Errichiello, Francesco (2025) Valorization of winery by-products by a green chemistry approach in the frame of circular economy. [Tesi di dottorato]

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Abstract

The ever-increasing request for environmental sustainability and the interest to comply with the principles of the circular economy has been driving scientific research to explore innovative strategies for the valorization of agro-industrial by-products. Grape pomace, the bulkiest solid residue of winemaking, constitutes a promising source of high-value bioactive compounds with diverse potential applications in many sectors ranging from the food industry to the pharmaceutical and nutraceutical, from the textile to the cosmeceutical ones, among others. The primary objective of this Ph.D. thesis was to investigate the chemical characterization of grape pomaces from grape varieties widely used for winemaking in the Campania Region. This chemical analysis served the purpose of identifying abundant valuable metabolites to be recovered by sustainable extraction methods. This study focused on the investigation of the metabolic content of Aglianico (Vitis vinifera L.) red grape pomace that was selected on account of its richer metabolic contents compared to other analyzed white grape pomaces. The study was conducted by a multidisciplinary approach based on: - conventional and green extraction techniques, - advanced spectroscopic and spectrometric analyses (1D- and 2D-NMR, LC-MS/MS, HPLC-DAD), - environmental impact assessments of the set-up extraction protocols, - pharmacological evaluation of the obtained extracts. The study began with the analysis of the metabolic profile of four ancient white grape varieties (Fenile, Ginestra, Pepella, and Ripoli) from the Amalfi Coast to compare with data already available in literature on the Aglianico red grape. This comparison was aimed at choosing the variety with the most interesting metabolic profile, from both a qualitative and quantitative point of view. Once selected the Aglianico variety as the most suitable, a traditional 14-day fermentation was carried out, with the double goal of 1) collecting sufficient grape pomace to be used as biological material for subsequent studies; 2) studying the evolution of polyphenol extraction during maceration. This was instrumental for providing winemakers with strategic knowledge indispensable for a proper management of this challenging grape variety, characterized by elevated tannin contents. Indeed, the 14-day maceration period appeared to be too long. It turned out that it would be recommendable to adopt an 11-day maceration in order to prevent the over-extraction of polyphenols that may detrimentally affect the sensory characteristics of wines. Following the fermentation, sufficient amount of grape pomace was collected. Its chemical analysis brough to light the occurrence of paramount quantities of polyphenols. The recovery of these compounds was investigated by using both conventional solvents and Deep Eutectic Solvents (DES). The DES-based extraction (Choline chlorine based with Malic acid and Oxalic acid at room temperature and 40°C) demonstrated superior efficiency, achieving up to 1500% recovery of total phenols compared to conventional solvents. Another important outcome of the comprehensive chemical analysis of Aglianico grape pomace was the detection, for the first time, of an interesting triterpenoid, namely oleanolic acid. Oleanolic acid was found to be occurring at concentration hovering around 0.45 mg/g of fresh weight. Given the impressive quantity of this compound in the analyzed grape pomace, in order to optimize its recovery, extraction trials were conducted using both conventional solvents (acetone, ethyl acetate, n-butanol) and green solvents (dimethyl carbonate [DMC] and 2-tetrahydrofuran). DMC proved to be the best option by achieving a recovery rate of up to 38%. Also, DMC showed a high selectivity of about 61%, further highlighting the efficiency and sustainability of these methodologies compared to conventional solvents. Additionally, cyclic extraction tests were performed to evaluate the reusability of the solvents and the efficiency of the extraction process. DMC showed excellent stability and recovery, maintaining over 90% of its extraction efficiency after three cycles. Again, the environmental and economic advantages of green solvents over conventional ones was emphasized. Finally, the obtained oleanolic acid-enriched extracts were pharmacologically investigated. In in-vitro studies, they turned out to enhance the mitochondrial activity and to increase the glucose uptake, highlighting their potential as antidiabetic agents. Finally, also their antitumoral activity was demonstrated, since the tested extracts rich in oleanolic acid modulated cellular responses to Camptothecin-induced DNA damage, thus increasing cancer cell death compared to controls. For the first time, a comprehensive chemical characterization of Aglianico grape pomace was performed, highlighting its rich and diverse metabolic profile. This study undisclosed the incredible potential of Aglianico grape pomace as a valuable source of bioactive compounds, including polyphenols and oleanolic acid, whose recovery was studied by means of both conventional and green solvents. The superiority of green extraction methods was unequivocally demonstrated. Furthermore, the biological evaluation of the obtained oleanolic acid-enriched extracts revealed significant antidiabetic and anticancer properties, making them promising candidates for future pharmaceutical and nutraceutical applications.

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