Studies on barley malt kernel heterogeneity
Jenkinson, Helen Ruth
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Standard analysis of malt flour can mask the heterogeneity of hydrolytic enzyme activity. Kernel heterogeneity can lead to brewhouse problems and a product with unpredictable nitrogen and fermentable sugar content. The variability between individual grains of important malting characteristics was measured in malt samples produced under aerobic and anaerobic conditions. Various parameters (including germinative energy, germinative capacity, moisture content, β-glucanase activity, friability and homogeneity) were measured to ensure that the 5 d aerobic Optic malt, produced in Heriot-Watt university micromaltings, was viable and of commercial quality. The 5 d aerobic malt kernels produced at Simpsons Maltings in Berwick-Upon- Tweed were heavier than the micromalt. Commercially produced malt kernels had higher levels of fermentable sugars and soluble nitrogen than the micromalt despite lower α-amylase, β-amylase and ‘total’ limit dextrinase activity. Differences between the 5 d aerobic micromalt and the 5 d aerobic commercially produced malt are indicative of why micromalting cannot always be used as a model system for what is happening industrially and must be modelled on commercial practice. Subjecting 5 d aerobic micromalt to 24 h anaerobic incubation resulted in increased levels of fermentable sugars per l wort. 24 h anoxia also resulted in increased α-amylase and limit dextrinase activities. There are potential industrial applications for this anaerobic wort. Limit dextrinase inhibitor protein present in crude extract prepared from mature barley, eluted from a gel filtration column at a higher molecular weight than expected. The limit dextrinase inhibitor protein either aggregates or binds to other proteins in a high molecular weight complex.