## 3. Fermentation as the Method of Food Preservation Increasing the Health Benefits of Plant Food  
The oldest and safest method of food conservation is fermentation. It can be employed in a wide range of plant-food products, especially those prone to spoilage, including vegetables and fruits. Nowadays this technology of food preservation is applied on a commercial scale. Due to versatile biochemical processes and numerous interactions between fermentative microorganisms and the plant matrix, the nutritional and functional properties of food are enhanced. Additionally, fermentation modifies food sensory features, making them more attractive to consumers, who appreciate their flavor [37]. Physicochemical methods of plant-food preservation may lead to degradation of prebiotics [75]. Microorganisms can take advantage of fermented plant-based matrices. In various biochemical pathways, they can metabolize proteins, saccharides, and other molecules while contributing to the enhanced digestibility and bioavailability of nutritional ingredients. Undigested and hence not absorbed plant proteins can potentially increase the risk of allergic reactions [33,76]. The effect of fermentation depends on the type of protein (amino acid content), microorganism used, and fermentation conditions. Plant fermentation contributes to the increase in phenolic compounds, especially their free forms of greater bioavailability [77,78]. In the study of [PERSON] et al., fermentation with probiotic strains (_Lactobacillus johnsonii_ LAI, _Lactobacillus reuteri_ SD2112, _Lactobacillus acidophilus_ LA-5) of flours from whole grain barley and oat groat resulted in an increased level of free phenolic acids [79]. Fermentation can reduce the anti-nutritional compounds of plant food (Figure 1) [31]. In some plant foods, such as legumes, anti-nutritional factors (e.g., plytic acid, raffinose, condensed tannins, alkaloids, lectins, pyrimidine glycosides, saponins) decrease nutrients' bioavailability and digestibility [80]. In the study of [PERSON] et al., nineteen legumes were fermented with selected lactic acid bacteria strains (_Lactobacillus plantarum_ C48, _Lactobacillus brevis_ AM7). The effect of microbial fermentation was the decreased level of anti-nutritional raffinose and condensed tannins in legumes [81]. The anti-nutritional compound of cereals, phytic acid, limits the bioavailability of food minerals, proteins, and amino acids. It can be degraded by probiotic bacteria phytases [34]. In the study of [PERSON] et al., twelve of thirteen studied LAB strains isolated from spontaneously fermented wheat bran sourdough exhibited the ability to degrade phytate. Authors suggested that by increasing plant-food mineral bioavailability, LAB strains could successfully improve the nutritional value of fermented products and could be applied in bread making [80,82]. Moreover, proteolytic enzymes produced by probiotic strains can degrade proteins such as gluten and gliadin, which can be important for predisposed consumers (non-celiac gluten-/wheat-sensitive) or celiac patients [83,84]. Vitamins present in plant foodstuffs are cherished by consumers. Some fruits, vegetables, legumes, cereals, grains, tea leaves, and herbs are recognized as a rich source of essential vitamins, i.e., citrus and berries--vitamin C, nuts--vitamins E and B, and grains--vitamin B, folate [85]. The fermentation can increase the content of plant-food vitamins, especially vitamin C and the complex of vitamin B [78]. Moreover, some probiotic strains can produce vitamins (K, B, folate), which can augment the effect of plant-derived vitamins [86]. [PERSON] et. al. reported that fermentation by autochthonous strains (_L. plantarum_ M1, _Leuconostoc mesenteroides_ C1, _Pediococcus pentosaceus_ F40) of carrots, French beans, or marrows significantly increased the content of vitamin C [87]. Tempeh is a traditional Indonesian fermented soybean fungal food.