No abstract

Gewürztraminer grapes with a sugar content of around 212 g/L (21.7°Brix) were dried at 17°C, 40% relative humidity and 1.5 m/sec air flow in a 300 L thermo-conditioned tunnel. Control grapes were dried traditionally in a window ventilated room, under uncontrolled environmental conditions varying with outside climate. Tunnel-dried grapes reached the desired sugar concentration (305 g/L, 29.5°Brix) in 17 days, loosing 36% of their weight. Control grapes lost only 22% of their weight and grey mould developed in several bunches at the last sampling. Titratable acidity decreased for tunnel-dried and control grapes from 6.5 g/L to 4 g/L and 5 g/L, respectively. Lipoxygenase (LOX) activity declined in both samples from 120 to 90 U/mg protein dw, with a subsequent significant increase after 20% weight loss in tunnel-treated grapes while the control grapes showed a small peak (150 U/mg protein dw) at 13% weight loss. Six carbon compound evolution showed a loose correlation with LOX activity. Alcohol dehydrogenase specific activity and the concentrations of ethanol and of acetaldehyde plus ethyl acetate showed fluctuating patterns of change, with the evolution of these three variables showing similarity, particularly evident in the tunnel-dried grapes. Carotenoids declined significantly, to increase slightly at the end of the experiment in both samples, with the decline more rapid in the control grapes. Traditional, uncontrolled conditions, did not permit constant dehydration, and provoked a rapid stress to the berries (10% of weight loss). Controlled conditions permitted uniform dehydration, postponed water stress, giving a higher quality product without loss of berries. AbbreviationsABA abscisic acid; ADH alcohol dehydrogenase; C6 six carbon; dw dry weight; FTIR Fourier transformed infrared spectroscopy; LOX lipoxygenase; MA malic acid; RH relative humidity; SVP saturation vapour pressure; TA titratable acidity; VP vapour pressure; VPD vapour pressure deficit Effects of postharvest water stress 143Effects of postharvest water stress

Detached wine grapes ( Vitis vinifera cv. 'Trebbiano', white skinned) were treated for 3 days with 30 kPa of CO(2) and then transferred to air for an additional 9 days to partially dehydrate (about 20% weight loss). At the end of the CO(2) treatment on withering berries, total polyphenols and flavonoids were maintained in the skin, but to a more limited extent in the pulp. An induction of the proanthocyanidin synthesis appeared to be one of the responses to the treatment because both (+)-catechin and (-)-epicatechin concentrations increased in the skin. The skin and pulp of the grape berries showed different molecular responses to a high CO(2) treatment. As revealed by microarray hybridizations, 217 and 75 genes appeared differentially expressed in the skin and pulp of treated samples, respectively. Functional categorization and gene enrichment analyses pointed out that epicarp cells undergo more pronounced changes in transcript profiling at the end of the incubation period. Highly represented categories in both tissues were related to protein, stress, transcript, RNA, and hormone (ethylene, ABA) metabolism. Fermentation, CHO metabolism, and redox regulation functional categories were represented only in the skin.

For certain food products, postharvest controlled stresses or treatments with specific elicitors are applied to induce desired physical/chemical changes and/or to positively affect phytochemical content. This is the case of wine grapes where both strategies, singularly applied or coupled, can be used to modulate berry composition and, as a consequence, affect wine quality traits. Since the knowledge of the effects of these postharvest treatments on berry metabolism and the regulation of gene expression is very limited, a large-scale transcriptome analysis has been carried out, using an oligo-based microarray (14,562 probes) on skins of wine grape (Vitis vinifera L.) berries subjected to dehydration, at different rates, up to 30% of weight loss or to ethylene treatment (500 ppm for 7 days) after harvest. A number of differentially expressed targets was detected following both treatments, indicating that grape berries are still reactive at advanced stages of postharvest dehydration and that ethylene induces marked changes in transcriptome after harvest also in non-climacteric fruit such as grape berries. INTRODUCTIONPostharvest dehydration of grape berries is applied for raisin production and for making wines (often called dessert wines) that are characterized, as result of both concentration process and metabolic changes occurring in berry flesh and skin, by high sugar and/or alcohol content and peculiar taste and aroma. The rate and the intensity of postharvest berry dehydration, often reaching 40-50% of weight loss (WL), markedly affect the resulting wines and this is due, primarily but not exclusively, to differences in terms of sugar and organic acid content of flesh cells. Following berry dehydration, sugar concentration increases whereas organic acid content tends to remain stable (or slightly reduced) due to increments of tartaric acid (concentration effects) and decreases of malic acid that is likely consumed as substrate for respiration. Costantini et al. (2006) report an increase of CO 2 production in wine grape ('Malvasia') berries undergoing postharvest dehydration starting from a WL of 10% and reaching the highest values around 22% WL. Bellincontro et al. (2004) suggest that a shift from aerobic to anaerobic metabolism occurs when grape berries lose about 10-15% of fresh weight. As consequence of concentration and increased respiration rate, sugar/organic acid and tartaric/malic acid ratios increase whereas glucose/fructose ratio decreases. Water loss from detached fruit may induce marked changes also in terms of secondary metabolism (Kays and Paull, 2004): limited water stress (1-3% of WL), induce increases in abscissic acid (ABA) and ethylene biosynthesis, and pectolitic (e.g., polygalacturonase) enzyme activities. At higher dehydration rate (3-5%), loss of membrane integrity, altered volatile pattern and phenol metabolism occur.Considering specifically grape berry, limited information is available on metabolic aspects induced by postharvest dehydration. Costantini et al. (2006) observed, ...

No abstract