Spectrophotometric method for exploring 3-methyl-2-butene-1-thiol (MBT) formation in lager

The disappearance of riboflavin absorbance at 445 nm from beers or model beers on light exposure is directly linked to light-struck character formation. The addition of (+)-catechin, (-)-epicatechin, tryptophol, or ascorbic acid was able to reduce, but not stop, absorbance loss or light-struck character formation in either model beer or mainstream lager that was exposed to light. When isohumulone was present in model beer, the inhibitory effect of (+)-catechin, (-)-epicatechin, or tryptophol decreased with increasing isohumulone. The spectrophotometric method used in this study is a simple and effective method for determining light-struck susceptibility.     

(+)-Catechin-aldehyde condensations: competition between acetaldehyde and glyoxylic acid

(+)-Catechin reaction with two aldehydes (acetaldehyde and glyoxylic acid) was studied in winelike model solution. The two aldehydes were reacted either individually or together with (+)-catechin and in molar excess. The reactions were followed by HLPC-UV and HPLC-ESI/MS to monitor (+)-catechin disappearance as well as dimer and polymer appearance. In all reactions a reaction order of close to 1 for (+)-catechin disappearance was observed. (+)-Catechin disappearance was slower in the presence of acetaldehyde (t(1/2) = 6.7 +/- 0.2 h) compared to glyoxylic acid (t(1/2) = 2.3 +/- 0.2 h). When the two aldehydes were reacted together, (+)-catechin disappearance was faster (t(1/2) = 2.2 +/- 0.5 h). When aldehydes were reacted separately, the dimer appearance was independent of the type of aldehyde used but the ethyl-bridged dimer disappearance was slower with acetaldehyde. When aldehydes were reacted together, the dimer appearance changed. Ethyl-bridged dimers appeared before carboxymethine-bridged dimers, and their disappearance occurred earlier. Copolymers containing both ethyl and carboxymethine bridges were also observed.     

Identification of procyanidins and anthocyanins in blueberries and cranberries (Vaccinium spp.) using high-performance liquid chromatography/mass spectrometry

Blueberries and cranberries were analyzed for procyanidins using normal-phase HPLC/MS. Monomers, identified as (+)-catechin and (-)-epicatechin, and a series of oligomers were detected in blueberries, and MS data confirmed that the oligomers consisted of (epi)catechin units that were exclusively singly linked (B-type). The procyanidin "fingerprints" were similar for Tifblue and Rubel but higher than that for lowbush blueberries. In whole cranberries, (-)-epicatechin was present, along with a complex series of oligomers. Both A-type (contained only one double linkage per oligomer) and B-type oligomers were present. Two commercial cranberry juices exhibited similar procyanidin profiles, except that one contained increased quantities. There were processing effects on the procyanidin content of cranberry extract and juices when compared to those of the unprocessed fruits. Monomer, dimers, and A-type trimers were the primary procyanidins, with only trace levels of the B-type trimers and A-type tetramers and with an absence of the higher oligomers in cranberry extract and juices.     

The role of copper(II) in the bridging reactions of (+)-catechin by glyoxylic acid in a model white wine

The influence of copper(II) on the bridging reactions between (+)-catechin and glyoxylic acid was studied in a white wine-like medium. When the reaction was performed in darkness at 45 degrees C, copper(II) increased the maximum levels of carboxymethine-linked (+)-catechin dimer and xanthylium cation pigment as monitored by high-performance liquid chromatography/photodiode array detection (HPLC/DAD) and liquid chromatography/mass spectrometry (LC/MS). At 10 degrees C, similar results were observed except that the xanthene intermediate was monitored and found to also increase in concentration at higher copper(II) concentrations. The kinetics for the formation of these species suggested that copper(II) accelerated the bridging of two (+)-catechin units by glyoxylic acid. The acid group of glyoxylic acid allowed copper(II) to influence this reaction, as no copper(II) enhancement was observed when acetaldehyde was used in place of glyoxylic acid.     

Competition between (+)-catechin and (-)-epicatechin in acetaldehyde-induced polymerization of flavanols.

The reactions of (+)-catechin and (-)-epicatechin in the presence of acetaldehyde were studied in model solution systems. When incubated separately with acetaldehyde and at pH values varying from 2.2 to 4. 0, reactions were faster with (-)-epicatechin than with (+)-catechin. In mixtures containing both (+)-catechin and (-)-epicatechin with acetaldehyde, new compounds besides the homogeneous bridged derivatives were detected. These compounds were concluded to be hetero-oligomers consisting of (+)-catechin and (-)-epicatechin linked with an ethyl bridge. In this case, the reaction of (-)-epicatechin was faster than that of (+)-catechin. This was also observed in solutions containing the two flavanols and the (+)-catechin-ethanol intermediate. Under these conditions, the homogeneous (+)-catechin bridged dimers and heterogeneous dimers were obtained by action of the intermediate on (+)-catechin and (-)-epicatechin, respectively. In addition, the homogeneous (-)-epicatechin ethyl-bridged dimers were also detected, showing that ethyl linkages underwent depolymerization and recombination reactions.     

Novel oxidations of (+)-catechin by horseradish peroxidase and laccase

Horseradish peroxidase (HRP; EC 1.11.1.7) catalyzed the H(2)O(2)-dependent oxidative coupling of (+)-catechin 1 to form three different biphenyl C-C dimers 2-4, whereas Rhus vernicifera laccase catalyzed the formation of two new catechin-hydroquinone adducts 5 and 6. Spectroscopic evidence showed that HRP dimers were linked through position 8 of the A-ring of one catechin moiety to C-5' of ring B in 2 and 4 and to C-2 of ring C in 3. The unusual catechin dicarboxylic acid dimer 4 was obtained by ortho cleavage of the E-ring. Hydroquinone served as both a shuttle oxidant and a reactant by coupling at C-2' and C-5' of the catechin B-ring during laccase oxidations. HRP and laccase oxidation products were compared to D,L-alpha-tocopherol and (+)-catechin for their abilities to inhibit iron-induced lipid peroxidation in rat brain homogenates and Fe(3+)-ADP/NADPH in rat liver microsomes, as measured by the intensity of thiobarbituric acid reactive substance. All metabolites exhibited anti-lipid peroxidation with IC(50) values approximately 2-8 times higher than those of standard compounds. Characteristic reaction products may prove to be novel markers for (+)-catechin antioxidant reactions in living systems.     

Impact of glutathione on the formation of methylmethine- and carboxymethine-bridged (+)-catechin dimers in a model wine system

This study was performed to assess the impact of glutathione on the reaction between (+)-catechin and carbonyl compounds in wine-related conditions. (+)-Catechin (0.50 mM) and either glyoxylic acid (0.25 mM) or acetaldehyde (0.25 mM) were added to a model wine system with 0.0, 0.25, and 2.5 mM of glutathione added. UPLC-DAD and LC-MS analysis showed that the formation of carbonyl-bridged (+)-catechin dimers was inhibited in the samples with a glutathione to carbonyl ratio of 10:1 compared to the samples without glutathione. At a ratio of 1:1, glutathione inhibited the acetaldehyde-bridged dimers but only had a minor impact on the glyoxylic acid-bridged dimers. Further investigations showed that this trend of inhibition by glutathione on the glyoxylic acid-derived dimer was independent of temperatures, 20 °C vs 45 °C, or the presence of metal ions, 0.2 mg/L copper(II) and 5 mg/L iron(II). (1)H NMR analysis and LC-MS analysis provided evidence that glutathione inhibited dimer formation via different mechanisms depending on the carbonyl compound. For acetaldehyde-derived dimers, the main mode of inhibition was the ability of glutathione to form a (methyl-glutathionyl-methine)-(+)-catechin complex. Alternatively, the formation of a glutathione-glyoxylic acid addition product impeded the reaction between glyoxylic acid with (+)-catechin. These results demonstrate that glutathione, at sufficient concentration, can have a substantial impact on carbonyl-derived polymerization reactions in wine-like conditions.     

Identification of adducts between an odoriferous volatile thiol and oxidized grape phenolic compounds: kinetic study of adduct formation under chemical and enzymatic oxidation conditions

HPLC-MS and (1)H, (13)C, and 2D NMR analyses were used to identify new addition products between 3-sulfanylhexan-1-ol (3SH) and o-quinones derived from (+)-catechin, (-)-epicatechin, and caftaric acid. The kinetics of formation of these adducts were monitored in a wine model solution and in a must-like medium by HPLC-UV-MS with the aim of understanding the chemical mechanism involved in reactions between volatile thiols and o-quinones. One o-quinone-caftaric acid/3SH adduct, three o-quinone-(+)-catechin/3SH adducts, and three o-quinone-(-)-epicatechin/3SH adducts were characterized. Caftaric acid was oxidized faster than (-)-epicatechin and (+)-catechin when these phenolic compounds were incubated in a one-component mixture with polyphenoloxidase (PPO) in the presence of 3SH. Consequently, o-quinone-caftaric acid formed adducts with 3SH more rapidly than o-quinone-(+)-catechin and o-quinone-(-)-epicatechin in the absence of other nucleophilic species. Furthermore, o-quinone-(-)-epicatechin reacted faster than o-quinone-(+)-catechin with 3SH. Sulfur dioxide decreased the yield of adduct formation to a significant extent. Under chemical oxidation conditions, the rates and yields of adduct formation were lower than those observed in the presence of PPO, and o-quinone-caftaric acid was slightly less reactive with 3SH, compared to oxidized flavan-3-ols. The identification of o-quinone-caftaric acid/3SH and o-quinone-(+)-catechin/3SH adducts in a must matrix suggests that the proposed reaction mechanism is responsible for 3SH loss in dry wines during their vinification and aging process.     

Furfuryl ethyl ether: important aging flavor and a new marker for the storage conditions of beer

Recently, it was reported that furfuryl ethyl ether is an important flavor compound indicative of beer storage and aging conditions. A study of the reaction mechanism indicates that furfuryl ethyl ether is most likely formed by protonation of furfuryl alcohol or furfuryl acetate followed by S(N)2-substitution of the leaving group by the nucleophilic ethanol. For the reaction in beer, a pseudo-first-order reaction kinetics was derived. A close correlation was found between the values predicted by the kinetic model and the actual furfuryl ethyl ether concentration evolution during storage of beer. Furthermore, 10 commercial beers of different types, aged during 4 years in natural conditions, were analyzed, and it was found that the furfuryl ethyl ether flavor threshold was largely exceeded in each type of beer. In these natural aging conditions, lower pH, darker color, and higher alcohol content were factors that enhanced furfuryl ethyl ether formation. On the other hand, sulfite clearly reduced furfuryl ethyl ether formation. All results show that the furfuryl ethyl ether concentration is an excellent time-temperature integrator for beer storage.     

Hydrogen peroxide and flavan-3-ols in storage roots of cassava (Manihot esculenta crantz) during postharvest deterioration

Cassava storage roots are an important staple food throughout the lowland humid tropics. However, cassava suffers from a poorly understood storage disorder, known as postharvest physiological deterioration (PPD), which constrains its exploitation. In an attempt to broaden the understanding of PPD, nine different cassava cultivars were analyzed for specific compounds accumulating during the process. The production of hydrogen peroxide (H(2)O(2)) is involved in the early stages of PPD in cassava roots. H(2)O(2) was quantified and localized histochemically at the tissue and cell level in deteriorating roots. This reactive oxygen species accumulated during the first 24 h after harvest, especially in the inner parenchymatic tissue. Three flavan-3-ols, (+)-catechin, (+)-catechin gallate, and (+)-gallocatechin, accumulated during the storage of cassava roots. However, these potential antioxidants cannot be related to early storage disorders or wound responses because they start to accumulate only after 4-6 days.     

茶叶添加方式对酿造啤酒理化特性及感官品质的影响

在啤酒酿造工艺的煮沸和主发酵阶段分别添加乌龙茶,探讨茶叶不同添加方式对啤酒理化特性、抗氧化能力、啤酒贮存稳定性以及感官特性的影响。结果显示,与未添加茶叶的啤酒产品(对照组CG)相比,在煮沸阶段(煮沸添加组BG)和主发酵阶段(主发酵添加组MG)分别添加0.3g/L的茶叶均提高了酵母发酵速率;添加茶叶的两个茶啤酒产品(煮沸添加组和主发酵添加组)的DPPH自由基清除能力分别提升至82.74%和89.21%、ABTS+自由基清除能力分别提升至41.53%和51.49%、铁离子还原能力分别提升至36.49和43.83 mg/L,且成品茶啤酒贮藏期间的抗老化能力提高;茶啤酒中总酚以及儿茶素(EGC、C、EGCG、EC、GCG、ECG)和咖啡碱(CAF)含量升高,其中,主发酵添加组茶啤酒样品总酚和EGCG含量显著高于对照组和煮沸添加组啤酒(P0.05),分别达到734.40和8.43 mg/L。进一步的感官品评结果显示添加茶叶提高了啤酒产品的茶香气和茶滋味,其中主发酵添加组啤酒的茶香气、茶滋味及酒体协调性最好。由此可知,在啤酒酿造工艺中添加茶叶提高了酵母发酵速率,增强了啤酒中酚类物质含量及其抗氧化和抗老化性能,同时也为啤酒增添了新的茶风味产品。     

Comparative study of the products of the peroxidase-catalyzed and the polyphenoloxidase-catalyzed (+)-catechin oxidation. Their possible implications in strawberry (Fragaria x ananassa) browning reactions

The peroxidase- and polyphenoloxidase-catalyzed oxidations of (+)-catechin yield several products showing different degrees of polymerization, which are apparently responsible for the pigment decay and the associated browning reaction that occurs in processed strawberry fruits and their derived foods. In this work, we have purified both peroxidase and polyphenoloxidase from Oso Grande cv. strawberry fruits, and comparatively analyzed the products of their enzyme-mediated (+)-catechin oxidation. The joint analysis by reversed-phase and size-exclusion HPLC of the (+)-catechin oxidation products obtained with both enzymes indicate that they were qualitatively the same: dehydrodicatechin B4, a (+)-catechin quinone methide, dehydrodicatechin A, a (+)-catechin trimer, and a (+)-catechin oligomer with polymerization degree equal to or greater than 5. The main quantitative differences between the oxidative reactions were the great amount of oligomer formed in the case of the polyphenoloxidase-mediated reaction and the low amount of (+)-catechin reacted in the case of the peroxidase-mediated reaction. One of the possible reasons for such low levels of (+)-catechin consumption in the case of the peroxidase-mediated reaction was the possible inhibition by products of the enzyme-catalyzed oxidation. In fact, the peroxidase-mediated (+)-catechin oxidation was differentially inhibited by dehydrodicatechin A, showing a competitive type inhibition and a k(I) of 6.4 microM. In light of these observations, these results suggest that brown polymer formation, estimated as oligomeric compounds resulting from (+)-catechin oxidation, in strawberries is mainly due to polyphenoloxidase, and although peroxidase also plays an important role, it is apparently auto-regulated by product (dehydrodicatechin A) inhibition.     

Yeast-induced inhibition of (+)-catechin and (-)-epicatechin degradation in model solutions

(+)-catechin and (-)-epicatechin degradation in water-alcohol solutions containing Fe2+ and tartaric acid was studied in the presence and absence of yeasts. On the basis of the results, yeast partially inhibited the degradation of both flavans, with much slower formation of browning products absorbing at 420 and 520 nm. In comparative terms, yeast was found to be more efficient toward the degradation products of (+)-catechin absorbing at the latter wavelength. Likewise, the presence of yeast decreased the yield of a group of colored compounds eluting at high retention times in HPLC and indicated these as important contributors to color darkening in white wines. This inhibitory effect may in part account for the resistance to browning observed over periods of several years in sherry wines subjected to biological aging under flor yeast.     

Role of vinylcatechin in the formation of pyranomalvidin-3-glucoside-+-catechin

Reactions between malvidin-3-glucoside (mv3glc) and 8-vinylcatechin were carried out to synthesize pyranomv3glc-(+)-catechin pigment and to study the formation of intermediates. A rapid decrease of mv3glc content concomitant with the formation of more complex structures such as mv3glc-vinylcatechin [precursor of pyranomv3glc-(+)-catechin pigment] and mv3glc-divinylcatechin was observed. On the other hand, 8-vinylcatechin undergoes acid-catalyzed dimerization in model wine solution, giving rise to 8-vinylcatechin dimers. These compounds were also found in the reaction between mv3glc and (+)-catechin mediated by acetaldehyde, which provides evidence for the formation of 8-vinylcatechin and its involvement in the formation of pyranoanthocyanins in aged red wines.     

Colorimetric sensor arrays for the analysis of beers: a feasibility study

Eighteen commercial beers have been analyzed in both liquid and gas phases using colorimetric sensor arrays made from selected chemically responsive dyes printed on a hydrophobic membrane. Digital imaging of the dye array before and after exposure to the complex analytes in either the liquid phase or the head-gas provides a color change profile as a unique fingerprint for the specific analyte. The digital data libraries generated were analyzed using statistical and chemometric methods, including principal component analysis (PCA) and hierarchical clustering analysis (HCA). In either liquid- or gas-phase experiments, facile identification of specific beers was achieved using comparison of the color change profiles; using HCA statistical analysis the error rate of identification was <3%. Differentiation between even very similar beers proved to be straightforward. In addition, differentiation of pristine beer from the effects of watering or decarbonation proved to be possible. These results suggest that colorimetric sensor arrays may prove to be useful for quality assurance/quality control applications of beers and perhaps other beverages.     

Catechin contents of foods commonly consumed in The Netherlands. 2. Tea, wine, fruit juices, and chocolate milk

Catechins, compounds that belong to the flavonoid class, are potentially beneficial to human health. To enable an epidemiological evaluation of catechins, data on their contents in foods are required. HPLC with UV and fluorescence detection was used to determine the levels of (+)-catechin, (-)-epicatechin, (+)-gallocatechin (GC), (-)-epigallocatechin (EGC), (-)-epicatechin gallate (ECg), and (-)-epigallocatechin gallate (EGCg) in 8 types of black tea, 18 types of red and white wines, apple juice, grape juice, iced tea, beer, chocolate milk, and coffee. Tea infusions contained high levels of catechins (102-418 mg of total catechins/L), and tea was the only beverage that contained GC, EGC, ECg, and EGCg in addition to (+)-catechin and (-)-epicatechin. Catechin concentrations were still substantial in red wine (27-96 mg/L), but low to negligible amounts were found in white wine, commercially available fruit juices, iced tea, and chocolate milk. Catechins were absent from beer and coffee. The data reported here provide a base for the epidemiological evaluation of the effect of catechins on the risk for chronic diseases.     

Phenol antioxidant quantity and quality in foods: beers and the effect of two types of beer on an animal model of atherosclerosis

The free phenols have been measured in 15 lagers, 6 porters and ales, and 11 light and nonalcoholic beers. Phenols were measured colorimetrically using an oxidation-reduction reaction with Folin-Ciocalteu reagent and catechin as the standard. The order of phenol concentration was ales > lagers > low calorie > nonalcoholic. The quality of antioxidants of the major phenols in beers and the quality of beer antioxidants were measured by (1) dose-response inhibition of lower density lipoprotein oxidation and (2) concentration of phenols in the beers at which 50% of the peroxide was destroyed in a luminescent assay for antioxidant activity. The beers' lipoprotein antioxidant quality was clearly superior to that of vitamin antioxidants and to that of the phenol ingredients, suggesting synergism among the antioxidants in the mixture. The average per capita consumption of beer in the United States in 2000 was 225 mL/day, equivalent to 42 mg/day of catechin equivalents. Beer provides more antioxidants per day than wine in the U.S. diet. A dark beer and a lager beer were given at two concentrations to cholesterol-fed hamsters, an animal model of atherosclerosis. At the high dose ((1)/(2)-diluted beer) both lager and dark beer significantly inhibited atherosclerosis compared to a control of 2% alcohol. At the high dose, lager significantly decreased cholesterol and triglycerides, and both beers acted as in vivo antioxidants by decreasing the oxidizability of lower density lipoproteins. At the low dose ((1)/(10)-diluted beer) only the lager beer significantly decreased atherosclerosis compared to the 0.4% alcohol control. The polyphenols in the beers appear to be responsible for the benefits of beer in this model. Lager beer inhibited atherosclerosis at a human equivalent dose in this hamster model of atherosclerosis.     

Investigation of the beta-damascenone level in fresh and aged commercial beers

This study investigated the increase of beta-damascenone content during aging in a variety of commercial Belgian beers. Quantities detected in fresh beers were generally low (from 6 ng/g to 25 ng/g). After 5 days at 40 degrees C, the level increased (to as much as 210 ng/g) in most of the beers studied, according to the type of beer. Further experiments showed that wort initially contains large quantities of beta-damascenone (450 ng/g), but that degradation of the compound during fermentation accounts for the low concentrations observed in fresh beers. Production during beer aging can be partially explained by acid hydrolysis of glycosides.     

Application of NMR spectroscopy and LC-NMR/MS to the identification of carbohydrates in beer

The application of LC-NMR/MS for the direct identification of carbohydrates in beer has been studied. Carbohydrates are major beer components, and their structural characterization by NMR alone is seriously hindered by strong spectroscopic overlap. Direct analysis of beer by LC-NMR/MS enables the rapid (1-2 h) identification of dextrins with degree of polymerization (DP) of up to nine monomers, with degassing being the only sample treatment required. Although the presence of alpha(1-->6) branching points is easily indicated by NMR for each subfraction separated by LC, difficulties arise for the unambiguous assignment of linear or branched forms of high DP dextrins. The two beer samples investigated in this work were found to have significantly different oligosaccharide compositions, reflecting the different production conditions employed. The use of hyphenated NMR for the rapid characterization of the carbohydrate composition of beers may be the basis of a useful tool for the quality control of beer.     

Characterization of a colorless anthocyanin-flavan-3-ol dimer containing both carbon-carbon and ether interflavanoid linkages by NMR and mass spectrometry

Direct addition of anthocyanins and flavan-3-ols was investigated in a model system by incubating malvidin 3-glucoside and (-)-epicatechin in ethanol. Analysis of reaction products by high-performance liquid chromatography coupled to electrospray ionization mass spectrometry (HPLC/ESI-MS) before and after thiolysis showed the formation of colorless dimers detected at m/z 781 in the negative ion mode, with retention times and spectroscopic characteristics identical to those of compounds detected in wine, which contain one malvidin 3-glucoside unit and one flavanol unit. On the basis of their resistance to thiolysis, these compounds were postulated to be bicyclic dimers linked with both carbon-carbon and ether bonds as observed in the case of A type proanthocyanidins. The major dimer analyzed by NMR experiments was identified as malvidin 3-glucoside(C2-O-C7,C4-C8)epicatechin, confirming this hypothesis. A similar assay was performed with (+)-catechin instead of (-)-epicatechin, and the formation of bicyclic dimers was also observed.