DIASTATIC POWER IN MALTED BARLEY: CONTRIBUTIONS OF MALT PARAMETERS TO ITS DEVELOPMENT AND THE POTENTIAL OF BARLEY GRAINBETA-AMYLASE TO PREDICT MALT DIASTATIC POWER*

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Abstract
The malt parameters alpha-amylase, beta-amylase, limit dextrinase, protein and beta-glucan were each linearly related to the diastatic power measured in malted barley, with beta-amylase having the highest coefficient of variation (r2 = 0.63). Multivariate regression analysis derived a model comprising beta-amylase, alpna-amylase and limit dextrinase, with no significant interactions (p < 0.05). The model accounted for over 79% of the variation in diastatic power. These three malt parameters might be usefully targeted in breeding programs aiming to improve diastatic power in malted barley. The analysis of samples from two harvests showed that malt diastatic power is also significantly related to total grain beta-amylase activity (r2 ranging up to 0.61). This suggests that total grain beta-amylase can be used as a screening procedure for the diastatic power of experimental barley breeding lines. However the relationship is subject to significant genotypic (cultivar) and environmental influences (p < 0.001) and regression analysis found that diastatic power was significantly related to beta-amylase and cultivar (r2 = 0.76). Thus the use of a single regression curve comprising pooled data from several cultivars to relate diastatic power and total grain beta-amylase might be misleading. For barley breeding programs, the most effective use of the beta-amylase model as a criterion to identify experimental lines with unacceptable diastatic powers is to apply as a benchmark the total grain beta-amylase activity of a reference variety at each location, accepting lines with consistently higher beta-amylase activities for micromalting and further testing.