Measurement and prediction of the mechanical properties of a two-component food during freezing (original) (raw)
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Analysis of stresses during the freezing of solid spherical foods
International Journal of Refrigeration, 2006
An analytical model is presented to calculate thermal stresses and strains during the freezing of a spherical food, taking into account both the expansion during phase change and subsequent thermal contraction due to temperature decrease. The Young modulus and Poisson ratio are assumed to undergo a step change at the freezing point. The expansion due to phase change cause a uniform and virtually constant isotropic tensile stress in the unfrozen core. In the frozen shell, this expansion gives rise to tensile radial stress and compressive tangential stress. The thermal contraction subsequent to phase change causes reverse effects, i.e. uniform compressive stress in the unfrozen core and compressive radial stress in the frozen shell, while tangential stress is tensile on the outside and compressive on the inside of the frozen shell. The effect of thermal contraction is noticeable only at cryogenic temperatures.
Thermal stresses during freezing of a two-layer food
International Journal of Refrigeration, 2007
Thermal stresses during freezing of a two-layer material, that can contribute to crack formation, are studied. A 3D numerical model of a two-layer food with food analog Tylose Ò and chocolate is presented. An apparent specific heat formulation was used to model the heat transfer with phase change over a temperature range. The mechanics model considered viscoelasticity in Tylose Ò ; thermal strains were imposed due to the increase in volume from ice formation in Tylose Ò and the decrease in volume from freezing of the chocolate. Results show that complex evolution of stresses, that include compressive and tensile values, occur during freezing. Sensitivity analysis showed that the Poisson's ratio was a very important parameter that affects the magnitude of stress. Variations in calculated stresses were found to be proportional to variations in Young's modulus. Knowing the stresses, the possibilities of undesired cracking of a chocolate coating applied onto another material such as ice cream could be evaluated.
Stresses and cracking in freezing spherical foods: a numerical model
Journal of Food Engineering, 2005
Thermal stresses during the freezing of a spherical food were simulated with an elastic model, using realistic thermal and mechanical properties. It was found that to explain observed cracking patterns, both expansion due to phase change and thermal contraction subsequent to it must be taken into account. During freezing, the unfrozen core is always under uniform isotropic tensile stress, but that is unlikely to explain the cracking pattern. Cracking during cryogenic freezing is more likely due to tensile tangential stresses caused by thermal contraction, with vitrification at the surface possibly playing a role in crack initiation. The calculations suggest that once a crack forms at the surface it will propagate towards the centre, as has been observed experimentally.
Structural Studies on Unpackaged Foods during Their Freezing and Storage
Journal of Food Science, 2006
During the freezing and frozen storage of unpackaged foods, their surface is exposed to mass transfer with the environment. Basically, ice sublimes and forms a dry, porous layer. This fact alters the sensory characteristics of the products and originates an important quality loss. In this work, a mathematical model was used to predict the thickness of the dehydrated layer, taking into account the influence of operating conditions and food characteristics. Based on the predictions of the numerical model, 2 regression equations were proposed to calculate the size of the dehydrated layer after freezing and storage, having the operating conditions and food properties as parameters. Besides, the frozen storage of the products was studied over different time periods (1, 2, and 3 mo) using beef cylinders and slices, as well as minced beef balls and hamburgers. The dimension of the dehydrated layer and the induced changes in the food surface structure were determined by image analysis and environmental scanning electron microscopy (ESEM). The experiments determined an increase in the depth of the dehydrated layer when storage times are longer, which could be adequately related to storage conditions through the predictions from the numerical model and the regression equations.
Finite Element Method for Freezing and Thawing Industrial Food Processes
Foods
Freezing is a well-established preservation method used to maintain the freshness of perishable food products during storage, transportation and retail distribution; however, food freezing is a complex process involving simultaneous heat and mass transfer and a progression of physical and chemical changes. This could affect the quality of the frozen product and increase the percentage of drip loss (loss in flavor and sensory properties) during thawing. Numerical modeling can be used to monitor and control quality changes during the freezing and thawing processes. This technique provides accurate predictions and visual information that could greatly improve quality control and be used to develop advanced cold storage and transport technologies. Finite element modeling (FEM) has become a widely applied numerical tool in industrial food applications, particularly in freezing and thawing processes. We review the recent studies on applying FEM in the food industry, emphasizing the freezi...
International Journal of Refrigeration, 2008
The freezing process is widely used in the food industry. In the 70s, French regulation authorities have created in collaboration with the food industry the concept of «surgé lation» process with the objective of improving the image of high quality frozen foods. The process of ''surgé lation'' which could be translated as ''super freezing'' corresponds to a freezing process for which a final temperature of À18 C must be reached ''as fast as possible''. This concept was proposed in opposition to a conventionally ''freezing'' process for which no specific freezing rate is expected and the final storage temperature can be of À12 C only. The objective of this work is to propose a methodology to evaluate the mean amount of frozen ice in a complex food as a function of temperature and to deduce a target temperature that must be considered as the temperature for which the food may be considered as ''frozen''. Based on the definition proposed by the IIF-IIR red book, this target temperature has been defined as the temperature for which 80% of the freezable water is frozen. A case study is proposed with a model food made of two constituents.
Thermal Properties of Frozen Food: A Review Article
International Journal of Engineering Applied Sciences and Technology, 2020
Food is a mixture of solutes and water particles. The properties of the food material vary by the state of water particles present in them. The density, viscosity are some of the factors that attribute to the difference in thermal properties between frozen and unfrozen food. Several studies have been made in analyzing the thermal properties of frozen food of different varieties from frozen soup pouches to frozen meat. Several properties related to thermic properties such as thermal conductivity, latent heat, heat capacity is also under consideration. For instance, density is found using the known volume of the sample, porosity using water, and so on. Thus thermal properties of frozen food are of immense importance for developmental processes.
Journal of Food Engineering, 2000
Cylindrical gelatin gels were frozen at atmospheric pressure with dierent operating conditions (air-blast freezing at dierent air temperatures and brine freezing). A method to calculate a local freezing rate was proposed to take into account the variation of freezing rate as a function of the radius. A linear evolution of the local freezing rate according to the radius was observed whatever the freezing process was. Frozen gels were freeze-dried and sliced perpendicularly to the heat¯ux. The ice crystal marks were measured according to the radial position with image analysis software. Each radial distribution of ice crystal size was characterised by the mean representative diameter. A linear regression permitted to link the ice crystal mean representative diameter to the radial position. On addition, the variation in the mean diameter with the local freezing rate was ®tted by a power law.
Transactions of the ASAE, 1974
A LTHOUGH the freezing of food has become an accepted preservation process for many food commodities, the design of the equipment utilized for freezing is usually based on experimental data which may or may not correspond to the design conditions. In addition, very few attempts have been made to design the freezing process to assure optimum product quality. Most freezing design computations lead to determination of refrigeration requirements and/ or freezing rate for the product. Although the refrigeration requirement for freezing depends only on the final temperature of the frozen product, the rate of freezing may have a significant influence on product quality. Probably the most basic characteristic of a frozen food needed in freezing design computations is the relationship between the frozen water fraction and temperature. Accurate knowledge of this relationship allows calculation of all factors required in the design of the system for freezing of food. Experimental approaches to design normally involve measurement of total heat content of the product at various temperatures in the freezing temperature range. There are several inherent limitations to these measurements including experimental errors and the inability of the experimental conditions to simulate all design conditions. The objectives of the investigation were: 1 To develop an approach which will allow prediction of the unfrozen water fraction as a function of tempera
Quality evaluation of foodstuffs frozen in a cryomechanical freezer
Journal of Food Engineering, 2002
Cryomechanical freezing is recommended for delicate products, with poor mechanical resistance (shrimps, raspberries, strawberries) or those that change their appearance during freezing (chicken, mushrooms, shrimps). The aim of this work is to study the quality aspects related to the application of cryomechanical freezing compared to the use of a conventional mechanical freezer. In order to determine whether or not the use of the combined freezer provokes an improvement in the quality of the final product, different kinds of foodstuffs were chosen and analysed before and after freezing by both methods. The selected products were: chicken escallops, hamburgers, strawberries, asparagus and mushrooms. The quality parameters analysed for this purpose were: drip loss during thawing, texture and colour. The variation in mechanical resistance was also evaluated as a function of the immersion time to determine the hardness of the protective crust formed by the liquid N 2 pretreatment.