Optimized analytical parameters for the viscometric determination of pasting temperatures of barley malt

Abstract

Starch pasting is the prerequisite for subsequent enzymatic hydrolysis, required in numerous fermentation based industrial processes. Thermal pasting is induced by exceeding a raw material specific pasting temperature which can be determined viscometrically. The analytical parameters for this indirect analysis must however be adapted to raw material characteristics. For unmalted cereals several viscometric procedures were developed and approved. Although barley malt represents a major starch and enzyme source for the production of drinking alcohol, the analytical parameters were not adapted to the modifications induced by germination.The aim of this study was to investigate and evaluate parameters enabling a precise and reproducible determination of the pasting temperature of barley malt on basis of the commonly used rotational viscometer Rapid-Visco-Analyser.An optimal sample concentration (1:4) was determined by performing dilution series. The comparison of different evaluation criteria resulted in a slope threshold (5 mPa s/6 s) providing most accurate and reproducible results. Enzymatic inhibition with silver nitrate showed no alteration of the resulting pasting temperatures, proving that the grains intrinsic pasting temperature is independent of its amylolytic activity.The analytical parameters were evaluated intern- and externally by the analysis of heterogeneous samples. The resulting pasting temperatures ranged from 61.5 to 65.9 °C featuring a satisfying repeatability of 0.24 °C and reproducibility of 0.34 °C. The results were thereby independent of the laboratory or the used RVA model.Therefore, the newly developed procedure proved its applicability to determine the intrinsic pasting temperature of germinated barley and thus supplements existing procedures of unmalted grains. The method might be transferred to other germinated cereals in the future.