No abstract

No abstract

Summary Ohmic heating is a food processing operation in which heat is internally generated within foods by the passage of alternating electric current. The process enables solid particles to heat as fast as liquids, thus making it possible to use High Temperature Short Time sterilization techniques on particulate foods. Ohmic heating rates are critically dependent on the electrical conductivities of the foods being processed, about which little information is available. This paper reports experiments to determine the changes in electrical conductivity which occur during ohmic heating of some common foods. A number of effects which occur during conventional heating, such as starch transition, melting of fats and cell structure changes, are shown to affect the electrical conductivity. In some cases the presence of an electric field induces enhanced diffusion of cell fluids in the food which increases the rate of change of conductivity with temperature above that found by conventional heating. Preheating is found to increase the electrical conductivity of some foods, making them acceptable for ohmic processing.

in Wiley InterScience (www.interscience.wiley.com).High pressure high temperature processing is a candidate food sterilization process in which heat is generated volumetrically within the food as a result of rapid pressurization to 600 MPa or higher. For commercial viability the temperature profile in the process should be as uniform as possible. A model has been developed to predict the flow and temperature fields inside a pilot scale (35 L) vessel during the pressure heating, holding and cooling stages of the process. Simulations on the empty vessel show that thermal conduction causes excessive cooling. The model agrees well with experimental results in which thermocouples are used to measure temperature throughout a metallic composite carrier inserted into the vessel. The model is used to design a Polytetrafluoroethylene (PTFE) carrier which produces thermal uniformity within the carrier. Predicted variations of sterility resulting from a process are produced using the F 0 -value distribution. No significant reduction of spores was seen in the empty vessel, while more than 94.6% of the PTFE carrier volume achieved a reduction greater than 10 12 .

There is an increasing need to understand how food formulations behave in vivo from both food and pharma industries. A number of models have been proposed for the stomach, but few are available for the other parts of the gastrointestinal tract. An experimental rig that simulates the segmentation motion occurring in the small intestine has been developed. The objective of developing such an experimental apparatus was to study mass transport phenomena occurring in the lumen and their potential effect on the concentration of species available for absorption. When segmentation motion was applied the mass transfer coefficient in the lumen side was increased up to a factor of 7. The viscosity of the lumen, as influenced by guar gum concentration, had a profound effect on the mass transfer coefficient. The experimental model was also used to demonstrate that glucose available for absorption, resulting from starch hydrolysis, can be significantly reduced by altering the lumen viscosity. Results suggest that absorption of nutrients could be controlled by mass transfer. Practical Application: To address health-related diseases such as obesity, novel foods that provide advanced functions are required. To achieve the full potential offered by the latest developments in the field of food material science, a fundamental understanding of the behavior of food structures in vivo is required. Using the developed gut model we have demonstrated that absorption of nutrients can be controlled by mass transfer limitations.

No abstract

Fouling of food process plant surfaces and the subsequent cleaning needed is a significant industrial problem, and as the cost of water and chemical disposal increases, the problem is becoming more significant. Current literature on water-based cleaning is reviewed here according to the classification of 3 types of cleaning problems. By doing this, it is hoped that new knowledge can be highlighted applicable to improving industrial cleaning. (i) For type 1 deposits (that can be cleaned with water alone)-Cleaning time appears related to Reynolds number and surface shear stress. An increase in Reynolds number seems to decrease cleaning time. Cleaning temperatures greater than 50• C do not appear beneficial.(ii) For type 2 deposits (biofilms)-Removal behavior of biofilms seems to be dependent on the microbial aging time on the surface. Keeping a material hydrated on a surface enables easier removal of it with water. a. Water rinsing: Temperature and wall shear stress have varied effects on removal. b. Chemical rinsing: Flow and temperature were seen to have the biggest effect at the start of cleaning, but contact time was more important as cleaning progressed at a given sodium hydroxide solution flow and temperature. (iii) For type 3 deposits (that require a cleaning chemical)-For specifically, protein-based systems excessive chemical forms a deposit difficult to remove. Increasing wall shear stress and temperature was most beneficial to cleaning rather than concentration. The action of temperature can reduce the use of a chemical for type 2 and type 3 soils. The findings suggest that the right combination of flow characteristics at a given temperature and concentration is crucial to achieving fast cleaning in all cases. There are a number of cleaning monitoring methods at various stages of commercialization that may be capable of monitoring bulk cleaning and cleaning at the surface. To optimize cleaning will require integration of measurement methods into the cleaning process.

No abstract