Mass transport phenomenon during ultrasound-assisted osmotic dehydration of skipjack tuna (Katsuwonus pelamis)

Abstract

Ultrasound has emerged as a promising technique for enhancing mass transfer efficiency in meat processing, but the mechanisms of material movement must be thoroughly investigated prior to scaling for commercial applications. For this reason, the study assessed the influence of ultrasound on the mass transfer kinetics of skipjack tuna (Katsuwonus pelamis) chunks during osmotic dehydration (OD). Fresh tuna, with an initial moisture level of 73.9%, was soaked in a 20% NaCl solution through static OD and ultrasound-assisted osmotic dehydration (US-OD) at frequencies of 20, 28, and 40 kHz. The results indicated that ultrasound significantly improved moisture loss and solute gain when compared to static OD. Water loss was also more rapid than salt infusion due to the semi-permeable nature of cell membranes. Ultrasound reduces the formation of salt layers on the surface by promoting cavitation and the development of microchannels, enhancing internal diffusion. Mass transfer kinetics was modelled using a time-dependent power function, and statistical results (R² close to one; χ², RMSE, and MBE values close to zero) indicated a good fit of experimental and predicted data, implying that the models are acceptable representations of NaCl absorption. Depth profiling revealed a curvilinear pattern of diffusion under ultrasound, with more salt building up at both the surface and bottom layers of the tuna chunks, particularly at the 28 kHz frequency. The maximum diffusion coefficient (1.57 × 10⁻⁸ m² s⁻¹) was achieved at this frequency. Energy-dispersive X-ray (EDX) mapping confirmed a more uniform distribution of salt at 28 kHz. Conversely, 40 kHz encourages excessive microchannel development, leading to diminished salt retention. In summary, 28 kHz ultrasound was found to be the best frequency for boosting salt movement and enhancing osmotic dehydration effectiveness in tuna chunks.