Because β-citronellol and nerol could not sufficiently be separated by the
analytical method applied, the corresponding results are displayed as sum of β-citronellol plus nerol throughout the paper. Regarding the used enzyme codes, the reader is again referred to Table 1. As shown in Table 3, all β-glucosidase preparations (GL, GO, mTOR inhibitor GA) were able to release monoterpenes, the highest concentrations were detected with GO. According to the scheme of sequential precursor hydrolysis as proposed by Gunata et al. (1988), arabinosidase and rhamnosidase preparations were always applied in combination with the β-glucosidase from O. oeni (GO). The use of the same glucosidase (GO) in all assays with enzyme combinations was intended to obtain comparable results. Fungal (GO/AA) and bacterial (GO/AO) arabinosidase could release equal amounts of total terpenes. Addition of the Pediococcus acidilactici rhamnosidase
R to GO caused only a small further increase in terpene concentrations, compared to treatment with GO alone. http://www.selleckchem.com/products/abt-199.html The highest terpene concentrations were released when applying the combinations GO/AO/R and GO/N. At this point, it is important to note that N, which was applied as a fungal rhamnosidase preparation, is in fact a complex mixture containing additional activities of α-l-rhamnosidase, β-d-glucosidase, β-d-galactosidase, β-d-xylosidase, and α-l-arabinosidase (see activity profile in Fig. 1). Subsequently, two brands of red grape juice (“St. Laurent”, “Happy Day”), both commercially available at Austrian markets, were used as substrates for enzyme assays. “St. Laurent” is a highly aromatic grape variety Tangeritin that is often cultivated in Eastern Austria (Lower Austria, Burgenland), while the latter is a commercial bulk product which is probably an undefined blend of several grape varieties. The aim of these assays was to take the effects of the juice matrix, especially of sugar inhibition
at still optimal pH (adjusted to pH 5.5) into account (see Table 2 for juice composition). At first, the total amounts of released terpenes differed significantly between the two varieties (Table 4), most likely due to different concentrations of aroma precursors. The overall release of terpenes from “St. Laurent” was low, while higher concentrations were detected in “Happy Day” after enzyme treatment. Nevertheless, the results from both juices followed similar trends. Remarkably, both glucosidase (GA) and arabinosidase (GO/AA) from Aspergillus niger were almost inactive under these conditions ( Table 4). These results are in agreement with the finding that the fungal glucosidase GA was strongly inhibited by glucose in tests with pNP-β-d-glucopyranoside (3.6% residual activity at 500 mM glucose, corresponding to 90 g/L). In contrast, GO still exhibited 36% residual activity at 500 mM glucose.
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