Wine aroma and flavor are influenced by grape-derived compounds, which exist as free volatiles and/or as sugar-bound glycosides [1,2,39]. Products of grape glycoside hydrolysis include aliphatic residues, monoterpenes, sesquiterpenes, norisoprenoids, and shikimic acid metabolites [2]. Glycosides may exist as mono-or disaccharides, with sugar moieties occurring as ß-D-glucose, 6-O-α-L-rhamnopyranosyl-ß-D-glucopyranose, 6-O-α-L-arabinofuranosyl-ß-D-glucopyranose, and 6-O-α-Lapiofuranosyl-ß-D-glucopyranose [36]. ß-D-glucopyranosides appear to predominate [38]. Grape glycosides are a source of varietal aroma and flavor [39], and their hydrolysis may lead to increased wine quality [2,13].Glycoside hydrolysis may occur enzymatically through glucosidases or via acid hydrolysis [13,20,37]. Enzymatic hydrolysis of disaccharide glycosides occurs as a two-step process. In the case of monoglucosides, the glucosidase acts directly [12]. Acid hydrolysis cleaves glycosides of activated alcohols, producing a carbocation capable of causing aroma and flavor changes [22,32,33,37]. Enzyme hydrolysis cleaves the glycosidic bond without altering the aglycone [33]. Endogenous grape ß-glucosidases result in some hydrolysis during fruit maturation, but show low activity [19]. Enzymes from molds and yeasts may also release aglycones [22]. McMahon et al. [29] found glycosidic activity in five strains of Brettanomyces bruxellensis. Although often deemed as a spoilage organism, Brettanomyces may result in enhanced aroma and complexity and may impact red wine color [14]. Mono-glucosylated anthocyanins are the primary red pigments in Vitis vinifera grapes [34] and comprise a large portion of the total glycoside concentration [24,40]. Hydrolysis of glucose usually results in a corresponding anthocyanidin, which is converted to the colorless pseudobase [23], which may affect color and stability.An increase in glucose concentration coinciding with malolactic fermentation (MLF) has been documented [5,10] and may be caused by glycoside hydrolysis [27]. Grimaldi et al. [16] demonstrated ß-glucosidase activity in 12 strains of Oenococcus oeni. However, it is difficult to link bacterial enzyme activity with glycoside hydrolysis, as increased glucose concentrations may be the result of residual grape or yeast hydrolytic enzymes [10]. ß-Glucosidases can be inhibited by pH, temperature, sugars, ethanol, and phenols [17,22]. The degree of inhibition of production and/or activity is dictated by the organism and strain [3,11,16,30]. The acidic conditions in wine may result in denaturation and inhibition of enzymatic hydrolysis [11]. However, one strain of Oenococcus oeni was found to retain 78% of maximum ß-glucosidase activity at pH 3.5 [5]. The optimum temperature for yeast ß-glucosidases has been found to be 45 to 50°C [11]. At ethanol concentrations of 10% (v/v), glucosidases of Aspergillus niger, Saccharomyces cerevisiae, and Candida wickerhamii showed no loss of activity [22]. Thus, a number of factors may limit the production and/or activity of ß-...
