Aroma release from wines under dynamic conditions

Aroma release from wines and model ethanolic solutions during dynamic headspace dilution was measured in real time using atmospheric pressure chemical ionization-mass spectrometry. Model ethanolic solutions maintained the headspace concentration of volatile compounds close to equilibrium values during gas phase dilution over 10 min. Wine samples (with the same ethanol content) did not maintain the headspace concentration of volatiles to the same extent. Wine components and acidity ((+(-catechin, glycerol; pH 3.6) in model ethanolic solutions (120 mL/L) had no effect on the volatile headspace concentration during dynamic headspace dilution. However, in the presence of certain proteins (β-lactoglobulin, β-casein, bovine serum albumin), the model ethanolic solutions failed to maintain their volatile headspace concentration upon headspace dilution, but other proteins (thaumatin, mucin, lysozyme) had no effect. Thermal imaging of the model ethanolic samples (with and without β-casein) under dynamic headspace dilution conditions showed differences in surface temperatures. This observation suggested perturbation of the ethanol monolayer at the air-liquid interface and disruption of the Marangoni effect, which causes bulk convection within ethanolic solutions. Convection carries volatile compounds and warm liquid from the bulk phase to the air-liquid interface, thus replenishing the interfacial concentration and maintaining the gas phase concentration and interfacial surface temperature during headspace dilution. It is postulated that certain proteins may exert a similar effect in wine. © 2009 American Chemical Society

Regulation and manipulation of ABA biosynthesis in roots

Overexpression of 9-cis-epoxycarotenoid dioxygenase (NCED) is known to cause abscisic acid (ABA) accumulation in leaves, seeds and whole plants. Here we investigated the manipulation of ABA biosynthesis in roots. Roots from whole tomato plants that constitutively overexpress LeNCED1 had a higher ABA content than wild-type (WT) roots. This could be explained by enhanced in situ ABA biosynthesis, rather than import of ABA from the shoot, because root cultures also had higher ABA content, and because tetracycline (Tc)-induced LeNCED1 expression caused ABA accumulation in isolated tobacco roots. However, the Tc-induced expression led to greater accumulation of ABA in leaves than in roots. This demonstrates for the first time that NCED is rate-limiting in root tissues, but suggests that other steps were also restrictive to pathway flux, more so in roots than in leaves. Dehydration and NCED overexpression acted synergistically in enhancing ABA accumulation in tomato root cultures. One explanation is that xanthophyll synthesis was increased during root dehydration, and, in support of this, dehydration treatments increased beta-carotene hydroxylase mRNA levels. Whole plants overexpressing LeNCED1 exhibited greatly reduced stomatal conductance and grafting experiments from this study demonstrated that this was predominantly due to increased ABA biosynthesis in leaves rather than in roots. Genetic manipulation of both xanthophyll supply and epoxycarotenoid cleavage may be needed to enhance root ABA biosynthesis sufficiently to signal stomatal closure in the shoot