Introduction
Grape pomace, a by-product of grape processing, is recognized as an economically valuable commodity due to its richness in bioactive substances, which are associated with health implications and technological applications. Grape pomace phenolic compounds have been found to be natural antioxidants and antimicrobial compounds that can prevent lipid oxidation and extend the shelf life of various food products, preserving quality and nutritive value.
Methods
This study investigated the phenolic profile of grape pomace from a variety of Vitis vinifera L. cultivars produced on the Island of Madeira. Green extraction techniques—micro-QuEChERS and micro-liquid–liquid extraction—were used, as well as ultrahigh-performance liquid chromatography with photodiode array detection (UHPLC-PDA), for the identification and quantification of polyphenols. The antimicrobial activity of the extracts of grape pomace was also tested against Escherichia coli and Staphylococcus aureus.
Results
The Tinta Negra grape variety presented the highest content of polyphenols (10.31 mg/100 g), followed by Malvasia Roxa (8.35 mg/100 g), Complexa (7.50 mg/100 g), Boal (6.78 mg/100 g), Malvasia São Jorge (6.66 mg/100 g), Sercial (6.03 mg/100 g), Verdelho (5.80 mg/100 g), and Terrantez (5.30 mg/100 g). Red grape pomace presented, on average, 1.4 times more polyphenols (8.72 mg/100 g) than white grape pomace (6.12 mg/100 g). The major polyphenols identified were gallic acid (2.15–3.35 mg/100 g), catechin (0.96–3.08 mg/100 g), and trans-resveratrol (0.32–1.82 mg/100 g), which represented 74% of the polyphenolic fraction. Sercial and Complexa exhibited the biggest inhibition zones against S. aureus (11.5 and 11.3 mm, respectively) and E. coli (7.50 and 7.10 mm, respectively).
Conclusions
The results indicate that grape pomace is an important natural source of antioxidants and antimicrobials with huge potential application in the food and pharmaceutical industries. Grape pomace valorization follows the guidelines of a circular bioeconomy because it transforms winemaking by-products into value-added functional products.
