Influence of water and nitrogen deficit on fruit ripening and aroma potential of Vitis vinifera L cv Sauvignon blanc in field conditions

S‐Cysteine conjugate precursors of three volatile thiols were monitored in Vitis vinifera L cv Sauvignon blanc grapes during fruit ripening to assess the influence of vine water and nitrogen status on the grape aroma potential in field conditions. Four dry farmed plots were studied in the Pessac‐Léognan and Graves appellations (Bordeaux area) in 1998, which was a very dry vintage, and in 1999, when regular summer rainfall occurred. Soil water‐holding capacity ranged from very low to high. Soil total nitrogen content was related to soil organic matter content, which was highly variable on the four plots. Vine vigour was enhanced by both high water and nitrogen status. Major compounds in grapes depended mainly on vine water status. Water deficit‐stressed vines produced small berries with low sugar and low total acidity. Grape aroma potential was highest in vines under mild water deficit and moderate nitrogen supply. Severe water deficit stress seemed to limit aroma potential, as did nitrogen deficiency. Consequences for site selection and irrigation management for Sauvignon blanc are discussed. Copyright © 2004 Society of Chemical Industry     

Review: the interaction between rootstocks and cultivars (Vitis vinifera L.) to enhance drought tolerance in grapevine

Water scarcity is a key limiting factor in agriculture. Grapevines react at the physiological, biochemical and genetic level to tolerate water constraints. Even though grapevines are considered relatively tolerant to water deficits, grapevine growth and yield can be seriously reduced under water deficit. Drought‐tolerant rootstocks are expected to enable the scion to grow and yield when water supply is limited. Genetic machinery allows rootstocks to control water extraction capacity and scion transpiration. Numerous works have demonstrated the positive role of drought‐tolerant rootstocks on the control of cultivar's leaf stomatal conductance and therefore on canopy transpiration. The mechanisms, in terms of signalisation and gene functioning, need further study. Furthermore, there is no standardised methodology to rank rootstocks in terms of their tolerance to drought. A potential effect of rootstocks on stomatal development is also discussed. This review will critically discuss the current knowledge of the mechanisms of drought tolerance afforded by rootstocks, taking into account the scion/rootstock interaction, and will present some of the challenges for future investigations.     

水与黄酒酿造酒质的关系和要求

简叙了水在黄酒酿造中的作用以及水中无机成分与酒质的关系，同时将绍兴鉴湖水质和日本酿造用水进行了比较，在此基础上提出了黄酒酿造不同用水的要求和水质的净化处理方法。     

Water‐use efficiency in grapevine cultivars grown under controlled conditions: effects of water stress at the leaf and whole‐plant level

Background and Aims: Improving water‐use efficiency (WUE) is desirable for future grapevine growth and grape production, especially in Mediterranean areas where water is predicted to be limiting. Understanding the genetic variability in WUE is important to identify the most appropriate cultivars to be used in semi‐arid areas. Most previous studies have focused at leaf‐level WUE, while information on whole‐plant level is scarce. This study explored the genetic variability of grapevine in whole‐plant WUE (WUE_WP) to determine whether several leaf WUE (WUE_l) indicators are suitable as proxies of WUE_WP. Methods and Results: Three similar experiments were performed to compare WUE in up to eight different grapevine cultivars under irrigation and water‐stress treatments. Although WUE_l and WUE_WP varied with cultivar and treatment, WUE_l was not a reliable parameter to predict WUE_WP. Conclusions: Large variability in WUE_WP between grapevine cultivars was observed, although this variability was not described by leaf‐level indicators of WUE. Significance of the Study: This study showed that the large variability existing for WUE_WP in different cultivars offers an potential method for selecting the more suitable cultivars to grow in water‐scarce viticulture areas, although WUE_l is not reliable for estimating WUE_WP.     

A research note: the potential for transfer of Salmonella from irrigation water to tomatoes

The transmission of Salmonella Enteritidis from soil to fruit by contaminated irrigated water was studied using 20 patio tomato plants. In order to track the presence of Salmonella in the soil and plants a luminescent strain transformed with the full luxCDABE gene cassette from Photorhabdus luminescens was used. The tomato plants were irrigated every other day by direct application of water containing Salmonella Enteritidis (10⁵ CFU ml^?1) to the soil. Samples of soil, stem, leaf and fruit were taken weekly and assayed for Salmonella by plating onto Luria Bertani agar containing 50 µg ml^?1 ampicillin. There was a significant difference (P < 0.05) in Salmonella counts from soils sampled during the course of the study. No Salmonella were recovered from the leaf, stem, and fruit samples taken from the tomato plants. This indicates that, under these test conditions, watering with contaminated water directly into the soil does not result in the transmission of Salmonella, and possibly other pathogens, to tomatoes. Copyright © 2004 Society of Chemical Industry     

Rapid and non‐destructive method to assess in the vineyard grape berry anthocyanins under different seasonal and water conditions*

Background and Aims: Monitoring of anthocyanins (Anth) in winegrape (Vitis vinifera L.) is fundamental for the production of top‐quality red wines. This work was aimed at testing a new fluorescence‐based sensor for Anth detection in the vineyard. Significance of the Study: The present study showed a new important innovative technology for viticulture. The sensor evaluation of the large spatial and temporal heterogeneity in Anth accumulation can be useful as support parameter in the harvest date decision or for vineyard zoning of phenolic maturity. Methods and Results: Anth in grape (cv. Aleatico) bunches attached to the vine were monitored non‐destructively in the field using a fluorescence‐based sensor during the 2008 and 2009 seasons and under different water regimes. The ANTH_RG index = log(far‐red‐fluorescence_R/far‐red‐fluorescence_G), with fluorescence signals excited with red (R) and green (G) light, was inversely correlated through an exponential function (r² = 0.875) to the Anth concentration derived from the HPLC analysis of berry skin extracts. ANTH_RG was effective in detecting the earlier ripening process in 2009 with respect to 2008 and differences in the Anth accumulation between seasons and in relation to different water regimes. Water deficit imposed in 2009 enhanced Anth concentration in berries because of a reduction in berry size but also an increase of Anth biosynthesis. This effect was observed by both destructive and ANTH_RG non‐destructive measurements. Conclusions: Our results show that the employed fluorescence sensor represents a reliable, rapid and non‐invasive tool for monitoring and determining Anth accumulation in situ.     

Use of a polymerase chain reaction for specific detection of the malolactic fermentation bacterium Oenococcus oeni (formerly Leuconostoc oenos) in grape juice and wine samples

A PCR method has been developed that enables rapid and direct identification of the malolactic bacterium Oenococcus oeni from grape must or wine samples. Two primers, based on unique, highly conserved regions within the 16S rRNA gene of O. oeni , were used to amplify a 995 bp fragment which is specific for O. oeni . Other species of bacteria from Lactobacillus, Pediococcus and Acetobacter which may be found in grape must or wine were not detected using this technique. This diagnostic test is able to specifically detect in the order of 10³colony forming units per mL of O. oeni in a wine sample, and can be used for monitoring bacterial growth during malolactic fermentation.     

Preparation of spent brewer's yeast β-glucans for potential applications in the food industry

A preparation of β‐glucan, obtained from spent brewer's yeast, was evaluated for potential food applications. This material was autolysed and the cell walls that were obtained were homogenized, extracted firstly with alkali, then with acid, and then spray dried. Effects of the homogenization on the chemical composition, rheological properties and functional properties of β‐glucan were investigated. Homogenized cell walls exhibited higher β‐glucan content and apparent viscosity than those which had not been homogenized because of fragmentation of the cell walls. When compared with commercial β‐glucan from baker's yeast, it was found that the β‐glucan obtained from this study had higher apparent viscosity, water‐holding capacity and emulsion stabilizing capacity, but very similar oil‐binding capacity. These findings suggest that β‐glucan obtained from brewer's yeast can be used in food products as a thickening, water‐holding, or oil‐binding agent and emulsifying stabilizer.     

By‐products from viticulture and the wine industry: potential as sources of nutrients for ruminants

BACKGROUND: This work aimed to study the chemical composition, in vitro digestibility, ruminal degradability and intestinal digestibility of nutrients of vine shoot (VS), grape marcs (GMG and GMM), white (WL), red (RL) and sherry (SL) wine lees and grape marc plus lees (GML). The effect of polyethylene glycol (PEG) on nutrient availability was also studied. RESULTS: By‐products had variable crude protein (CP) and cell walls (from 44.8 to 203 and from 122 to 741 g kg^?1 dry matter (DM) for CP and neutral detergent fibre (NDF) respectively). DM and CP in vitro digestibility ranged from 0.30 to 0.91 and from 0.51 to 0.84 respectively. The effective ruminal degradability of DM and CP was low (from 0.27 to 0.36 and from 0.34 to 0.53, respectively). The intestinal digestibility of the ruminally undegraded fraction was 0.25 and 0.29 for VS and GMG, respectively. The effect of PEG was different in VS and GMG. CONCLUSION: This is the first information available on ruminal and intestinal availability of nutrients from a diversity of vine and winery by‐products. The use of a combination of the different by‐products studied may represent a valuable source of energy and protein for ruminants. Further research on the effect of diets including these by‐products on animal performance and the quality of products is necessary. Copyright © 2007 Society of Chemical Industry     

Volatile profile and potential of inactive dry yeast‐based winemaking additives to modify the volatile composition of wines

BACKGROUND: With the objective of determining the potential of winemaking additives based on inactive dry yeast (IDY) to modify the volatile composition of wines, gas chromatography coupled to mass spectrometry was employed to characterize the volatile profile of a widely used IDY preparation. To have the most accurate picture of the volatile compounds, pressurized liquid extraction technique (PLE) was used with different solvents and extraction temperatures. Complementary headspace solid‐phase microextraction was applied to gain insight into the volatile composition. In addition, the ability of some target volatile (pyrazines) to be released into model wines was investigated. RESULTS: The PLE technique was mainly suitable for the extraction of volatile compounds with a low to medium molecular weight and the best extraction yields were obtained by using apolar solvents (hexane) and high temperatures (150 °C). PLE in combination with solid‐phase microextraction allowed the identification of 35 volatile compounds, most of them heterocyclic‐containing nitrogen compounds formed during the processing of IDY that could be released into the wines: the signal of four target masses corresponding to 2,5‐dimethylpyrazine, trimethylpyrazine, methylbutylpyrazine and 2‐ethyl‐3,5‐dimethylpyrazine increased in the synthetic wines after 13 days when IDY was left in the model wines. CONCLUSION: The study confirmed that some volatile compounds identified in IDY which were formed during processing could be released into the wines which might modify wine aroma composition. Copyright © 2009 Society of Chemical Industry     

Adsorption of β-Lactoglobulin variants A and B to the air–water interface

Summary The adsorption of proteins to interfaces is a vital and complex process for the formation and stabilization of multiphase food systems (emulsions and foams). The process of protein adsorption is generally understood only at the phenomenological level, as the complexity of protein unfolding during adsorption is very difficult to predict and model. By comparing proteins with very similar structures, it is possible to attribute observed changes in adsorption behaviour. The A and B genetic variants of β-lactoglobulin (β-lg) differ by only two amino acids (Asp-64, Val-118 in A, and Gly-64, Ala-118 in B), thus making them ideal candidates for this type of comparison. In this study we monitored the surface behaviour of β-lg A and B, measuring the surface tension and surface dilational modulus of adsorbed protein, and the compression behaviour of spread protein films. At pH 7, variant B lowered the surface tension and increased the surface dilational modulus more rapidly than variant A. Raising the pH to 7.8 should increase the level of dissociation into monomers. Indeed, this was confirmed by the rate of adsorption, which increased in both cases. Also, the surface tension of both variants was much lower than at pH7. Variant B was less sensitive to the change of pH than A. Regardless of pH, after 3 h adsorption the difference between the variants in surface tension or surface dilational modulus was negligible. The differences in surface behaviour between the variants are discussed in terms of interactions between monomers at and with the interface, and the dimer : monomer equilibrium in the bulk solution.