## 4 Discussion
In analyses of bio-ferments, the following phenolic acids were identified: gallic acid, protocatechuric acid, caffeic acid, neochlorogenic acid, and coumaric acid, which are characterized by antioxidant, anti-inflammatory, antibacterial, and anticancer properties [65; 66; 67]. Our study showed that a bio-ferment from pomace had the highest significant content of phenolic acids, which contained the highest amounts of gallic acid (44.25 \(\pm\) 3.29 mg/L) and caffeine acid (41.42 \(\pm\) 2.81 mg/L)--Table 4. Data in the literature show that pomace has a rich composition of phenolic compounds and high antioxidant activity. Moreover, using pomace in the fermentation process highlights an additional advantage, that of a closed-loop economy. It also has implications for technical and environmental factors, such as lowering the carbon footprint when using plant biomass waste [65; 68; 69; 70; 71]. The acidity of the tested bio-ferments was found to be 360 \(\pm\) 5 mmol COOH/L for B-P, 410 \(\pm\) 5 mmol COOH/L for B-E, 310 \(\pm\) 5 mmol COOH/L for B-O, and 420 \(\pm\) 5 mmol COOH/L for B-S (Table 3). The acidity of bio-ferments (which is due to the presence of carboxyl groups) is mainly influenced by lactic acid content (Figure 1) and carboxyl derivatives of phenolic compounds (Table 4). The acidity results obtained (Table 1) correlate with the results of lactic acid determination by GC-MS (Figure 1). The GC-MS analysis revealed that the highest lactic acid efficiency was achieved on the 14 th day of fermenting milk thistle seeds (B-S: LA efficiency = 59%). The maximum yields of lactic acid were also observed on the 14 th day of fermentation for the extract, oil, and pomace, and the yield values of LA were, respectively, B-E (53%), B-O (51%), and B-P (50%). By the 14 th day of fermentation, the lactic acid contents were as follows: B-P: 240 mmol LA/L, B-E: 254 mmol LA/L, B-O: 248 mmol LA/L, and B-S: 287 mmol LA/L--as shown in Figure 1. Later, a gradual decrease in LA was observed in the bio-ferments. Lactic acid bacteria are microorganisms of industrial importance, known for their fermentation abilities, mainly for probiotic benefits, as well as lactic acid production. When conducting fermentation, inhibition of LA production often occurs, and a gradual decrease in the growth rate of lactic acid bacteria cells is observed [72]. Therefore, a gradual decrease in lactic acid concentration is observed as the process is prolonged (Figure 1). The inhibition of lactic acid is caused by the ability of the undissociated lactic acid to dissolve in the cytoplasmic membrane, while the dissociated lactate remains insoluble. This leads to acidification of the cytoplasm and the disruption of proton motive forces. This event impacts the pH gradient across the cell membrane and reduces the cellular energy available for growth [72]. The hydrophilicity of all investigated bio-ferments (Figure 2) and distilled water (Figure S6) was determined (B-P c.a.-av. = 66.7\({}^{\circ}\)\(\pm\) 1.5; B-E c.a.av. = 78.5\({}^{\circ}\)\(\pm\) 2.6; B-O c.a.-av. = 74.8\({}^{\circ}\)\(\pm\) 3.5; B-S c.a.-av. = 75.4\({}^{\circ}\)\(\pm\) 3.0; and control sample c.a.-av. = 57.8\({}^{\circ}\)\(\pm\) 1.0). This characteristic is mainly attributed to phenolic compounds (TPC) and lactic acid [26]. The higher contact angle possesses higher hydrophilicity for all bio-ferments due to the phenolic acids and lactic acid in these cosmetic raw materials [36]. Thus, these bio-ferments can only be used in lipid bilayers in the aqueous core of liposomes, not in the lipid envelope. Liposomes are spherical vesicles consisting of one or more lipid bilayers arranged concentrically. The core of liposomes is a droplet of water. Wettability studies showed that all bio-ferments are highly hydrophilic and can accumulate in lipid bilayers in the aqueous core of liposomes [33]. Our study showed that all the bio-ferments obtained from _S. marianum_ were classified as readily degradable (Table 5).