Influence of Different Dehydration Levels on Volatile Profiles, Phenolic Contents and Skin Hardness of Alkaline Pre-Treated Grapes cv Muscat of Alexandria (Vitis vinifera L.)

Abstract

A dehydration experiment was carried out on Vitis vinifera L. cv Muscat of Alexandria (synonym Zibibbo) following the process for the production of renowned special dessert wines produced on Pantelleria island (Sicily, Italy). Harvested berries were pre-treated in a sodium hydroxide dipping solution (45 g/L, dipped for 185 s, 25 °C) to accelerate the drying process, rinsed, and dehydrated in simulated conditions (relative humidity 30%, 30 °C temperature, air speed 0.9 m/s). Three dehydration levels were achieved, corresponding to “Passolata”, “Bionda”, and “Malaga” stages (35%, 50%, and 65% of weight loss, respectively) of the Pantelleria denomination of origin (DOC). Grape skin mechanical properties, technological parameters, phenolics, and aroma profile varied considerably during dehydration. The most important aroma compounds for their olfactory impact, such as linalool, geraniol, nerol, and citronellol, especially in glycosylated forms, significantly increased in dried grapes compared to fresh ones, even if aroma profile modification occurred. A decrease in break skin force could have induced higher release of flavonoids. The findings showed relevant changes, allowing winemakers to better select the ratio of fresh and dehydrated grapes in the function of the final desired wine.

Analysis of Intact Glycosidic Aroma Precursors in Grapes by High-Performance Liquid Chromatography with a Diode Array Detector

“…Peak 15 (54.89 min; Figure 2) was the next abundant monoterpenediol, with a higher absorbance at 190, 205 and 282 nm (Figure 3O). Several researchers have pointed out that the most abundant monoterpenediols in Muscat of Alexandria grapes are 8-hydroxylinalool, 2,6-dimethyl-3,7-octadiene-2,6-diol, 3,7dimethyl-1,5-octadiene-3,7-diol, 3,7-dimethyl-1,7-octadiene-3,6-diol, 8-hydroxynerol and 8-hydroxygeraniol [16,[35][36][37]. Therefore, it could be associated with aglycone of the more important monoterpenediols identified above.…”

Moscato Cerletti, a rediscovered aromatic cultivar with oenological potential in warm and dry areas

“…The free and glycosylated varietal aroma compounds were extracted from three replicates of 50 fresh grape berries, which were processed following the procedure described by Fracassetti et al (2017) and Corona et al (2020). The berries were de-seeded and the pulp was separated from the skin by adding Na2S2O5 (100 mg).…”

“…The GC-MS conditions which were used are reported by Corona et al (2020). The detection was carried out by electron impact mass spectrometry in total ion current (TIC) mode using an ionisation energy of 70 eV.…”

Free and Bound Volatile Aroma Compounds of ´Maraština´ Grapes as Influenced by Dehydration Techniques

“…The accumulation of desirable key metabolites during postharvest dehydration is inhibited by rapid dehydration conditions that shorten the berry lifetime. Metabolomics and transcriptomics have demonstrated that the dehydration process results in modulation of the expression of various genes implicated in grape metabolism, such as secondary metabolism of phenols, terpenes, and lipids [10]. The water loss is reflected in the cell metabolism that transitions from aerobic to anaerobic [18,29].…”

“…Chamber-drying techniques in controlled conditions as an alternative to traditional sun drying revealed a significant impact of the dehydration rate and temperature on the modification of volatile compounds from the grapes [4][5][6]. Grape dehydration causes substantial water loss and a gradual increase in sugar concentration, which promotes the synthesis of metabolites that lead to the formation of the typical flavor of the sweet wines [4,[7][8][9][10]. Therefore, grape dehydration is one of the most important steps in the production of naturally sweet wine Prošek that influences the production of key volatile compounds in the grape variety used.…”