Control Paramethers for Sous-vide Cook-chill Processing of Swiss Chard (Beta vulgaris) Stems
Within the various stages involved in the preparation of swiss chart stems (Beta vulgaris) as a `V gamme' product, this work concentrated on heating and subsequent cooling, since these are the stages which cause the most drastic changes in the quality parameters of the product. For the detailed analysis, a 3D finite-difference conductive heat transfer model has been developed. This model takes into account vegetal physico-chemical properties (humidity, density, thermal conductivity) as well as their thermoresistance. The texture is one of the parameters that most influences the organoleptic quality of this product, both as an indicator of the extent of cooking and for reflecting the level of homogeneity. Its temperature dependence has been determined by means of a texturometer, confirming a first-order Arrhenius type behavior. Assuming a pasteurization level corresponding to the absence of Listeria monocytogenes in its vegetative form with a margin of 7 logarithmic units as appropriate, the solution of the model enables the establishment of the time necessary for each processing temperature (from 65 to 95 °C). Given the marked temperature gradients observed, various geometric configurations of the stems have been simulated in order to find the most homogenous product.