{4}{*}{[54]} \\  & & & & & \\ \cline{1-1} \cline{4-5}  & & & & \\ \cline{1-1} \cline{4-5}  & & & & \\ \hline \hline \end{tabular}
\end{table}
Table 1: Examples of innovative probiotic and symbiotic plant-based products.