Abstract
Nowadays, approximately 1 billion kg/y of grape stalks, with a remarkable polyphenols content, are produced worldwide. In this paper, the extraction process intensification of polyphenols in water was achieved under ultrasound-assisted recovery, focusing on kinetics and scaling-up factors. Immersion and cup-horn systems were exploited as acoustic cavitation sources, and the total phenolic content (TPC) was chosen to assess the process efficiency. The kinetics were evaluated by Peleg’s hyperbolic model, and the effect of both the initial feedstock granulometry and ultrasound size-reduction were determined. The results were compared with conventional extraction methods (data analysis by ANOVA). The best polyphenols yield was obtained after 45 min of sonication, giving between 29.71 and 31.89 mg/g (gallic acid equivalents over the dry matter). The extracts were characterized using HPLC-DAD, UPLC-ESI-MS/MS, DPPH• assay (2,2-diphenyl-1-picrylhydrazyl), TEAC assay (Trolox equivalent antioxidant capacity), and proanthocyanidin content determination. The flow-mode extraction procedure of grape stalks (2 kg) was carried out in a 15 L reactor. A semi-industrial decanter unit and a bag-filter were the keys units of the downstream operations. The resulting particle-free solution underwent nanofiltration on a membrane pilot skid, providing a final polyphenols-enriched stream concentrated up to 355.91%, as shown by the antioxidant activity and TPC.
Highlights
Viticulture (Vitis vinifera L.) is one of the world’s most important agricultural activities, producing up to 77 million tons of grapes every year
The thermogravimetric analysis revealed that the biomass was efficiently desiccated, with a residual humidity of 8.92%
This value was used to normalize the yields of the following tests, with the total phenolic content (TPC) and dry extracts being expressed in relation to the dry matrix (DM)
Summary
Viticulture (Vitis vinifera L.) is one of the world’s most important agricultural activities, producing up to 77 million tons of grapes every year. Besides being essentially composed of cellulose and lignin [5,6], the grape-bunch skeleton contains lipophilic compounds (e.g., sterols and triterpenes) [7] and polyphenols, which can be divided into flavonoids, e.g., flavonols, anthocyanins, and flavan-3-ols (monomer, dimers, oligomers, and polymers), and non-flavonoids, mainly phenolic acids and stilbenes [8,9]. All of these compounds can have a beneficial influence on human health, including anti-carcinogenic, anti-atherogenic, and anti-mutagenic effects; protection against cardiovascular diseases; and anti-inflammatory activity [10]. The shelf-life of food products, especially when they contain oils and fats, can be prolonged by the addition of natural and safe secondary metabolites of wine [12]
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