Engineering processes in meat products and how they influence their biophysical properties.

Food engineering aspects of cooking of meat products in relation to their biophysical properties, such as water- and fat-holding, have been reviewed. Moreover, some of the new emerging, mild cooking technologies, such as high pressure and electro-based heating (radio frequency cooking and ohmic heating) have been discussed in relation to the biophysical properties of the meat products treated. The holding of the bulk water (about 70% of the muscle weight) was discussed, arguing capillary forces to be one of the dominating mechanisms for this holding, whereas the losses of water and fat (the flow) within the meat are governed by Darcy's law. If we compare the fat-holding in beef burgers and emulsion sausages (frankfurter type) beef burgers lose much larger part of the fat than the emulsion sausages and for the former the fat losses increase with fat content. For emulsion sausages, however, fat losses are independent of fat content and the properties of the fat and the protein matrix are more interrelated. It has been shown experimentally during double sided pan frying of beef burgers that the pressure driven water loss (up to 80% of the water loss) is a substantially more important mechanism governing the water loss than the evaporation losses occurring at the surface crust. Fat losses increased significantly with fat content and were not influenced to any large extent by the cooking temperature and were in the form of drip. By using processing technologies such as high pressure and/or electro-based heating (radio frequency cooking and ohmic heating) a more homogenous heating can be achieved, the reason being volumetric heating. In comparison with conventional heating shorter cooking times were obtained and with smaller temperature gradients lower water- and fat-losses occurred and the yield can be substantially improved. High pressure processing (100-1000MPa) is a preservation technology that allows the reduction of the microbial load at low or moderate temperature. The highest potential application for meat products might be to pressurise finally sealed packages of contaminated sliced high value salami and ham products as the colour of those products can resist high pressure. Ohmic heating is based on the passage of electrical current through a food product having an electrical resistance. For radio-frequency (RF) cooking and micro-wave heating the food product forms a dielectric media between the two electrodes and the heating is caused by the internal friction of the polar molecules. The used frequencies for RF-cooking are lower in the MHz range than for micro-wave heating being in the GHz range.