CONTENTS OF SIMPLE,POLYMERIC AND COMPLEXED FLAVANOLS IN WORTS AND BEERS AND THEIR RELATIONSHIP TO HAZE FORMATION

The highest concentrations of complexed and polymeric flavanols were found in the early runnings from a small-scale mash tun. Formation of break during and after boiling was accompanied by the removal of flavanols from solution, especially the complexed and polymeric fractions. Variations in boiling procedure affected the amount of break formed, the amount of residual soluble flavanols and the colloidal stability of the resultant worts. Colloidal stability in beer was influenced by the contents of simple flavanols and the availability of air during storage. Dimeric and trimeric flavanols seemed especially susceptible to oxidation which implied an important role in haze formation. Flavanols found in commercial beers were mainly monomeric and complexed forms.     

TANNING PROPERTIES OF FLAVANOLS IN BARLEY AND HOPS MEASURED BY REACTION WITH CINCHONINE SULPHATE IN RELATION TO HAZE FORMATION IN BEER

The flavanoid polyphenol extracts from barley and hops were each separated into six fractions by adsorption chromatography on Sephadex LH20. These fractions were further characterised by several analytical methods, including high-performance liquid chromatography and a colorimetric measurement of polymerisation index. The tanning powers of the fractions were graded according to their reactivities with cinchonine sulphate solution in a standardised turbidometric test. Whereas, almost 75% of the flavanols from Ark Royal barley were non-tanning oligomers almost 96% of the flavanols from Bullion hops were polymeric tannins. Reactivity of most of the barley flavanols with cinchonine sulphate was increased greatly by oxidation with peroxidase and hydrogen peroxide. Some effects of polymerisation, caused by enzyme action or by exposure to air, on oxidisable polyphenols (non-tannins) were measured using (+)-catechin, procyanidin B3 and prodelphinidin B3 in model systems. These, and other measurements on experimental and commercial beers indicated that oxidation of simple flavanols from barley produced polymers with tanning properties. In contrast, the hop flavanols when extracted apparently in their native forms, were capable of co-precipitating with polypeptides in beer. Treatment of beers with different stabilising agents, such as Polyclar AT and silica hydrogel, retarded haze formation by restricting ‘protein-polyphenol’ interactions.     

ANALYSIS COMMITTEE OF THE EUROPEAN BREWERY CONVENTION THE MEASUREMENT OF TOTAL POLYPHENOLS IN WORTS AND BEERS

A modification of the De Clerck & Jerumanis method for total polyphenols in beer is recommended for use in studying their relationship to haze in general and to the action of adsorbents in particular.     

THE REACTIONS BETWEEN POLYPHENOLS AND ALDEHYDES AND THE INFLUENCE OF ACETALDEHYDE ON HAZE FORMATION IN BEER

The reactions and interactions between proteins and polyphenols are, among other phenomena, responsible for haze formation in beer. The participation of aldehydes in the polymerisation of polyphenols is considered. The formation of phenolic Baeyer-type condensation products containing phenolic residues linked by CH₃CH-bridges through reaction with acetaldehyde is possible at the pH of beer (4.0). These and other reactions with acetaldehyde in beer participate in beer haze formation.     

PHENOLIC ACIDS IN BEERS AND WORTS

The total contents of phenolic acids measured by high-performance liquid-chromatography were 5–8 mg/litre in beers brewed in Ireland whereas 16–40 mg/litre were present in four other beers. In all beers the predominant phenolic acids were vanillic, p-coumaric and ferulic acids. Free phenolic acids were extracted from Emma barley grains and malt in very small amounts (15–28 mg/kg) but larger quantities (191 mg/kg) were released on mashing the malt. Little change occurred in the contents of phenolic acids on processing a lager wort through to the finished beer. Treatment with excess Polyclar AT removed astringent flavour and phenolic acids from an experimental ale but this flavour loss could not be accounted for by the adsorption of phenolic acids. The flavour threshold for a nine-component phenolic acid mixture in lager was between 50 mg/litre and 100 mg/litre.     

ESTIMATION OF CARBOHYDRATES IN WORTS AND BEERS BY GAS CHROMATOGRAPHY

Modifications of existing methods using trimethylsilyl ethers for estimating wort and beer carbohydrates are described. Samples to which a known amount of phenyl β-D-glucopyranoside is added as internal standard are quickly dried in vacuo at 40° C. prior to trimethylsilylation and chromatography. Peak areas of separated sugars are measured relative to the standard and are computed as the concentrations present in the original samples by way of calibration factors, obtained by similar treatment of known amounts of pure sugars. Standard deviations of less than 5% are obtained for glucose, maltose and maltotriose from twelve replicate analyses of a given wort. The technique, applied to a number of worts and beers of varied composition, compares favourably with existing methods of estimating individual sugars in worts and beers.     

THE MEASUREMENT OF DIMETHYL SULPHIDE PRECURSOR IN MALTS,ADJUNCTS, WORTS AND BEERS

Dimethyl sulphide in beer originates from a precursor in the malt. A method is described for the measurement of this precursor in brewing raw materials, wort and beer. The precursor levels in various green malts, kilned malts, and adjuncts are given. Excess methionine inhibits precursor uptake by yeast during fermentation. Residual precursor is still present in some commercial bottled beers.     

Chemical and sensory analyses of spray- and freezedried extracts of rooibos tea (Aspalathus linearis)

Spray- and freeze-dried rooibos tea extracts were prepared, and the soluble solids which precipitated upon cooling of the concentrate were isolated. Their effect on composition and sensory qualities of the dried tea was determined. Preparation of soluble rooibos teas resulted in significant flavour differences, but no preference for freshly brewed tea was found. The method of dehydration and removal of precipitated solids did not affect the flavour of the dried tea extract significantly. Removal of the precipitate resulted in marked decreases in total polyphenol, flavonoid, tannin, flavanol and proanthocyanidin content of the dried soluble product.     

茶多酚的应用及提取方法

茶多酚是一种天然的抗氧化剂,在食品加工、医药、日用化工等领域具有重要的应用.主要介绍了茶多酚的组成、性质及应用并对它主要的提取方法作了简要介绍.     

NITROGENOUS COMPONENTS OF WORTS AND BEERS BREWED FROM ALL-MALT AND MALT PLUS WHEAT FLOUR GRISTS

Worts and beers prepared from grists containing malt and wheat flour contain more and larger proteins than those prepared from grists containing only malt. These properties are related to the superior foam stability possessed by malt plus wheat flour beers. Malt solubilizes some of the wheat flour protein during mashing without subjecting it to significant proteolysis. Only very limited enzyme inhibition is exhibited. Finings residues in draught beers increase the precipitability of protein by sodium chloride and are particularly effective with malt plus wheat flour beers. The proteinaceous material isolated in this way has marked foam-stabilizing properties. The relationship between the protein removed by chilling the beer and salt-precipi-table protein and foam stability is also examined. Non-fining hazes from certain malt plus wheat flour beers are related to other beer protein fractions and some recommendations for brewery practice are made.     

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.     

ESTIMATION OF AMINO NITROGEN IN WORTS AND BEERS USING EITHER NINHYDRIN OR 2,4,6-TRINITROBENZENE-1-SULPHONIC ACID

Colorimetric methods of estimating amino nitrogen have been calibrated, taking either glycine or leucine as the standard, and used to measure the amino nitrogen contents of worts and beers. Comparison of the 2,4,6-trinitrobenzene-1-sulphonic acid method with the ninhydrin procedure shows that amino nitrogen values differing by up to 15–20% can be obtained for the same sample and moreover that worts behave differently from beers.     

茶多酚水提与醇提的比较研究

通过实验研究比较了茶多酚水提与醇提两种工艺的优缺点。采用正交试验,比较相同因素水平下水提与醇提茶多酚的提取率,结合生产成本,对两种工艺进行优劣评价。结果：同等条件下,醇提的效果好于水提,如果茶多酚需进一步通过树脂柱纯化,则水提工艺的后续成本低于醇提。结论：生产含量较低的茶多酚,宜选用醇提;生产高纯度的茶多酚,宜选用水提。     

THE USE OF 14C-LABELLED POLYPHENOLS TO STUDY HAZE FORMATION IN BEER

Haze formation in beer is claimed to involve the gradual polymerization of polyphenols and their subsequent reaction with proteins to form insoluble complexes. The mechanism of haze formation has now been studied using ¹⁴C-labelled epicatechin and dimeric catechin. Epicatechin does not polymerize to form dimeric or trimeric polyphenols when beer is stored and is only incorporated into beer haze to a small extent. Some of the epicatechin combines with nitrogen-containing compounds during storage to form soluble complexes. However, dimeric catechin does not form soluble complexes with nitrogen-containing compounds and instead there is a substantial incorporation of this dimer into beer haze. Dimeric polyphenols are important haze precursors which form insoluble complexes with one or more of the polypeptides of beer, probably by an oxidative coupling mechanism.     

FLAVOUR AND HAZE STABILITY DIFFERENCES IN UNHOPPED AND HOPPED ALL-MALT PILSNER BEERS BREWED WITH PROANTHOCYANIDIN-FREE AND WITH REGULAR MALT

Unhopped and hopped all-malt Pilsner beers were brewed with proanthocyanidin-free malt (ant 13–13×Rupal) and with regular malt (Gatinais). A tannin-free hop extract was used. The beers were analysed chemically and presented both to an expert and an untrained taste panel to detect possible preferences and differences in bitterness and astringency. The colloidal stability of the proanthocyanidin-free beers is superior to that of the regular ones. Paired comparison tests show that at the 3% significance level there is a difference in the appreciation of bitterness of the unhopped beers, the proanthocyanidin-free beer being the more bitter. The panelists do not detect differences in astringency and they have no preference for either beer. In the case of the hopped beers no bitterness, astringency or preference differences are found in paired comparison tests. Finally, no differences between hopped and unhopped proanthocyanidin-free and regular beers were found at the 5% significance level when using both an expert and an untrained panel in triangular experiments.     

FLAVOUR AND HAZE STABILITY DIFFERENCES DUE TO HOP TANNINS IN ALL-MALT PILSNER BEERS BREWED WITH PROANTHOCYANIDIN-FREE MALT

All-malt Pilsner beers were brewed with proanthocyanidin-free malt (ant 13 × 13 × Rupal). Hopping was with n-hexane tannin-free hop extract with or without n-hexane extracted hop residue or with whole leaf hops. The different beers were analysed chemically and presented to an expert panel to detect possible preferences and differences in bitterness and astringency. The impact of hop proantho-cyanidins on haze formation is comparable to that of malt proanthocyanidins. No differences between the beers were found in triangular tests. Statistical analysis of the paired comparison tests showed that hop proanthocyanidins do not contribute to the bitterness of beer since beer brewed with tannin-free hop extract is slightly more bitter than beer brewed with whole leaf hops. No differences in astringency were noted between beers brewed with or without hop proanthocyanidins and it was found that the panel expressed a very slight preference for beer brewed with n-hexane hop extract over beer brewed with both n-hexane hop extract and extracted hop residue.     

FLAVOUR AND HAZE STABILITY DIFFERENCES DUE TO HOP AND MALT TANNINS IN ALL-MALT PILSNER BEERS BREWED WITH PROANTHOCYANIDIN-FREE AND WITH REGULAR MALT

All-malt Pilsner beers were brewed with and without hop and malt proanthocyanidins by using regular malt and whole leaf hops as well as proanthocyanidin-free malt and n-hexane tannin-free hop extract. The different beers were analysed chemically and presented to an expert panel to detect possible differences in bitterness and astringency. The impact of proanthocyanidins on the formation of haze was demonstrated clearly. No differences between the beers were found in triangular tests although their levels of total polyphenolics and anthocyanogens differed by about 225 and 85 mg/litre. Statistical analysis of the paired comparison tests showed only very slight differences between beers with or without hop and malt proanthocyanidins. Thus, proanthocyanidin-free beer was considered less than slightly more bitter and astringent than regular beer and there was a very slight preference for the latter.     

ORAL PERCEPTION OF VISCOSITY IN FLUID FOODS AND MODEL SYSTEMS

The perceived in-mouth thickness ( T ) of a range of fluid foods and model systems was assessed by a trained sensory panel, using a ratio scaling technique, and correlated with objective measurements of viscosity (η_N). For Newtonian samples a simple linear correlation (r²= 0.98) is observed between log T and log η with exponent η= 0.22. The linear relationship between log T and log η for Newtonian materials was used to calculate the equivalent Newtonian viscosity (η_N) from subjective panel scores for the non-Newtonian samples studied. The shear rate at which observed viscosity is equal to η_N decreases with η_N, as reported previously by Shama and Sherman, but also decreases with increasing shear-rate dependence of viscosity. This implies oral perception of viscosity over a range of shear rates. Comparison of flow curves for samples assigned similar thickness scores, but showing very different shear thinning behaviour, suggests that the perceived thickness of extremely shear-thinning materials is dominated by their high viscosity at low rates of shear. As a simple practical index, viscosity at 10 s⁻¹ shows a better correlation (r²= 0.95) with the perceived thickness of the samples studied than values calculated by the methods suggested by Wood, or by Shama and Sherman (r²= 0.90 in both cases). The close agreement between panel scores for perceived thickness and perceived stickiness previously observed for concentrated solutions of random coil polysaccharides does not apply for several of the food systems studied, or for very concentrated solutions of xanthan.     

BROWNING BEHAVIOR OF TAURINE AND PROLINE IN MODEL AND DRIED SQUID SYSTEMS

Model systems containing taurine or proline mixed with glucose at pH 6.4 were adjusted for water activity (Aw) to 0.99, 0.90, 0.84, 0.75 and 0.60 with celite. The browning rates measured during 96 h at temperatures between 5° and 45°C increased with increased temperature and reduced water activity. The model system containing taurine had a higher browning rate than that with proline at the same Aw and temperature. The browning rate with taurine at Aw = 0.60 increased 34 times at 45°C and 7 times at 35°C compared to that at 25°C. Decreases in Aw from 0.90 to 0.60 resulted in increased browning rate, 4.1 times at 45°C and 1.3 times at 35°C. The browning rate in model systems with proline followed the same pattern. Temperature had a more pronounced effect on browning rate than Aw. Browning was very slow in model systems at temperatures below 25°C. Evidence is provided that the Maillard reaction occurred in the mantle of squid (Illex argentinus) during air drying at 35°C. Dehydration resulted in loss of 50% of the taurine (from 22.3 to 11.6 mmoles/100g dry mass) and more than 60% of the proline (from 23.4 to 8.9 mmoles/100g dry mass). Total free amino acids remained unchanged when the moisture level was above 50% or Aw = 0.95. The browning intensity of the squid mantle increased 5 fold during drying. Taurine and proline were digested most at water activity above 0.95, while other amino acids were lost at a greater rate in the intermediate water activity range.     

大孔吸附树脂对苹果渣中苹果多酚吸附性能的研究

研究了8种大孔吸附树脂对苹果渣中苹果多酚的吸附与解吸性能,其中AB-8、NKA、X-5、D4006树脂具有较大吸附量和解吸率,其静态吸附量:AB-8>X-5>D4006>NKA,解吸附率:X-5>NKA>AB-8>D4006,吸附速率:AB-8>X-5>NKA>D4006,从中选出AB-8树脂对苹果多酚进行纯化。动态吸附实验研究了提取液浓度、pH、流速对AB-8树脂吸附量的影响,适合的上柱浓度为1.1528mg/mL,pH为4.80,吸附流速为2BV/h,4倍树脂床体积的70%乙醇以1BV/h的流速进行洗脱即可基本将苹果多酚从AB-8树脂上解吸下来。