低嘌呤酿酒酵母的ARTP法诱变育种

采用常压室温等离子体(ARTP)诱变育种系统对酿酒酵母菌株A、B分别进行诱变,选育诱变菌株发酵的啤酒用高效液相色谱(HPLC)法测定腺嘌呤、鸟嘌呤、黄嘌呤、次黄嘌呤的含量,4种嘌呤在1~16 mg/L的测定范围内,相关系数R20.999,具有良好的线性关系。实验结果表明:诱变酵母菌株A-3发酵啤酒中嘌呤含量为77.67 mg/L,比初始菌株A的101.64 mg/L降低23.6%;诱变酵母菌株B-4发酵啤酒中嘌呤含量为76.26 mg/L,比初始菌株A的96.84 mg/L降低21.3%。诱变菌株A-3、B-4进行连续传代10次并进行发酵啤酒实验,诱变菌株A-3、B-4的发酵性能、发酵啤酒中总嘌呤含量和啤酒品质保持稳定。这表明ARTP诱变方法选育低嘌呤酿酒酵母菌种是可行的。     

DYNAMIC CHANGES IN THE COMPOSITION AND PHYSICAL BEHAVIOUR OF DISPENSED BEER FOAM

Beer foam generated under conditions encountered at dispense was separated from beer, allowed to collapse and sampled at regular intervals. The yield of collapsed beer foam decreased logarithmically with time. Analysis of the composition of collapsed beer foam fractions over a period of time, considered to be relevant to actual consumption of beer (30 minutes) showed that polypeptide material and isomerised α acids were selectively partitioned in beer foam. The concentration of total polypeptides, soluble polypeptides, isomerised α acids and foam precipitate material in collapsed beer foam, firstly increased with foam collapse time and then approached maximal values. Under these conditions the concentration of polypeptide material and isomerised α acids increased 10–30 fold and 7 fold respectively as compared to beer. No evidence was obtained for the preferential partition of purine nucleosides and free bases in foam (adenosine + deoxyadenosine, guanosine + deoxyguanosine, adenine, guanine and xanthine).     

尿酸和嘌呤在水和磷酸盐缓冲介质中溶解度的测定

目的：测定尿酸和4种嘌呤（鸟嘌呤、次黄嘌呤、黄嘌呤、腺嘌呤）在水和磷酸盐缓冲介质中的溶解度,以期为嘌呤在体内的代谢及其终产物尿酸对心血管作用的研究提供参考。方法：在室温20℃下,将上述5种物质分别溶于蒸馏水及磷酸盐缓冲液（0.05 mol/L,p H=7.40）中制成饱和溶液,采用紫外分光光度法分别测定其浓度。结果：在水中的溶解度由高至低依次为腺嘌呤（66.15 mg/100 m L）、次黄嘌呤（39.95 mg/100 m L）、尿酸（6.23mg/100 m Ll）、黄嘌呤（1.14 mg/100 m L）和鸟嘌呤（0.17 mg/100 m L）;在磷酸盐缓冲液中溶解度由高至低依次为尿酸（194.54 mg/100 m L）、腺嘌呤（65.22 mg/100 m L）、次黄嘌呤（29.27 mg/100 m L）、黄嘌呤（2.27 mg/100m L）和鸟嘌呤（〈0.1 mg/100 m Ll）。结论：尿酸在磷酸盐缓冲液中的溶解度远远高于水中,是水中的32倍;腺嘌呤、次黄嘌呤和黄嘌呤在2种介质中的溶解度相近,鸟嘌呤在2种介质中均最难溶,甚至在磷酸盐介质中几乎不溶。     

高效液相色谱法测定海水鱼中嘌呤含量

本文建立同时检测海水鱼中腺嘌呤、鸟嘌呤、次黄嘌呤、黄嘌呤的高效液相色谱检测方法。对部分海水鱼可食用部分及内脏中的4种嘌呤含量进行检测。结果表明,当使用Agilent ZORBAX Eclipse XDB-C18(4.6 mm×250 mm,5μm)色谱柱,以水-甲醇-冰乙酸-20%四丁基氢氧化铵(V/V/V/V=879/100/15/6)为流动相,设置流速为0.8 mL/min,柱温30℃,检测波长254 nm,进样量10μL时,4种嘌呤可完全分离且峰型较好。经方法学验证,得出此方法在0.1~400 mg/L范围线性关系良好,相关系数(R)在0.9998~1.0000之间,方法检出限范围0.0465~0.1056 mg/L。高效液相色谱检测方法精密度RSD在0.0200%~0.7000%之间,样品处理重复性腺嘌呤、鸟嘌呤、次黄嘌呤、黄嘌呤依次为1.2421%,0.9711%,0.8836%,1.9727%。加标回收率在94.2888%~102.9188%之间,适用于海水鱼中4种嘌呤的测定。经检测,不同种类海水鱼可食用部分(鱼眼睛、腹部鱼肉、背部鱼肉、鱼皮)嘌呤总含量由高到低依次为海鲈鱼、大菱鲆、金仓鱼、黄花鱼、美国红鱼、踏板鱼、鳕鱼。     

Technical note: A new high-performance liquid chromatography purine assay for quantifying microbial flow

An HPLC method was developed to quantify the purines adenine and guanine and their metabolites xanthine and hypoxanthine in hydrolysates of isolated bacteria and omasal digesta and to assess the effect of using either purines only or purines plus metabolites as microbial markers for estimating microbial flow from the rumen. Individual purines and their metabolites were completely resolved on a C18 column using gradient elution with 2 mobile phases. Intraassay coefficient of variation ranged from 0.6 to 3.1%. Hydrolytic recovery of the 4 purine bases from their corresponding nucleosides averaged 101% (control), 103% (when added to bacterial isolates), and 104% (when added to omasal digesta). Mean concentrations of adenine, guanine, xanthine, and hypoxanthine were, respectively, 53, 58, 2.8, and 3.5 μmol/g of dry matter in omasal bacteria and 10, 12, 7.5, and 7.5 μmol/g of dry matter in omasal digesta, indicating that xanthine plus hypoxanthine represented 5% of total purines in bacterial hydrolysates but 41% of total purines in digesta hydrolysates. A significant negative relationship (R² = 0.53) between the sum of adenine and guanine and the sum of xanthine and hypoxanthine in digesta samples (but not bacterial isolates) indicated that 89% of the adenine and guanine originally present in ruminal microbes were recovered as xanthine and hypoxanthine. These results suggested that, when total purines are used as the microbial marker, both purines and their metabolites should be quantified and used to compute microbial nonammonia N and organic matter flows.     

Proteins and amino acids in beers,their contents and relationships with other analytical data

Fluorometry, ion-exchange chromatography, electrophoretic separations and Fourier transform–infrared (FT–IR) spectra were used to determine and characterize amino acids and proteins in 15 different beer samples. Proteins precipitated by ammonium sulfate yielded complex electrophoretic patterns. The major bands corresponded to 45–40 kDa as determined by a two-dimensional gel electrophoresis (2-DE). Proteins and some amino acids are partially responsible for nutritional value and stability of beer. Therefore, electrophoretic analysis revealed that protein characterization of beer during all technological stages might be useful in its quality. FT–IR protein spectra showed the presence of I, II and III amide bands. Protein distribution and amino acid composition of beer differ significantly, depending on the raw materials and enzymatic reactions used in beer technology. Concentrations of histamine (3.02–3.23 mg/l), proline (1.60–3.13 mg/l) and tyramine (3.61–7.4 mg/l) increased during beer fermentation. Statistically significant change was registered in the protein content of the final product, which was less than that in wort (p<0.005). Levels of tyramine and proline, which were higher than in wort (p<0.025) showed significant changes. This investigation shows that, in Israeli, Mexican and Brazilian beers, the contents of protein and amino acids are in accordance with the international standards.     

控制啤酒中残留草酸含量的探讨

通过对酿造原料（包括麦芽、大米、酒花）的考察，发现不同的麦芽品种中草酸含量各不相同，酒花对麦汁中的草酸含量影响较大，添加辅料大米有助于降低草酸，酵母发酵对草酸含量影响很小。当麦汁中的钙离子含量达到80mg／L时，啤酒中的钙离子浓度在60mg／L，啤酒中的草酸15mg／L左右。     

Dietary purines in vegetarian meat analogues

BACKGROUND: The meat alternatives market offers a wide range of products resembling meat in taste, flavour or texture but based on vegetable protein sources. These high protein–low purine foods may find application in a low purine or purine‐free diet, which is sometimes suggested for subjects with increased serum urate levels, i.e. hyperuricaemia. RESULTS: We determined purine content (uric acid, adenine, guanine, hypoxanthine, xanthine) in 39 commercially available meat substitutes and evaluated them in relation to their protein content. Some of the products contained a comparable sum of adenine and hypoxanthine per protein as meat. Analysis of variance showed an influence of protein source used. Mycoprotein‐based products had significantly higher contents (2264 mg kg^?1) of adenine and hypoxanthine per kg of 100% protein than soybean‐based products (1648 mg kg^?1) or mixtures consisting of soybean protein and wheat protein (1239 mg kg^?1). CONCLUSION: Protein‐rich vegetable‐based meat substitutes might be generally accepted as meat alternatives for individuals on special diets. The type of protein used to manufacture these products determines the total content of purines, which is relatively higher in the case of mycoprotein or soybean protein, while appearing lower in wheat protein and egg white‐based products. These are therefore more suitable for dietary considerations in a low‐purine diet for hyperuricaemic subjects. Copyright © 2010 Society of Chemical Industry     

Effects of β‐Glucans and Environmental Factors on the Viscosities of Wort and Beer

This paper reports on the influence of molecular weight and concentration of barley β‐glucans on the rheological properties of wort and beer. Environmental conditions such as pH, maltose level in wort, ethanol content of beer, shearing and shearing temperature were also examined for their effects on wort and beer viscosities. In the range of 50–1000 mg/L, β‐glucans increased solution viscosity linearly with both molecular weights (MW) of 31, 137, 250, 327, and 443 kDa and concentration. The influence of MW on the intrinsic viscosity of β‐glucans followed the Mark‐Houwink relationship. Shearing wort and beer at approximately 13,000 s^?1for 35 s was found to increase the wort viscosity but reduce beer viscosity. Shearing wort at 20°C influenced β‐glucan viscosity more than shearing at 48°C and 76°C whereas the shearing temperature (0, 5 and 10°C) did not effect the viscosity of beer. At lower pHs, shearing was found to reduce the viscosity caused by β‐glucans in wort but had no effect in beer. Higher concentrations of maltose in wort and ethanol in beer also increased the viscosity of β‐glucan polymers. It was found that β‐glucans had higher intrinsic viscosities in beer than in wort (5°C), and lower critical overlap concentrations (C^*) in beer than in wort.     

Physicochemical characterization of special persimmon fruit beers using bohemian pilsner malt as a base

This study involved the production of special fruit ale beers with different concentrations (100:0%, 75:25%, 50:50% and 25:75% v /v) of barley malt and persimmon juice from the ‘Rojo Brillante’ variety. Fermentation took place under beer quality control parameters and the influence of persimmon juice on beer quality was investigated. Colour, turbidity, pH, titratable acidity, total soluble solids, sugars, organic acids, total phenolic compounds, antioxidant capacity and ethanol formation were determined during the fermentation process. These fruit beers, whose alcoholic contents were within the standards (3.6–5.63% v /v ethanol), were characterized by a normal acid pH (3.97–4.13) with citric and lactic acids the most abundant organic acids, a clear golden colour without turbidity [2.05–2.83 European Brewery Convention units], intermediate total phenolic compound values (283.0–327.1 mg GAE/L) and antioxidant activities between 1.65 and 5.78 mm TE/L. The persimmon beverage which contained 75% fruit juice was the most valued and preferred by the panelists followed by the 50:50% wort–persimmon beer. Copyright © 2017 The Institute of Brewing & Distilling     

Analysis of flavour compounds in beer with extruded corn starch as an adjunct

Extruded corn starch (ECS) was used as an adjunct during beer fermentation and the fermentable sugars in the wort made with ECS and cooked corn starch (CCS) were determined using high‐performance liquid chromatography. The flavour compounds of beer made using ECS and CCS were determined using headspace solid‐phase micro‐extraction gas chromatography–mass spectrometry, and eight volatile compounds in ECS and CCS beer were quantified using gas chromatography (GC). Five fermentable sugars (fructose, glucose, sucrose, maltose, maltotriose) were detected in both samples, and their content in ECS wort was higher than in CCS wort, except for maltose. Seventy‐three flavour compounds were identified and quantified in ECS beer, while 58 compounds were determined in CCS beer. Both ECS and CCS can be used to produce beer; however, the concentration of characteristic beer flavour compounds in ECS beer was higher than in CCS beer. Copyright © 2018 The Institute of Brewing & Distilling     

THE CONCENTRATION AND SIGNIFICANCE OF PYRUVATE IN BEER

Excretion of pyruvate takes place during the yeast-growth phase of fermentation, and, in batch fermentation, the extent of its accumulation varies directly with the extent of growth. Pyruvate excretion is not related to the content of pyruvate decarboxylase in the cells and is not influenced by the addition of thiamine or alanine to the wort; the pH of the wort exerts a slight influence on pyruvate excretion. Pyruvate may be metabolized by yeast towards the end of fermentation and during conditioning, so that the quantity present in beer is influenced by the extent and timing of yeast separation. The addition of sodium pyruvate to beer alters beer flavour by affecting the ‘mouth feel’ aspect of flavour; the minimum quantity required to do this varies in different beers over a range of 50–400 mg/litre.     

Enrichment of xanthohumol in the brewing process

Xanthohumol (XN), a component of hops, is lost in significant quantities in the conventional brewing process. In commercial beers less than 0.2 mg XN/L are found. In order to increase the yield of XN in the brewing process, the parameters of XN recovery were studied. During wort boiling, XN is largely isomerised to isoxanthohumol. Further losses are owing to the precipitation and absorption of XN to yeast cells and haze particles and by filtration. The use of XN-enriched hop products combined with a late hop dosage during wort boiling proved to be effective in increasing the XN content in beer. The yield was further raised by a low-pitching rate and the abnegation of beer stabilisation. The use of dark malts had a positive effect on the XN recovery. Investigations of roasted malt extracts revealed several high-molecular substances that are able to form complexes with XN. These complexes proved to be stable in the brewing process. Depending on the addition of roasted malt or special XN-enriched roasted malt extracts, dark beers with more than 10 mg XN/L were achieved. Results obtained led to a brewing technology that produced on an industrial scale pale wheat beer with more than 1 mg XN/L.     

A novel approach for the production of a non‐alcohol beer (≤0.5% abv) by a combination of limited fermentation and vacuum distillation

Despite the increasing demand, the production of non‐alcohol beers is still limited by unsatisfactory or artificial flavour and taste. In this study, a novel approach to producing non‐alcohol beer is presented, in which the alcohol‐reducing techniques, limited fermentation and vacuum distillation were combined. Starting from barley and wheat malts, wort with a low level of fermentable sugars was prepared by infusion mashing and lautering. Limited fermentation was carried out by Saccharomycodes ludwigii at 18°C. When the level of fermentable sugar was reduced by 25%, the fermented wort was quickly cooled from 18 to 0°C and held at that temperature for two days. The young beer was obtained after degassing and removal of yeast and was then subjected to vacuum distillation at 0.06 MPa to remove the alcohol. The concentrated extract is suitable for storage and transportation. The final product of non‐alcohol beer was obtained by dilution with deoxygenated water and carbonation with 6.0 g/L CO₂, followed by addition of 8–12% of regular beer and equilibration for 2–3 days to develop normal beer aroma. The results showed that the non‐alcohol beer had several favourable properties, including the alcohol level of <0.5% (v /v), colour 7.0 (EBC), thiobarbituric acid value of 1.05 and ratio of alcohols to esters of 1.08. Compared with other methods for the production of non‐alcohol beer, this novel approach produced a favourable alternative to regular beers with similar flavour characteristics and satisfactory stability. Copyright © 2017 The Institute of Brewing & Distilling     

A SIMPLE METHOD FOR THE ISOLATION OF PURINE NUCLEOSIDES FROM WORT AND BEER USING COLUMN CHROMATOGRAPHY

Column chromatography using a variety of dextran based gel matrices was used to fractionate nucleosides in wort and beer. The gel matrices Sephadex G10 and Sephasorb HP Ultrafine were found to elute guanosine, deoxyguanosine, adenosine and deoxyadenosine in a single fraction whereas Sephadex LH20 and Sephadex G25 both yielded two fractions containing nucleosides. The first nucleoside containing fraction from Sephadex LH20 contained guanosine and the second fraction contained deoxyguanosine, adenosine and deoxyadenosine. In contract the first nucleoside containing fraction from Sephadex G25 contained both adenosine and deoxyadenosine and the second fraction contained guanosine and deoxyguanosine. Fractionation of low molecular weight components from wort and beer by column chromatography provides a simple technique for the isolation of purine nucleosides. This may be used to monitor directly the presence of purine nucleosides throughout the brewing process and to obtain quantitative estimates of the content of purine nucleosides in beer.     

Nucleic Acid, Purine and Proximate Analyses of Mechanically Separated Beef and Veal

Deoxyribonucleic acid (DNA), ribonucleic acid (RNA), purine (adenine, guanine, hypoxanthine and xanthine) and proximate analyses of mechanically separated (MS) beef and veal were conducted to verify and evaluate changes in nucleic acid content which may result from mechanical separation. DNA and total nucleic acid levels were higher in both MS beef and veal whereas RNA levels were higher only in MS beef compared to hand deboned (HD) counterparts. Adenine, guanine and xanthine levels were higher in MS beef and veal, and hypoxanthine levels were lower compared to HD counterparts. Total purine content of MS beef did not differ from HD beef, whereas the purine content of MS veal was slightly higher than HD veal. It would appear that the addition of MS products to the diet would not significantly alter total purine consumption and hence should pose no risk to hyperuricemic individuals.     

Differences in protein content and foaming properties of cloudy beers based on wheat malt content

To investigate differences in protein content, all barley malt beer, wheat/barley malt beer and all wheat malt beer were brewed, and the protein during mashing, wort, fermentation and beer determined. It was shown that protein was mainly extracted during mashing and the protein rest phase, decreased in the early stages of fermentation and remained almost steady during wort boiling and cooling, in the middle and late stages of fermentation. By separating beer foam from beer, similar protein bands of 51.7, 40.0, 27.3, 14.8, 6.5 and < 6.5 kDa appeared in the three beers, defoamed beers and beer foams using the sodium dodecyl sulphate polyacrylamide gel electrophoresis. Quantitatively, protein bands of 6.5–14.8 and <6.5 kDa had the highest contents in the three beers. Unique bands at 34, 29.2, 23.0, 19.7 and 17.7 kDa were found in beer, defoamed beer and beer foam from wheat beer and all‐wheat malt beer, respectively. Wheat beer foam showed the best foam stability and the protein in all barley malt beer showed the best migration to the foam. The beer foam properties were influenced by not only protein content but also protein characteristics and/or origin. It is suggested that the barley malt contributed the beer foam ‘skeleton protein’ while protein components from wheat malt kept the foam stable. © 2018 The Institute of Brewing & Distilling     

Increased protein–thiol solubilization in sweet wort by addition of proteases during mashing

The flavour stability of beer is of major concern for breweries and is closely linked to oxidative processes in the beer. In this study, a new approach to boost the antioxidative capacity of beer was investigated. Protease treatment during mashing was performed in order to solubilize or extract more thiol‐containing protein‐derived compounds into the wort. Five different proteases were tested, and they were all capable of solubilizing increased amounts of thiols in wort during mashing but with different efficiencies. The wort was characterized by measuring total nitrogen by Kjeldahl, protein concentration by the Bradford method and protein composition by SDS–PAGE, in combination with matrix‐assisted laser desorption ionization–mass spectrometry. The results indicated that the proteases increased thiol concentrations by solubilizing thiol‐containing peptide fractions and not full‐length proteins. Copyright © 2014 The Institute of Brewing & Distilling     

THE OCCURRENCE OF TWO GEOMETRICAL ISOMERS OF 2,4,5-TRIMETHYL-1,3-DIOXOLANE IN BEER

Two geometrical isomers of 2,4,5-trimethyl-1,3-dioxolane have been detected in a range of commercial and experimental beers at levels up to ca 0.1 ppm. These compounds, plus a number of other dioxolanes, are present in unboiled wort but are lost by evaporation during wort boiling. The trimethyldioxolanes are then reformed during subsequent fermentation. The flavour threshold of a mixture of the two trimethyldioxolanes was found to be ca 0.9 ppm, at which concentration it produced in beer ‘phenolic’ and ‘astringent/drying’ flavour notes. However, these compounds are not present in sufficiently high concentrations to make a significant contribution to the flavour of beer.     

The effect of wort aeration on fermentation,maturation and volatile components of beer produced on an industrial scale

The aim of the study was to determine the effect of the initial beer wort aeration on the process of fermentation, maturation, content of the volatile components of beer and abundance and vitality of yeast biomass. The experiments were performed on an industrial scale, with fermentation and maturation performed in fermentation tanks with a capacity of 3800 hL. The wort was aerated with sterile air in quantities as follows: 7, 10 and 12 mg/L. During fermentation and maturation, the changes in the content of the extract, yeast growth and vitality and more importantly volatile components were investigated. The experiments showed that differentiated aeration has a significant impact on the course of fermentation and metabolic changes. With the increase in wort aeration, the content of acetaldehyde decreased and the concentration of higher alcohols increased. On the other hand, the contents of esters and vicinal diketones did not change. The level of aeration did not affect the final quality of beer. Copyright © 2017 The Institute of Brewing & Distilling