## 3 Results and Discussion
### Biological Assays  
To assess the cosmetic potential of the phenolic-rich fraction obtained from defatted seeds, biological tests were performed using human skin fibroblast cells. As a cosmetic additive should be safe and display no adverse effects on the cells, cytotoxicity of the extract was verified based on 24-h, 48-h, and 72-h assays of cell viability and cell metabolism. Two complementary assays were applied, including the neutral red test indicating the capacity to bind the dye within the lysosomes of viable cells, and MTT, showing the action of mitochondrial dehydrogenases, important enzymes responsible for metabolic activity [32; 33]. The results are shown in Figure 4.  
In general, at the tested concentrations, the extract was non-toxic throughout the entire evaluation period. Furthermore, after 24- and 48-h exposures to the highest tested concentration, both cell proliferation and cell metabolism were stimulated, increasing up to 132% in MTT and 115% in NR tests after 24 h. After 48 h, the values rose to 118% and 109%, respectively, compared to the untreated control. No negative impact on cellular cytoskeleton was also observed (Figure 4c). Figure 4: Impact of the different concentration of the extracts from Defatted strawberry seed on: (**a**) cell metabolism (MTT), (**b**) cell viability (NR) expressed as a % of control (dashed red line) after 24, 48 and 72 h of exposure. The data are means (\(n=3\)) \(\pm\) SD. * Indicates statistically significant difference between extract samples and control at \(p<0.05\). (**c**) F-actin cytoskeleton organization-staining with TRITC-phalloidin. ROS-scavenging activity is another highly appreciated feature of cosmetic products, as oxidative stress and excessive exposure to reactive oxygen species (ROS) promote skin aging and the development of skin inflammatory states [34]. Oxidative stress may lead to the disruption of the organization of the collagen network, resulting in structural changes in the skin and the occurrence of wrinkles. Furthermore, the damage to skin cells resulting from ROS action provokes increased production of cytokines and favors inflammation. Thus, supporting the endogenous antioxidative systems with effective exogenous antioxidants is essential for protection against the adverse effects of free radicals. Figure 5 displays the effects of the extract from defatted strawberry seeds on skin fibroblasts with induced oxidative stress using H2O2 treatment as a model. The 2',7'-dichlorydrofluorescein diacetate (H2 DCFDA) reagent was used to investigate the impact of the extract on the redox imbalance caused by H2O2 stimulation. Nonfluorescent H2 DCFDA is deacetylated by intracellular esterases, next oxidized by ROS and converted to fluorescent 2',7'-dichlorofluorescein (DCF). As shown in Figure 5a, H2O2 stimulation increased ROS levels by approximately 33% compared to the control. The cells, when pretreated with the extract, hindered the generation of excessive ROS, and at the highest tested concentration, ROS levels reduced to those observed in the untreated control. The extract also provided protection against H2O2 induced cytotoxicity (Figure 5b). In the experimental setting, a significant decline in cell viability was observed in the cells following treatment with H2O2, with the number of visible cells reduced to 59% compared to the control. In cells pretreated with the extract before the addition of H2O2, cell viability was restored, and at higher concentrations, it reached the level of the untreated control. This suggests that incorporating the extract mitigates the detrimental cellular impacts of H2O2 and acts as a protective measure under conditions of oxidative stress. The beneficial effect of the extract on skin fibroblasts is likely attributed to the presence of ciliroside, 3-glucosidase of kaempfer, and ellagic acid, as indicated by numerous scientific papers detailing their biological activities.