Germination kinetics and amylolytic activity of ultrasound-pretreated purple corn during malting

BACKGROUND: Purple corn (Zea mays L.) is a pigmented cereal of Andean origin with documented nutraceutical and brewing potential. Malting performance depends critically on amylolytic enzyme activity, and power ultrasound has been proposed as a pretreatment to enhance germination and enzymatic potential in cereals. RESULTS: Hydrated corn grains were sonicated (37 kHz, 32.5 W L⁻¹) for 5, 10, and 15 min in an ultrasound water bath prior to germination. Germination kinetics were evaluated for 4 days using a modified Gompertz model, and α- and β-amylase activities were monitored throughout germination and drying (50 °C, 0.2 m s⁻¹). Ultrasound pretreatment tended to reduce germination percentage at exposure times ≥10 min, although no significant changes were observed in the intrinsic kinetic parameters. α-Amylase activity was not significantly affected, whereas β-amylase activity decreased by approximately 40% after 72 h germination at longer treatments. Drying kinetics, moisture–water activity relationships during drying, and enzymatic stability during drying were not influenced by ultrasound. CONCLUSION: These results indicate that power ultrasound, under the tested conditions, which included a temperature rise consistent with thermosonication, does not enhance purple corn malting performance and may negatively affect β-amylase activity. Future studies should incorporate temperature-matched controls, starch and reducing sugar quantification, and evaluation of additional malt-quality endpoints to fully characterize the impact of ultrasound on pigmented maize malting.