Effect of Mashing Temperatures and Endo-β-Glucanase on β-Glucan Content of Malt Worts

Similar basal levels of β-D-glucans were released into worts produced at 45°C from enzymically active or inactivated flours of milled malts. In contrast, significantly higher levels of β-D-glucans were found in worts derived from either enzymically active or inactivated malt flours mashed at 65°C. In general, mashing temperature may play a more important role in releasing β-D-glucans during mashing than enzymes described as β-glucan-releasing. In this context, the physical release of β-D-glucan during mashing should be separated from the enzymic release and degradation of β-D-glucan which occur during malting.     

β-GLUCAN AND β-GLUCAN SOLUBILASE IN MALTING AND MASHING

During malting the water-insoluble β-glucan of barley is diminished whilst water-soluble gum is little decreased. The amount of β-glucan surviving into malt depends on variety but barleys rich in glucan give malts with high β-glucan levels. The β-glucan content of barley depends on variety and growth site. β-Glucan solubilase survives mashing and catalyses the release of hemicellulose into solution. There is no correlation between the β-glucan content of malt and the amount released into wort. However, barley adjuncts containing high levels of β-glucan give worts rich in β-glucan. β-Glucan dissolution in mashing is dependent on time, temperature, grist particle size and liquor: grist ratio. Use of adjuncts derived from barley contribute relatively more β-glucan in wort, coinciding with reduced rates of wort separation, but these can be increased by using a β-glucanase produced by growing the fungus Trichoderma viride on spent grains.     

THE INFLUENCE OF β-GLUCANASE ON EFFICIENCY OF WORT SEPARATION

Treatment of mixed grists of malt and either barley flakes or barley flour with β-glucanase during infusion mashing at 65°C improves both the rate of run-off of wort and the total yield of extract. The total amount of non-starchy polysaccharide in solution is increased but the high molecular weight β-glucan fraction is decreased by the addition of β-glucanase. An improvement in wort separation is associated with a lowering of wort viscosity but it is concluded that the major factor influencing wort separation is the structure of the mash bed and the presence of inert material to which protein, glucan and pentosans can bind. A micro-mashing unit is described which simulates the problems of wort separation encountered with certain grists in deep infusion mash tuns.     

THE DEGRADATION OF β-GLUCAN DURING MALTING AND MASHING: THE ROLE OF β-GLUCANASE

Significant β-glucanolysis takes place during mashing and is catalysed by a β-glucanase which is specific to mixed-linkage β-glucans. The enzyme develops during the germination of barley, but is rapidly and extensively destroyed in kilning. Partially-purified preparations of β-glucanase are protected from denaturation by heat if their solutions are adjusted to pH 4 or if bovine serum albumin is added. However the most effective stabiliser of the enzyme is reduced glutathione. Oligosaccharides containing three and four glucosyl units are produced by the action of β-glucanase and they are further converted during malting and mashing by a different enzyme(s) to disaccharides and glucose.     

啤酒生产过程中氧化还原酶系的研究

啤酒生产过程中的氧化还原酶与啤酒风味陈化紧密相关。低水分下，其耐温活性远高于其它几种酶，在麦芽中酶活升高比例最大（与大麦中的酶活相比），其在糖化过程中氧化多酚的能力远大于多酚氧化酶。糖化过程中迅速失活，而脂肪酸氧化酶在糖化起始的低温阶段仍有部分酶活，影响不饱和脂肪酸的氧化。焙燥过程中适当延长50～70℃温度段时间，可有效降低麦芽中氧化还原酶的酶活。结合这些酶的性质，从部分抑制它们的活性角度出发，在糖化过程中，于50～60℃进行隔氧处理，可经济、有效的减少影响风味氧化的前驱物质的含量。同一质量等级不同品种的麦芽的氧化还原酶系差别相当大，相应制得的麦汁中与风味氧化有关的物质含量也有较大差别，这可能是造成不同批次原料酿造的成品啤酒风味保鲜期不稳定的原因之一。     

Changes in the Concentrations of the Polyphenolic Constituents of Sorghum during Malting and Mashing

Sorghum varieties differed widely in their content of polyphenolic compounds. The concentrations of all phenolic compounds increased several-fold during malting and the degree of increase differed with variety. The concentration of polyphenols extracted in wort was dependent, to a great extent, on the temperature of mashing.     

Malt Performance is More Related to Inhomogeneity of Protein and β‐Glucan Breakdown than to Standard Malt Analyses

Nitrogen analyses of the grains of samples of commercial malts indicate that β‐glucan breakdown and the uniformity of malt modification are influenced by uniformity of distribution of grain protein. It is proposed that for normal malting barley, variations in malt modification are related to the different percentages of grains which contain high levels and different types of proteins which resist enzymic modification during malting. This kind of inhomogeneity of malt modification can cause brewhouse problems but cannot be detected with precision by standard malt analyses.     

Alterations of the Profiles of Iso‐α‐Acids During Beer Ageing,Marked Instability of Trans‐Iso‐α‐Acids and Implications for Beer Bitterness Consistency in Relation to Tetrahydroiso‐α‐Acids

Age‐induced decomposition of iso‐α‐acids, the main bittering principles of beer, determines the consistency of the beer bitter taste. In this study, the profiles of iso‐α‐acids in selected high‐quality top‐fermented and lager beers were monitored by quantitative high‐performance liquid chromatography at various time intervals during ageing. The degradation of the iso‐α‐acids as a function of time is represented by the ratio, in percentage, of the sum of the concentrations of trans‐isocohumulone and trans‐isohumulone to the sum of the concentrations of cis‐isocohumulone and cis‐isohumulone. This parameter is relevant with respect to the evaluation of bitterness deterioration in aged beers. Trans‐iso‐α‐acids having a shelf half‐life of less than one year proved to be significantly less stable than cis‐iso‐α‐acids, but it appears feasible to counteract degradation if a suitable beer matrix is available. The fate of the trans‐iso‐α‐acids in particular adversely affects beer bitterness consistency. In addition to using hop products containing low amounts of trans‐iso‐α‐acids, brewers may profit of the remarkable stability of tetrahydroiso‐α‐acids, even on prolonged storage, for the production of consistently bitter beers.     

Comparing effects of α‐ vs. β‐chitosan coating and emulsion coatings on egg quality during room temperature storage

Effects of α‐ and β‐chitosan (CH), soybean oil (SO) and their emulsions (CH:SO = 2:3) as coating materials on selected internal quality and sensory properties of eggs were evaluated during 5 weeks storage at 25 °C. After 3 weeks of storage, α‐ and β‐CH‐coated eggs changed to B grade, while SO‐ and emulsion‐coated eggs preserved grade A quality. Weight loss of eggs coated with SO and CH:SO emulsions was <2.0% vs. 5.3–5.8% for noncoated and CH‐coated eggs after 5 weeks of storage. β‐CH (0.9%) maintained lower weight loss of eggs than α‐CH (1.2%) only at 1‐week storage. Albumen pH of eggs coated with SO and CH:SO emulsions decreased progressively throughout storage. Eggs coated with β‐CH:SO emulsion and SO were significantly glossier than noncoated eggs. Consumers indicated positive purchase intent (69.17–76.67%) for all coated eggs. Overall, α‐CH:SO and β‐CH:SO emulsions extended egg shelf life by at least 3 weeks during room temperature storage.     

α-GLUCOSIDASE ACTIVITY OF SORGHUM AND BARLEY MALTS

Sorghum malt α-glucosidase activity was highest at pH 3.75 while that of barley malt was highest at pH 4.6. At pH 5.4 employed in mashing sorghum malt α-glucosidase was more active than the corresponding enzyme of barley malt. α-Glucosidase was partly extracted in water but was readily extracted when L-cysteine was included in the extraction buffer, pH 8. Sorghum malt made at 30°C had higher α-glucosidase activities than the corresponding malts made at 20°C and 25°C. Nevertheless, the sorghum malts made at 20°C and 25°C produced worts which contained more glucose than worts of malt made at 30°C. Although barley malts contained more α-glucosidase activity than sorghum malts, the worts of barley had the lowest levels of glucose. The limitation to maltose production in sorghum worts, produced at 65°C, is due to inadequate gelatinization of starch and not to limitation to β-amylase and α-amylase activities. Gelatinization of the starch granules of sorghum malt in the decantation mashing procedure resulted in the production of sorghum worts which contained high levels of maltose, especially when sorghum malt was produced at 30°C. Although the β-amylase and α-amylase levels of barley malt was significantly higher than those of sorghum malted optimally at 30°C, sorghum worts contained higher levels of glucose and equivalent levels of maltose to those of barley malt. It would appear that the individual activities of α-glucosidase, α-amylase and β-amylase of sorghum malts or barley malts do not correlate with the sugar profile of the corresponding worts. In consequence, specifications for enzymes such as α-amylase and β-amylase in malt is best set at a range of values rather than as single values.     

Free α-amino nitrogen production in sorghum beer mashing

Free α-amino nitrogen (FAN) is an essential nutrient for yeast growth during fermentation. Under normal conditions of sorghum beer mashing, 60°C at pH 4.0, production of FAN by proteolysis accounts for approximately 30% of wort FAN, the remaining 70% being preformed in the malt and adjunct. The quality of the FAN in sorghum beer worts is good as it does not contain a high percentage of proline. Optimum conditions for FAN production during mashing are 51°C and pH 4.6. Wort FAN was increased proportionally by raising the ratio of sorghum malt to adjunct and conversely decreased by raising the ratio of adjunct to malt. FAN was also increased by the addition to the mash of a microbial proteolytic enzyme. Wort FAN is directly proportional to malt FAN.     

ESTIMATION OF β-GLUCANASE

A radial gel diffusion procedure for the estimation of β-glucanase in malt has been compared with the Recommended Method of the Institute of Brewing in an informal collaborative trial. The Analysis Committee judged that the results obtained by both methods were not sufficiently precise and agreed that neither method would be included in Recommended Methods. However, reference will be made that both methods have been published and are available for use in commercial transactions.     

Inhibitory activities of kaempferol,galangin, carnosic acid and polydatin against glycation and α‐amylase and α‐glucosidase enzymes

The activities of four natural phenolics, kaempferol, galangin, carnosic acid and polydatin in scavenging free radicals, inhibiting advanced glycation end‐product (AGE) formation, α‐amylase and α‐glucosidase and trapping methylglyoxal (MGO), were evaluated in this study. Carnosic acid and galangin had the highest activity in scavenging free radicals. Kaempferol and galangin had the greatest activity in preventing bovine serum albumin (BSA) against glycation and reducing glycated proteins. Polydatin had the greatest performance in trapping MGO to reduce glycation reaction. However, there was no significant difference for kaempferol, galangin and carnosic acid in inhibiting AGE formation by BSA‐MGO reaction. Kaempferol, galangin and carnosic acid were the competitive inhibitors for α‐amylase, while kaempferol and carnosic acid were noncompetitive inhibitors for α‐glucosidase. However, polydatin showed as a mixed noncompetitive inhibitor for both α‐amylase and α‐glucosidase. The results indicated that the four natural phenolics have potential in inhibiting AGE production and the digestive enzymatic activity with different mechanisms.