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Reduced-temperature pasteurization of apple juice using a flow-through sonicator
Sara Maghami1, Kimmo Rumpunen2, Örjan Johansson1
1Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sweden.
Abstract:
Thermal pasteurization is widely applied to ensure the microbial safety of fruit juices; however, it can degrade heat-sensitive nutritional and sensory attributes. In this study, a reduced-temperature processing approach based on combined acoustic and hydrodynamic cavitation was investigated using a flow-through sonication system. The sonicator design was validated through both simulation and experimental results. It enables an efficient combination of acoustic and hydrodynamic cavitation, improving energy transfer, pressure localization, generation of transient cavitation, and increased field complexity. The effects of excitation mode (single and dual-frequency), temperature (30-55 °C), and treatment time were evaluated in terms of microbial inactivation, microstructural modification, and physical stability. Dual-frequency excitation at 50-55 °C (DF-4) showed the highest performance, achieving a log reduction of 3.6 for yeast, 2.7 for mold, and 2.8 for aerobic microorganisms as a hygiene indicator after 450 s efficient time. SEM observations confirmed progressive cellular disruption, while sedimentation tracking indicated improved stability due to reduced particle size and improved dispersion. The proposed approach improves microbial inactivation and modifies the microstructure and stability of the juice, highlighting its potential for processing at reduced-temperatures of apple juice.
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