Visual study of material expansion using DIC process completed by temperature and pressure history

The DIC process (instant controlled pressure drop) is a new technology used for transformation of raw foods to ready-to-eat products by changing their structure and size. The DIC process resembles commonly used puffing, but two essential differences, that is detente into vacuum and the instantaneity of detente, enable us to obtaine more important effects and also to expose product to lower pressure and temperature. Two foods, cheese emmental and coagulated soy milk – tofu, were treated by DIC process. The products were exposed for a short time (40 – 50 s) to saturated steam (0.3 – 0.6 MPa) in an autoclave and then the pressure was abruptly decreased to a vacuum level (about 10 kPa). This abrupt pressure drop provoked auto-vaporization of the superheated vapour and volatile compounds which induced expansion and instantaneous cooling of the product. The effects of two parameters of DIC process namely pressure and heating time on product expansion were studied using the central composite experimental plan and response surface methodology. An increase of the product volume as high as four times was achieved. After a final hot air drying stage, the end product structure was crispy. The most important parameter was the steam pressure. The temperatures of steam and product in the autoclave as well as the pressure were measured during the whole process. The pressure drop was described by an exponential function with a time constant between 0.2 and 0.4 s, which corresponds to a pressure drop rate of 1.5 MPa/s