Co-inoculation with Yeast and LAB Under Winery Conditions: Modification of the Aromatic Profile of Merlot Wines

The present work reports the impact of yeast/LAB co-inoculation on the aromatic profile of Merlot winesmade in wineries. This study was carried out over two consecutive years on five Merlot wines in Bordeauxand Swiss wineries, using Saccharomyces cerevisiae and Oenococcus oeni starter cultures. Seventy aromaticcompounds were quantified and, in addition, the sensory profiles of two wines were determined in orderto compare the aromatic notes of the sequential and co-inoculated wines. The influence of the timing ofinoculation with lactic acid bacteria (LAB) on the metabolic profile of wines was observed. It confirmedprevious work carried out on a micro-scale but, for the first time, the impact of yeast/LAB co-inoculationwas significantly demonstrated from a sensory point of view under winery conditions. In particular, thefruity and lactic notes, as well as the markers associated with these descriptors, such as esters and diacetyl,were altered. Co-inoculation does not always favour fruity expression, nor does it reduce the diacetylcontent and lactic aroma intensity. All of the trends were observed either in the production and degradationof metabolites, or by the development of an aromatic mask over the short and long term

Analyse du cis- et trans-resveratrol dans les vins produits au portugal

Nous mettons au point une méthode d'analyse du resveratrol (trallS-3,5,4'-trihydroxystilbene) à I'aide de Ia chromatographie en phase gazeuse et détection par ionisation de tlamme (FID), apres une extraction du vin par I'éther et sylilation par I'hexaméthyldisilazane (HMDS). Le seuil de détection est de 5 IIgII.Une séparation parfaite des différents isom"res tralls et eis du resveratrol est obtenue et permet leur détermination dans tous les vins étudiés. Ainsi nous montrons que I'isomere eis est toujours présent dans le vin et peut atteindre de 30 à 70 p. cent du resveratrol total. Nous présentons ici une premiere étude sur la composition en resveratrol des vins provenant de différentes régions du Portugal. Les vins analysés présentent des teneurs en isomeres trans de l'ordre de 120 à 500 Ilglldans les vins blancs, et de 400 à 4500 IIgIIdans les vins rouges. Une étude plus particuliere du Vinho Verde (vin du Nord dUPortugal) a été effectuée.Trans-resveratrol (trans-3,5,4'-trihydroxystilbene) has been reported as contributing to the health promoting properties of wine. In this study wines made exclusively from native Portuguese varieties were assayed for the levels of trans-resveratrol. The method developed uses GC-FID and GC-MS determinations of TMS derivatives; derivatisation by hexamethyldisilazane following ether extraction of wines. Two currently used food antioxydants nordihydroguaiaretic acid (NDGA) and 2' ,4' ,5' -trihydroxybutyrophenone (THBP), were employed as internai standards, being extracted and derivatised in exactly the same way as the determined resveratrol. These internal standards permitted the verification of a good linearity and reproducibility for this determination, with a detection limit of 5 μg/l. A characteristic of this method is the enhanced discrimination between cis- and trans- isomers of resveratrol with the consequent possibility of the determination of cis-resveratrol. The levels of resveratrol from wines of different regions of Portugal was studied. There appeared to be considerable variation in the concentrations encountered in the various wines although generally red wines contained much higher levels than white wines. The use of glucosidase enzymes in winemaking led to an increase of 3 - to 4 - fold in the levels of resveratrol encountered in Vinho Verde wines. Differences were noted between the resveratrol levels of specifie varietal wines from the Vinho Verde

Influence of phenolic acids on growth and inactivation of Oenococcus oeni and Lactobacillus hilgardii

Aims: To determine the effect of several wine-associated, phenolic acids on the growth and viability of strains of Oenococcus oeni and Lactobacillus hilgardii. Methods and Results: Growth was monitored in ethanol-containing medium supplemented with varying concentrations of hydroxybenzoic acids (p-hydroxybenzoic, protocatechuic, gallic, vanillic and syringic acids) and hydroxycinnamic acids (p-coumaric, caffeic and ferulic acids). Progressive inactivation was monitored in ethanolcontaining phosphate buffer supplemented in a similar manner to the growth experiments. Hydroxycinnamic acids proved to be more inhibitory to the growth of O. oeni than hydroxybenzoic acids. On the other hand, some acids showed a beneficial effect on growth of Lact. hilgardii. p-Coumaric acid showed the strongest inhibitory effect on growth and survival of both bacteria. Conclusions: Most phenolic acids had a negative effect on growth of O. oeni, for Lact. hilgardii this effect was only noted for p-coumaric acid. Generally, O. oeni was more sensitive to phenolic acid inactivation than Lact. hilgardii. Significance and Impact of the Study: Eight wine-derived, phenolic acids were compared for their effects on wine lactic acid bacteria. Results indicate that phenolic acids have the capacity to influence growth and survival parameters. The differences found between phenolic compounds could be related to their different chemical structures

Effet de la souche de levure sur les proprietes organoleptiques des vins issus de cinq cepages blancs portugais

Neuf souches de levures commerciales, appartenant au genre Saccharomyces (six souches de S. cerevisiae et trois souches de S. bayanus), ont ete testees lors de la fermentation de moths issus de cinq cepages portugais: Loureiro, Trajadura, Pedernk Azal e Avesso. Pour un même cepage la levure d'implantation semble ne pas avoir d'influence sur la teneur en alcool et sur l'acidité totale des vins produits. Les variations des quantites produites en esters ethyliques d'acides gras (BRAG) et acetates d'alcools superieurs (AAS) peuvent varier d'un facteur 2.1 et 4.3 respectivement, pour un même cepages les teneurs maximales en AAS sont observêes avec les deux mêmes souches pour tour les cepages, a une exception pres. En ce qui concerne les alcools superieurs, les souches plus ou moths productrices different pour chaque cépage. Une etude statistique a permis d'etablir une correlation entre l'analyse chimique et l'analyse sensorielle. D'un point de vue organoleptique, les vins prefer-es sont riches en acides gras et en EEAG mais relativement pauvres en AAS

A Fluorescent Probe for Diacetyl Detection

A water-soluble fluorescent probe, rhodamine B hydrazide (RBH), was prepared and its properties for recognition of diacetyl were studied. The method employs the reaction of diacetyl with RBH, a colorless and non-fluorescent rhodamine B spiro form derivative to give a pink-colored fluorescent substance. In weakly acidic media, RBH reacts more selectively with diacetyl than with other carbonyls, causing a large increase in fluorescence intensity and thereby providing an easy assay for the determination of diacetyl

Observation of hard scattering in photoproduction events with a large rapidity gap at HERA

Events with a large rapidity gap and total transverse energy greater than 5 GeV have been observed in quasi-real photoproduction at HERA with the ZEUS detector. The distribution of these events as a function of the $\gamma p$ centre of mass energy is consistent with diffractive scattering. For total transverse energies above 12 GeV, the hadronic final states show predominantly a two-jet structure with each jet having a transverse energy greater than 4 GeV. For the two-jet events, little energy flow is found outside the jets. This observation is consistent with the hard scattering of a quasi-real photon with a colourless object in the proton.Comment: 19 pages, latex, 4 figures appended as uuencoded fil

D* Production in Deep Inelastic Scattering at HERA

This paper presents measurements of D^{*\pm} production in deep inelastic scattering from collisions between 27.5 GeV positrons and 820 GeV protons. The data have been taken with the ZEUS detector at HERA. The decay channel $D^{*+}\to (D^0 \to K^- \pi^+) \pi^+$ (+ c.c.) has been used in the study. The $e^+p$ cross section for inclusive D^{*\pm} production with $5<Q^2<100 GeV^2$ and $y<0.7$ is 5.3 \pms 1.0 \pms 0.8 nb in the kinematic region {$1.3<p_T(D^{*\pm})<9.0$ GeV and $| \eta(D^{*\pm}) |<1.5$}. Differential cross sections as functions of p_T(D^{*\pm}), $\eta(D^{*\pm}), W$ and $Q^2$ are compared with next-to-leading order QCD calculations based on the photon-gluon fusion production mechanism. After an extrapolation of the cross section to the full kinematic region in p_T(D^{*\pm}) and $\eta$(D^{*\pm}), the charm contribution $F_2^{c\bar{c}}(x,Q^2)$ to the proton structure function is determined for Bjorken $x$ between 2 $\cdot$ 10$^{-4}$ and 5 $\cdot$ 10$^{-3}$.Comment: 17 pages including 4 figure