Autolytic Action of Gumases in Malting and Brewing

130

A direct and specific enzymatic method is described for the determination of 1,3:1,4-p-glucans in barley grain and other cereals.In the procedure, purified, amylase-free, bacterial 1,3:1,4-p-glucan hydrolase is used to depolymerize the 1,3:1,4-p-glucan in autoclaved and ethanol-extracted flour prepared from whole grain. The liberated oligoglucosides are extracted with 80% (vol/vol) ethanol and, following acid hydrolysis, measured by the glucose oxidase method. The method can be used to measure total p-glucan and p-glucan in 65°C water-soluble and water-insoluble fractions of cereal grains. The procedure has been applied to barley grains allowed to develop under controlled environmental conditions and to a series of barleys of different geographical origins. The results for Canadian cultivars are compared with estimates based on viscometric data for the same samples. The 1,3:1,4-p-glucan content of a number of other cereals has also been measured.Key words: barley, glucan, P-glucanase. IntroductionWhen present in elevated levels, the l,3:l,4-/3-glucans of barley produce highly viscous solutions which can lead to problems during post-malting operations in the brewing process.3-13'30'31'*"'*0 High glucan levels in barley also lower the feeding quality of the grain." In view of these fac tors, methods for the quantification of the glucan are of practical significance in predicting the malting or feeding quality of grain samples, in monitoring changes in glucan level during malting and subsequent brewing processes and in assessing breeding programmes aimed at lowering the barley /S-glucan content. Since l,3:l,4-/3-glucans arc also found in the leaves, stems, husks, coleoptilcs and roots of cereals and other monocotyledonous plants,3 a method for their quantification has a more general significance.Preece & Mackenzie41 showed that not all barley 0-glucan is extractable with water and that subsequent extractions with alkali released more glucan. Chaotropic agents such as urea solutions also extract additional glucan.20'*8 Most of the previously documented methods, summarized in Table I, determine only glucan cxtractable in water at 40°C or 65°C. It is clear however that the originally insoluble glucan fraction which is released during malting and in mashing should be considered when assessing grain quality. It is this glucan fraction which is likely to be incompletely degraded and form viscous solutions and precipitates during the subsequent brewing operations. This paper reports a direct and specific enzymatic method for the determination of total, water-soluble and waterinsoluble p-glucan in cereal grains and other plant materials. The enzyme used is the /3-glucan endo-hydrolase (E.C. 3.2.1.73)"'" from Bacillus subtilis which specifically hydrolyses 1,4-linkagcs in /3-glucans containing both 1,3-and 1,4-linkages such as barley and oat /3-glucans, lichenin and the reduced Pneumococcal Type III polysaccharide.3 It has no action on either l,4-|3-glucans (cellulose) or 1,3-0-glucans of the callose type which are known to...

Section: Resultsmentioning

confidence: 99%

ENZYMATIC DETERMINATION OF 1,3:1,4-Β-Glucans IN BARLEY GRAIN AND OTHER CEREALS†

Anderson

Cook

Stone

1978

130

The VISCOSITY OF WORTS IN RELATION TO THEIR CONTENT OF Β-Glucan

Scott¹

1972

A procedure is given for assessing that proportion of wort viscosity which is attributable to β‐glucan. Worts obtained from unkilned samples of malt which have been processed for 54 or 72 h show enhanced viscosity. This is principally due to β‐glucan although the contribution of other constituents, absent from the wort of fully modified malt, is of significance. Barley variety is shown to have a pronounced effect on wort viscosity. Insoluble β‐glucan is brought into solution in mashes at 65° C. The β‐glucan isolated from malt which has been inactivated using aqueous ethanol prior to extraction at 65° C, is of higher specific viscosity than that isolated from control worts prepared at the same temperature. The introduction of a rest by mashing initially at 40° C results in the production of wort of lower viscosity, a decrease in the β‐glucan content of the wort and a reduction in the specific viscosity of the β‐glucan. There is no apparent relationship between the endo‐β‐glucanase content of the malts and either the viscosity of derived worts or the degree of breakdown of β‐glucan which occurred during malting and mashing. Abrasion of barley, which is a factor assisting the distribution of enzymes during malting, acts to reduce wort viscosity.

DETERMINATION OF NON-STARCH POLYSACCHARIDES IN BARLEY BREEDING PROGRAMMES¹

Bendelow

1975

A technique is described for the selection of low extractable non-starch polysaccharide content in early generations of barley breeding programmes. An estimate of extractable /9-glucan is obtained from the viscosity of an extract prepared by mashing barley at 50°C in an oc-aniylase-papain solution. The procedure is calibrated using solutions of known concentration of /9-glucan precipitated from barley extract by ethanol.