TUDIES ON THE FATTY ACID COMPOSITION OF HOP EXTRACT

Studies on fatty acids composition of hop extract obtained from Vurtenberg hop by extraction with a threecomponent mixture was carried out. It has been established that the content of fatty acids in hop extract is 0.3% ±5%. Fatty acids composition was determined by Gas-chromatographic analysis. The presence of the following unsaturated fatty acids has been proven: C_16:1; C_18:1; C_18:2; C_18:3; C_20:1 which represent about 40% of the general content of fatty acids in the extract.     

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.     

Identification and characterization of surface lipid components of the dried-bean beetle Acanthoscelides obtectus (Say) (Coleoptera: Bruchidae)

The dried-bean beetle Acanthoscelides obtectus is a major post-harvest pest, which can cause up to 30% losses from dry-stored beans. For the use of microbial agents for biocontrol of A. obtectus, it is of importance to identify cuticular lipids of this pest, if we are to understand the factors responsible for preferential adhesion or selective repulsion of entomopathogenic fungi that are potentially useful for biocontrol.The cuticular lipids of adult A. obtectus of both sexes were found to consist of hydrocarbons, aldehydes, methyl- and ethyl-esters of fatty acids, triacylglycerols, free fatty acids, alcohols and sterols. All the fatty acids identified in this study were found in both ether extracts and dichloromethane extracts. The dominant fraction of all the lipids isolated from this species consisted of C_16:0, C_18:0, C_18:1, C_18:2 and C_18:3 compounds. Males and females contained similar amounts of hexadecanoic acid, but there was a significant difference between the total amounts of C_18:0, C_18:1 and C_18:2 acids in the two groups. We have also successfully identified one of the sesquiterpenes present in the cuticle as α-farnesene.     

ISOMERIZED HOP EXTRACTS IN EXPERIMENTAL BREWING

The later that isomerized hop extracts were added during the brewing process the better was the utilization. Thin layer chromatography of the beers produced from a range of experimental brews using isomerized hop extracts showed that the ratios of the various bitter substances derived from hops differed only slightly. The utilization of isomerized extract is enhanced if residues normally discarded during the manufacture of extracts are added to wort.     

THE EFFECT OF HOP SUBSTANCES ON THE PRODUCTION OF FUSEL OIL

Unhopped beers contain more fusel oils than the corresponding normally hopped beers when certain strains of yeasts are used during fermentation. Water soluble fractions of hops and some soft resin constituents can influence fusel oil production. When hops are completely replaced by isomerized hop extracts the use of some additional hop fraction in the copper leads to the resulting beer having a similar fusel oil content to one hopped in the usual way. Partially hopped beers (0·25 lb./brl.) usually have similar fusel oil contents to beers produced using the normal quantity of hops (1·0 lb./brl.).     

Insect-derived compounds affect the behaviour of Liposcelis bostrychophila: Effects of combination and structure

A methanol fraction (MFr), prepared from 80% methanol extracts of whole Liposcelis bostrychophila, repels conspecifics when presented to groups of insects at 8000 ppm. To examine the reason for this repellent effect, bioassays tested a mixture of fatty acids and fatty acid methyl esters that are present in the MFr at concentrations ranging from 0.02 to 1.2 mM. This mixture of compounds contributes significantly to the repellence of the MFr. Therefore, an interaction among compounds can affect the settling behaviour of L. bostrychophila, even though the individual compounds do not have any effect. Other experiments further investigated the repellence of C₁₆ and C₁₈ fatty acids. In the majority of instances groups of insects consistently settled on the disc impregnated with either stearic acid or the compound with the most saturated bonds. The one exception was C_18:2 versus C_18:3 where more insects settled on C_18:3. This repellent effect of unsaturated fatty acids was also evident in five-way choice tests using a series of C₁₈ fatty acids, where stearic acid (10 mM) was consistently selected by groups of L. bostrychophila instead of oleic, linoleic and linolenic acid. The discrimination between and among fatty acids could be due to the differences in their physical properties which affect how the compounds are perceived by the insects. The fact that the most unsaturated fatty acids repel the insects presents the possibility that volatile insect-derived compounds could be utilised as repellents for this increasingly important pest.     

THE HIGH PERFORMANCE LIQUID CHROMATOGRAPHY OF HOP RESINS

Hop resins are eluted from a specially developed weak anion exchange bonded phase silica using citric acid, methanol, water, mixtures as eluent. Fresh and deteriorated hops and isomerized extracts have been examined. The ratio of the humulone congeners in different hop varieties and the conversion of α-acid to iso-α-acid during the hop boil have been measured.     

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.     

THE MANUFACTURE OF HOP CONCENTRATES AND EXTRACTS*

Manufacture of the traditional hop concentrate (i.e., a product containing the chemically unchanged natural hop constituents apart from useless inert material) is increasing both in Europe and in America; this traditional concentrate, which is added to the copper, retains the varietal characteristics of the parent hop. In determining replacement ratios it is important to assess bitterness by tasting trials, as analytical assessments of bitterness may give misleadingly low results when concentrates are used. Although chemically pre-isomerized extracts can be prepared for addition to sweet beer, it is improbable that this type of extract will be used extensively until a great deal more is known about transformations which take place during hop boiling; such an extract, however, does allow maximum utilization of hop bittering principles. The selection of hops for high α acid content and the separate addition of the flavour components such as hop oil appears to be a desirable development for the near future.     

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 fatty acid composition of the main phospholipid fractions of the rumen and abomasum tissues of foetal and adult sheep

The fatty acid composition has been determined on phosphatidyl choline, phos-phatidyl ethanolamine and sphingomyelin fractions earlier isolated from the rumen and abomasum tissues of foetal and of adult Romney sheep. The major proportion of polyunsaturated fatty acids was found in the phosphatidyl ethanolamine (17 to 43%) fraction and this was reduced in the phosphatidyl choline (7 to 25%) and sphingomyelin (1 to 4%) fractions. These features are in keeping with the results for mammalian tissues generally. The phosphatidyl ethanolamine fractions were further characterised by the low content of palmitic acid (<8%) compared with 25 to 30 % in the phosphatidyl choline fractions and 29 to 52% in the sphingomyelin fractions and by the occurrence of cyclopropane fatty acids. Consistent with the findings of other workers on mammalian tissues, the sphingomyelin fractions contained a relatively high content (16 to 27%) of higher w-saturated fatty acids including 22:0,23:0,24:0 and 25:0 and of tetracos-14-enoic (24:1 ω9) acid (5 to 16%). The total amounts of acids above C₂₀ tended to vary inversely with the levels of palmitic acid whereas the levels of stearic acid were relatively constant at 13 to 17%. Changes in fatty acid composition with age were generally not marked but the tissues of the foetus were distinguished from those of the foetus were distinguished from those of the adult by their substantial amount of eicosa-5,8,11-trienoic (20:3 ω9) acid together with relatively low contents of linoleic (18:2 ω6) and linolenic (18:3 ω3) acids and to a leser extent by reduced level of acids of the ω3 series. This was particularly reflected by the ratios of ω6/ω3 C₂₀ + C₂₂ acids in the phosphatidyl ethanolamine fractions, the valucs for the foetal rumen and abomasum tissues being 1.03 and 1.07, respectively, compared with corresponding values of 0.78 and 0.72 found in adult sheep. The results are consistent with a requirement for C₂₀ and C₂₂ polyunsaturated acids of the ω3 and ω6 series and some penetration of maternal fatty acids through the placenta. The resemblance between the fatty acid make-up and composition of foetal and maternal phospholipids suggests the possibiligy of transference of intact or lyso-phospholipids from the mother to the foetus through the placenta. However, such a possibility is counter-indicated by consideration of previous work using labelled intermediates and by the mechanism of conversion of linoleic and linolenic acids requiring their CoA derivatives in the formation of the corresponding polyunsaturated C₂₀ + C₂₂ acids. Nevertheless, the sharp cut-off of exogenous maternal fatty acids from the foetal triglycerides and their inclusion in the foetal phospholipids are not readily explainable.     

狮子头加工过程中脂肪及脂肪酸组分的变化

对狮子头加工过程中原料、凝胶、成型、炖煮等不同阶段的样品以及成品的粗脂肪含量、硫代巴比妥酸(TBARS)值及脂肪酸含量进行了测定。研究结果表明:狮子头在加工过程中脂肪含量显著下降(P0.05);从整体变化趋势上看,TBARS值逐渐增大,在加工过程中变化显著(P0.05);检测得出棕榈酸(C16:0)、硬脂酸(C18:0)、油酸(C18:1)以及亚油酸(C18:2)为主要脂肪酸组分。不同炖煮时间,狮子头所含饱和脂肪酸(SFA)含量变化显著(P0.05),单不饱和脂肪酸(MUFA)含量显著上升(P0.05),而多不饱和脂肪酸(PUFA)含量显著下降(P0.05)。在不同加工条件下,随着炖煮时间的延长,狮子头中脂肪含量呈减低趋势,因炖煮时间和温度及添加物的影响,狮子头中脂肪发生一定程度的氧化,其中脂肪酸组分含量也发生了一定的变化。     

The effect of oak tannin (Quercus robur) and hops (Humulus lupulus) on dietary nitrogen efficiency,methane emission,and milk fatty acid composition of dairy cows fed a low-protein diet including linseed

The objective of this study was to test the effects of inclusion of hop pellets (HP) and oak tannin extracts (OT) alone or in combination on N efficiency, methane (CH₄) emission, and milk production and composition in 2 experiments with dairy cows fed low-N rations supplemented with linseed. In both experiments, 6 lactating Holstein cows were assigned to 3 dietary treatments in a 3 × 3 duplicated Latin square design (21-d periods). Cows were fed a total mixed ration at a restricted level to meet their nutrient requirements. In experiment 1, 169 g dry matter (DM) of OT or 56 g DM of HP was included separately in the control diet (C1). In experiment 2, the additives were included together (OT-HP) in the control diet (C2) similar to C1. Diet C2 was compared with a control without linseed (C0). In experiment 1, the supplementation of the control diet with OT decreased urinary N excretion by 12%. In experiment 2, the combination of OT and HP decreased urinary N by 7%. Oak tannin extracts and HP alone or in combination did not influence the daily enteric CH₄ production of cows. Cows fed diet C0 produced 17% more enteric CH₄ daily than those fed diet C2. Intake of diet C2, which contained 6.7% extruded linseed on a DM basis (experiment 2), decreased the sum of 6:0 to 14:0 fatty acids (?16%) and palmitic acid (?26%) and increased the stearic acid (+50%), oleic acid (+36%), vaccenic acid (trans-11 18:1; +285%), rumenic acid (cis-9,trans-11 18:2; +235%), and α-linolenic acid (+100%) in milk fat. The supplementation of diet C2 with the OT-HP mixture further improved the milk's fatty acid composition. Intake of the OT alone increased α-linolenic acid by 17.7% (experiment 1). The results of this study show that at the economically acceptable dose we tested, hops had no effect on urinary N excretion, CH₄ emission, milk production, and milk composition. By contrast, supplementation of diets with oak tannin extract can be considered for reducing urinary N excretion. The combination of oak tannin and hops had no more effect than oak tannin alone except on the milk fatty acid profile, which was favorably influenced from a nutritional point of view.     

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.     

Reducing power of hop cultivars and beer ageing

Since lipid auto-oxidation during wort boiling is a determining for the appearance of staling flavour in aged beers, we have investigated the reducing power of hops added in the boiling kettle. An assay based on the inhibition of linoleic acid oxidation in the presence of an initiator [2,2′-azobis(2-amidino-propane) dihydrochloride=AAPH] enabled us to distinguish hop varieties and conditionings. Large differences in hop flavanoid contents explained the higher antioxidant activity of low-α-acid samples versus bitter varieties and CO₂ hop extracts. As expected, adding hop pellets to the kettle effectively increased the overall reducing activity of wort. Supercritical CO₂ hop extracts had no significant effect due to their extremely low level of polyphenols. The concentration of the very well-known marker of beer ageing, trans-2-nonenal, was lower in boiled wort exhibiting a better reducing power. The AAPH reducing power test applied to hops or worts was thus efficient to predict the nonenal synthesis during boiling. Hop varieties and conditionings emerged from this work as key-parameters for improving the reducing power of wort and the flavour stability of the final product.     

RAPID METHODS FOR THE ANALYSIS OF THE FATTY ACIDS OF FERMENTING WORT AND BEER (C6-C10) AND YEAST (C6-C18)

Relatively rapid and simple methods for measuring the content of the free C₆-C₁₀ fatty acids in fermenting wort and beer and of the total C₆-C₁₈ fatty acids in yeast are described. The acids are extracted, after saponification in the case of yeast, using a small volume of chloroform and analysed by gas chromatography as free fatty acids. The precision of the procedures is reasonable.     

Changes in the composition and state of unesterified C14–C32 fatty acids during their passage through the ovine digestive tract

The total amounts of C₁₄–C₃₂ and their composition in the free and anionic state (fatty acid soaps) in the diet, entering and leaving the small intestine and excreted in the faeces were determined in sheep fed white clover or white clover plus corn oil. Only small amounts of fatty acid soaps were found in the digesta entering the small intestine while the hind gut was the major site of soap formation as 66-73% of the faecal fatty acids were present as fatty acid soaps. In the digesta and faeces the distributions of the C₁₄ and C₃₂, expressed as a percentage of the total fatty acids, within the free and anionic states were similar. In contrast to the C₁₄–C₁₈ fatty acids no significant apparent absorption of the C₁₉–C₃₂ fatty acids occurred.     

Composition of adipose tissue triglycerides of neonatal and year-old lambs

Triglyccrides were isolated from perinephric (internal) and subcutaneous (external) adipose tissue obtained from neonatal lambs and from lambs which had been fed, until they were a year old, on a semi-synthetic ration or on a diet of grass cubes. the triglycerides went analysed for their fatty acid composition (including trans unsaturated acids) and for the intramolecular distribution of these acids between the primary and secondary alcoholic groups of the glycerol moiety. Whereas in the year-old lambs (and in adult sheep previously examined), the triglycerides of internal adipose tissue had a higher content of stearic acid and trans unsaturated acid than those of external tissues, the triglycerides from the perinephric and subcutaneous tissues of the neonatal lambs were very similar in fatty acid composition. Palmitic acid and C₁₈ mono-unsaturated acid together constituted more than 80% of the total acids. This composition resembles that of the subcutaneous triglycerides of the grown animal and suggests that, at all stages of growth, the triglycerides of external tissues are largely the result of endogenous synthesis. The fatty acids of the adipose tissues of the neonatal animals did not contain any of the acids of exogenous origin, such as those with trans double bonds, which characterise the triglycerides of the growing and mature animals, particularly those of the internal depots. Nevertheless, the intramolecular disposition of the fatty acids in the triglycerides formed in utero was similar to that previously observed in triglycerides from both the internal and external depots of the adult sheep. Saturated acids (palmitic and stearic acids) predominated amongst those esterified in the 1-and 3-positions of the glycerol moiety and unsaturated acids (almost entirely oleic acid) were the major components esterified in the 2-position. While the triglycerides from corresponding body sites in the two groups of year-old lambs were generally quite similar with respect to their content of palmitic acid, stearic acid and C₁₈ mono-unsaturated acid, the contribution of trans isomer to the total C₁₈ mono-unsaturated acid was considerably greater in the tissues (particularly perinephric tissue) of the animals fed on grass cube than in the tissues of those given the semi-synthetic ration. This difference between the two groups of lambs was associated with a corresponding difference in the proportions of C₁₈ trans unsaturated acid in the lipids of the rumen contents of the animals.     

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.     

Determination of fatty acid composition and total trans fatty acids of Turkish biscuits by capillary gas-liquid chromatography

 In this research, fatty acid composition and total trans fatty acid contents of six types of biscuit produced by four different Turkish companies were determined by capillary gas-liquid chromatography. Total fat contents of the biscuit samples ranged between 8.5% and 26.0%. The highest fat content was determined in sesame biscuits (average 24.4%) and the lowest in petit beurre biscuits (average 13.5%). Total fat contents varied even for the same type of biscuit as a result of the use of different recipes by each company. The major fatty acids in the samples were C_16 : 0, C_18 : 0, trans C_18 : 1, C_18 : 1, trans C_18 : 2 and C_18 : 2. Depending on the biscuit type, total unsaturated fatty acid contents were between 52.1% and 72.8%. The ranges of total trans fatty acid contents in biscuit types were petit beurre 1.9–29.0%, sesame 15.0–23.1%, baby 3.0–30.5%, oat 17.6–22.4%, cocoa 1.5–22.9% and finger 1.0–24.7%. It is clear from the results that the percentage of trans fatty acids in the total fat content is significant because of the use of hydrogenated vegetable oils in biscuit production. Received: 26 July 1999 / Revised version: 9 September 1999