EFFECT OF STORAGE ON HOP EXTRACTS

Representative commercial hop extracts suffered no appreciable loss either of α- or β-acids or of bittering value when kept for 2 to 21 months in closed containers. Though there was loss of α- and β-acids on prolonged exposure of the extracts to air, it did not lead to a corresponding loss of bittering value. Of a range of commercial isomerized extracts, most proved satsifactorily stable on storage. However, when large losses of iso-α-acids did occur they were accompanied by corresponding reductions in bittering value. With reference to bittering compounds, there appeared to be no significant differences in the storage stability of beers bittered using hops or extracts of various types.     

酒花制品中异α-酸浓度的测定方法

采用分光光度法探索测定异α 酸、四氢异α 酸异构体、六氢异α 酸异构体等酒花制品中异α 酸的浓度 ,利用该方法对已知标准样品中异α 酸浓度进行检测 ,其重复性与精密度的结果表明 ,该方法的变异系数≤ 1 %,回收率在 99 8%～ 10 0 5 %之间 ;方法操作简单 ,可作为啤酒企业衡量评价异α 酸、四氢异α 酸异构体、六氢异α 酸异构体等酒花制品中异α 酸浓度的检测方法     

啤酒花浸膏的异构化工艺研究

α-酸是啤酒花软树脂中的一个重要组分,在啤酒酿造过程中会生成苦味更强、水溶性更好的异α-酸,是啤酒苦味的主要来源,也是提供啤酒防腐能力的主要成分。以正交试验为基础,直接以啤酒花浸膏为原料,不分离浸膏中的啤酒花油和β-酸等软树脂类,考察了溶剂、反应温度、反应体系的pH值、催化剂镁盐的使用量、以及反应时间等多个因素对异构化反应的影响。试验结果表明,尽管啤酒花浸膏的黏度较高,但无需添加溶剂稀释即可完成反应;在保证浸膏中α-酸完全异构,而啤酒花风味和β-酸基本不发生变化的情况下,镁盐与α-酸的摩尔比为2．0：1、反应温度为100℃、反应时间为60min、pH值为11．0作为异构化反应的最佳条件,并在此条件下进行了放大验证,浸膏中的异α-酸收率超过96％。     

PROPOSALS FOR THE EFFICIENT AND ECONOMICAL USE OF HOPS IN BREWING

The hop lupulin glands, which contain the essential oils and resin acids, can be separated effectively from the bulky and worthless bracts and residues in a mechanical process which avoids solvent contamination. The separation is accomplished in an air stream through a centrifugal sifter after the lupulin has been rubbed off in a disc pin mill. The separated lupulin can be broken open by grinding in a colloid mill and used to obtain a dry hop aroma in beers by an ‘instant’ process. The lupulin can be used to bitter beers either directly in the copper or in a pre-boiling process. It can also be used in an aqueous extraction process to yield, nearly quantatively, pure and separate extracts of the α- and β-acids. The α-acids can then be isomerized almost quantitatively and the β-acids can be oxidized to give a 50% yield of hulupones. The hop residues, when boiled with wort, give an approximately 50% utilization of the remaining α-acids. These isohumulones can then be enhanced by those obtained from the extracted α-acids and the bitterness can be supplemented by the hulupones obtained from the β-acids. Overall, this process is calculated to give a bitterness utilization equivalent to 87% calculated on the original α-acids.     

HUMULINIC ACID IN ISOMERIZED HOP EXTRACTS

Humulinic acid, which is not bitter, behaves similarly to iso-α-acids in some analytical estimations of beer bitterness. The humulinic acid content of a number of isomerized hop extracts was estimated using thin layer chromatography.     

QUANTITATIVE ANALYSIS OF HOPS AND HOP EXTRACTS BY HIGH PRESSURE ION EXCHANGE CHROMATOGRAPHY

A new analysis for hop acids in hops and hop extracts is described. It is based on recent developments in high pressure liquid chromatography using pellicular anion exchange column filling material. Quantitative evaluation of α-acids, β-acids and oxidation products in hops and hop extracts is carried out by standard addition of pure humulone. The α-acids are completely separated from other hop substances before quantitation. The results of α-acids determinations must therefore be more accurate than was formerly possible and they are compared with conductometric titration results which are systematically higher. This is to be expected as it becomes more and more obvious that paper strip and conductometric analysis are not selective enough and determine fractions as “α-acids” which are in fact oxidation products of the hop acids.     

THE DETERMINATION OF α- AND β-ACIDS IN HOPS AND HOP PRODUCTS USING HPLC

A rapid reversed phase HPLC method for the analysis for α- and β-acids in hops and hop products is described and has been evaluated. The method uses citric acid in the eluent as a complexing agent to overcome the irreversible adsorption effects shown by some columns, thus allowing optimum eluent pH to be selected. The precision of the method for analysis of hop extract has been determined giving relative standard deviations of 1·0% and 2·1% for α- and β-acids respectively. General agreement with results obtained using a polarimetric α-acids analysis method for hop extracts and hops has been demonstrated.     

QUANTITATIVE DETERMINATION OF HOP BITTER SUBSTANCES AND THEIR DERIVATIVES IN HOP EXTRACTS BY THIN LAYER CHROMATOGRAPHY

A method is described which allows the separation of hop bitter components and derivatives present in hop extracts by thin-layer chromatography on a mixture of silica gel and cellulose. This method can be used to evaluate the purity of hop extracts, isomerized hop extracts and complementary base extracts.     

CHEMISTRY OF HOP CONSTITUENTS. PART XXXIII REACTIONS OF β-ACIDS

Reactions of β-acids in wort and in mineral acids and alkali have been investigated. Under acidic conditions colupulone lost isopentenyl side chains forming two isomeric butenols. Under alkaline conditions two after-bitter compounds were formed, the structures of which were elucidated. They were also found in an isomerized hop extract.     

ORIGIN AND ESTIMATION OF THE GUSHING POTENTIAL OF ISOMERIZED HOP EXTRACTS

Two types of gushing promoter have been isolated from isomerized hop extracts. One type is a humulinicacid dehydration product which occurs rarely insuch extracts. The other type of gushing promoter consists of a mixture of oxidation products of hop resins, and is present in all the isomerized extracts examined. The higher the concentration of these oxidation products in a beer the greater is its tendency to gush. α-Acids and cohulupone have been shown to be effective gushing inhibitors. The gushing potential of an isomerized extract appears to be determined mainly by the relative proportions of oxidized materials and unchanged α-acid, present as contaminants. A method for determining the gushing susceptibility of a beer is described.     

PAPER STRIP ANALYSIS OF SUBSTANCES DERIVED FROM HOPS

Reasonably satisfactory methods exist for the analysis of α acids in hops. The analysis of iso α acids in beer is not so well developed. The same determinations for hop extracts and isomerized hop extracts are much more difficult. A new method for these determinations is now described. It is based on a chromatographic technique using buffered paper strips and is applicable not only to hop extracts, isomerized or not, but also to hops and to beer. The percentage of α acids and iso α acids can be determined in one analysis. Eventually the determination of humulinic aci ds β acids and hulupones will also be possible. After separating these substances from one another their amounts are determined spectrophotometrically. The method is very fast and is more accurate than any other known method.     

ESTIMATION OF α-, β- AND ISO-α-ACIDS IN HOPS,HOP PRODUCTS AND BEER USING HIGH PERFORMANCE LIQUID CHROMATOGRAPHY

Methods are described in which high performance liquid chromatography (HPLC) is used to estimate α-, β- and iso-α-acids in hops, hop products and beer. The chromatography relies on an isocratic elution of components from a polythene ‘cartridge’ column, and the method is calibrated with the pure substances as primary standards. Using such a column over 1000 analyses have been carried out without any significant loss in resolution or precision. The procedures are sufficiently rapid for use in commercial transactions and for quality control purposes. For hops and hop extracts coefficients of variation (%) of 2·5 and 0·8 were obtained respectively for α-acids. Values of 0·9 and 0·3 were obtained for iso-α-acids in isomerised extracts and beers respectively. For some isomerised extracts it has been observed that peaks in addition to those given by the iso-α-acids are present on the chromatogram. The current method recommended by the EBC over estimates the iso-α-acid content since these other constituents are included in the analysis.     

啤酒花苦味酸对血糖调节作用的研究

观察啤酒花超临界CO2 浸膏、β- 酸和六氢β- 酸对糖尿病小鼠血糖的调节作用。对四氧嘧啶复制的糖尿病小鼠的动物模型进行为期1w 的啤酒花超临界CO2 浸膏、β- 酸和六氢β- 酸的高、低剂量(30、15mg/kg)组和阳性药物格列本脲片灌胃治疗,观察小鼠的糖尿病“三多一少”的症状和治疗前后血糖和糖耐量的变化。与模型对照组相比,治疗组糖尿病小鼠的“三多一少”症状得到明显地改善,治疗前后血糖和糖耐量的变化结果表明,超临界CO2 浸膏和β- 酸的高剂量组治疗后的血糖值与正常组(p ＞ 0.05)无明显差异。对治疗后小鼠的血糖值采用单一自由度正交比较的方差分析表明,正常组小鼠的血糖值与模型组有极显著的差异,模型对照组与治疗组之间也具有非常显著的差异(p ＜ 0.01);在各治疗组之间,灌胃优降糖片的小鼠的治疗效果与灌胃不同剂量的β- 酸、六氢β- 酸和超临界CO2 浸膏样品的小鼠的总体治疗效果相当(p ＞ 0.05)。啤酒花超临界CO2 浸膏、β- 酸和六氢β- 酸对小鼠糖尿病症状均有一定的治疗作用,该作用与灌胃样品的剂量呈正相关关系。     

ISO-α-ACIDS CONTENT OF ISOMERIZED HOP EXTRACTS

Two chromatographic procedures for the analysis of iso-α-acids in isomerized extracts have been tested. Although one of the methods—a variant of the Hansen, Hetzel & Miller procedure—performed better than the other, it still falls short of the demands of commercial transactions. The methods available for the assay of iso-α-acids are reviewed.     

EUROPEAN BREWERY CONVENTION: ANALYSIS COMMITTEE SUB-COMMITTEE ON ANALYSIS OF HOPS AND EXTRACTS METHODS OF ANALYSIS OF HOP EXTRACTS

For the conductometric analysis of hop extracts the method described by Bishop,⁶ is satisfactory provided the extract is composed entirely of resins; extracts which contain additional water-soluble material should be analysed by an abbreviated Wöllmer technique. For isomerized extracts a qualitative examination should first be made, either by paper-strip chromatography or by thin-layer chromatography. A rapid counter-current distribution procedure is suitable for the analysis of isomerized extracts: the modified Rigby & Bethune method²² is appropriate only with extracts which are known to be free from α and β acids.     

AUTOMATED REPORTING ON THE QUALITY OF HOPS AND HOP PRODUCTS

The quality of a hop variety or a hop product can readily be assessed by a fully automated sequence of selective extraction, fractionation and quantitative analysis. To illustrate the elegance of the method, nine hop varieties and three hop extracts were compared with respect to the content of important marker compounds in the hop oils and of the hop acids. Supercritical fluid extraction at different densities of carbon dioxide was applied to extract selectively, the hop oils and the hop acids, respectively. The hop oils were further fractionated into an apolar and a polar fraction by solid phase extraction and consecutive elution with n-hexane and ethyl acetate. Separation and identification were achieved by capillary gas chromatography coupled to mass spectrometry. Myrcene, β;-caryophyllene, α;-humulene and β;-farnesene in the apolar fraction, linalool, undecan-2-one, tridecan-2-one and humuladienone in the polar fraction were selected for quantitative evaluation of the respective hop oils. Sulphur-containing compounds were revealed by capillary gas chromatography using sulphur-selective atomic emission detection. Complete separation and quantification of all hop α;-acids and β;-acids was effected by microemulsion electrokinetic chromatography coupled to diode array detection .     

ON THE ANALYSIS OF HOP BITTER ACID

A High Performance Liquid Chromatography (HPLC) method for automated routine analysis of the hop bitter acids is described. It allows the simultaneous determination of α-acids, β-acids, cohumulone and colupulone. This analysis based on two chromatographic runs takes less than 1/2 h. With this new method as reference, the defects of existing conductometric titration techniques were studied and a new improved conductometric method based on toluene-buffer extraction was developed. The new methods are applicable to all forms of hop products containing α- and β-acids. Analysis for α-acids with ether-acid aqueous methanol extraction gives results which are too high because of several basic defects.     

ANALYSIS OF ISOMERIZED HOP EXTRACTS PART I. ESTIMATION OF ISOHUMULONES

A rapid spectrophotometric method for the estimation of the isohumulone content of isomerized hop extracts is described. This method has given acceptable reproducibility even in the hands of inexperienced personnel; it also gives results in close agreement with those obtained by counter-current distribution techniques, which are also described.     

PREPARATION OF HOP EXTRACTS WITHOUT USING ORGANIC SOLVENTS

Extraction of hops with liquid carbon dioxide at ambient temperature provides an attractive means of producing hop extracts which are rich in α-acids and free from hard resins, polyphenols, pigments and residual organic solvents. The resulting yellow extracts give beer with a clean bitter flavour when they are added during wort boiling. Manufacturing costs using the process are likely to be substantially less than in a conventional hop extraction plant.     

Analysis of hop acids by capillary electrophoresis

Micellar electrokinetic chromatography (MEKC) was used to separate components of hop extracts. The separation of a sample of iso-α-acids by MEKC was better and faster than by an established HPLC method, giving <0.8% RSD on migration times and 5–10% RSD on peak areas. MEKC was also successfully used to separate the oxidation products of the α- and β-acids and thus to monitor the stability of hop products containing them. Furthermore, MEKC distinguished among samples of reduced iso-α-acids (rho-, tetrahydro- and hexahydro- derivatives).