Unveiling potential functional applications of grape pomace extracts based on their phenolic profiling, bioactivities, and circular bioeconomy

Abstract Grape pomace (GP), a by-residue from the wine industry, contains bioactive molecules such as phenolic compounds, and anthocyanins, among others, with potential health benefits. In the current study, these bioactive molecules were extracted from GP of different Vitis vinifera L. varieties (Tinta Negra, Complexa, Malvasia Roxa, Malvasia, Sercial, Verdelho, Boal, Terrantez) using the micro quick, easy, cheap, effective, rugged, and safe (µQuEChERS) procedure. The GP extracts were investigated using ultra-high performance liquid chromatography (UHPLC-PDA) to establish the phenolic fingerprint, and by in vitro assays to assess the antibacterial, anti-inflammatory, and antioxidant activities. Nine phenolic compounds were identified and quantified in GP extracts, with gallic acid (ranging from 10.4 to 12.9 g/100 g), catechin (2.97 to 5.08 g/100 g), quercetin (2.17 to 2.85 g/100 g), and trans -resveratrol (0.28 to 1.82 g/100 g) being the most prominent. GP from the Complexa variety exhibited the highest levels of total anthocyanin content (TAC, 6.67 mgCGE/100 g), total phenolic compounds (TPC, 4727 mgGAE/100 g), and antioxidant activity (DPPH, 9472 mgTE/100 g), while the Tinta Negra variety had the highest total catechin content (TCC, 947 mgCATE/100 g). A strong correlation ( p < 0.001) was observed between the TPC-TAC, TPC-DPPH, DPPH-TAC, and TAC-TCC. Moreover, o-coumaric acid and quercetin are significantly ( p < 0.001) correlated with TPC, TAC, TCC, and DPPH assays. The investigated GP extracts, at a concentration of 100 µg/mL, showed promising inhibition of albumin protein denaturation compared to aspirin (reference standard). The findings showed that the GP extracts were more useful at inhibiting Staphylococcus aureus compared to Escherichia coli . It is important to emphasise that the GP extracts demonstrated antioxidant, anti-inflammatory, and antibacterial properties, positioning it as an agro-waste with promising potential for use in the development of innovative functional foods, dietary supplements, and cosmetics, aligning with the circular bioeconomy model for its valorisation.