THE DETECTION OF ISINGLASS FININGS IN BEER

A method for the detection of isinglass finings in beer is described. Protein is precipitated from the beer with a large excess of sodium alginate and hydrolysed; the hydrolysate is examined colorimetrically for the presence of hydroxyproline. The presence of this imino acid, which is found in substantial proportions only in collagen and gelatin, indicates that the beer has been fined.     

EFFECTS OF LINOLEIC ACID SUPPLEMENTS ON THE SYNTHESIS BY YEAST OF LIPIDS AND ACETATE ESTERS

The concentrations of acetate esters in beer were reduced by up to 85% by addition of linoleic acid to the fermentation or by pitching with yeast previously enriched with this unsaturated fatty acid. Linoleic acid was rapidly incorporated into yeast lipids and was effective in reducing the rate of ethyl acetate formation within 2 h. Addition of linoleic acid altered the pattern of synthesis of fatty acids by yeast, causing a shift from medium toward long chain acids. Secondly, the amount of squalene in yeast was reduced by up to 70% whereas that of lanosterol was increased threefold. Since total yeast lipid synthesis was reduced by up to 40%, we conclude that less acetylCoA is synthesized in the presence of linoleic acid. Further, high concentrations of linoleic acid decreased the proportion of acetylCoA consumed by the synthesis of acetate esters. Therefore linoleic acid may directly decrease acetate ester synthesis in addition to its effect via reduction of acetylCoA availability.     

LIPID METABOLISM AND THE REGULATION OF VOLATILE ESTER SYNTHESIS IN SACCHAROMYCES CEREVISIAE

The specific rates at which ethyl acetate and iso-amyl acetate are produced by yeast increase markedly at that point in fermentation where syntheses of lipids (i.e. saturated fatty acids and squalene) stop. An increase in the acetyl-CoA: CoASH ratio, or a reduced availability of substrates (fatty acyl-CoAs) for acyl transferases, are possible reasons for such a stimulation of ester synthesis. Increased rates of ester production are not sustained but contribute significantly (ca. 30% for ethyl acetate) to the total concentration of acetate esters in beer fermented from 1·040 all-malt wort. Addition of linoleic acid (50 mg litre^?1) suppresses the induction of ester synthesis and reduces overall formation of both ethyl and iso-amyl acetates by ca. 80%. Possibly, linoleic acid exerts these effects either by directly inhibiting the activity of an ester-synthesising enzyme, or by allowing alternative use of acetyl-CoA for the synthesis of saturated fatty acids.     

气相色谱-质谱联用法分析苏尼特羔羊肉中共轭亚油酸含量

共轭亚油酸是亚油酸的一组几何和位置异构体，具有多种生理功能。作为瘤胃微生物的产物，反刍动物肉制品是共轭亚油酸异构体较丰富的天然来源，本研究利用气相色谱-质谱联用法分离测定了5月龄苏尼特羔羊肌肉和腹部脂肪中共轭亚油酸总含量，研究结果表明，背最长肌间脂肪中CLA相对百分含量平均为0．83％，腹部脂肪中CLA相对百分含量平均为0．99％。     

THE BITTERNESS OF HOP-DERIVED MATERIALS IN BEER

The bitterness of trans- and cis-isohumulones obtained both from beer and by alkaline isomerization of α-acids has been compared with the bitterness of hop resins and other materials extractable from beer. Trans-isohumulones and cis-isohumulones, obtained either from beer or by alkaline isomerization of α-acids, and hulupones have been shown to be the most bitter materials. Hulupones were only slightly less bitter than trans-and cis-isohumulones, which showed little difference in bitterness value when prepared directly, although the collective tasting results show a bias for a greater bittering associated with the cis-component. The hulupones, like the parent β-acid, possessed a distinctive aromatic flavour. α-Acids and other unidentified materials obtained from beer brewed with hops of a normal age have been found to possess a much lower level of bitterness. The observation that aged hops impart normal levels of tastable bitterness to beer has been confirmed at significant brewery level (60 brl.) using grists consisting solely of six year old hops. Approximately 35% of this bitterness is provided by isohumulones and the greater part of the remainder arises from materials soluble in low-boiling paraffinic hydrocarbon solvents. A known β-acid oxidation material has been isolated from fresh and old hops and from beers brewed with either fresh or old hops.     

THE DETERMINATION OF PAPAIN IN BEER

The quantitative determination of papain in beer has been achieved by means of turbidity measurements on a casein substrate. The method, which is quick and simple, will measure activities of the order of 1–20 p.p.m. of crude papain. This will cover any amount likely to be found in beer     

THE ORIGIN OF THE MEDIUM CHAIN LENGTH FATTY ACIDS PRESENT IN BEER

The medium chain length fatty acids that are excreted during fermentation are produced by synthesis and not by degradation. The fermentation of a wort supplemented with propionic acid (C₃) or valeric acid (C₅) leads to the excretion of nonanoic acid (C₉) in addition to the usual even chain acids. C₉ acid was not detected in the beer when the inoculated yeasts contained a high proportion of pentadecanoic acid (C₁₆) and heptadecanoic acid (C₁₇) or when the C₁₇ acid was added to the wort, demonstrating that a degradative route is unimportant. The content of the medium chain length fatty acids in beer varies directly with their content in yeast; thus the fatty acid composition of the beer reflects changes in the content of these acids in yeast brought about by alteration in the supply of oxygen or by the addition of C3 acid to wort.     

THE ROLE OF ACTIVE AND INACTIVATED PAPAIN IN BEER CHILLPROOFING

The mechanism of chillproofing of beer by papain has been studied in a series of three experiments. Changes in the molecular size of proteins and polypeptides have been monitored by chromatographic profiles on Sephadex G-25 columns. Simultaneously the production of free amino acids and changes in the colloidal stability of the beer were determined. The addition of active papain to beer affected all three parameters. By contrast when inactivated papain was added to beer neither the chromatographic profile nor the concentration of free amino acids were altered but an increase in colloidal stability occurred. The removal of active papain from beer did not affect its colloidal stability but the removal of inactivated papain from beer stabilised with this agent eliminated the chillproofing effect.     

THE ISOELECTRIC FOCUSING OF BEER PROTEINS IN POLYACRYLAMIDE GEL

A technique has been developed for fractionating beer proteins by isoelectric focusing in polyacrylamide gel which enables protein species with isoelectric points differing by as little as 0·1 pH unit to be separated as clearly defined bands. The isoelectric profile of an all-malt beer was found to be similar to that of the parent wort but significant changes occurred when a beer was stabilized in the laboratory by three different treatments.     

FURTHER STUDIES ON THE FOAM-STABILIZING SUBSTANCES IN BEER

A material containing both carbohydrate and protein together with some ferulic acid, and which has pronounced foam-stabilizing activity, has been isolated from beer. A fraction similar in constitution and activity to the beer constituent has been recovered from an aqueous extract of barley flour. These materials are comparable with a glycoprotein present in wheat flour; the latter has been shown to be effective in the stabilization of beer foam. There was little difference in the amount and activity of extracts prepared from different varieties of barley.     

METHODS FOR THE DETERMINATION OF VOLATILE NITROSAMINES IN MALT,WORT AND BEER

Methods for the analysis of beer, wort and malt for NDMA at the one in 10⁹ level using the thermal energy analyzer have been evaluated. The beer and wort procedure using Preptube extraction has been shown to give excellent results. For malt, the preparation of an aqueous extract, followed by analysis by the beer procedure, also gives excellent results. Vacuum distillation from mineral oil has also been examined for the analysis of malt. Providing sufficient aqueous phase is initially present, this procedure yields results similar to those from aqueous extraction. The methods will also detect NDEA, although no NDEA has been observed in any of the beer, wort or malt samples examined. NDMA has been observed to be present in bound forms in malt and Preptubes and is released by the addition of water     

PHENOLIC CONSTITUENTS OF BEER AND BREWING MATERIALS. II. THE ROLE OF POLYPHENOLS IN THE FORMATION OF NON-BIOLOGICAL HAZE

Simple and polymeric polyphenols differ in the way in which they influence the development of chill and permanent hazes in bottled beer. The addition of simple anthocyanogens to beer causes a marked increase in the rate of haze formation whereas added polymeric materials induce immediate and intense turbidities. Beer anthocyanogens constitute a class of materials ranging in complexity from simple compounds to heterogeneous polymers which sometimes include polyphenolic units that are incapable of yielding anthocyanidins with acid. The extent to which the various anthocyanogens present in beer are involved in haze formation is not reflected by their contributions to the overall anthocyanogen value of the beer. Haze-inducing polymers which contain no anthocyanogen residues may also be present in beer. The nature and origin of polyphenolic substances in beer and the methods by which they may polymerize to give immediate haze precursors are discussed.     

A COMPARISON OF PROTEIN ASSAYS FOR THE DETERMINATION OF THE PROTEIN CONCENTRATION OF BEER

Seven protein assays have been compared for determination of the protein content of beer. Dialysis and ultrafiltration have been used to investigate possible interference and the protein content of the samples has been simultaneously monitored by sodium dodecyl sulphate-polyacrylamide gel electro-phoresis. The Fisons NA2000 Nitrogen/Protein Analyzer gave identical results to the standard Kjeldahl method but both measure nitrogen-containing compounds rather than protein. Colorimetric methods based upon the biuret reaction (including the Lowry and bicinchoninic acid protein assays) are particularly prone to interference from reducing substances and gave protein concentration values dependent upon the sample volume. The protein dye-binding assays (Coomassie Brilliant Blue and pyrogallol red-molybdate methods) were optimal for beer protein analysis displaying minimal inter ference and giving reproducible protein concentration values consistent with the protein content of the beers as indicated by electrophoresis.     

EFFECT OF VARIOUS POLYPHENOLS ON THE RATE OF HAZE FORMATION IN BEER

The effect of the addition of a range of monomeric, dimeric and polymeric polyphenols to beer on the rate of haze formation has been examined. Monomeric polyphenols had no significant effect on haze formation. The addition to beer of dimeric or polymeric polyphenols caused a large increase in the rate of haze formation.     

ON THE DETERMINATION OF VOLATILE THIOLS IN BEER

The method of Ikeya for the determination of volatile thiols in beer by aspiration of these compounds into mercuric acetate has been examined. Cadmium acetate has been found to be unsuitable as an absorbant for removing hydrogen sulphide since it also combines with thiols. This reagent has been replaced by aqueous zinc acetate in a separate absorption trap. The proposed modification has the advantage of enabling estimations of hydrogen sulphide and of volatile thiols to be carried out on the same sample.     

DIFFERENCES IN UTILISATION OF THE ESSENTIAL OIL OF HOPS DURING THE PRODUCTION OF DRY-HOPPED AND LATE-HOPPED BEERS

Late-hopped and dry-hopped beers were prepared and their lipophilic constituents extracted using Amberlite XAD-2 resin. Examination of the volatile constituents by GC-MS confirmed that most of the hop oil added towards the end of wort boiling is lost by evaporation. Part of the material which survives boiling is chemically transformed by yeast during fermentation. Dry-hopped beer contained compounds more representative of the original hop oil than did the corresponding late-hopped beer. A liquid carbon dioxide extract of hops, rich in essential oil, has been fractionated by column chromatography on alumina-silica giving preparations which simulate either late-hop or dry-hop character.     

CHEMICAL CONSTITUENTS OF NYLON-66 BEER ADSORBATE. II. THIN-LAYER CHROMATOGRAPHY OF THE ACIDIC AND ALKALINE HYDROLYSIS PRODUCTS

The preparations obtained from the acidic and caustic desorbates of Nylon-66 beer adsorbates have been submitted to different hydrolytic procedures and the phenolics thus obtained examined by means of uni- and two-dimensional chromatography with the aid of appropriate reference compounds. A number of polyphenols and phenolic as well as cinnamic acids has been identified. The presence of trans-o-coumaric acid has not been previously reported in beer.     

THE ESTIMATION OF p-HYDROXYBENZYLAMINE IN BEER

A simple method has been developed to allow the estimation of p-hydroxy-benzylamine in beer in the presence of other amines including tyramine. Analysis of commercial beers has shown a low and variable content. At the levels found, p-hydroxybenzylamine seems unlikely to be of physiological significance even when monoamine oxidase inhibitor drugs are being taken. The biosynthetic route for p-hydroxybenzylamine has not been identified but synthesis of the compound appears to be associated with the barley husk.