Influence of postharvest water stress on lipoxygenase and alcohol dehydrogenase activities, and on the composition of some volatile compounds of Gewürztraminer grapes dehydrated under controlled and uncontrolled thermohygrometric conditions

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

Electronic nose to study postharvest dehydration of wine grapes

“…Costantini et al (2006) identified the second significant step of metabolic change around this value, with a significant increase in alcohol dehydrogenase activity in Malvasia grape, and this was later confirmed by Wright et al (2009), who observed a change in inflection point in fluorescence (Fo) and in the fructose/glucose ratio at 20-25% of mass loss in table grapes. Grape cell stress through water loss does not only depend on the amount of mass transfer (water), and other factors, such as continuous change in the surrounding vapour pressure, could accelerate the rate of stress (Chkaiban et al, 2007), and the rate of water loss is affected by environmental parameters and varietal characteristics . Malic acid decreased significantly at 10°C, probably due to the shift from harvest temperature down to 10°C (Table 1).…”

“…Critical levels of mass loss (weight loss) for these changes have been identified at 10% and 20%, respectively. Chkaiban et al (2007) have, in addition, demonstrated that the stability of dehydration conditions are very important in order to have a ''regular" water stress process in terms of the metabolic changes described above; indeed, if grape berry undergoes continuous change in temperature and relative humidity during dehydration the stress metabolism is accelerated. Wright, DeLong, Lada, and Prange (2009) have shown that the level of mass loss greatly affects fluorescence emission and the critical level is around 20% of mass loss, confirming what was observed by Bellincontro et al (2009) in Cesanese grape using destructive analyses as well as non-destructive techniques.…”

“…Research on the volatile compound marker is an important objective for following the progress of dehydration metabolism. Ethanol, acetaldehyde, acetic acid and ethyl acetate are compounds which change during grape dehydration (Chkaiban et al, 2007;Costantini et al, 2006). Identification of sensors which can detect small metabolic changes during grape dehydration to interface with equipment which manages the environment of grape dehydration facilities could be an important innovation in this sector.…”

Identification of Putative Stage-Specific Grapevine Berry Biomarkers and Omics Data Integration into Networks

“…Additional class a transcripts were related to the oxidative burst that occurs at veraison (Pilati et al, 2007). Transcripts in the response-to-stimulus category were found in both classes a and b, including those involved in ethylene (class a) and gibberellin (class b) signaling, whereas several transcripts encoding transcription factors were found in classes b and c. Class c (withering-specific) transcripts included those involved in cell wall metabolism, stress responses, aerobic fermentation, volatile compound synthesis, and cell death, as suggested by previous genomic studies (Zamboni et al, 2008;Rizzini et al, 2009) and physiological investigations (Bellincontro et al, 2004;Costantini et al, 2006;Chkaiban et al, 2007).…”

“…Proteins involved in primary/cellular metabolic processes, sugar catabolism, cellular component organization, and biogenesis were more likely to group in class b, reflecting the activation of glycolysis and gluconeogenesis during ripening (Sarry et al, 2004;Negri et al, 2008). Proteins involved in the switch to aerobic fermentation during ripening (Sarry et al, 2004) and withering Costantini et al, 2006;Chkaiban et al, 2007) were found between classes b and c along with those involved in the production of flavonoids (Coombe and McCarthy, 2000).…”