Unveiling the nutritional potential of different vineyards grape leaves by physico-chemical and biochemical analyses

Background Leaf removal and modern grape harvesting are the main practices generating significant wastes of vine leaves. This grape-processing by-product remains largely underutilized, yet its valorization could promote more sustainable agriculture while yielding high-value compounds. Objective Herein, different varieties of grape leaves from Slovenian and Tunisian vineyards were thoroughly characterized by a systematic analytical methodology involving multiple techniques and aiming to unveil their nutritional benefits. Methods The mineral composition was analyzed by XRD and ICP-OES. The total phenolic content was quantified spectrophotometrically, while the phenolic profile was determined by HPLC-MS-ESI-Q-TOF. The glutathione reductase was evidenced by UV-Vis spectrophotometry. Results Higher potassium content was found in the Slovenian varieties, while calcium, magnesium and iron were present in higher quantities in the Tunisian ones. In terms of phenolic content, the values of TPC of the methanolic extracts of grape leaves evidenced an effective phenolic character, with the highest value for the Pinot gris extract (15.32 mg GAE/g dry leaves). Consequently, this extract was subjected to HPLC-MS-ESI-Q-TOF analysis, observing nineteen phenolic compounds. The most abundant compounds were quercetin glucuronide (∼50% of relative contribution) and caftaric acid. Lastly, the enzymatic antioxidant glutathione reductase was detected in all the analyzed grape leaves varieties, with specific activity ranging from 0.15 to 0.50 µmol NADPH min −1 mg −1 protein. Conclusion The different analyses have highlighted the potent and diversified nutritional aspects of the selected grape leaves especially the Slovene Pinot gris variety. Grapevine leaves are likely to offer an even wider range of uses as supplements in food and medicines.