Synchronous fluorescence as a rapid method for the simultaneous determination of folic acid and riboflavin in nutritional beverages

A rapid synchronous spectrofluorimetric method was first developed for the simultaneous determination of folic acid and riboflavin in nutrimental beverages. Folic acid could be detected by using H(2)O(2) plus Cu(II) as oxidation system to produce pterine-6-carboxylic acid, which had strong fluorescence in aqueous solution, and riboflavin itself was obviously fluorescent. Various operational parameters were thoroughly discussed in terms of their effects on the fluorescence signals, including instrumental parameters, concentration of the oxidation system, and pH. Under optimum conditions, the calibration curves were linear in the ranges of 100-250 μg/L for folic acid and 1-250 μg/L for riboflavin, and the detection limits were 2.0 and 0.014 μg/L, respectively. In addition, this method was applied to the determination of folic acid and riboflavin in nutrimental beverages with satisfactory results.     

Occurrence of Odorant Polyfunctional Thiols in Beers Hopped with Different Cultivars. First Evidence of an S-Cysteine Conjugate in Hop ( Humulus lupulus L.)

Forty-one thiols, mainly β-sulfanylalkyl acetates, β-sulfanylalkyl alcohols, and β-sulfanylalkyl carbonyls, were recently evidenced in hop. In a beer hopped with the Tomahawk cultivar, most of them were found at higher levels than expected. The aim of the present work was to investigate the polyfunctional thiols in beers hopped with different varieties. A few thiols proved not to come only from hop (mainly 2-sulfanylethyl acetate, μg/L levels, and 1-sulfanylpentan-3-one and 1-sulfanylpentan-3-ol, ng/L levels, internal standard (IST) equivalents). The thiol profile of Saaz-hopped beer proved similar to that of the reference beer produced without hop. A high level of 3-sulfanyloctan-1-ol emerged as an indicator of the use of Tomahawk hop (140 ng/L, IST equivalents; FD (flavor dilution) = 65536). In both Cascade- and Tomahawk-hopped beers, 3-sulfanylhexan-1-ol and 3-sulfanylheptan-1-ol were smelled at high flavor dilutions, although only for the latter, significant amounts of the unreduced 3-sulfanylheptanal were found in hop. As already claimed for hop authentication, 3-sulfanyl-4-methylpentan-1-ol remains a good marker of Nelson Sauvin-hopped beers (548 ng/L, IST equivalents; FD = 65536), together with 4-sulfanyl-4-methylpentan-2-one (128 ng/L, FD = 4096). As illustrated by the huge production occurring during fermentation, accurate prediction of hop varietal impact requires quantitating thiol adducts in hop. S-3-(1-Hydroxyhexyl)cysteine was evidenced here for the first time in Cascade hop.     

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.     

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.     

Determination of the hop-derived phytoestrogen, 8-prenylnaringenin, in beer by gas chromatography/mass spectrometry

A method was developed to determine 8-prenylnaringenin, a novel hop-derived phytoestrogen, in beer. Matrix purification involved solid-phase extraction on octadecyl silica followed by liquid/liquid extraction on a ChemElut 1010 column connected to a Florisil adsorption/desorption cartridge. 8-Prenylnaringenin was eluted from the tandem columns using a 1:1 mixture of diethyl ether and ethyl acetate and subsequently determined as tris(trimethylsilyl) ether by GC/MS-SIM. The recovery of 8-prenylnaringenin in beer samples was between 61.1 +/- 6.6 and 82.2 +/- 8.8% for levels of 37 and 92.5 microg L(-1), respectively, and the detection limit was approximately 5 microg L(-1). Although most beers do not contain 8-prenylnaringenin in detectable quantities, the highest concentration found was 19.8 microg L(-1). The concentration of 8-prenylnaringenin in beers and, possibly, its absence depend on the selection of particular hop varieties, the hopping rate, or the type of hop product used in brewing. The efficiency of transfer of 8-prenylnaringenin from hops to beer is between 10 and 20%.     

Determination and levels of the biocide ortho-phenylphenol in canned beers from different countries

A method was developed for the determination of the biocide ortho-phenylphenol (biphenyl-2-ol; OPP) in beer, using deuterated OPP as an internal standard. A new liquid-liquid extraction procedure, employing acetonitrile, diethyl ether, and n-pentane, afforded rapid phase separation. The evaporated extract was derivatized with pentafluorobenzyl bromide in a water-acetonitrile mixture that was buffered with potassium carbonate, followed by extraction of the derivative into cyclohexane and analysis by gas chromatography-mass spectrometry in electron ionization mode. The method enables the detection of OPP in 50 mL of beer at concentrations as low as 0.1 microg/L and provides a linear range of quantification of 0.5-40 microg/L. Samples from 61 beers canned over the past 12 years and sold in 27 countries were analyzed for OPP. In 40 of them, the target compound was present at concentrations of 1.2-40 microg/L. Our investigations indicate that the ends of the cans, which contain sealing material presumably treated with OPP, are responsible for this contamination.     

Simultaneous determination of thiamin and riboflavin in mushrooms by liquid chromatography

A simple, fast, inexpensive, and reliable method useful for the simultaneous, routine determination of thiamin and riboflavin in mushrooms is examined. It uses the extraction procedure, with slight modifications, proposed by the AOAC for the extraction of thiamin and riboflavin, followed by a liquid chromatographic separation on a reversed-phase Spherisorb ODS column with methanol/water as mobile phase gradient. Fluorometric detection is used at the following excitation and emission wavelengths, respectively, 360 and 425 nm in the case of thiamin and 422 and 515 nm for riboflavin. The analytical parameters of linearity, the precision of the method (RSD = 2.45 and 2.51% for thiamin and riboflavin, respectively), and the results of the comparison with the corresponding AOAC fluorometric methods show that the studied method is useful for the measurement of thiamin and riboflavin in fresh mushrooms.     

Phenol and terpene quenching of singlet- and triplet-excited states of riboflavin in relation to light-struck flavor formation in beer

Phenolic compounds present in beer were shown by fluorescence spectroscopy and laser flash photolysis to deactivate both singlet- and triplet-excited states of riboflavin with bimolecular rate constants close to the diffusion control ranging from 2.8x10(9) to 1.1x10(10) M-1 s-1 and from 1.1x10(9) to 2.6x10(9) M-1 s-1, respectively. Enthalpies of activation were low (up to 33.2 kJ mol-1), and entropies of activation were positive, ranging from 17 to 92 J mol-1 K-1, as derived from temperature dependence, indicating a compensation effect. From a Stern-Volmer analysis of the singlet-excited riboflavin quenching by phenols it was found that high amounts of phenolic compounds (>0.3 M) would be needed to hinder triplet-excited riboflavin generation. On the other hand, a phenolic content of 0.36 mM is likely to quench 90% of the triplet-excited state. Phenol photodegradation was found to be complex, and using ESI-MS analysis it was not possible to identify specific photooxidation products of the phenolic compounds; only the photoproducts of riboflavin could be detected and structurally assigned. The rate of reaction of triplet-excited riboflavin with phenolic compounds in acetonitrile/citrate buffer (pH 4.6, 10 mM) is 550 times faster than the reaction with iso-alpha-acids from hops, indicating that triplet-excited quenchers such as phenols may be involved in the early steps in light-struck flavor formation in beer through radical formation. Terpenes present in herb-flavored beers were found to be nonreactive toward singlet- and triplet-excited-state riboflavin, and any protection depends on other mechanisms.     

Determination of arsenic in beer by dry ashing, hydride generation atomic absorption spectroscopy

A method has been developed for determination of arsenic in beer. Organic matter is destroyed by the dry-ashing technique, the ash is dissolved in HCl, and hydrides of arsenic are generated by addition of sodium borohydride prior to atomization in a flame-heated quartz cell and atomic absorption spectroscopy measurement. The analytical features of the method are detection limit 0.1 ng/g beer, precision 8%, and recovery 97 +/- 7%. The arsenic contents of different brands from Spain and other European countries were analyzed. In all samples, the arsenic levels found were well below maximum levels allowed in Spanish legislation (100 ng/g). The quantities of arsenic in Spanish beers do not differ from those found in foreign beers. No differences were found between bottled and canned beers, and no correlation exists between metal content and original specific gravity of the beers.     

Determination of estrogenic activity in beer by biological and chemical means

It has been suspected that beer drinking may change the hormonal status of men caused by phytoestrogens. Five different Austrian lager beers have been investigated for estrogenic activity by a yeast two-plasmid system harboring the human estrogen receptor alpha, after concentration by solid phase extraction. The beer concentrate was further fractionated by reversed phase HPLC, and then the fractions were characterized by the biological assay and GC-MS. The most potent fraction did not contain a known phytoestrogen. The total activity corresponded to an average of 43 ng of 17beta-estradiol/L of beer. It was concluded that the human health hazard of beer drinking originating from compounds activity on the estrogen receptor alpha is negligible.     

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.     

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.     

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.     

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.     

Analysis of organic acids and inorganic anions in different types of beer using capillary zone electrophoresis.

Two methods for the investigation of different types of beer by capillary zone electrophoresis are presented. The first separation system described in this work allows the quantitative analysis of beers with respect to their contents of low molecular mass anionic components using indirect ultraviolet detection as well as conductivity detection, providing relative standard deviation between 0.5 and 6.6% for the peak areas and excellent limits of detection (LOD) ranging from 0.02 mg L(-)(1) for chloride to 0.41 mg L(-)(1) for phosphate. The second method offers the possibility of fast determination of amino acids in beer samples without the necessity of any sample pretreatment. LODs obtained for the investigated solutes were found to be strongly dependent on their spectroscopical properties and in the range of 0.5-50 mg L(-)(1). Despite this restriction, this analytical method can be regarded as a suitable tool for the screening of beers with respect to their amino acid patterns.     

Assay of riboflavin in sample wines by capillary zone electrophoresis and laser-induced fluorescence detection

To routinely assay the concentration of riboflavin (RF) in wines, a rapid and sensitive method was developed and evaluated. The method is based on a simple sample preparation, capillary zone electrophoretic separation and laser-induced fluorescence detection (CZE-LIF). Sample preparation required only dilution and filtration. Under optimized conditions, the limit of detection of riboflavin was 0.5 micro g/L, using a hydrodynamic sample introduction of 10 s at 54 mbar. The method was fully validated: the recovery of RF in wines was >95%. The concentrations of RF within the three sample types of Italian wines investigated here ranged from 69 to 151 micro g/L with a mean value (+/-SD) of 112 +/- 25 micro g/L, from 74 to 193 micro g/L with a mean value of 115 +/- 45 micro g/L, and from 156 to 292 micro g/L with a mean value of 226 +/- 40 micro g/L, for white, rosé, and red wines, respectively. Such an accurate and highly sensitive CZE-LIF method represents a powerful improvement over previous methods in terms of sensitivity, simplicity, and efficiency. It is well suited to satisfy the demands for accurate and sensitive detection with minimal sample preparation and cleanup.     

Phytoestrogen content of beverages, nuts, seeds, and oils

Phytoestrogens are secondary plant metabolites that have received increasing attention for their bioactivity, in particular due to their structural and functional similarity to 17beta-estradiol. Although urinary and plasma phytoestrogens can be used as biomarkers for dietary intake, this is often not possible in large epidemiological studies or in the assessment of general exposure in free-living individuals. Accurate information about dietary phytoestrogens is therefore important, but there are very limited data concerning food contents. In this study was analyzed a comprehensive selection of tea, coffee, alcoholic beverages, nuts, seeds, and oils for their phytoestrogen content using a newly developed sensitive method based on LC-MS incorporating (13)C 3-labeled standards. Phytoestrogens were detected in all foods analyzed, although the contents in gin and bitter (beer) were below the limit of quantification (1.5 microg/100 g). Lignans were the main type of phytoestrogens detected. Tea and coffee contained up to 20 microg/100 g phytoestrogens and beer (except bitter) contained up to 71 microg/100 g, mainly lignans. As these beverages are commonly consumed, they are a main source of dietary lignans. The results published here will contribute to databases of dietary phytoestrogen content and allow a more accurate determination of phytoestrogen exposure in free-living individuals.     

热压凝胶法制备营养质构米及其营养性质研究

为弥补食用精白米导致营养不良的状况,以大米加工过程中产生的碎米作为原料和载体,产生的米糠作为天然营养强化剂,采取热压凝胶法制备营养质构米。在预试验的基础上,采用响应面法考察热压凝胶过程条件包括喂料含水率,螺杆转速,5个加热区机筒温度对营养质构米的质构和营养特性的影响,得出制备最佳工艺条件:当喂料转速为30r/min,米糠添加量为4%,物料含水率为30%,螺杆转速为17.7r/min,5个区机筒温度分别为50,65,85,100,95～97℃。在此条件下制备的营养质构米含有质量分数总膳食纤维11.44%,蛋白质11.62%,脂肪6.49%,而维生素为B12.07μg/g,维生素B20.31μg/g和γ-谷维素12.04mg/100g。相比于天然精白米,质构特性相近,但维生素B1,维生素B2,γ-谷维素分别增加了1.17,0.06,5.83μg/g,为营养质构米工业化生产提供参考。     

Determination of free phenolic acids in wort and beer by coulometric array detection

The simultaneous determination of 19 phenolic compounds was performed directly in wort and beer by a combination of reverse-phase high-performance liquid chromatography coupled with coulometric array detection. Chromatographic separation was achieved with an appropriate gradient of flow and a binary solvent based on phosphate buffer, methanol, and acetonitrile in a 45-min run. Eight serial coulometric detectors were used for on-line generation of voltammetric data to resolve coeluting compounds. The method was reliable and sensitive, the regression coefficient of standard calibration curves is 0.972 < or = r < or = 1.000, and the standard deviation value ranges from 0.010 to 0.129 mg/L for wort and from 0.002 to 0.332 mg/L for beer. The mean concentrations of phenolic acids were 22.1 and 33.8 mg/L, respectively, in worts and beers produced in Italy. These amounts represent 5 and 10% of the non-tannic, non-flavonoid phenols in wort and beer, respectively.     

Inhibition of induced DNA oxidative damage by beers: correlation with the content of polyphenols and melanoidins

Beers are a source of dietary flavonoids; however, there exist differences in composition, alcohol concentration, and beneficial activities. To characterize these differences, three kinds of lager beer of habitual consumption in Spain, dark, blond, and alcohol-free, were assayed for total phenolic content, antioxidant activity, superoxide and hydroxyl radical scavenging activities, and in vitro inhibitory effect on DNA oxidative damage. Furthermore, their melanoidin content and correlation with antioxidant activity were evaluated. Dark beer contained the highest total phenolic (489 +/- 52 mg/L) and melanoidin (1.49 +/- 0.02 g/L) contents with a 2-fold difference observed when compared to the alcohol-free beer. For the three kinds of beer, the antioxidant activity measured as N,N-dimethyl-p-phenylenediamine dihydrochloride concentration was strongly correlated with the total polyphenol content (R(2) = 0.91102, p < 0.005) and with the melanoidin content (R(2) = 0.7999, p < 0.05). The results support a positive effect of beers on the protection of DNA oxidative damage, by decreasing the deoxyribose degradation, DNA scission (measured by electrophoresis), and inhibition of 8-hydroxydeoxyguanosine (8-OH-dG) formation. Furthermore, a correlation between the total melanoidin content (R(2) = 0.7309, p < 0.01) and inhibition of 8-OH-dG was observed.