Grape metabolism

Table I. Conversion of L-Ascorbic Acid the Grape (Metabolic Period, [U C] to Tartaric, 25 h) Acid in [6- C]...

Grape metabolism, depending on the variety, as well as soil, climate, and vineyard management techniques. 

The grape is more than an accnmnlation organ it maintains an intense activity (respiration and biochemical transformations) dnring maturation. Veraison also corresponds to the synthesis of new enzyme activities and the release of inhibition of other ones. These variations in gene expression cause profound changes in grape metabolism (Robinson and Davies, 2000). 

Malic acid is a very active intermediary product of grape metabolism. The vine contains the L-(—) malic isomer. The vine assimilates carbon dioxide in the air by a C3 mechanism (Ruflher et al., 1983). In this manner, during the dark phase of photosynthesis, the leaves and young green grapes fix CO2 on ribulose 1,5-diphosphate to produce phospho-glyceric acid, which condenses to form hexoses and may also become dehydrated into phosphoenol pyruvic acid. CO2, catalyzed by PEP carboxylase, is fixed on this acid to form oxaloacetic acid, which is, in turn, reduced into malic acid. 

Some flavonoids, such as procyanidins, have antidiabetic properties because they improve altered glucose and oxidative metabolisms of diabetic states (Pinent and others 2004). Extract of grape seed procyanidins (PE) administered orally to streptozotocin-induced diabetic rats resulted in an antihyperglycemic effect, which was significantly increased if PE administration was accompanied by a low insulin dose (Pinent and others 2004). The antihyperglycemic effect of PE may be partially due to the insuli-nomimetic activity of procyanidins on insulin-sensitive cell lines. 

Bobek P, Ozdin L and Hromadova M. 1998. The effect of dried tomato, grape and apple pomace on the cholesterol metabolism and antioxidative enzymatic system in rats with hypercholesterolemia. Nahrung 42(5) 317— 320. 

Chloro-ort/2o-toluidine has been identified in field samples of plant materials treated with chlordimeform, e.g., in young bean leaves at concentrations of less than 0.1-0.2 ppm [mg/kg], in grape stems at 0.02-0.3 ppm [mg/kg], in a mixture of grape stems and berries at 0.02-0.5 ppm [mg/kg] and in prunes and apples at less than 0.04 ppm [mg/kg] (Kossmann et al., 1971). In an experimental field application (one to three treatments with chlordimeform, harvesting 42 days after last treatment), 4-chloro-ort/zo-toluidine was found in rice grains at 3-61 ppb [ Xg/kg] and in straw parts at 80-7200 ppb [pg/kg] (lizuka Masuda, 1979). 4-Chloro-ort/70-toluidine was detected as a metabolic product in cotton plants following treatment with chlordimeform (Bull, 1973). 

The next step of the biotechnical sequence, yeast fermentation, is of the utmost importance to the chemistry of winemaking as well as to the formation of flavor substances. We have investigated this previously using 14C-tagged compounds (16). Amino acids, for example, enter the yeast fermentation with a quasi biochemical valence with regard to the formation of metabolic side products like alcohols and esters. In that respect, the composition of the fermentation substrate, the grape must, is highly important to the formation of aroma substances by yeasts. 

Pereira, G. E., Gaudillere, J. P., Pieri, P., Hilbert, G., Maucourt, M., Deborde, C., Moing, A., and Rolin, D. (2006). Microclimate influence on mineral and metabolic profiles of grape berries.. Agric. Food Chem. 54, 6765-6775. 

Winemaking by carbonic maceration (CM) is a process exploiting the adaptability of intact grape berries to an oxygen-deprived medium enriched with carbon dioxide (C02). This adaptation is reflected almost instantly inside each berry by the transition from a respiratory to fermentative anaerobic metabolism (AM). 

FIGURE 1.1 Scheme of carbonic maceration winemaking. AM, anaerobic metabolism of grape berries YAF, yeast alcoholic fermentation M, maceration qd = pair temperature (q°C) action duration (days). (Figure from CEnologie—fondements scientifi-ques et techniques. Flanzy et al. collection Sciences Techniques Agroalimentaires. Technique Documentation, 1998, p. 780. Reproduced with the permission of the Editor.)... 

VI. SPECIFIC CHARACTERISTICS OF GRAPE BERRIES IN CARBONIC MACERATION ANAEROBIC METABOLISM... 

The distinctive feature of CM is the exploitation of grape-cell AM. Intact berries quickly shift from oxidative to fermentative metabolism under anaerobic conditions (atmospheres with oxygen contents <1%). 

---