Abstract
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.
Highlights
Malted barley is predominantly used in the brewing and distilling industry as a combined source of starch and amylolytic enzymes to produce ethanol
Gelatinization onset temperatures (GTO ), which were obtained by differential scanning calorimetry (DSC) measurements, ranged from 54.5 to 57.1 ◦ C (Figure 1), which are in a similar range as reported by others [12] for barley starch
It is important to highlight that these results did not overlap with the viscometrically determined pasting onset temperatures (PTO ), ranging from 57.5 to 59.8 ◦ C
Summary
Malted barley is predominantly used in the brewing and distilling industry as a combined source of starch and amylolytic enzymes to produce ethanol. The resulting grist is blended with tempered water (mashing) to induce swelling and partial disruption of the microscopic starch granules as well as further increase the contact surface for enzymatic hydrolysis This transformation occurs in the presence of excess water at a characteristic temperature, which is referred to as either gelatinization (GT) or pasting temperature (PT). It was proposed that the optimal initial mashing temperature should be as high as necessary to ensure quick starch accessibility, but concurrently, as low as possible to preserve the activity of thermolabile enzymes as long as possible Up to now this optimal process temperature, considering fluctuating raw material properties, has been unknown and was not applied in breweries and distilleries. The impact on starch morphology, particle size distribution, viscometric behavior as well as the production of fermentable sugars was investigated in the presence and absence of amylolytic inhibitors, allowing us to differentiate between morphological and enzymatic effects
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