## 2 Materials and Methods
### Preparations of Fermented Stems Extract (FSE)  
Fermenting _S. aromatic_ L. stems in the presence of lactic acid bacteria yielded new fermented plant extracts (FSEs). The raw material for lactic acid production was beet molasses, a by-product of the sugar industry. The total content of 6-carbon sugars (Brix) in the molasses was evaluated using a refractometer (KRUSS Optronic DR301-95, A. Kruss Optronic GmbH, Hamburg, Germany). The process uses beet molasses, eliminating the need for mineral salts such as (NH4)2 SO4, CaCl2, and KH2 PO4, which was necessary in the case of fermentations using sugar cane molasses [3; 45]. Preliminary tests have confirmed the activity of molasses in the fermentation process. For this objective, molasses aqueous solutions were fermented with 3.20% inoculum (content determined based on previous experiments) but without mineral salts. The inoculum was a mixture of six strains of lactic acid bacteria: _L. reuteri_ MI_0168, _L. salivarius_ LY_0652, _L. brevis_ LY_1120, _L. acidophilus_ MI-0078, _L. rhamnus_ MI-0272, and _L. plantarum_ MI-0102 [3]. Preliminary studies have shown that beet molasses contains sufficient nitrogen and phosphorus, necessary for the production of lactic acid [46]. This nitrogen is mainly represented by amino acids such as glutamic acid, aspartic acid, and alanine, and also by ammonium salts [47; 48]. Adequate growth of lactic acid was observed in all molasses solutions to a similar extent to fermentations carried out in the presence of certified cane molasses requiring the additional use of mineral salts such as ammonium sulphate (0.64%), calcium chloride, and potassium dihydrogen phosphate (0.32%) [3]. Next, the stems were fermented with lactic acid bacteria. The fermentation was carried out until the maximum level of lactic acid (LA) was attained, the concentration of which was monitored using the GC-MS technique. The amount of total polyphenol content (TPC) was also measured during fermentation. Polyphenolic glucosides found in stems were transformed into more bioactive compounds (anthocyanin glucosides to aglycone forms and free phenolic acids), resulting in greater phenolic content in fermented plant extracts. In addition, the simpler structure of the derived metabolites contributes to the higher antioxidant activity of FSEs, with an increase in the ability to reduce DPPH radicals, relative to non-fermented extracts [49]. In addition to the plant matrix, the kind of LAB strain utilised influences the bioavailability of phenolic chemicals. Therefore, the fermentation of stems was carried out using six distinct LAB strains: _L. reuteri_ MI_0168, _L. salivarius_ LY_0652, _L. brevis_ LY_1120, _L. acidophilus_ MI-0078, _L. rhamnus_ MI-0272, and _L. plantarum_ MI-0102. The inoculum was prepared according to a previously developed methodology [3]. The following raw materials were placed in a 500 mL conical flask: beet molasses (the amount of which was controlled depending on the process parameter under study, while maintaining an initial sugar content of 1.60-4.60%), distilled water, plant material constituting stems (the amount of which was controlled depending on the process parameter under study, while maintaining content of 0.032-12.80%), and inoculum (3.20%). The contents of the flask were stirred until the molasses was entirely dissolved, after which the fermentation process began (at a temperature of 37.5 \({}^{\circ}\)C) for the proper duration. During the fermentation process, samples were collected and tested for lactic acid concentration (GC-MS) and also performed determinations for levels of phenolic compounds (spectrophotometric method utilising the Folin-Ciocalteu technique). Fermentation was carried out until the highest lactic acid yield (LAe) was obtained. Fermentations were completed by performing two independent experiments. After the process was completed, lipase was added to hydrolyse the bacterial cell wall.