Effect of exogenous organic acids on chemical compositions and sensory attributes of fortified sweet wines from dehydrated grapes

In this study, acidity was regulated with the addition of exogenous tartaric acid and citric acid before bottling. The effect of exogenous organic acids on chemical compositions and sensory attributes of fortified sweet wines from dehydrated grapes were investigated. The results indicated that exogenous organic acids promoted the conversion of monomeric anthocyanins to copigmented anthocyanins in wines. Specifically, the combination of malvidin-3-O-glucoside and flavanols (catechin and epicatechin) was facilitated to form copigmented anthocyanins. Sensory analysis suggested that exogenous organic acids improved the balance of sugar and acidity and benefited the harmony in wines on the taste. Wines with a residual sugar and titratable acidity ratio of about 11:1 exhibited the more harmonious taste. In addition, it was also observed changes in the aroma profile related to volatile compounds, namely, more intense fruity aroma in wines with the addition of organic acids.

Role of partial dehydration in a naturally ventilated room on the mycobiota, ochratoxins, volatile profile and phenolic composition of Merlot grapes intended for wine production

Dehydration of grapes has been used in various regions of the world to produce special wines, aiming to add value to oenological products. Post-harvest dehydration in rooms may be carried out regardless of weather conditions, without the additional cost of a specific infrastructure, in addition to the benefits of protecting the grapes from damages and environmental pollution. The objective of this study was to verify, for the first time, the impact of the dehydration in a naturally ventilated room on the quality of Merlot grapes. Physicochemical characteristics, mycobiota, occurrence of mycotoxins, volatile profile and phenolic composition of grapes were monitored on 7th, 14th and 21st days of dehydration (weight loss of 10, 20 and 27%, respectively). A decrease in aw (6%), pH (4%), and berry hardness (58%), along with an increase in total soluble solid content (15%) were observed during dehydration. The presence of Pestalotiopsis clavispora, Neopestalotiopsis clavispora, Colletotrichum siamense and Alternaria porri was favored during the dehydration process, while a decrease in the occurrence of Aspergillus niger and Phanerochaete sp. was verified. A. niger isolates showed no potential to produce forms of ochratoxins. These toxins were also not found in the grape samples. Regarding the volatile profile, 1-hexanal, 2-hexenal, and 1-octanal gave rise to the corresponding alcohols during dehydration, such as 1-hexanol, 2-hexen-1-ol, and 1-octanol. Acids (hexanoic, decanoic, and 3-hexenoic) resulted in the respective ethyl esters (hexanoate, decanoate, and ethyl 3-hexenoate) during dehydration. Terpenes as limonene, myrcene, and geraniol decreased throughout dehydration, while their biotransformation products (α-terpineol, 6-methyl-5-hepten-2-one, and linalool, respectively) had an increase in concentration. The phenolic content oscillated during dehydration, with an emphasis on increased levels of four hydroxybenzoic acids (ethyl gallate, p-hydroxybenzoic acid, gallic acid-hexose, and gallic acid), two hydroxycinnamic acids (caffeic acid and caftaric acid), two flavonols (kaempeferol galactoside and quercetin) and two anthocyanins (peonidin 3-O-hexoside and delphinidin 3-O-hexoside). Grapes of satisfactory quality were produced by dehydration in a naturally ventilated room. Even small wine producers can be encouraged to implement this procedure for the diversification of oenological products, as it has no costs related to the implementation of chambers/tunnels.

Moscato nero (Vitis vinifera L.)

Moscato nero d'Acqui is an Italian aromatic black winegrape variety characterized by a low content of anthocyanins (mostly tri-substituted), a satisfactory content of high molecular mass tannins, and a fair amount of terpenes. The grapes were subjected to a postharvest dehydration process under controlled thermohygrometric conditions (16-18°C, 55-70 RH%, 0.6m/s air speed) with the aim to produce three different special wine types (fortified, sfursat, and passito) from fresh, partially dehydrated (27°Brix), and withered (36°Brix) grapes, respectively. Chemical traits of produced grapes and wines were then evaluated through spectrophotometric, HPLC, and GC-MS methods. Increased contents of skin phenolic compounds and reduced extractable contents of seed phenolic compounds were observed as dehydration progressed. Few significant differences were found in the anthocyanin profile of grapes, although the relative abundance of coumaroylated anthocyanins was higher in dehydrated grapes. The predominant free volatile compound found in grapes was geraniol, which decreased with increasing water loss, whereas the contents of major glycosylated volatile compounds increased even above the concentration effect. The changes in the phenolic composition among wines agreed with those among grape skins. Fortified wines were chromatically unsatisfactory probably due to the low content of total anthocyanins, whereas sfursat and passito wines meet good chromatic characteristics as a result of the concentration effect during grape dehydration. Fortified and sfursat wines had free aroma profiles richer in 2-phenylethanol and citronellol, whereas passito wines were mainly composed of 2-phenylethanol and 2-phenylethyl acetate, citronellol being the predominant terpenol in all the wine types studied.