Table of Contents
A method for the determination of hop diastatic power - part 1
P. C. Wietstock, T. Luetzenberger, M. Biendl, B. Gibson
The enzymatic potential of hops has only recently become a subject of investigation because of a rising interest in hop forward beer styles which are often dry-hopped. In this work, a method for quantification of the diastatic activity of hops was developed. Hops were incubated with a potato starch substrate for 48 hours. Using response surface methodology, the independent factors: starch concentration (1 - 3 % w/v), hop concentration (5 - 15 g/L), and incubation temperature (25 - 35 °C) were varied and optimized. Fructose, glucose, maltose, and maltotriose were analyzed by HPLC after incubation. Because hops possess amyloglucosidase activity, which can degrade one maltose unit to two glucose units, measuring solely maltose or glucose cannot be recommended. Total mono hexoses, as the sum of glucose plus two times maltose, was found to produce more appropriate results and was followed for measuring the diastatic activity of hops. A starch concentration of 3 % (w/v), a hop concentration of 15 g/L, and an incubation temperature of 35 °C were found to be the optimal process parameters for determining hop diastatic activity. 14 different German hop varieties were tested with the optimized methodology and were correlated with the release of fermentable sugars from a lager beer by hop diastatic enzymes. Furthermore, the pH of the starch substrate, which in initial tests was pH 6.6, was adjusted to pH 5.5 or pH 4.5 in subsequent tests. While all substrates showed significant Pearson correlation coefficients for maltose and total mono hexoses, a pH of 6.6 showed the best correlation (r = 0.849 - 0.853, p < 0.001) and a linear coefficient of determination of R2 = 0.72 was found. Using a beta-limit dextrin substrate instead of potato starch yielded very low and insignificant correlations. Further investigations will aim at looking for even more suitable starch or dextrin substrates. Altogether, this approach shows promise for the development of a reliable and reproducible method to determine hop diastatic activity.
Descriptors: hops, hop creep, amylases, diastatic activity, enzymes
BrewingScience, 74 (July/August 2021), pp. 92-99
