Drying characteristics and kinetic modelings of triploid Fujian oysters Crassostrea angulata under different drying methods

Background Fresh oysters contain a high moisture content and are prone to spoilage during storage and transport. Drying effectively reduces their water activity and extends shelf life; however, traditional sun drying suffers from low efficiency, unstable product quality, and a lack of theoretical guidance.

Objective This study aims to clarify the drying characteristics of oysters under different drying methods, identify the most suitable technique and its kinetic model, and provide a theoretical basis for process design and production control.

Methods Triploid Fujian oysters (Crassostrea angulata) were dried using sun drying (SD), vacuum drying (VD), hot air drying (HAD), and far-infrared radiation assisted hot air drying (FIRHAD). The moisture ratio (MR), drying rates, and effective moisture diffusion coefficient (D_eff) were systematically investigated, and thirteen classic thin-layer drying models were fitted to the drying curves to establish the kinetic model for each method.

Results All four processes were governed by internal moisture diffusion, and exhibited a typical falling-rate drying characteristic without a distinct constant-rate period. Specifically, FIRHAD was the fastest to reach MR=0.2 (8 h), whereas VD was the earliest to reach a constant weight (22 h). The D_eff ranked as SD (3.311×10⁻¹⁰ m²/s)<FIRHAD (1.704×10⁻⁹ m²/s) <HAD (2.590×10⁻⁹ m²/s)<VD (2.826×10⁻⁹ m²/s). Non-linear relationships between MR and drying time were observed in all methods. The Two-term model effectively described SD and FIRHAD processes, while the Midilli model provided a good fit for the VD and HAD processes.

Conclusion FIRHAD at 50 ℃ is optimal for producing low-moisture dried oysters (MR=0.2), whereas VD at 50 ℃ is the fastest method to produce fully dried oysters. The Two-term and Midilli models are recommended for describing and predicting the drying behavior of oysters.