Thermostability variation in alleles of barley beta-amylase |
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Authors: | JK Eglinton P Langridge DE Evans |
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Institution: | The University of Adelaide, Waite Campus, Department of Plant Science, Glen Osmond, SA 5064, Australia |
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Abstract: | Thermostability assays in conjunction with IEF and molecular mapping were used to identify three beta-amylase alleles (Bmyl-Sd1, -Sd2L, -Sd2H) in cultivated barley and an additional allele (Bmy1-Sd3) in an accession of wild barley Hordeum vulgare ssp. spontaneum. The four forms of beta-amylase exhibit different rates of thermal inactivation in barley extracts. This variation was shown to persist after the proteolytic processing of the enzyme that occurs during germination. Three forms of beta-amylase representing the range of thermostabilities were purified and shown to have T50 temperatures of 56·8°C for the Sd2L enzyme, 58·5°C for the Sd1 enzyme, and 60·8°C for the Sd3 beta-amylase from wild barley. Analysis of the relationship between beta-amylase thermostability and fermentability, i.e. the yield of fermentable sugars obtained from starch hydrolysis during brewing in 42 commercial malt samples suggests that increased thermostability results in more efficient starch degradation. Screening for specific beta-amylase alleles is proposed as a method for increasing fermentability in malting barley. |
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Keywords: | beta-amylase thermostability mapping fermentability abr|AAL = apparent attenuation limit EBC = European Brewing Convention IOB = Institute of Brewing IEF = isoelectric focusing BSA=bovine serum albumin QTL=quantitative trait loci SDS = sodium dodecyl sulphate PAGE = polyacrylamide gel electrophoresis DP = diastatic power |
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