Efficient enzymatic hydrolysis of cereal starches requires a proper hydrothermal pre-treatment. For malted barley, however, the exact initial temperature is presently unknown. Therefore, samples were micro-mashed according to accurately determined gelatinization and pasting temperatures. The impact on starch morphology, mash viscometry and sugar yields was recorded in the presence and absence of an amylase inhibitor to differentiate between morphological and enzymatic effects. Mashing at gelatinization onset temperatures (54.5–57.1 °C) led to negligible morphological and viscometric changes, whereas mashing at pasting onset temperatures (57.5–59.8 °C) induced significant starch granule swelling and degradation resulting in increased sugar yields (61.7% of upper reference limit). Complete hydrolysis of A-type and partial hydrolysis of B-type granules was achieved within only 10 min of mashing at higher temperatures (61.4–64.5 °C), resulting in a sugar yield of 97.5% as compared to the reference laboratory method mashing procedure (65 °C for 60 min). The results indicate that the beginning of starch pasting was correctly identified and point out the potential of an adapted process temperature control.
Modern varieties of malting barley allow mashing to proceed efficiently to enable saccharification and other biochemical processes. A prerequisite for starch hydrolysis is the disruption of starch granule structure by exceeding a grain specific pasting temperature. For grains, several viscometric methods based on the Rapid‐Visco‐Analyser were developed to determine variations in the pasting temperature reproducibly. Absolute pasting temperatures, as they are necessary to optimize the isothermal mashing process, cannot be determined owing to constructional and data evaluation related limitations. The aim of this research is to investigate and compensate for temperature deviations caused by standard data evaluation and lagging heat transfer from the heating unit into the sample. Accordingly, an improved determination of the pasting onset and a formula to compensate for temperature lags were developed. The optimized data leads to more accurate and reduced pasting temperatures compared with the standard method. The heat transfer was reproducibly quantified (Δϑ: 2.9–5.8°C) and integrated into a compensation formula (R2 = 0.99). It was found that the lag is strongly dependent on the actual sensor temperature but independent of the unpasted sample's initial viscosity. The results were applied on viscometric analyses (n = 161) to calculate the intrinsic pasting temperatures of barley malt. The determined temperature range is considerably lower than anticipated (56.7–60.5°C). Winter barley exhibits significantly lower pasting temperatures. The outcome of this work can be used to improve the accuracy of prospective analysis and to correct already existing viscometric raw data. Copyright © 2017 The Institute of Brewing & Distilling
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