Ultrasound-assisted processing improves germination and mashing efficiency and the functional quality of pumpkin seed-based fermented beverages.

Abstract

This study evaluated the combined effects of ultrasound-assisted hydration (25 kHz, 38 W/L, 20 min, 25 °C), followed by germination (72 h at 25 °C), and ultrasound-assisted mashing performed under 0 %, 50 %, or 100 % ultrasound application during each isothermal resting stage (25 kHz, 38 W/L, 25 °C). The effects of these processing conditions on the technological performance, fermentation kinetics, and bioactive potential of fermented beverages produced from pumpkin seed flour were evaluated. Ultrasound-assisted mashing, particularly when combined with ultrasound pretreatment and germination, enhanced compound release, increasing total soluble solids, reducing sugars, and soluble proteins by up to 2.5-, 25.4-, and 5.8-fold, respectively. The improved substrate availability accelerated fermentation, increasing acidification rates by up to 2.21-fold and reducing fermentation time by up to 44 % to reach the final endpoint of pH 4.6. During refrigerated storage (15 days at 5 °C), pH and acidity remained stable (p > 0.05), while probiotic viability remained above 9 log CFU/mL. Ultrasound-assisted mashing also increased beverage luminosity and whiteness index, whereas germination enhanced yellowness index. The combined processing strategy improved the functional quality of the beverages, increasing total phenolic content (2.3-fold), in vitro antioxidant activity (up to 5.1-fold by ABTS and 4.9-fold by DPPH), as well as in vitro α-glucosidase inhibitory activity (2.6-fold) and in vitro angiotensin-converting enzyme (ACE) inhibitory activity (1.9-fold) after fermentation. Overall, the integration of ultrasound-assisted hydration, germination, and ultrasound-assisted mashing improved compound release, fermentation efficiency, and the functional quality of the resulting beverages. Both ultrasound-assisted mashing conditions were effective, although continuous sonication (100 %) generally provided the greatest functional improvements.