# Designing the Quality Characteristics of Berry Processing Byproducts Using Fermentation
## 4 Discussion
The results showed that TPC increasedby over 38%, 29%, and 16% for blackcurrant, chokeberry, and strawberry pomace samples, respectively. In the case of raspberry pomace, the increase in TPC was not statistically significant compared to the control sample. The increase in phenolic compounds in fermented pomace is due to the action of cellulolytic, lignolytic, and pectinolytic enzymes, which are produced mainly during the growth of fungi [66; 67]. These enzymes effectively break down the cell wall components and hydrolyze the ester bonds that connect individual phenolic compounds with the cell wall. Consequently, this process increases valuable secondary metabolites in berry pomace. However, fermentation with a mixture of lactic acid bacteria (namely, _Lactobacillus acidophilus_, _Lactococcus lactis_ subsp. _lactis_, and _Lactobacillus rhamnosus_) led to a reduction in TPC of about 35% and 25% for chokeberry and raspberry pomace samples, respectively. In the case of strawberry pomace, the increase in TPC was not statistically significant compared to the control sample. Phenolics can bind with sugar or amino acids [65], thus lowering soluble phenolic contents [68]. During fermentation, the total soluble phenolics that increase in the fermented fruit substrate might also be mobilized and degraded, resulting in lower phenolic contents [69]. Fermentation with a mixture of lactic acid bacteria and yeast led to the growth of TPC by over 25%, 15%, and 14% in blackcurrant, chokeberry, and strawberry pomace samples, respectively. In the case of fermented raspberry pomace, a reduction in TPC was observed. Different factors influence antioxidant activity in complex heterogeneous biological systems; thus, an evaluation cannot rely only on a one-assay protocol. For this reason, three assays (namely, ABTS, DPPH, and FRAP) were chosen to evaluate the antioxidant capacity of berry pomace during fermentation. While ABTS is based on the hydrogen atom transfer mechanism, DPPH and FRAP are based on the electron transfer mechanism [70]. After fermentation with lactic acid bacteria, the free radical scavenging capacity showed a slight reduction in the case of chokeberry and raspberry pomace samples, which may be attributed to the decrease in the polyphenic content. These results are in agreement with an earlier study [64] that reported a reduction in antioxidant activity in cashew apple juice after fermentation with lactic acid bacteria. However, in the case of blackcurrant and strawberry pomace samples, no statistical difference in comparison with the control sample was observed. Fermentation of berry pomace with _Saccharomyces cerevisiae_ led to increased antioxidant activity, as evidenced by the enhanced DPPH, FRAP, and ABTS radical scavenging activities. A significant increase in antioxidant activity was detected for chokeberry, raspberry, and strawberry pomace samples. For example, the antioxidant activity of raspberry pomace in the DPPH, FRAP, and ABTS assays increased by 67%, 74%, and 80%, respectively, compared to the control sample. In the case of blackcurrant pomace, the increase in radical scavenging activities was not statistically significant, with the exception of the DPPH assay. The results also indicated that the antioxidant activity of fermented chokeberry pomace is positively correlated with TPC and vitamin C contents. In the case of blackcurrant pomace, DPPH radical scavenging activity is also positively correlated with TPC and vitamin C contents. Fermentation with a mixture of lactic acid bacteria and yeast led to an increase in antioxidant activity, as assessed via DPPH and ABTS assays, specifically for strawberry pomace. Moreover, this was positively correlated with TPC and vitamin C contents. In the case of chokeberry pomace, this fermentation process caused an increase in radical scavenging activities, as evidenced by the DPPH and FRAP methods. This was also positively correlated with TPC and vitamin C contents.