## 4 Discussion
A pH range of approximately 3.5 to 4.5 in the final product may help buffer the pH increase in the gastrointestinal tract, thus enhancing the stability and beneficial features of consumed probiotic strains [57]. The viability of probiotic bacteria is an important criterion for the use of probiotics in functional foods, because they should survive with minimal densities of 6 log CFU/mL at the end of the shelf life. In our study, the functionality of buckwheat mashes was proven with high viable bacterial lactobacilli counts (6.0-7.7 log CFU/mL) at the end of the storage period. An exception was observed in water-based mash, where the density of _L. plantarum_ HM1 at the end of 14 days was 5.8 log CFU/mL. [PERSON] et al. [44] evaluated densities of lactobacilli in 10 commercial fermented drinks. During 30 days of cold storage, a slow decrease in counts was noted (0.8-1.9 log orders); nonetheless, the population of microorganisms remained above 5 log CFU/mL, the minimum level suggested by some authors. Our study confirmed a positive effect of lactic acid bacteria fermentation on both phenolic compound contents and antioxidant activity. It can be supposed that the mentioned mechanisms were applied to the fermentation process. The phenolics in buckwheat and cranberry are mainly in the form of soluble free compounds and soluble conjugates [14; 15; 28]. Lactic acid bacteria, through the acidification and hydrolysis of glycosylated forms, enhanced the total phenol and flavonoid content. The observed higher levels of measured parameters of water-based products in comparison to milk-based products are probably related to the complex formation between phenolics and milk components (proteins, lipids, and peptides), which makes them less able to be assayed. Milk protein-phenolic interactions increase with an increasing number of hydroxyl groups in phenolic compounds [58]. On day 4 of fermentation, the decrease in phenolic content and antioxidant activity in several mashes was noticed, and may be attributed to changes in enzyme activities during fermentation. [PERSON] et al. [59] measured amylase, xylanase, and \(\beta\)-glucosidase activities during cereal fermentation with _Aspergillus oryzae_, and the maximum enzyme activities recorded on the 5 th day of incubation. Similarly, the authors observed a linear correlation between enzyme activities and total phenolics and flavonoids. Further metabolic pathways recognized in lactic acid bacteria involve decarboxylation and/or reduction. Lactobacillus can produce phenolic acid reductase, feruoylesterase, and phenolic acid decarboxylase [50; 60]. Caffeic, ferulic, and \(p\)-coumaric acids are decarboxylated into corresponding vinyl derivatives, which can be subsequently reduced to corresponding ethyl derivatives. Phenolic acid reductase reduces phenolic acids to hydroxyphenylpropionic acids (e.g., dihydroracaffeic and dihydroreurlic acid) [51; 60; 61; 62]. Our results confirmed the loss of ferulic and \(p\)-coumaric acids during fermentation. No significant changes (\(p>0.05\)) or degradation of caffeic acid were only recorded in unflavored samples with \(L\). _Hammosus_ GG. The increase in the caffeic acid level in the remaining samples can be attributed to the hydrolysis of chlorogenic acid into their two constituents--caffeic and quinic acids [60]. These conclusions indicate that phenolic metabolism is specific to the substrate, substrate concentration, and microbial strain [60]. Buckwheat is an important source of rutin and catechin. We observed declining rutin content (about 1.7-27.2%) during fermentation in contrast to an increasing amount of quercetin (about 46.2-160.2%). Our findings are in agreement with the study of [PERSON] et al. [63], where the authors noted the conversion of rutin into quercetin. Rutin (quercetin-3-O-rhammoglucide) can be hydrolyzed by \(\alpha\)-rhammosidase to quercetin-3-glucose, and further converted by \(\beta\)-glucosidase to free quercetin, and eventually directly into quercetin by hesperidinase.