Changes in monosaccharides, organic acids and amino acids during Cabernet Sauvignon wine ageing based on a simultaneous analysis using gas chromatography-mass spectrometry.

BACKGROUND: Monosaccharides, organic acids and amino acids are the important flavour-related components in wines. The aim of this article is to develop and validate a method that could simultaneously analyse these compounds in wine based on silylation derivatisation and gas chromatography-mass spectrometry (GC-MS), and apply this method to the investigation of the changes of these compounds and speculate upon their related influences on Cabernet Sauvignon wine flavour during wine ageing. This work presented a new approach for wine analysis and provided more information concerning red wine ageing. RESULTS: This method could simultaneously quantitatively analyse 2 monosaccharides, 8 organic acids and 13 amino acids in wine. A validation experiment showed good linearity, sensitivity, reproducibility and recovery. Multiple derivatives of five amino acids have been found but their effects on quantitative analysis were negligible, except for methionine. The evolution pattern of each category was different, and we speculated that the corresponding mechanisms involving microorganism activities, physical interactions and chemical reactions had a great correlation with red wine flavours during ageing. CONCLUSION: Simultaneously quantitative analysis of monosaccharides, organic acids and amino acids in wine was feasible and reliable and this method has extensive application prospects. © 2017 Society of Chemical Industry.

Differential Expression of VvLOXA Diversifies C6 Volatile Profiles in Some Vitis vinifera Table Grape Cultivars.

C6 volatiles are synthesized through lipoxygenase-hydroperoxide lyase (LOX-HPL) pathway and these volatiles play important roles in the aromatic quality of grape berries. This study investigated the evolution of both C6 volatiles and the key genes in the LOX-HPL pathway in different table grape cultivars during the berry development period, and further assessed the correlation between the accumulation of C6 volatiles and the expression of these genes in these cultivars. Results showed that hexanal, (E)-2-hexenal, (E)-2-hexen-1-ol and (Z)-3-hexen-1-ol were found to be the dominant C6 volatiles in these ripened grape cultivars under two consecutive vintages, and their flavor notes were incorporated in the overall aroma of these cultivars. The cultivar "Xiangfei" showed the most abundant level of C6 aldehydes and C6 acid, whereas the cultivar "Tamina" and "Moldova" possessed the highest C6 alcohol content. The "Muscat of Alexandria" cultivar was found to contain the highest level of C6 esters. C6 volatiles were grouped into three evolutionary patterns in these cultivars during berry development, and their evolution was consistent with the evolution of the LOX-HPL pathway genes' expression. Pearson's correlation analysis indicated that the LOX-HPL-pathway-related genes were correlated to the accumulation of C6 volatiles in these cultivars, and VvLOXA appeared to be an important gene that regulated the synthesis of all C6 volatiles.

A systematic analysis strategy for accurate detection of anthocyanin pigments in red wines.

RATIONALE: To develop a reliable and accurate method for the identification of anthocyanins and their subsequent derivatives formed during red grape fermentation and wine maturation. METHODS: By using a Poroshell 120 EC-C18 column in a high-performance liquid chromatography/triple-quadrupole tandem mass spectrometry (HPLC/QqQ-MS/MS) system, combined with multiple reaction monitoring (MRM), it was possible to establish and validate a method for the determination of anthocyanin and a range of complex reaction products. A selected range of six 3-O-glucosidic anthocyanins were used as standards. A database was established from these results. Then various red wines were examined and quantified by this method. RESULTS: With the range of accuracy and precision being 86.97-111.39% and 0.09-4.32%, respectively, the HPLC/QqQ-MS/MS method was found to be a reliable method for anthocyanin detection. By using this HPLC/QqQ-MS/MS method combined with the inclusive database, accurate identification of 95 anthocyanin compounds of different families from various wine samples was systematically achieved in 29 min. CONCLUSIONS: By combining this analytical system with an inclusive database, it was possible to determine a wide range of anthocyanins and related complex derivatives for the first time. We consider that it should be possible to extend this method further to include more complex anthocyanins, and to other complex compounds. Copyright © 2016 John Wiley & Sons, Ltd.

Varietal Dependence of GLVs Accumulation and LOX-HPL Pathway Gene Expression in Four Vitis vinifera Wine Grapes.

Variety is one of the major factors influencing grape and wine aromatic characteristics. Green leaf volatiles (GLVs), derived from lipoxygenase-hydroperoxides lyase (LOX-HPL) pathway, are important components for the aromatic quality of grapes and wines. However, the varietal difference regarding GLVs accumulation and related gene expression are poorly studied. This work exhibited that the accumulation of various GLVs and the expression of LOX-HPL pathway genes in four Vitis vinifera wine grape cultivars: Syrah, Muscat Tchervine, Gewürztraminer and Chardonnay. The results showed a variety dependence of GLVs profile. Muscat Tchervine harvested grapes contained less C6 aldehydes and the most abundant esters, which corresponded to very low VvLOXA and VvHPL1 expression abundance as well as high VvAAT transcript in this variety. High expression level of both VvLOXA and VvHPL1 paralleled with higher level of C6 aldehydes together with higher alcohols in Syrah grape. Gewürztraminer and Chardonnay grapes had high aldehydes and alcohols as well as low esters, which were resulted from their higher expression level of VvLOXA or VvHPL1 and lower VvAAT. From these above corresponding relations, it is concluded that VvLOXA, VvHPL1 and VvAAT in the LOX-HPL pathway are targets for altering GLVs composition in the grape varieties.

Dibasic Ammonium Phosphate Application Enhances Aromatic Compound Concentration in Bog Bilberry Syrup Wine.

A nitrogen deficiency always causes bog bilberry syrup wine to have a poor sensory feature. This study investigated the effect of nitrogen source addition on volatile compounds during bog bilberry syrup wine fermentation. The syrup was supplemented with 60, 90, 120 or 150 mg/L dibasic ammonium phosphate (DAP) before fermentation. Results showed that an increase of DAP amounts accelerated fermentation rate, increased alcohol content, and decreased sugar level. Total phenol and total flavonoid content were also enhanced with the increase of DAP amounts. A total of 91 volatile compounds were detected in the wine and their concentrations were significantly enhanced with the increase of DAP. Ethyl acetate, isoamyl acetate, phenethyl acetate, ethyl butanoate, ethyl hexanoate, ethyl octanoate, ethyl decanoate, isobutanol, isoamyl alcohol, levo-2,3-butanediol, 2-phenylethanol, meso-2,3-butanediol, isobutyric acid, hexanoic acid, and octanoic acid exhibited a significant increase of their odor activity value (OAV) with the increase of DAP amounts. Bog bilberry syrup wine possessed fruity, fatty, and caramel flavors as its major aroma, whereas a balsamic note was the least present. The increase of DAP amounts significantly improved the global aroma attributes, thereby indicating that DAP supplementation could promote wine fermentation performance and enhance the sensory quality of bog bilberry syrup wine.

Polyphenolic Compositions and Chromatic Characteristics of Bog Bilberry Syrup Wines.

Phenolic compounds determine the color quality of fruit wines. In this study, the phenolic compound content and composition, color characteristics and changes during 6 months of bottle aging were studied in wines fermented with bog bilberry syrup under three different pHs. The total anthocyanins and total phenols were around 15.12-16.23 mg/L and 475.82 to 486.50 mg GAE/L in fresh wines and declined 22%-31% and about 11% in bottle aged wines, respectively. In fresh wines, eight anthocyanins, six phenolic aids and 14 flavonols, but no flavon-3-ols were identified; Malvidin-3-O-glucoside, petunidin-3-O-glucoside and delphinium-3-O-glucoside were the predominant pigments; Chlorogentic acid was the most abundant phenolic acid, and quercetin-3-O-galactoside and myricetin-3-O-galactoside accounted for nearly 90% of the total flavonols. During 6 months of bottle storage, the amounts of all the monomeric anthocyanins and phenolic acids were reduced dramatically, while the glycosidyl flavonols remained constant or were less reduced and their corresponding aglycones increased a lot. The effects of aging on blueberry wine color were described as the loss of color intensity with a dramatic change in color hue, from initial red-purple up to final red-brick nuances, while the pH of the fermentation matrix was negatively related to the color stability of aged wine.

Identification of a plastid-localized bifunctional nerolidol/linalool synthase in relation to linalool biosynthesis in young grape berries.

Monoterpenoids are a diverse class of natural products and contribute to the important varietal aroma of certain Vitis vinifera grape cultivars. Among the typical monoterpenoids, linalool exists in almost all grape varieties. A gene coding for a nerolidol/linalool (NES/LINS) synthase was evaluated in the role of linalool biosynthesis in grape berries. Enzyme activity assay of this recombinant protein revealed that it could convert geranyl diphosphate and farnesyl diphosphate into linalool and nerolidol in vitro, respectively, and thus it was named VvRILinNer. However, localization experiment showed that this enzyme was only localized to chloroplasts, which indicates that VvRILinNer functions in the linalool production in vivo. The patterns of gene expression and linalool accumulation were analyzed in the berries of three grape cultivars ("Riesling", "Cabernet Sauvignon", "Gewurztraminer") with significantly different levels of monoterpenoids. The VvRILinNer was considered to be mainly responsible for the synthesis of linalool at the early developmental stage. This finding has provided us with new knowledge to uncover the complex monoterpene biosynthesis in grapes.

Identification of SNP loci and candidate genes genetically controlling norisoprenoids in grape berry based on genome-wide association study.

Obtaining new grapevine varieties with unique aromas has been a long-standing goal of breeders. Norisoprenoids are of particular interest to wine producers and researchers, as these compounds are responsible for the important varietal aromas in wine, characterized by a complex floral and fruity smell, and are likely present in all grape varieties. However, the single-nucleotide polymorphism (SNP) loci and candidate genes genetically controlling the norisoprenoid content in grape berry remain unknown. To this end, in this study, we investigated 13 norisoprenoid traits across two years in an F1 population consisting of 149 individuals from a hybrid of Vitis vinifera L. cv. Muscat Alexandria and V. vinifera L. cv. Christmas Rose. Based on 568,953 SNP markers, genome-wide association analysis revealed that 27 candidate SNP loci belonging to 18 genes were significantly associated with the concentrations of norisoprenoid components in grape berry. Among them, 13 SNPs were confirmed in a grapevine germplasm population comprising 97 varieties, including two non-synonymous mutations SNPs within the VvDXS1 and VvGGPPS genes, respectively in the isoprenoid metabolic pathway. Genotype analysis showed that the grapevine individuals with the heterozygous genotype C/T at chr5:2987350 of VvGGPPS accumulated higher average levels of 6-methyl-5-hepten-2-one and ß-cyclocitral than those with the homozygous genotype C/C. Furthermore, VvGGPPS was highly expressed in individuals with high norisoprenoids concentrations. Transient overexpression of VvGGPPS in the leaves of Vitis quinquangularis and tobacco resulted in an increase in norisoprenoid concentrations. These findings indicate the importance of VvGGPPS in the genetic control of norisoprenoids in grape berries, serving as a potential molecular breeding target for aroma.

Sub-Regional Variation and Characteristics of Cabernet Sauvignon Wines in the Eastern Foothills of the Helan Mountain: A Perspective from Phenolics, Visual Properties and Mouthfeel.

As one of the most promising wine regions in China, the eastern foothills of the Helan Mountain (EFHM) in the Ningxia Hui Autonomous Region has attracted great attention recently. Geographically, EFHM is divided into six sub-regions, namely Shizuishan, Xixia, Helan, Qingtongxia, Yongning and Hongsipu. However, there have been few reports on the character and differences between wines in the six sub-regions. In this experiment, a total of 71 commercial Cabernet Sauvignon wines from six sub-regions were collected, and their phenolic compounds, visual properties and mouthfeel were investigated. The results showed that wines from the six sub-regions of EFHM showed distinctive phenolic profiles and could be distinguished through the OPLS-DA mode using 32 potential markers. In terms of color, Shizuishan wines showed higher a* values and lower b* values. The sensory evaluation showed that Hongsipu wines had higher astringency strength and lower tannin texture. The overall results implied that the phenolic compounds of wines in different sub-regions were affected by terroir conditions. To the best of our knowledge, this is the first time that a wide coverage of phenolic compounds has been analysed for wines from the sub-regions of EFHM, which could provide valuable information in deciphering the terroir of EFHM.

Isolation and characterization of two hydroperoxide lyase genes from grape berries : HPL isogenes in Vitis vinifera grapes.

C6 compounds are the major fraction of the volatile profiles of grape berries, contributing the typical 'green' aroma to the grape and wine. Hydroperoxide lyase (HPL) catalyzes the cleavage of fatty acid hydroperoxides to produce C6 compounds. Two hypothetical genes, VvHPL1 and VvHPL2 were cloned from grape berries (Vitis vinifera L. Cabernet Sauvignon). Bioinformatics analysis revealed that the proteins encoded by these two genes both belong to subfamily of cytochrome P450 and contain typical conserved domains of HPLs, and have high identity with HPLs from other plants. Prokaryotically-expressed VvHPL1 and VvHPL2 with thioredoxin-6xHis-fusion partner were confirmed to have enzymatic activity. VvHPL1 is specific for 13-HPOD (T) producing C6 aldehydes with relatively higher activity and VvHPL2 catalyzes the cleavage of both 9- and 13-hydroperoxides producing C6 aldehydes and C9 aldehydes respectively. Analysis of real time-PCR showed that VvHPL2 was highly expressed in the leaves and the flowers of the grapes, while relatively low transcript abundance was detected in the berries, tendril and stems; VvHPL1 had high expression in all detected tissues. During grape berry development, the expression of these two isogenes presented similar trends with a rapid increase after veraison and a decrease at full-ripen stage, which roughly corresponded to the accumulation of their volatile products. These data lay an essential foundation for further study on the accumulation and control of C6 volatiles in grape berries.

Molecular cloning and expression of gene encoding aromatic amino acid decarboxylase in 'Vidal blanc' grape berries.

The pleasantly fruity and floral 2-phenylethanol are a dominant aroma compound in post-ripening 'Vidal blanc' grapes. However, to date little has been reported about its synthetic pathway in grapevine. In the present study, a full-length cDNA of VvAADC (encoding aromatic amino acid decarboxylase) was firstly cloned from the berries of 'Vidal blanc', an interspecific hybrid variety of Vitis vinifera × Vitis riparia. This sequence encodes a complete open reading frame of 482 amino acids with a calculated molecular mass of 54 kDa and isoelectric point value (pI) of 5.73. The amino acid sequence deduced shared about 79% identity with that of aromatic L: -amino acid decarboxylases (AADCs) from tomato. Real-time PCR analysis indicated that VvAADC transcript abundance presented a small peak at 110 days after full bloom and then a continuous increase at the berry post-ripening stage, which was consistent with the accumulation of 2-phenylethanol, but did not correspond to the trends of two potential intermediates, phenethylamine and 2-phenylacetaldehyde. Furthermore, phenylalanine still exhibited a continuous increase even in post-ripening period. It is thus suggested that 2-phenylethanol biosynthetic pathway mediated by AADC exists in grape berries, but it has possibly little contribution to a considerable accumulation of 2-phenylethanol in post-ripening 'Vidal blanc' grapes.

Molecular characterization and expression analysis on two isogenes encoding 3-deoxy-D-arabino-heptulosonate 7-phosphate synthase in grapes.

3-Deoxy-D-arabino-heptulosonate 7-phosphate synthase (DAHPS) is an entry enzyme of the shikimate pathway that connects primary carbohydrate metabolism with the biosynthesis of most secondary metabolites in plants. In the present study, two DAHPS cDNAs were cloned from grape berries (Vitis vinifera) and designated as VvDAHPS-1 and VvDAHPS-2. These two cDNA sequences share 75.7% of the identities. Their DNA corresponding to the two isogenes both contain four introns. The deduced proteins from two cDNAs had different NH(4)-terminal regions and putative mature regions sharing sequence, molecular size and pI value similarity. Both of VvDAHPSs had a close evolution relationship with Populus trichocarpa DAHPSs. The prokaryotically-expressed VvDAHPSs both manifested DAHPS catalytic activity and Mn(2+)-activated effects. Analysis by real time-PCR showed that VvDAHPS-1 and VvDAHPS-2 were expressed in all the tested tissues, but their expression patterns accompanying with berry mature varied in the skin, pulp and seeds. The results give new insight into further study on regulatory mechanism of grape phenolics biosynthesis.

The influence of NaCl on the dynamic perception of the pungency sensation elicited by Sichuan pepper oleoresins.

A cross-modal interaction may exist between the perception of saltiness and the pungency elicited by Sichuan pepper oleoresin (Spo). Thirty-one hypersensitive panelists were selected to participate in this study. Spo solutions dissolved in different NaCl concentrations, ranging from 1.25 g/L to 167.9 g/L, were used as the test samples. The rated difference from control, the generalized labeled magnitude scale (gLMS), and the time-intensity (TI) method were used to determine the detection threshold (DT), the recognition threshold (RT), the intensity, and the dynamic perception of pungent sensation. The results revealed that the pungency thresholds increased significantly (p < 0.01) in the solution with a high NaCl (167.9 g/L) concentration. Furthermore, high NaCl solutions suppressed the pungency intensity at all Spo concentrations except for 0.02 g Spo/L in water (p < 0.05). The TI and principal component analysis (PCA) results showed that an increase in the Spo concentration prolonged the duration of the pungency sensation. However, the maximum intensity, the time to reach maximum intensity, the decay time of perception, and the end time of perception of the Spo solutions ranging from 2.13 g/L to 4.69 g/L were significantly reduced at medium (42.95 g/L) and high NaCl concentrations. Since the salty and pungency sensations exhibited by NaCl and Spo are common flavor combinations in food products and dishes, studying the influence of saltiness on the dynamic perception of pungent sensation not only aids the development of oral cleaners during pungency evaluation but also presents significant theoretical and practical value in creating pungent food and cuisine based on consumer preferences.

Characterization of free and glycosidically bound volatile compounds, fatty acids, and amino acids in Vitis davidii Foex grape species native to China.

Berries of six Vitis davidii Foex (spine grape) cultivars ('Baiputao', 'Gaoshan 1', 'Gaoshan 2', 'Seputao', 'Miputao', and 'Tianputao') were harvested from a commercial vineyard in Hunan Province in China. Free and bound volatile compounds and fatty acids were analyzed by GC-MS, and amino acids were analyzed by HPLC. 'Tianputao' and 'Miputao' were characterized by relatively higher concentrations of aromatic amino acids and lower concentrations of branched-chain amino acids. The major free volatile compounds of spine grapes were hexanal, (E)-2-hexenal, 1-hexanol, (E)-2-hexenol, (E)-ß-damascenone, and benzeneacetaldehyde. The major glycosidically bound volatile compounds identified were 1-hexanol, menthol, nerol, 1-butanol, 3-methyl-3-butenol, benzenemethanol, ß-phenylethanol, eugenol, and guaiacol. (E)-ß-damascenone, benzeneacetaldehyde, guaiacol, and eugenol had odor activity values (OAVs) > 1 in all cultivar grapes. Partial least squares discriminant analysis (PLS-DA) revealed 'Tianputao' to be distinct from the other cultivars due to its relatively higher concentrations of major terpenoids, norisoprenoids, higher alcohols, and aromatic amino acids.

Characterization and differentiation of key odor-active compounds of 'Beibinghong' icewine and dry wine by gas chromatography-olfactometry and aroma reconstitution.

Freezing-thawing events contribute to the unique aroma profile of icewines. Differences in key odor-active volatile compounds between 'Beibinghong' (Vitis amurensis × V. vinifera) icewines and dry wines were investigated by gas chromatography-olfactometry and gas chromatography-mass spectrometry. Acceptable agreement between the olfactometric and quantitative results was obtained. 'Beibinghong' icewine was characterized by high concentrations of volatile phenols, lactones, (E)-ß-damascenone, and phenylacetaldehyde, which were associated with on-vine freezing-thawing events in grape. Low concentrations of higher alcohol acetates and ethyl esters of fatty acids were attributed to hyperosmotic stress during fermentation. The overall aroma of icewine could be mimicked by reconstitution containing 44 identified volatiles. Partial least squares regression analysis demonstrated that the concentrations of these volatile compounds determined the distinct sensory profiles of icewines, which have higher intensities of honey/sweet, smoky, caramel, dried fruit, apricot/peach, and floral aromas, and lower intensities of fresh fruity and herbaceous notes in comparison with dry wines.

Phenolic Analysis and Theoretic Design for Chinese Commercial Wines' Authentication.

To develop a robust tool for Chinese commercial wines' varietal, regional, and vintage authentication, phenolic compounds in 121 Chinese commercial dry red wines were detected and quantified by using high-performance liquid chromatography triple-quadrupole mass spectrometry (HPLC-QqQ-MS/MS), and differentiation abilities of principal component analysis (PCA), partial least squares discriminant analysis (PLS-DA), and orthogonal partial least squares discriminant analysis (OPLS-DA) were compared. Better than PCA and PLS-DA, OPLS-DA models used to differentiate wines according to their varieties (Cabernet Sauvignon or other varieties), regions (east or west Cabernet Sauvignon wines), and vintages (young or old Cabernet Sauvignon wines) were ideally established. The S-plot provided in OPLS-DA models showed the key phenolic compounds which were both statistically and biochemically significant in sample differentiation. Besides, the potential of the OPLS-DA models in deeper sample differentiating of more detailed regional and vintage information of wines was proved optimistic. On the basis of our results, a promising theoretic design for wine authentication was further proposed for the first time, which might be helpful in practical authentication of more commercial wines. PRACTICAL APPLICATION: The phenolic data of 121 Chinese commercial dry red wines was processed with different statistical tools for varietal, regional, and vintage differentiation. A promising theoretical design was summarized, which might be helpful for wine authentication in practical situation.

Free and glycosidically bound volatile compounds in sun-dried raisins made from different fragrance intensities grape varieties using a validated HS-SPME with GC-MS method.

The conditions of sample pretreatments and HS-SPME for extracting volatile compounds from raisins were optimized, and the method was validated in the study. Free and glycosidically bound volatile compounds in three different fragrance intensities raisins were analysed using this method. There were 91 compounds identified, and 72, 26 and 8 of these compounds came from fresh grapes, the auto-oxidation of unsaturated fatty acids (UFAO) and the Maillard reaction, respectively. The aroma profiles of Thompson Seedless raisins (TSRs) and Centennial Seedless raisins (CSRs) were similar, while the floral, fruity, green and roasted aromas of CSRs were higher than those of TSRs due to the contributions of benzeneacetaldehyde, 2-pentylfuran, (E)-2-nonenal and 3-ethyl-2,5-dimethyl pyrazine. Decanal, rose oxide, geraniol, linalool and ß-damascenone made the floral and fruity aromas of Zixiang Seedless raisins (ZSRs) greater than those in TSRs and CSRs, but the green and roasted aroma intensities of ZSRs were lower.

Striking changes in volatile profiles at sub-zero temperatures during over-ripening of 'Beibinghong' grapes in Northeastern China.

The evolution of free and glycosidically bound volatile compounds in 'Beibinghong' (Vitis vinifera×Vitis amurensis) grape berries throughout on-vine over-ripening and freezing processes was studied in two vintages. The aroma profiles of 'Beibinghong' icewine berries were characterized by C6 compounds, higher alcohols and terpenoids in free fractions and carbonyl compounds, higher alcohols, C6 alcohols and terpenoids in bound fractions. With regard to free volatile compounds, there was a decrease in the concentration of C6 compounds, terpenols and norisoprenoids and an increase of terpene oxides during over-ripening process. A striking alteration of volatile profile occurred at sub-zero temperatures, particularly for the free fractions such as C6 alcohols, higher alcohols and oxidative terpene derivatives. These changes were attributed to a series of reactions (biotransformation, oxidation and anaerobic metabolism) induced by water loss and especially freeze-thaw cycles. PCA revealed temperature and rainfall affected the accumulation of volatile compounds during over-ripening processes.

Role of glucose-6-phosphate dehydrogenase in freezing-induced freezing resistance of Populus suaveolens.

To explore the role of glucose-6-phosphate dehydrogenase (G6PDH, EC 1.1.1.49) in the enhancement of freezing resistance induced by freezing acclimation, G6PDH was purified from the leaves of 8-week-old Populus suaveolens cuttings. The G6PDH activity in the absence or the presence of reduced dithiothreitol (DTT(red)) were determined, and the changes in superoxide dismutase (SOD), peroxides (POD) and cytosolic G6PDH activities, malondial-dehyde (MDA) content as well as freezing resistance (expressed as LT(50)) of P. suaveolens cuttings during freezing acclimation at -20 degrees C were investigated. The results showed that the purified G6PDH was probably located in the cytosol of P. suaveolens. Freezing acclimation increased the activities of SOD, POD and cytosolic G6PDH, and decreased the MDA content and LT(50) of cuttings, while 2 d of de-acclimation at 25 degrees C resulted in a decrease in SOD, POD and cytosolic G6PDH activities, and caused an increase in MDA content and LT(50). The change in cytosolic G6PDH activity was found to be closely correlated to the levels of SOD, POD and MDA, and to the degree of freezing resistance of cuttings during freezing acclimation. It is suggested that the enhancement of freezing resistance of cuttings induced by freezing acclimation is related to the distinct increase in cytosolic G6PDH activity, which may be involved in the activation of SOD and POD, and the induction of freezing resistance of cuttings.

Study of free and glycosidically bound volatile compounds in air-dried raisins from three seedless grape varieties using HS-SPME with GC-MS.

Volatile compounds in air-dried raisins from Turpan, China were analysed, with 77 volatiles identified in Flame Seedless, Thompson Seedless, and Crimson Seedless raisins, 37 of which had never been reported as raisin volatiles. Odour activity values (OAVs) of these volatiles were calculated; 20 compounds had OAVs above 1. The aroma characters of the three varieties were quite similar except for some differences in the intensity of each aroma character. The main free-form volatiles were ethyl acetate, hexanoic acid, (E,E)-2,4-heptadienal and geraniol, with ß-damascenone, 3-ethyl-2,5-dimethylpyrazine, 1-octen-3-ol and hexanal making the highest contribution to the aroma. Fruity and floral were the main characteristics of the free-form aromas in raisins. The main bound-form volatiles were benzyl alcohol and acetoin, with ß-damascenone contributing most to the bound-form aromas, enhancing the floral, fruity and fatty aroma.