Effects of genotype and environment on β-glucan and dietary fiber contents of hull-less barleys grown in Turkey

In this study, the effects of cultivar and environment on β-glucan and total dietary fibre (TDF) contents and various quality characteristics of hull-less barley samples grown in Turkey were investigated. There were significant differences among the barley genotypes and different locations in terms of β-glucan and TDF content (p < 0.05). Significant correlations were found between β-glucan content and some quality criteria (sieve analysis and 1000 kernel weight). The correlations between TDF and grain yield, hectolitre weight, 1000 kernel weight and protein content were also generally significant. These results indicated that environmental and genetic factors are involved in the total β-glucan content of barley.     

EFFECTS OF GAMMA IRRADIATION OF BARLEY AND MALT ON MALTING QUALITY

Two two-rowed barley cultivars, Tokak and Clerine, were irradiated at two different dose ranges (0.05–0.75 kGy and 0.5–5.0 kGy) using a ⁶⁰Co source. Irradiation of barley at the medium levels before malting had detrimental effects on most of the malt quality criteria. The detrimental effects of irradiation was lower at doses up to 0.25 kGy. Irradiation of malt samples caused either slight or no deterioration of quality characteristics .     

Changes in β-glucan and other carbohydrate components of barley during malting

Changes in total (1→3), (1→4)-β-glucan content were followed during the micro-malting of nine varieties of barley with a wide range of malting qualities. These changes were related to estimates of endosperm modification based upon staining with Calcofluor. β-Glucan content declined from an average of 3.54% in the barley to 0.75% in the malt. Pentosan and total starch (including starch-derived oligosaccharides) levels showed comparatively little change during malting. β-Glucan composition of the barley was a poor indicator of malting performance. However, the β-glucan, starch and xylose contents of the malt all showed significant correlations with malt extract. Estimation of malt β-glucan content gave the best indication of malt quality. Direct determination of β-glucan may be of more value in assessing malt quality than indirect techniques based upon assessing modification of stained grains.     

THE RELATIONSHIP BETWEEN TOTAL β-GLUCAN OF MALT AND MALT QUALITY

The total β-glucan content of barley and malts has been determined using a direct enzyme degradation method incorporating measures to ensure inactivation of any contaminating amyloglucosidase. Results for barleys range between 2·7 and 4·4% w/w and indicate genetic variation in the β-glucan content. Malts produced by both a laboratory micromalting procedure and commercially have been analysed for total β-glucan, extract and 70°C mash viscosity at different stages of germination and in the end product. A very good correlation has been found between total β-glucan and fine-concentrated extract difference values showing that in a fully modified malt having a negligible extract difference value, all the β-glucan material is degraded. The extract difference value had been demonstrated earlier to be closely linked with brewhouse extract yield. The total β-glucan of malt, therefore, is directly associated with achievable extract in the brewhouse and is the most important biochemical factor determining the extractability of a malt.     

EVALUATION OF MALTING QUALITY IN A BARLEY BREEDING PROGRAMME USE OF α-AMYLASE AND β-GLUCAN LEVLES IN MALT AS PRESELECTION TOOLS

Analysis according to the EBC protocol, immunological determination of a α-amylase and estimation of malt β-glucan using the Calcofluor-FIA method, were used to screen 327 barley breeding lines for malting quality. The results obtained with the α-amylase and β-glucan methods are highly correlated to the important malt quality paramters: extract yield and β-glucan content in the wort. It is recommended that either of the two methods, which are simple to perform are used as prescreening tools in breeding programmes for malting barley.     

COLD STERILE FILTRATION: A SMALL SCALE FILTRATION TEST AND INVESTIGATION OF MEMBRANE PLUGGING

Beer brewed from 24 commercially and bag malted samples by a small scale brewing method was assessed by a micro-filtration efficiency (MFE) test designed to emulate the cold-sterile (membrane or micro-) filtration process. The level of malt derived beer components with the potential to reduce MFE, such as β-glucan, arabinoxylan, protein and polyphenol, were consistent over duplicate beer batches suggesting that beer quality was reproducible using the small scale method. The small scale MFE test was able to differentiate (P<0.001) between beer brewed from distinct malt samples in a reproducible fashion, suggesting that the test is effective in assessing beer MFE in the laboratory. Subsequently, the effects of various malt derived beer components on micro-filtration were investigated. MFE (measured as <i>V_max) was negatively correlated with beer arabinoxylan content (r=–0.62, P<0.01), suggesting that the arabinoxylan content of malt, and subsequently beer, may influence MFE. Total beer β-glucan was not significantly related to beer MFE (r=-0.36). However, it was likely that β-glucan molecules of high molecular weight influenced MFE more so than the total β-glucan content. Beer viscosity, which was correlated to both beer β-glucan and arabinoxylan content (r=0.86, P<0.001 and r=0.68, P<0.05, respectively), correlated with V_max (r=-0.81, P<0.001) .     

FACTORS INFLUENCING THE HARDNESS (MILLING ENERGY) AND MALTING QUALITY OF BARLEY

The hardness of samples of 41 barley cultivars grown in Australia was determined by measuring milling energy. The milling energy was negatively correlated (r= ?0.49) with the starch and positively correlated (r=0.50) with the β-glucan content. The correlation with protein content was not significant. This suggests that a low starch content and a high β-glucan content may contribute to hardness but other factors may probably also be involved. The extent of modification of these barley samples measured by Calcofluor staining after steeping and 48 h of germination was correlated with the grain hardness (r= ?0.56). Factors contributing to grain hardness may limit the rate of endosperm modification during malting, indicating the value of selecting softer cultivars for malting.     

A RAPID AND SIMPLE METHOD FOR THE DETERMINATION OF STARCH AND β-GLUCAN IN BARLEY AND MALT

A simple and precise method suitable for the routine determination of starch and β-glucan in barley and malt is described. Perchloric acid (50 mM) was used to effect rapid (3 min) and exhaustive extraction of both glucans which were then measured directly from this single extract by specific enzymic hydrolysis of the individual glucans to glucose. The glucose was also measured enzymically. Little or no acid hydrolysis of starch or β-glucan was observed under the extraction conditions used; most or all of the free glucose could be attributed to hydrolysis of sucrose. Complete solubilisation of the gum and hemicellulosic components of β-glucan was achieved. Preincubation of the acid extracts with protease prior to amyloglucosidase digestion resulted in higher measurements (approximately 4% w/w) of starch. The method was used to measure the levels of starch and β-glucan in five varieties of barley with contrasting malting quality, in micro-malts prepared from these samples and in commercial lager and ale malts.     

A SIMPLE AND RAPID TEST FOR ASSESSMENT OF ENDOSPERM PROTEIN MODIFICATION DURING MALTING*

A simple test has been developed for the quantitation of endosperm protein modification in malts. Barley meals or ground malts were extracted with a suitable solvent and the clarified hordein extract diluted into an appropriate precipitant. Of a variety of extractants and precipitants investigated, 1M urea-1% (v/v) mercaptoethanol and 1M sodium chloride were respectively found to be most suitable. Under these conditions a turbid suspension forms; the turbidity of extracts decreased progressively during malting. Turbidity was due to selective precipitation of a specific group of “B” hordeins. In an analysis of nine varieties differing in malting qualities, a significant correlation between the reduction in extract turbidity and cell wall modification (Calcofluor staining) was observed at 48 hours' malting. In addition, for each variety examined, protein modification occurred about one day before carbohydrate modification. Analysis of commercial malts and several samples of selected cultivars from regional trials found good correlations between malt turbidities and percent malt extract and Kolbach index. The test is rapid (10–90 mins) and can be used to screen large numbers of samples; since it is simpler than alpha—amino nitrogen or Kolbach index determination, it may be of use in analysis of malts for protein modification.     

DIFFERENCES IN MALTING PERFORMANCE BETWEEN BARLEYS GROWN IN SPAIN AND SCOTLAND

Two barley genotypes were grown, in 2 seasons, at sites in both Scotland and Spain. The development of enzyme levels and endosperm modification were assayed, over the final 3 days of malting. Spanish grown samples demonstrated faster and more extensive synthesis of both α-amylase and β-glucanase, more rapid cell wall modification and a greater reduction in milling energy during malting than Scottish grown samples. Malt milling energy was strongly associated with cell wall breakdown, which was a limiting step in modification of Scottish, but not Spanish, grown samples. Extract levels were not related to α-amylase activity, but Kolbach index exhibited an association with extract at both sites.     

A comparative study of oat (Avena sativa) cultivars as brewing adjuncts

Brewing with high levels of unmalted oats (Avena sativa) has proven to be successful despite their high contents of β-glucan, protein, and fat. However, little is known about the effect of different oat cultivars on the quality and processability of mashes and worts. Therefore, the aim of this study was to compare the mashing performance of eight oat cultivars, selected because of their low contents of β-glucan, protein, fat, and/or high starch content, when substituting 20 or 40 % barley malt. For this purpose, seven husked (A. sativa L. ‘Lutz’, ‘Buggy’, ‘Galaxy’, ‘Scorpion’, ‘Typhon’, ‘Ivory’, ‘Curly’) and one naked oat cultivar (A. sativa var. nuda ‘NORD 07/711’) were fully characterized using standard methods, Lab-on-a-Chip capillary electrophoresis, and scanning electron microscopy. The rheological behavior of mashes containing up to 40 % of each oat cultivar was measured during mashing by applying a Physica MCR rheometer. In addition, the quality of worts obtained from laboratory-scale mashing trials was analyzed particularly with regard to their cytolytic, proteolytic, and amylolytic properties. The substitution of up to 40 % barley malt with husked or naked oats resulted in significantly higher pH values, β-glucan contents, and viscosities as well as significantly lower soluble nitrogen and polyphenol contents, color values, filtration rates, and apparent attenuation limits. Naked oats contained significantly less β-glucan as well as more protein and starch than the seven husked oat cultivars. The replacement of barley malt with naked oats resulted in a constant extract yield, whereas the use of husked oats caused significant extract losses.     

MALT CYTOLYTIC ACTIVITY OF BARLEYS OF DIVERSE ORIGINS AND ITS RELATION TO MALTABILITY*

The inter-relations of malt cytolytic activity, barley β-glucan (gum) content and two wort properties were studied for 12 two-row varieties. Although barley gum contents differed considerably, these differences were not correlated with wort viscosity of green malt, and the positive association with extract yield of green malt was only significant (r =0·83**) if one variety was omitted from the calculation. Cytolytic activity was directly correlated with extract yield (r = 0·77**) if another anomalous variety was excluded. The inverse relation (r =-0·57) between cytolytic activity and wort viscosity was not quite significant at the 5% level. The present study provides additional evidence of the importance of cytolytic activity in malting and it is suggested that testing for this character could be of importance in selection for potential malt extract and general maltability in breeding programmes involving barleys of diverse origins.     

Use of a scanning near-infrared reflectance spectrophotometer for assessment of the malting potential of barley

A scanning near-infrared reflectance spectrophotometer was calibrated for the estimation of barley protein, moisture, total β-glucan and predicted malt extract. About 50 samples covering the range normally encountered in selection in barley breeding were used for each calibration. The best prediction equations each using three wavelengths, gave the following root mean square differences for the samples used in the calibration; nitrogen, 0.042%; moisture, 0.22%; total β-glucan, 0.26%; predicted malt extract, 1.4%. However, prediction of samples not in the calibration set was always slightly less accurate. These four characters were predicted in about 25 s allowing rapid screening for malting quality of large numbers of barley samples. The speed and simplicity with which successful calibrations could be produced suggests that the regular updating of calibrations to include barley from new seasons or regions should be possible.     

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.     

Malting Performance of Barley Cultivar Mixtures from the UK and Poland

Two sets of barley cultivar mixtures, one from cultivars grown in the UK and one from cultivars grown in Poland, were included, along with their component cultivars, in trials at the Scottish Crop Research Institute over two seasons. In the second year, two levels of nitrogen fertilisation were compared. Laboratory scale malting revealed three mixtures with extracts equal to, or significantly higher than, those of all of their components. Increased nitrogen fertilisation gave higher diastatic power, but reduced hot water extract in mixtures and component cultivars. Polish mixtures and their component cultivars showed a higher Kolbach index but a slower rate of filtration, following malt extraction, than their UK counterparts. It was concluded that the malting performance of the mixtures was largely determined by the nature of the germplasm from which they were constructed and the conditions under which they were grown. Careful selection of components should, therefore, permit development of barley mixtures acceptable for malting.     

Malting Behaviour of Barleys Grown in Canada and Spain as Related to Hordein and Enzyme Content

To continue our effort to analyse the genetic (varietal) and environmental (sites and years) effects on malting quality of barley, we have field‐tested four barley varieties, two‐ and six‐rowed, European and North American, in Spain and Canada in 1998 and 1999. The Spanish trials were autumn‐sown whereas the Canadian ones were spring‐sown. Barley grain was analysed for total protein and hordein contents and micromalted. Canadian‐grown barleys had significantly lower contents of grain protein and all‐three hordein fractions than the Spanish ones. They also had lower malt respiratory losses, wort β‐glucan and viscosity but lower fine‐ and coarse‐ground malt extract yield, friability, free amino nitrogen, Kolbach index, α‐amylase and diastatic power. In other words, the Canadian‐grown barleys, despite showing lower protein and hordein contents, produced malt of inferior quality than their Spanish counterparts, which, overall, produced higher quantities of degrading enzymes (amylolytic, proteolytic and cytolytic) during germination, thus being able to attain higher extract yield levels.     

The impact of barley nitrogen fertilization rate on barley brewing using a commercial enzyme (Ondea Pro)

Two Australian (Buloke and Commander) and two Canadian (CDC Meredith and Bentley) barley varieties were grown under four levels of nitrogen fertilization (0, 20, 40 and 80 kg ha^?1). Barley samples were assessed by barley brewing with the Ondea Pro enzyme cocktail for mashing analysis and were compared with typical malt brewing quality specifications. The study observed that increased nitrogen fertilization resulted in increased barley kernel nitrogen content which significantly impacted a range of wort quality parameters including increased soluble nitrogen, free amino nitrogen and barley beta‐amylase level, but also reduced extract, barley Kolbach index, β‐glucan and colour. Increased grain nitrogen had relatively little effect on apparent attenuation limit, lautering and barley limit dextrinase level. Knowledge of the effects of interactions between barley of different qualities (e.g. nitrogen content) and the Ondea Pro enzymes on wort quality will result in enhanced barley to directly and efficiently brew good quality beer, to better satisfy the quality expectations of brewers. Copyright © 2018 The Institute of Brewing & Distilling     

ENZYMIC QUANTIFICATION OF (1→3) (1→4)-β-D-GLUCAN IN BARLEY AND MALT

A simple and quantitative method for the determination of (1→3) (1→4)-β-D-glucan in barley flour and malt is described. The method allows direct analysis of β-glucan in flour and malt slurries. Mixed-linkage β-glucan is specifically depolymerized with a highly purified (1→3) (1→4)-β-D-glucanase (lichenase), from Bacillus subtilis, to tri-, tetra- and higher degree of polymerization (d.p.) oligosaccharides. These oligosaccharides are then specifically and quantitatively hydrolysed to glucose using purified β-D-glucosidase. The glucose is then specifically determined using glucose oxidase/peroxidase reagent. Since barley flours contain only low levels of glucose, and maltosaccharides do not interfere with the assay, removal of low d.p. sugars is not necessary. Blank values are determined for each sample allowing the direct measurement of β-glucan in maltsamples.α-Amylasedoes not interfere with the assay. The method issuitable for the routineanalysis of β-glucan in barley samples derived from breeding programs; 50 samples can be analysed by a single operator in a day. Evaluation of the technique on different days has indicated a mean standard error of 0–1 for barley flour samples containing 3–8 and 4–6% (w/w) β-glucan content.     

HIGH PERFORMANCE LIQUID CHROMATOGRAPHY OF BARLEY PROTEINS: RELATIVE QUANTITIES OF HORDEIN FRACTIONS CORRELATE WITH MALT EXTRACT

Several high performance liquid chromatography (HPLC) approaches have been used to study the relationships between amounts of particular groups of grain storage proteins (hordeins) and malt extract, using two sets of barley samples. The areas of several chromatogram peaks varied between samples in a manner that correlated with malt extract. Size-exclusion HPLC of protein aggregates extracted by sonication gave negative correlations of the relative areas of the three largest chromatogram peaks with malt extract in a set of 39 samples of the one variety, but not in a set of samples of 8 varieties grown at 4–5 sites. Under reducing conditions, disulphide-bonded hordeins were quantitatively extracted and the proportion of hordein in the largest peak, comprised of D- and B-hordeins, correlated well with malt extract in both sets of samples. The hordeins sequentially extracted into 50% (v/v) 1-propanol and 50% (v/v) 1-propanol-50 mM dithiothreitol (DTT) were also analysed by reversed-phase HPLC, and could be resolved into several peaks of B-, C- and D- hordeins. Relationships between the amount of certain C- hordeins in the propanol extract, and certain B- hordeins in the propanol-DTT extract and malt extract were seen. As well as providing a better understanding of the relationship between barley grain protein composition and malting quality, these HPLC methods are useful additional methods to enable partial prediction of malt extract using un-malted barley.