Kefir-based fermentation products exhibit antioxidant and anti-inflammatory effects against oxidative stress, inflammation, platelet activation and aggregation, and other related manifestations, thereby preventing the onset and development of several chronic diseases. Specifically, water kefir, a symbiotic culture of various microorganisms used for the production of several bio-functional fermented products, has been proposed for its health-promoting properties. Thus, water kefir grains and its apple pomace-based fermentation beverage were studied for bioactive amphiphilic and lipophilic lipid compounds with antioxidant, antithrombotic, and anti-inflammatory properties. Total lipids (TL) were extracted and further separated into their total amphiphilic (TAC) and total lipophilic content (TLC), in which the total phenolic and carotenoid contents (TPC and TCC, respectively) and the fatty acid content of the polar lipids (PL) were quantified, while the antioxidant activity of both TAC and TLC were assessed in vitro, by the ABTS, DPPH, and FRAP bioassays, along with the anti-inflammatory and antithrombotic activity of TAC against human platelet aggregation induced by the thrombo-inflammatory mediator, platelet-activating factor (PAF) or standard platelet agonists like ADP.ATR-FTIR spectra facilitated the detection of specific structural, functional groups of phenolic, flavonoid, and carotenoid antioxidants, while LC−MS analysis revealed the presence of specific anti-inflammatory and antithrombotic PL bioactives bearing unsaturated fatty acids in their structures, with favorable omega-6 (n-6)/omega-3 (n-3)polyunsaturated fatty acids (PUFA), which further support the findings that the most potent antioxidant, anti-inflammatory and antithrombotic bioactivities were observed in the TAC extracts, in both water kefir grains and beverage cases. The detection of such bioactive components in both the uncultured water kefir grains and in the cultured beverage further supports the contribution of water kefir microorganisms to the bioactivity and the bio-functionality of the final fermented product. Nevertheless, the extracts of the beverage showed much stronger antioxidant, anti-inflammatory, and antithrombotic activities, which further suggests that during the culture process for producing this beverage, not only was the presence of bioactive compounds produced by kefir microflora present, but biochemical alterations during fermentation of bioactive components derived from apple pomace also seemed to have taken place, contributing to the higher bio-functionality observed in the apple pomace—water kefir-based beverage, even when compared to the unfermented apple pomace. The overall findings support further studies on the use of water kefir and/or apple pomace as viable sources of antioxidant, anti-inflammatory, and antithrombotic amphiphilic bioactive compounds for the production of novel health-promoting bio-functional fermented products.

Background/Objectives: Vitamin C is frequently used in several dietary supplements due to its proposed health-promoting properties, while phenolic compounds and especially flavonoids have been suggested to provide synergistic antioxidant and cardiovascular benefits. However, the specific interactions between these compounds and their individual contributions to biological activity remain underexplored. This study aimed to evaluate the antioxidant potential and anti-inflammatory and antiplatelet biological effects of a high-dose (1 g) vitamin C–low-dose (50 mg) bioflavonoid (VCF)-based supplement using both in vitro and in vivo approaches in human platelets. Methods: Total phenolic content was quantified and antioxidant capacity was assessed using DPPH, FRAP, and ABTS assays and compared to individual phenolic standard compounds, including (simple phenolics like gallic acid, flavonoids like quercetin and catechin, and polyphenols like curcumin and tannin), and a standard supplement containing only high-dose vitamin C (VC). ATR-FTIR spectroscopy was used to assess molecular interactions between vitamin C and flavonoids. In vitro anti-inflammatory and antiplatelet activities of all supplements and standards were assessed by quantifying their IC₅₀ values against ADP, PAF, and thrombin-induced platelet aggregation. The in vivo evaluation of the efficacy and synergy of VCF supplement versus VC was achieved by a two-arm clinical study in healthy volunteers by quantifying their platelet reactivity, which was measured via EC₅₀ values on the aforementioned platelet agonists (PAF, ADP, and Thrombin) before (t = 0) and after receiving either solely VC or VCF supplementation for four weeks. Results: From all phenolic standards, the flavonoids and especially a mixture of flavonoids (catechin + quercetin) showed higher in vitro antioxidant capacity and anti-inflammatory and antiplatelet efficacy, followed by polyphenols and then simple phenolics. The VCF supplement showed the most potent antioxidant capacity, but also the strongest anti-inflammatory and antiplatelet activities too, in comparison to the VC and the mixture of flavonoids, suggesting higher synergy and thus bio-efficacy as a result of the co-presence of flavonoids and vitamin C in this supplement. Platelet reactivity decreased over time for PAF and thrombin in both arms of the trial, but no significant differences were observed between treatment groups, suggesting that the number of flavonoids used was not sufficient to translate the in vitro findings to the in vivo setting. Conclusions: VC-containing supplements provide antioxidant, anti-inflammatory, and antiplatelet benefits, while the incorporation of flavonoids may provide synergistic health benefits, but more in vivo assessment is needed to fully evaluate the dose efficacy.

Flavonoids and vitamin C are two of the most extensively studied dietary bioactive compounds, with growing evidence supporting their roles in the modulation of oxidative stress, inflammation, thrombosis, and cancer progression. Flavonoids, a diverse subclass of polyphenols, exhibit promising antioxidant, anti-inflammatory, and anticancer properties. However, their clinical translation is frequently hindered by poor solubility, limited stability, and low bioavailability. Vitamin C (ascorbic acid), a well-known established antioxidant that can also exert pro-oxidant effects at pharmacological concentrations, demonstrates anti-inflammatory, antithrombotic, immune-modulatory, and endothelial-protective activities across various experimental and clinical disease models. Recent studies have highlighted a promising synergistic interaction between flavonoids and vitamin C, wherein flavonoids enhance the stability, recycling, and intestinal absorption of vitamin C, while vitamin C augments the antioxidant capacity and cellular bioactivity of flavonoids. This review critically summarizes current evidence regarding the independent and combined effects of flavonoids and vitamin C, with particular emphasis on their roles in cancer, cardiovascular diseases, and inflammation-related complications. Key molecular mechanisms, including redox signaling modulation, inhibition of pro-inflammatory pathways, and regulation of thrombosis- and angiogenesis-related processes, are discussed. Furthermore, therapeutic opportunities, limitations, and challenges related to bioavailability, dosing strategies, and clinical translation are addressed. Understanding the synergistic actions of flavonoids and vitamin C may provide valuable insights for the development of novel nutraceutical formulations or adjuvant therapeutic approaches in chronic and inflammation-driven diseases.