Quercetin solubility at 18 °C and 0 °C was determined in an hydroalcoholic buffer solution with pH 3.20 and in four Italian wines to study the formation of quercetin precipitate mechanism in wines. The wines selected were Barbera 2018 for the typically high content in bisulfite bleachable pigments, red Cirò 2014, for its typically high content of flavonoids, Sangiovese 2014, for the presence of quercetin deposits in bottle, and white Cirò 2018, for the absence of red pigments. All the samples were spiked with 30 mg/L quercetin. The amount of quercetin solubilized at 18 °C and 0 °C in the hydroalcoholic buffer was much lower than in wines, while that solubilised in Barbera was much higher compared to red Cirò, Sangiovese and white Cirò. Solubilised quercetin was lower in all wine samples stored at 0 °C than in those at 18 °C. The pigment composition of the three red wines examined suggested that the over-solubility of quercetin could be due to the formation of soluble co-pigmentation complexes between quercetin and monomer anthocyanins and/or bisulphate-bleachable flavanol-anthocyanin pigments. A positive correlation between quercetin solubility and bleachable pigment was noted: the richer the wine in bleachable pigments, the higher the solubility of quercetin. Quercetin haze formation appeared due to the release of quercetin from co-pigmentation complexes during wine maturation and storage ,as its counterpart, anthocyanins, form non-bleachable pigments or are degraded in hydrolytic or oxidation reactions. Quercetin in aged red wines seemed to reach a content similar to that of white wine spiked with quercetin. Nevertheless, the quercetin content of aged red wines in which a quercetin haze has been found could be lower than that when added white wine, due to its degradation probably being induced by oxidation reactions. Finally, the solubilized quercetin content in white Cirò, which was higher than the hydroalcoholic buffer solution, suggested that there may be different substances in wines than pigments that prevent the growth of quercetin crystals. However, their nature was not determined in this study.

Active alginate-based coatings with quercetin glycoside and complexes of hydroxyapatite/quercetin-glycoside were used to study the shelf life of fresh cut papaya stored at 6 °C. Hydroxyapatite was used as a carrier for the release of the bioactive compound. The parameters considered affecting the quality of the fruit during storage were weight loss, color, texture, sugars and volatile compounds. Active coatings with hydroxyapatite and quercetin glycoside proved a higher capacity to slow down the degradation phenomena studied, showing less weight loss, a lower reduction in glucose and fructose, as well as better firmness, than the other samples after 14 days of cold storage. Benzyl isothiocyanate, the characteristic odor compound of papaya fruit, ranged from approximately 10.0 μg/kg in fresh cut fruit to approximately 7.50 μg/kg in samples coated by alginate with hydroxyapatite/quercetin and 3.6 μg/kg in the fresh cut papaya without coating after 14 days of cold storage. The trials also indicated greater effectiveness of alginate coatings alone and with quercetin-glucoside in preserving the color of freshly cut papaya.

The aim of this study was to evaluate the effects of the prolonged post-fermentative maceration during the winemaking of Cabernet Sauvignon grapes in oak barrels and steel tanks and apply to this purpose a mathematical modelization to better and easily understand the dynamics and phenomena related to this process. The study focused on the time series of phenolic and volatile compounds in wines during the maceration with solid parts and residual components of the alcoholic fermentation, only for anthocyanins and non-anthocyanic flavonoids two mathematical models were proposed. The results showed that the presence of solid parts during the post-fermentative maceration phase provided a higher content of polyphenols and total flavonoids in both oak barrel and steel tanks. The largest contents of polyphenols and flavonoids were observed in oak barrels trials. Among the anthocyanins in both trials we have assisted to a decreasing trend in delphinidin-3 glucoside, cyanidin-3glucoside, petunidin-3-glucoside and peonidin-3-glucoside, with a more accentuated process for the first two molecules in barrique trial, also acetylated anthocyanins showed a decreasing trend more intense in barrique trial. Finally, the post fermentative maceration did not affect HCTA and flavonols concentrations in wines, but rather it affects their chemical stability through the time. Post-fermentative maceration improved the sensory characteristics in terms of intensity, complexity, and persistence at both olfactory and gustatory level, especially in oak barrel vinification.