## 3 Results
### Response Surface Method for Fermentation Process Optimisation
#### 3.2.2 Effect of Plant Raw Material Content and Fermentation Time  
Figure 2 show the changes in antioxidant activity (AA), total polyphenols content (TPC), and lactic acid efficiency (LAe) during the interaction of the studied process parameters. Figure 2A, showing the relationship between plant material content and fermentation time, shows that the highest antioxidant activities are obtained using a plant material content of 6.40% and a fermentation time of 9 to 10 days. Lowering the plant material content, regardless of the fermentation time, results in a decrease in the value of this function from about 1.70 mmol Tx/L to about 19.90 mmol Tx/L (Figure 2A). Figure 2B, showing the relationship between plant material content and fermentation time, shows that for a plant material content of 6.40% and a fermentation time of 9 to 10 days, it is possible to achieve the highest content of phenolic compounds in FPE. With the fermentation running time of 1 to 5 days (at the maximum plant raw material content), the value of this function gradually increases from about 10.70 mmol GA/L to about 10.90 mmol GA/L. The use of lower vegetable raw material contents (from 0.32 to 3.20%) results in a decrease in TPC from about 2.90 mmol GA/L to about 8.60 mmol GA/L. Figure 2B also shows that increasing the plant material content at the selected fermentation time (from 9 to 10 days) results in a significant increase in TPC from about 3.70 mmol GA/L (plant material content 0.32%) to about 8.60 mmol GA/L (plant material content 3.20%). Figure 2C, showing the relationship between the content of plant material and the duration of the fermentation process, shows that during 9 to 11 days of conducting the fermentation process, regardless of the amount of plant material used, it is possible to achieve the highest lactic acid efficiency. When conducting the fermentation of clove buds for 9 days using a plant material content of 1.60%, it is possible to achieve the highest value of this function. Increasing the duration of the process with a constant content of plant material results in a reduction in LAe from about 97 to about 92%. For higher plant material contents of 3.20 and 6.40%, such a significant reduction in the value of this function is no longer observed (Figure 2C). Figure 1: Lactic acid efficiency of fermented plant extracts: FPE-1, FPE-2, FFE-3, FPE-4, FPE-5, and FPE-6 obtained using 6 individual strains of lactic acid bacteria: 1. _L. reuteri MI_0168, 2. _L. salivarius_ LY_0652, 3. _L. brevis_ LY_1120, 4. _L. acidophilus_ MI-0078, 5. _L. rhamn_MI-0272, and 6. _L. plantarum_ MI-0102. Process conducts parameters: initial sugar content 3.20%; inoculum content 3.20%; plant material content 1.6%. Figure 2: (**A**) changes in antioxidant activity (AA); (**B**) changes in total polyphenols content (TPC); (**C**) changes in lactic acid efficiency (LA\({}_{\text{e}}\)), relationship: raw material content—reaction time. Constant parameters of the process: _L. rhamnosus_ strain MI-0272; initial sugar content: 3.20%; inoculum content: 3.20%; (**D**) changes in antioxidant activity (AA); (**E**) changes in total polyphenols content (TPC); (**F**) Changes in lactic acid efficiency (LA\({}_{\text{e}}\)), relationship: initial sugar content—reaction time. Constant parameters of the process: _L. rhamnosus_ strain MI-0272; raw material content 6.40%; inoculum content: 3.20%. Figure 2D, showing the relationship between changes in initial sugar content and fermentation time, shows that the highest values of AA antioxidant activity (about 34.90 mmol Tx/L) can be achieved by running the fermentation process from 9 to 10 days, using an initial sugar content of 4.60%. As the initial sugar content is lowered (from 3.20 to 1.60%), there is a reduction in AA values from about 33.90 mmol Tx/L to about 29.50 mmol Tx/L from 9 to 10 days. This phenomenon is related to the fact that the starting beet molasses contains antioxidants, which affect the increase in antioxidant activity in the fermented plant extract (Figure 2D).