Exploitation and Valorization of Agro-Food Wastes from Grape Harvesting: Production, Characterization of MAE-Extracts from Vitis vinifera Leaves and Stabilization in Microparticulate Powder Form

Grape harvesting generates a high amount of wastes, mostly leaves, which represent an economic and ecological problem for farmers. New products can be generated through these wastes, giving environmental, social, and economic advantages while also meeting the industry demand for novel natural ingredients. In this study, aqueous leaf-extracts from two cultivars of Vitis vinifera Aglianico (Agl) and Greco di Tufo (Gre) were produced by microwave-assisted extraction (MAE) and evaluated in composition by ATR- FTIR and HPLC to identify the main phenolic compounds, especially quercetin and kaempferol. The results showed that leaves extracts confirm to be a potential source of phenolic compounds. Dry extracts, although highly functional, show critical handling characteristics, being sticky and unstable in normal post-processing conditions. A stable and easy handling microparticulate ingredient was produced by spray drying containing the most phenolic-rich obtained extract (AGL-28). The microparticle powder form based on pectin/maltodextrin matrix was produced with high process efficiency. The microstructures were able to confer functional and chemical stability to the extract while also showing good technological characteristics (high water dissolution rate and flow properties), transforming the extract into a handling ingredient able to meet new industrial uses.