A model to design high-pressure processes towards an uniform temperature distribution
ABSTRACT A mathematical model has been developed to describe the phenomena of heat and mass transfer taking place during the high-pressure treatment of foods. It has proved that convection currents in the pressure medium play an important role in the thermal evolution of the processed samples especially when the filling ratio in the pressure vessel is low.This model shows to be an extremely useful tool to design high-pressure processes seeking a uniform temperature distribution.
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ABSTRACT: Nowadays, consumers look for minimally processed, additive-free food products that maintain their organoleptic properties. This has led to the development of new technologies for food processing. One emerging technology is high hydrostatic pressure, as it proves to be very effective in prolonging the shelf life of foods without losing its properties. Recent research has involved modelling and simulating the effect of combining thermal and high pressure processes (see Denys et al. (2000) , Infante et al. (2009) , Knoerzer et al. (2007) , Otero et al. (2007) ). The focus is mainly on the inactivation of certain enzymes and microorganisms that are harmful to food. Various mathematical models that study the behaviour of these enzymes and microorganisms during a high pressure process have been proposed (see Infante et al. (2009) , Knoerzer et al. (2007) ). Such models need the temperature and pressure profiles of the whole process as an input. In this paper we present two dimensional models, with different types of boundary conditions, to calculate the temperature profile for solid type foods. We give an exact solution and propose several simplifications, in both two and one dimensions. The temperature profile of these simplified two and one dimensional models is calculated both numerically and analytically, and the solutions are compared. Our results show a very good agreement for all the approximations proposed, and so we can conclude that the simplifications and dimensional reduction are reasonable for certain parameter values, which are specified in this work.Applied Mathematics and Computation 01/2014; 226:20–37. · 1.35 Impact Factor
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ABSTRACT: High-pressure processing (HPP) has become the most widely accepted nonthermal food preservation technology. The pressure range for commercial processes is typically around 100–600 MPa, whereas moderate temperature (up to 65 °C) may be used to increase microbial and enzymatic inactivation levels. However, these industrial processing conditions are insufficient to achieve sterilization since much higher pressure levels (>1,000 MPa) would be required to inactivate bacterial endospores and enzymes of importance in food preservation. The next generation of commercial pressure processing units will operate at about 90–120 °C and 600–800 MPa for treatments defined as pressure-assisted thermal processing or pressure-assisted thermal sterilization if the commercial food sterilization level required is achieved. Most published HPP kinetic studies have focused only on pressure effects on the microbial load and enzyme activity in foods and model systems. Published work on primary and secondary models to predict simultaneously the effect of pressure and temperature on microbial and enzymatic inactivation kinetics is still incomplete. Moreover, few references provide a detailed and complete analysis of the theoretical, empirical, and semiempirical kinetic models proposed to predict the level of microbial and enzyme inactivation achieved. This review organizes these published kinetic models according to the approach used and then presents an in-depth and critical revision to define the modeling research needed to provide commercial users with the computational tools needed to develop and optimize pasteurization and sterilization pressure treatments.Food Engineering Reviews 01/2014; X:1–33. · 2.81 Impact Factor
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ABSTRACT: Cooling is an important task in the food industry. Harvested agricultural produce is subjected to precooling before packaging, processing and transportation. Heat moves to surface of product in a mixed-mode of conduction and convection, and from surface to environment by convection. Therefore, estimation of thermal properties (like thermal diffusivity) is important to analyze heat transfer phenomena and design of refrigeration and processing equipments. This work presents a simple method to estimate thermal diffusivity variations of selected regular shaped food products subjected to natural convection cooling. Experimental investigations were carried out on fruits and vegetables. Samples chosen were melon, orange and potato (spherical) and bottle gourd (cylindrical). The experimental setup consists of a deep-freezer maintained at -10˚C and 1 atm. The variation of temperature within a product is measured along the radial direction using copper-constantan thermocouples. The output of thermocouples is read on a digital microvolt meter. The temperature of thermocouples was recorded at regular intervals of 5 minutes. Variation of surface temperature is obtained based on radial temperature profiles. Thermal diffusivity (α) variation is calculated for each time interval using one-dimensional Fourier's equation. Correlation for thermal diffusivity as a function of surface temperature is developed for each of the sample.The 3rd International Symposium on Processing of Foods, Vegetables and Fruits, The University of Nottingham Teaching Centre Level 2, Chulan Tower No 3 Jalan Conlay 50450 Kuala Lumpur, Malaysia; 08/2014