Fate of xanthohumol and related prenylflavonoids from hops to beer

The fate of three prenylated flavonoids of the chalcone type, xanthohumol, desmethylxanthohumol, and 3'-geranylchalconaringenin, was monitored with LC/MS-MS from hops (Humulus lupulus L.) to beer in two brewing trials. The three prenylchalcones were largely converted into their isomeric flavanones, isoxanthohumol, prenylnaringenins, and geranylnaringenins, respectively, in the boiling wort. Losses of prenylflavonoids were due to incomplete extraction from the hops into the wort (13-25%), adsorption to insoluble malt proteins (18-26%), and adsorption to yeast cells (11-32%) during fermentation. The overall yield of xanthohumol, after lagering of the beer and largely in the form of isoxanthohumol, amounted to 22-30% of the hops' xanthohumol. About 10% of the hops' desmethylxanthohumol, completely converted into prenylnaringenins, remained in the beers. 3'-Geranylchalconaringenin behaved similarly to desmethylxanthohumol. Solubility experiments indicated that (1) malt carbohydrates form soluble complexes with xanthohumol and isoxanthohumol and (2) solubility does not dictate the isoxanthohumol levels of finished beers.     

Novel application of square-wave adsorptive-stripping voltammetry for the determination of xanthohumol in spent hops

This paper reports the development of a novel electrochemical assay for xanthohumol (XN) by square-wave adsorptive-stripping voltammetry (SWAdSV) with a hanging mercury drop electrode. The method showed good repeatability (CV < 2%) and linearity (between 10 and 250 μg L(-1)), as well as suitable limits of detection (2.6 μg L(-1)) and quantification (8.8 μg L(-1)). The method was applied for the quantification of this compound in spent hops, and the results obtained were compared with the HPLC-UV method. XN contents determined by the SWAdSV method were 16 ± 1 and 100 ± 4 μg L(-1) for aqueous and methanolic extracts, respectively. The developed new methodology considerably reduces the analysis time, approximately from 25 min (HPLC-UV method) to 7 min, enabling a high sample throughput. In addition, the detection and quantification limits were approximately 5-fold lower than those obtained with the chromatographic method.     

Nitrogen biomarkers and their fate in soil

More than 90 % of the nitrogen (N) in soils can be organically bound, but the mechanisms and rates by which it is cycled have eluded researchers. The objective of this research was to contribute to a better understanding of the origin and transformation of soil organic N (SON) by using amino sugars and the enantiomers of amino acids as markers for microbial residues and/or aging processes. Studied samples presented here comprised (1) soil transects across different climates, (2) arable soils with different duration of cropping, and (3) radiocarbon‐dated soil profiles. The results suggested that increased microbial alteration of SON temporarily results in a sequestration of N in microbial residues, which are mineralized at later stages of SON decomposition. Microorganisms increasingly sequestered N within intact cell wall residues as frost periods shortened. At a mean annual temperature above 12–15 °C, these residues were mineralized, probably due to limitations in additional substrates. Breaking the grassland for cropping caused rapid SON losses. Microbial residues were decomposed in preference to total N, this effect being enhanced at higher temperatures. Hence, climate and cultivation interactively affected SON dynamics. Nevertheless, not all SON was available to soil microorganisms. In soil profiles, L‐aspartic acid and L‐lysine slowly converted into their D‐form, for lysine even at a similar rate in soils of different microbial activity. Formation of D‐aspartate with time was, therefore, induced by microorganisms while that of D‐lysine was not. The racemization of the two amino acids indicates that SON not available to microorganisms ages biotically and abiotically. In native soils, the latter is conserved for centuries, despite N deficiency frequently occurring in living terrestrial environments. Climate was not found to affect the fate of old protein constituents in surface soil. When native grassland was broken for cropping, however, old SON constituents had become available to microorganisms and were degraded.     

Methane production and its fate in paddy fields

Abstract

Oxidation of methane and total water soluble organic carbon (TOC) in the subsoil, which percolated from the plow layer, was investigated in a column experiment. The amounts of both methane and TOC in the leachate decreased by percolation in the subsoil.

Fe²⁺ percolated from the plow layer was nearly completely retained in the subsoil. The decomposition of methane and TOC in the subsoil was considered to result in the coupling with the formation of Fe²⁺. Methane was estimated to contribute ca. 19–21% to the total amount of Fe²⁺ formed in the subsoil by the organic materials in the leachate.     

Role of riboflavin in beer flavor instability: determination of levels of riboflavin and its origin in beer by fluorometric apoprotein titration

A method for the quantitative determination of riboflavin levels in beer was developed. The method is based on the quenching of riboflavin fluorescence, which occurs when riboflavin binds to the aporiboflavin-binding protein from egg white. The method does not require any pretreatment of the beer before analysis, other than dilution, and proved to be simple, reliable, and sensitive. The lowest concentration that could be detected was approximately 10 nM riboflavin. The possible interference of flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD) with the determination of the riboflavin content of beer was excluded, because beer contains only a very small amount of FAD (0.03 microM) and no FMN. The riboflavin levels of the types and brands of beer investigated were in the range of 0.5-1.0 microM. The origin of the riboflavin in beer proved to be the malt. Hop and yeast hardly contributed to the riboflavin content of beer. Besides its use in the determination of riboflavin levels, the aporiboflavin-binding protein also provides a way to remove riboflavin from beer, which reduces the light sensitivity and the related lightstruck off-flavor formation in beer.     

壤和堆肥中四环素类抗生素的检测方法优化及其在土壤中的降解研究

在对土霉素（OTC）、四环素（TC）和金霉素（CTC）3 种四环素类抗生素的高效液相色谱（HPLC）检测分析方法以及在土壤和堆肥中的提取方法进行改进和优化的基础上,采用该方法进行了 3 种抗生素在土壤中的降解试验。结果表明,选用 Agilent Eclipse XDB-C8（4.6150 mm,5 m）色谱柱,以 0.01 mol/L草酸/乙腈/甲醇（79/10.5/10.5,v/v/v）为流动相,紫外检测波长 268 nm,流速 1.0 mL/min,进样量 5 L,采用外标法定量,可使 3 种四环素类抗生素在 20 min 内全部洗脱并达到基线分离; 在 0~10 mg/L 范围内,抗生素浓度与峰面积呈显著的线性关系,相关系数（r）均 0.999。土壤和堆肥样品中的 OTC、TC 和 CTC可用1 mol/L NaCl/0.5 mol/L 草酸/乙醇（25/25/50,v/v/v）混合溶液提取,其回收率在 76.0%~92.5% 之间。加入到土壤中的抗生素在 25℃下避光培养 49 d 后,在壤土和红土中的降解率分别是 67%~72% 和 36%~46%,对应的半衰期分别为 2630 d 和 4675 d,说明抗生素在壤土中比红土中容易降解。此外,3种抗生素在壤土中的半衰期没有显著性差异,而在红土中 CTC 和 TC 的降解速率显著高于 OTC。     

Lipids from flax fibers and their fate in alkaline pulping

The chemical composition of lipids from bast fibers of flax (Linum usitatissimum), which are commonly used for high-quality paper pulp production, was thoroughly studied by gas chromatography-mass spectrometry. The main compounds identified were waxes, series of long chain n-fatty alcohols, n-aldehydes, n-fatty acids, and n-alkanes. Free and esterified sterols and triterpenols, steroid hydrocarbons, steroid and triterpenoid ketones, as well as sterol glycosides were also found in the flax bast fibers. On the other hand, the fate of these lipophilic compounds in alkaline pulping of flax fibers was investigated by analyzing two pulps obtained under distinct industrial cooking conditions. The results revealed that while waxes could be efficiently hydrolyzed during pulping depending on the alkali charge, most of the other lipophilic compounds present in flax fibers survived cooking and were present in the unbleached pulps.     

Presence of phytosterol oxides in crude vegetable oils and their fate during refining

The content of phytosterol oxidation products was determined in samples of crude vegetable oils: peanut, sunflower, maize, palm nut, and lampante olive oils that were intended for refining and not for direct consumption. The 7 alpha- and 7 beta-hydroxy derivatives of beta-sitosterol, stigmasterol, and campesterol and the 7-keto-beta-sitosterol were the principal phytosterol oxides found in almost all of the oils analyzed. In some oils, the epoxy and dihydroxy derivatives of beta-sitosterol were also found at very low levels. The highest total concentrations of phytosterol oxides, ranging from 4.5 to 67.5 and from 4.1 to 60.1 ppm, were found in sunflower and maize oils, respectively. Lower concentrations were present in the peanut oils, 2.7-9.6 ppm, and in the palm nut oil, 5.5 ppm, whereas in the lampante olive oils, only three samples of the six analyzed contained a low concentration (1.5-2.5 ppm) of oxyphytosterols. No detectable levels of phytosterol oxides were found in the samples of palm and coconut oils. Bleaching experiments were carried out on a sample of sunflower oil at 80 degrees C for 1 h with 1 and 2% of both acidic and neutral earths. The bleaching caused a reduction of the hydroxyphytosterol with partial formation of steroidal hydrocarbons with three double bonds in the ring system at the 2-, 4-, and 6-positions (steratrienes). The same sunflower oil was deodorized at 180 degrees C under vacuum for 1 h, and no dehydration products were formed with a complete recovery of the hydroxyphytosterols. A bleaching test with acidic earths was carried out also with an extra virgin olive oil fortified with 7-keto-cholesterol, dihydroxycholesterol, and alpha-epoxy-cholesterol. There was no formation of steratrienes from these compounds, but dihydroxycholesterol underwent considerable decomposition and alpha-epoxycholesterol underwent ring opening with formation of the dihydroxy derivative, whereas 7-ketocholesterol was rather stable     

异氰酸酯改性大豆油基木材胶黏剂的制备与性能

环氧大豆油丙烯酸酯（Acrylated Epoxidized Soybean Oil, AESO）具有原料来源丰富、环境友好、耐水性好等优点,以AESO为原料制备新型无醛木材胶黏剂是降低当前甲醛系胶黏剂用量的重要途径。针对AESO同时含双键、羟基和环氧基的结构特点,以六亚甲基二异氰酸酯（Hexamethylene Diisocyanate, HDI）为改性剂、过氧化苯甲酸叔丁酯为自由基引发剂,制备了改性大豆油基木材胶黏剂及其杨木胶合板材,分析了胶黏剂的化学结构、流变性、固化行为、胶合机理及其对胶合板物理力学性能的影响。结果表明：HDI改性后的胶黏剂具有更高的交联密度、内聚力和胶接力,其杨木胶合板的耐水胶合强度可达1.18 MPa;HDI可与AESO的羟基、环氧基反应生成氨基甲酸酯结构,同时HDI的加入降低了AESO树脂的黏度和最大固化温度,提高了胶黏剂的加工性能;HDI改性显著提高胶合板的物理力学性能（P<0.05）,当HDI与AESO的质量比为1∶9时,胶合板的横向静曲强度和弹性模量分别为57.6和5 920 MPa,且板材在120°C下2 h不开裂。该研究为以生物质大豆油为原料制备无醛胶黏剂提供了一种可行路径,有利于木材工业的绿色与可持续发展。     

Automated on-line solid-phase extraction-liquid chromatography-electrospray tandem mass spectrometry method for the determination of ochratoxin A in wine and beer

An automated on-line solid-phase extraction-liquid chromatography-electrospray tandem mass spectrometry (SPE-LC-ESI-MS/MS) method was developed for the determination of ochratoxin A (OTA) in alcoholic beverages. Mean recoveries for wine and beer were, respectively, 75 and 82%. Detection was achieved in negative ionization with a Q TRAP mass spectrometer operating in multiple-reaction monitoring (MRM) mode or enhanced product ion (EPI) mode, using the third quadrupole as linear ion trap. The MRM mode turned out to be more sensitive; the method allowed accurate determination of OTA in the range of 0.01-25 ng mL(-1) using external calibration. Within-day and between-day relative standard deviation percentages were <6.2 and <9.1%, respectively. In EPI mode, fragmentation spectra at the limit of quantification (0.03 ng mL(-1)) and good linearity could be obtained. Application of the method (MRM mode) to the analysis of several wine and beer samples purchased in local stores revealed OTA levels in the ranges of 0.03-1.44 ng mL(-1) for wines and 0.02-0.14 ng mL(-1) for beers.     

Identification of metabolites of (-)-epicatechin gallate and their metabolic fate in the rat

After intravenous administration of (-)-epicatechin gallate to Wistar male rats, its biliary metabolites were examined. Deconjugated forms of (-)-epicatechin gallate metabolites were prepared by beta-glucuronidase/sulfatase treatment and purified by HPLC. Five compounds were subjected to FAB-MS and NMR analyses. These metabolites were shown to be (-)-epicatechin gallate, 3'-O-methyl-(-)-epicatechin gallate, 4'-O-methyl-(-)-epicatechin gallate, 4' '-O-methyl-(-)-epicatechin gallate, and 3',4' '-di-O-methyl-(-)-epicatechin gallate. After oral administration, five major metabolites excreted in rat urine were purified in their deconjugated forms and their chemical structures identified. They were degradation products from (-)-epicatechin gallate, pyrogallol, 5-(3,4-dihydroxyphenyl)-gamma-valerolactone, 4-hydroxy-5-(3,4-dihydroxyphenyl)valeric acid, 3-(3-hydroxyphenyl)propionic acid, and m-coumaric acid. Time course analysis of the identified (-)-epicatechin gallate metabolites showed that (-)-epicatechin gallate and its conjugate appeared in the plasma with their highest levels 0.5 h after oral administration; their levels rapidly decreased, and then they disappeared by 6 h. The degradation products, mainly in their conjugated forms, emerged at 6 h, peaked at 24 h, and disappeared by 48 h. In urine samples, (-)-epicatechin gallate and its methylated metabolites were hardly detected and the degradation products began to be excreted in the 6-24 h period, peaked in the 24-48 h period, and then began to disappear. The most abundant metabolite in both the plasma and the urine was found to be the conjugated form of pyrogallol. On the basis of these results, a possible metabolic route of (-)-epicatechin gallate orally administered to the rat is proposed.     

Kinetic enzymatic determination of glycerol in wine and beer using a sequential injection system with spectrophotometric detection

A sequential injection system for the automatic determination of glycerol in wine and beer was developed. The method is based on the rate of formation of NADH from the reaction of glycerol and NAD+ catalyzed by the enzyme glycerol dehydrogenase in solution. The determination of glycerol was performed between 0.3 and 3.0 mmol L(-1) (0.028 and 0.276 g L(-1)), and good repeatability was attained (rsd < 3.6%, n = 5) for all samples tested. The determination rate was 54 h(-1), the reagent consumption was only 0.75 micromol of NAD+ and 5.4 ng of enzyme per assay, and the waste production was 2.12 mL per assay. Results obtained for samples were in agreement with those obtained with the batch enzymatic method.     

Analysis of hop-derived terpenoids in beer and evaluation of their behavior using the stir bar-sorptive extraction method with GC-MS

Hop aroma components, which mainly comprise terpenoids, contribute to the character of beers. However, pretreatments are necessary before analyzing these components because of their trace levels and complicated matrixes. Here, the stir bar-sorptive extraction (SBSE) method was used to detect and quantify many terpenoids simultaneously from small samples. This simple technique showed low coefficients of variation, high accuracy, and low detection limits. An investigation of the behavior of terpenoids identified two distinct patterns of decreasing concentration during wort boiling. The first, which was seen in myrcene and linalool, involved a rapid decrease that was best fitted by a quadratic curve. The second, which was observed in beta-eudesmol, humulene, humulene epoxide I, beta-farnesene, caryophyllene, and geraniol, involved a gentle linear decrease. Conversely, the concentration of beta-damascenone increased after boiling. As the aroma composition depended on the hop variety, we also examined the relationship between terpenoid content and sensory analysis in beer.     

Rapid determination of the attenuation limit of beer using middle-infrared (MIR) spectroscopy and a multivariate model

A new approach for the determination of the attenuation limit of beer samples using the specific fingerprint region of middle-infrared (MIR) spectroscopy in combination with multiple regression by partial least-squares (PLS) was developed using an attenuated total reflectance (ATR) module. A specific spectral region between 1200 and 800 cm(-1) was identified as highly informative for the quantification of the limit of attenuation. The absorptions in this region are induced by vibrational bands of ethanol (1080, 1040, and 880 cm(-1)) and dissolved extract, in majority maltotriose (1160-1140 and 1040-980 cm(-1)). The multivariate calibration results in a root mean squared error of calibration (RMSEC) of 0.40% and a validation procedure with independent samples results in a root mean squared error of validation (RMSEV) of 0.50%. A repeatability test, concerning the precision of the developed MIR method as well as the reference method, was analyzed using Student's t test. The test has shown no significant difference between the two random samples.     

Structural identification and distribution of proanthocyanidins in 13 different hops

Ten newly isolated hop proanthocyanidin oligomers and flavan-3-ol monomers from 13 different hops have been identified as gallocatechin, gallocatechin-(4alpha-->8)-catechin, gallocatechin-(4alpha-->6)-catechin, catechin-(4alpha-->8)-gallocatechin, catechin-(4alpha-->6)-gallocatechin, afzelechin-(4alpha-->8)-catechin, catechin-(4alpha-->8)-catechin-(4alpha-->8)-catechin, epicatechin-(4beta-->8)-epicatechin-(4beta-->8)-catechin, catechin-(4alpha-->8)-gallocatechin-(4alpha-->8)-catechin, and gallocatechin-(4alpha-->8)-gallocatechin-(4alpha-->8)-catechin, together with seven previously isolated oligomers, namely, catechin, epicatechin, epicatechin-(4beta-->8)-catechin, epicatechin-(4beta-->8)-epicatechin, catechin-(4alpha-->8)-catechin, catechin-(4alpha-->8)-epicatechin, and epicatechin-(4beta-->8)-catechin-(4alpha-->8)-catechin. These compounds were subjected to acid-catalyzed degradation in the presence of phloroglucinol or by partial or complete acid-catalyzed degradation and reaction with benzyl mercaptan followed by desulfurization. The resultant adducts when compared to authentic samples by high-performance liquid chromatography-atmospheric pressure chemical ionization tandem mass spectrometry and high-performance liquid chromatography-electrospray ionization tandem mass spectrometry served to identify the precursors. The composition of proanthocyanidins from 13 different hops was similar, but the concentration of individual compounds showed some differences, which indicated that hop proanthocyanidin profiles are affected by geographic origin and are variable depending on the cultivars.     

Analysis of hop acids and their oxidized derivatives and iso-alpha-acids in beer by capillary electrophoresis-electrospray ionization mass spectrometry

This study investigates the applicability of on-line coupling of capillary electrophoresis with electrospray ionization tandem mass spectrometry (CZE-ESI-MS) for the separation and characterization of alpha- and beta-acids and oxidized hop acids from crude extracts of different hop varieties. CZE-ESI-MS with negative-ion electrospray ionization proved to be a suitable technique for the determination of these types of natural compounds and their oxidized derivatives. The CZE parameters (pH, concentration, and buffer type) and ESI-MS parameters (nature and flow rate of the sheath liquid, nebulizer pressure, drying gas flow rate, temperature, and compound stability) were optimized. The optimized method provides the potential for a fast qualitative determination of hop acids and their oxidation compounds. The method was also applied to the determination of iso-alpha-acids in beer.     

Development and validation of a high-performance liquid chromatography method for the determination of diacetyl in beer using 4-nitro-o-phenylenediamine as the derivatization reagent

Diacetyl is a natural byproduct of fermentation and known to be an important flavor compound in many food products. Because of the potential undesirable effects of diacetyl on health safety and beer flavor, determination of its concentration in beer samples is essential and its analytical methods have attracted close attention recently. The aim of the present work is to develop and validate a novel high-performance liquid chromatography method for the quantification of diacetyl in beer based on the derivatization reaction of diacetyl with 4-nitro-o-phenylenediamine (NPDA). After the derivatization with NPDA in pH 3.0 at 45 °C for 20 min, diacetyl was separated on a kromasil C(18) column at room temperature in the form of the resulting 6-nitro-2,3-dimethylquinoxaline and detected by the ultraviolet detector at 257 nm. The results showed that the correlation coefficient for the method was 0.9992 in the range of 0.0050-10.0 mg L(-1) and the limit of detection was 0.0008 mg L(-1) at a signal-to-noise ratio of 3. The applicability of the proposed method was evaluated in the analysis of beer samples with the recovery range of 94.0-99.0% and relative standard deviation range of 1.20-3.10%. The concentration levels of diacetyl detected in beer samples from 12 brands ranged from 0.034 to 0.110 mg L(-1). The proposed method showed efficient chromatographic separation, excellent linearity, and good repeatability that can be applied to quantification of diacetyl in beer samples.     

Residues of spiroxamine in grapes following field application and their fate from vine to wine

Dissipation of the fungicide spiroxamine in grapes of two vine varieties, Roditis and Cabernet Sauvignon, exposed to field treatments was evaluated. Vines of a grape vineyard located in central Greece were sprayed once or twice with a commercial formulation of the fungicide at 30 g a.i./hL. Residues in grapes, must, and wine were determined by gas chromatography/IT-MS after extraction with cyclohexane-dichloromethane (9:1), with a limit of quantitation 0.02 mg/kg in grapes and 0.012 mg/kg in wine. Under field conditions, spiroxamine dissipation on grapes was faster during the first 2 weeks and then slower to the sixth week. About 7 days after application, half of the initial spiroxamine concentration remained on the grapes; the respective proportion at 42 days was about 10%. At 14 and 35 days, residues were lower than 0.44 and 0.22 mg/kg, respectively, values below the maximum residue levels set by the European Union (1 mg/kg). Spiroxamine residues transferred from grapes into the must and through the vinification process into the wine were also studied. Mean transfer factors of 0.26 and 0.55 were found from grapes into wine for the wines obtained without maceration and with maceration, respectively. Residues in wine, prepared from grapes with a spiroxamine content of 0.11-0.20 mg/kg, varied from <0.026 to 0.09 mg/kg. Spiroxamine diastereomer B was found to dissipate slower than diastereomer A in the field as well as during the vinification process.