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Pulsed Electric Field as a Means to Elevate Activity and Expression of α-Amylase in Barley (Hordeum vulgare L.) Malting

Zhang, Liang, Li, Chao-Qun, Jiang, Wei, Wu, Mangang, Rao, Sheng-Qi, Qian, Jian-Ya
Food and bioprocess technology 2019 v.12 no.6 pp. 1010-1020
Hordeum vulgare, RNA, alpha-amylase, barley, beers, calcium, calcium chloride, electric potential difference, enzyme activity, experimental design, genes, malting, malting barley, mashing, pulsed electric fields, regression analysis, response surface methodology, China
Poor quality of barley hinders badly the beer production in China. α-Amylase activity plays a very important role in malted barley (Hordeum vulgare L.) for beer production during the mashing process. Pulsed electric field (PEF) and Ca²⁺ in the form of CaCl₂ were introduced to elevate α-amylase activity of barley malt for modifying the quality, and positive consequences emerged. The influences of PEF operating parameters on α-amylase activity were investigated, and the parameter settings were optimized based on factorial experiments, and a highly (R² = 0.9859) correlated regression model was established using response surface methodology. An increment of about 29% for α-amylase activity was achieved at the optimal parameter settings as 8 kV of pulse voltage, 500 Hz of pulse frequency, 8 μs of pulse width, and 14 min of material residence time. The incorporation of PEF with Ca²⁺ demonstrated much better functions than the utilization of PEF or Ca²⁺ alone. The orthogonal experiment design was adopted to optimize the conditions for incorporation of PEF with Ca²⁺, and it showed that at 8 kV of pulse voltage, 500 Hz of pulse frequency, 7 μs of pulse width, 12 min of material residence time, and 80 mg L⁻¹ of Ca²⁺ concentration, the largest increment of over 54% for α-amylase activity was obtained. Evaluations of PEF and Ca²⁺ on Amy6-4, the gene responsible for α-amylase in barley seed, were made to look into the mechanism how they functioned in barley malting, and it was found that the elevation of α-amylase activity was because of the significant (P < 0.05) increase of the amounts of total RNA and Amy6-4 expression.