## 3 Results and Discussion  
Spray-dried biomass of microalgae generally contains 8-17% carbohydrates, representing the main products derived from photosynthesis and carbon fixation metabolism. The nondigestible oligosaccharides from microalgae can be isolated by hydrolytic processes in the food and feed industries. These oligosaccharides have been shown to selectively stimulate the growth and activity of bacteria primarily from the genera _Lactobacillus_ and _Bifidobacterium_, thus contributing to the improvement of the host's health [1,27]. However, the chemical profile and metabolic pathways of carbohydrates vary between species and the composition and properties of the cell wall also depend on the growth stage and cultivation conditions [4,7,15,28]. In particular, the polysaccharide profile of the _C. vulgaris_ cell wall contains rhamnose (45-54%) in combination with galactose (14-26%), xylose, mannose, arabinose, and glucose. The most important carbohydrate compound is \(\beta\)-1,3-glucan, a branched polysaccharide comprising units of \(\beta\)-D-glucose, which is very well fermentable in the colon. \(\beta\)-1,3-glucan is a water-soluble polysaccharide that has a positive effect on digestion and immunomodulatory activities [2,29]. In the present study, we utilized _Chlorella_ powder containing 50.3 g proteins, 8.1 g lipids, and 15.2 g carbohydrates per 100 g, as specified by the manufacturer. Growth-promoting effects of two concentrations of _Chlorella_ powder (1.0 and 3.0% \(w/v\)) were observed on four _Bifidobacteria_ strains. Following cultivation, the prebiotic effects were evaluated based on lactic and acetic acid production (Table 1), pH, and cell count. Production of both acids significantly increased in three strains (_Bifidobacterium breve_ CCDM 562, _Bifidobacterium animalis_ subsp. _Lactis_ BB-12(r), and CCDM 93), compared to that in the control (\(p<0.05\)). This increase was dependent on the concentration of _Chlorella_ added. The strains _B. breve_ CCDM 486 and CCDM 562 are isolates from human GIT and feces, unlike _B. animalis_ subs. _lactis_ BB-12 and CCDM 93, which are commercial cultures used in the dairy industry. Human isolates from the GIT are known to be more sensitive to the laboratory in vitro cultivation than commercially used strains, in which also their technological properties are considered. This factor could have an influence on the production of acids by _B. breve_ CCDM 486 and pH values after 24 h of this strain also correlated with decreased concentration of acids. Similar conclusions were obtained in previous studies evaluating the prebiotic or positive growth effects of _Chlorella_. [PERSON] et al. (2012) demonstrated that the addition of 0.5 or 1.0% (\(w/v\)) of _C. vulgaris_ and _Arthospira platensis_ in yogurt enriched with probiotics _Lactobacillus acidophilus_, and _Bifidobacterium animalis_ subsp. _lactis_ BB-12\({}^{\text{\text{\textregistered}}}\)[15] significantly increased the viability of both probiotic strains at the end of fermentation compared to the control yogurt. A study by [PERSON] (2020) supported the improved viability of _Bifidobacterium longum_ and _Lbc. plantarum_ in dairy products with the addition of _Chlorella sorokianiana_[10]. Additionally, the results indicated an antiviral effect of cells against rotavirus following treatment with probiotics and/or microalgae [10]. The immunostimulatory activities of microalgae are attributed to their polysaccharides [7,30]. In this study, we evaluated the ability of _C. vulgaris_ to stimulate cytokine secretion by hPBMCs isolated from eight healthy donors using multiplex analysis. The immunomodulatory effector was assessed based on the production of cytokines (IL-4, IL-6, IL-17, TNF-\(\alpha\), and IFN-\(\gamma\)) following stimulation with 3.0% and 1.0% (\(w/v\)) aqueous solution of _Chlorella_ (Table 2). The results showed a significant increase in the secretion of the inflammatory cytokines TNF-\(\alpha\) and IL-6 following stimulation with 1.0% (\(w/v\)) _Chlorella_ (\(p<0.05\)).