Raspberry pulp pasteurization: Computational fluid dynamics modeling and experimental validation of color and bioactive compound retention

This work evaluated the heat transfer, fluid flow, and different reactions that occur during the pasteurization of raspberry pulp. The pulp was packed in glass jars and thermal processing was conducted by immersion in a water bath. The process was evaluated by multiphysics modeling, with the aim of determining the temperature distribution, flow pattern, the slowest heating zone (SHZ) location, the microbial inactivation, and the quality changes taking place during processing. In order to simulate the process accurately, a model was developed using experimentally measured product and heat transfer properties (density, thermal expansion, specific heat, thermal conductivity, apparent viscosity, and convective heat transfer coefficient) and kinetics of thermal degradation of quality parameters (color, anthocyanin, and ascorbic acid). The model was successfully validated against experimental measurements of both temperature and quality losses. After validation, the model was used to design and evaluate equivalent thermal processing conditions. Improved processes were identified that minimized the changes of color and the bioactive compounds, while maintaining product safety and stability. Practical Applications Thermal processing of raspberries may induce several physicochemical changes that impair their sensorial properties, and may reduce the content of nutrients and bioactive compounds. Hence, the design and optimization of heat treatments is a key tool to guarantee safety while, at the same time, minimizing detrimental side effects which involve a loss of quality. In this investigation, we assessed the actual thermo-physical properties of raspberry pulp and the system heat transfer coefficients. Then, we developed a CFD model to predict the temperature and velocity transient profiles, the location of the SHZ, and the quality changes occurring in raspberry pulp during pasteurization. The findings of this study could be useful to food processors for optimizing pasteurization conditions in order to obtain safe and high-quality raspberry pulp preserves, as well as for reducing processing energy requirements.