Effect of high-intensity ultrasound-induced acoustic cavitation on enzymatic activity and quality attributes of granny smith apples during storage

Abstract

This study investigates the effects of high-intensity ultrasound (HIU), chemical treatments (ascorbic acid and calcium chloride), and thermal treatment (water bath at 65°C) on metabolic, structural, and physical changes in Granny Smith apples during a 14-day cold storage period. HIU, a non-thermal physical processing method, utilizes acoustic cavitation and microstreaming to induce mechanical and oxidative stresses at the cellular level, thereby inhibiting enzymatic browning, reducing microbial load, and preserving bioactive compounds. Treated apples were stored at 4°C and analyzed on Days 0, 7, and 14 for antioxidant capacity using 2,2-diphenyl-1-picrylhydrazyl (DPPH), ferric reducing antioxidant power (FRAP), and oxygen radical absorbance capacity (ORAC) assays; total phenolic content (TPC); total flavonoid content (TFC); ascorbic acid levels; and enzymatic activities of polyphenol oxidase (PPO) and pectin methyl esterase (PME). Additional quality parameters included texture, colorimetric properties, microbial counts, and sensory quality. Compared to chemical and thermal treatments, HIU treatment significantly preserved firmness and color parameters, reduced enzymatic activity, and enhanced antioxidant retention (p < 0.05). Ultrasound-treated samples also exhibited minimized off-odor development and decay. These results demonstrate that HIU, through mechanisms such as acoustic cavitation and shear forces that alter cellular structure and inhibit enzymatic activity, offers a promising, non-thermal, scalable approach for extending shelf life and maintaining the nutritional and sensory quality of fresh produce, meeting the growing demand for clean-label, minimally processed foods.