Thermal Food Processing

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Infrared Heating 517 T l (K) N l / N 10 373 353 333 313 293 273 1.4 1.2 1.0 0.8 0.6 0.4 0.2 V l : 2.0 × 10 -2 dm -3 V l / S h : 3.3 mm 3.22 kW m -2 5.22 kW m -2 6.02 kW m -2 0.0 0 10 20 30 40 FIGURE 16.22 (a) Transient behavior of bulk temperature of spore suspension irradiated by FIR. (b) Effect of FIR irradiation of spores of B. subtilis. (From Sawai, J. et al., J. Chem. Eng. Jpn., 30, 170–172, 1997.) number. Activated spores easily germinate under their suitable conditions, and their high heat resistance decreases extremely after the germination. These results suggest that the activation of the spore is possible by the FIR in a short time, and that FIR heating will be able to apply the pasteurization of bacterial spores. The pasteurizing action of FIR heating has been confirmed in some applications: the heating of oysters, 23 the heating of Japanese noodles, 48 and the secondary pasteurization of boiled fish paste. 32 FIR pasteurization is more effective than conventional heating under specific conditions, and is particularly effective at the surface of foods. Since some baked or cooked foods may be contaminated by (A) (B)
518 Thermal Food Processing: New Technologies and Quality Issues microorganisms in a later operation, it would be desirable to pasteurize such products after packaging. However, pasteurization using conventional heating methods requires such a long time and so high a temperature that the package would deform or the products would denature. FIR heating has been successfully used for the efficient pasteurization of packaged products such as sausages and boiled fish paste. 49 16.4.4 THAWING Recently, the quality of frozen foods has improved remarkably with the advancement of freezing technology. However, its quality may deteriorate in the thawing stage corresponding to the thawing conditions, such as thawing method, temperature, and speed. Frozen foods generally thaw more slowly than they freeze, because water has a lower thermal conductivity than ice. In conventional thawing methods, heat is supplied at the surface of the frozen food and is conducted slowly toward the interior. Conventional thawing methods involve several disadvantages: a long thawing time, undesirable changes in food quality, and product loss (drip loss). Microwave thawing is one possible method to reduce the thawing time. However, in microwave thawing, at temperatures slightly below 0°C, the outer layer of the food may absorb most of the microwave energy and cause “runaway heating” or overheating near the product surface. 50 This well-known phenomenon occurs due to the significant difference in the dielectric properties of frozen and unfrozen food, which decide the absorbability of microwave energy. 51,52 On the other hand, in the region of the IR wavelength, the values of the absorption coefficients for ice and water are approximately equal. 5 Thus, the runaway heating effect does not occur during FIR thawing; FIR has the potential for broad use in food thawing processes. In comparison with meat, which may be cooked after thawing, the quality of thawed fish that is eaten in the raw state, such as sashimi or sushi, is greatly affected by the thawing conditions. In particular, drip loss or discoloration of the red muscles of frozen tuna occurs readily during thawing. To minimize the extent of deterioration, the surface temperature of the tuna should be kept below 10°C during thawing. Since frozen food can be heated directly in FIR heating, regardless of the temperature of the circumference, it is possible to thaw a frozen food while its surface is cooled. Kimura 53 demonstrated experimentally that a frozen tuna could be thawed within 30 min without drip loss and discoloration by using FIR heating in association with cooling of the surface by cold air. It was also demonstrated that the surface temperature could be controlled by intermittent FIR irradiation to frozen foods under a low-temperature atmosphere. 54 In order to reduce the thawing time, if the heater temperature is kept at a higher temperature, the surface temperature of tuna may increase to an unacceptable level. Thus, it is important to know how temperature distribution is formed in the food corresponding to the thawing condition. The authors have investigated the effect of the thawing conditions on the temperature distribution of frozen tuna. 55 Simulation results of the temperature histories in changing the FIR heater temperature are shown in Figure 16.23. The simulation conditions are as follows: the food is assumed to be tuna of 15-mm thickness, initial temperature is −28°C, and
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Thermal Food Processing
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87. Polysaccharide Association Stru
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133. Handbook of Frozen Foods, edit
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Published in 2006 by CRC Press Tayl
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Various alternative thermal process
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Professor Sun is a fellow of the In
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Antonio Martínez Instituto de Agro
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Contents Part I: Modeling of Therma
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Chapter 17 Pressure-Assisted Therma
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1 CONTENTS Thermal Physical Propert
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Thermal Physical Properties of Food
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2 CONTENTS Heat and Mass Transfer i
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Heat and Mass Transfer in Thermal F
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5 CONTENTS Modeling Thermal Process
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Modeling Thermal Processing Using C
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6 CONTENTS Thermal Processing of Me
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Thermal Processing of Meat Products
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7 CONTENTS Thermal Processing of Po
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Thermal Processing of Poultry Produ
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9 CONTENTS Thermal Processing of Da
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Thermal Processing of Dairy Product
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10 CONTENTS UHT Thermal Processing
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UHT Thermal Processing of Milk 301
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11 CONTENTS Thermal Processing of C
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Thermal Processing of Canned Foods
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12 CONTENTS Thermal Processing of R
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Thermal Processing of Ready Meals 3
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14 CONTENTS Ohmic Heating for Food
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Ohmic Heating for Food Processing 4
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628 Index dielectric properties of,
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630 Index Joule heating, see Ohmic
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636 Index Reynolds stress models, 5
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638 Index Tea, 451, 510 Temperature
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640 Index Wax beans, 398, 411 Web s
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Thermal Food Processing

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