CONTROL PARAMETERS FOR SOUS-VIDE COOK-CHILL PROCESSING OF BORAGE (BORAGO OFFICINALIS) STEMS

Borage stems (Borago officinalis) are studied as a “V gamme” product. Of the various stages involved in its preparation, the heating and subsequent cooling cause the most drastic changes in the quality parameters. This process is simulated with a 3-D model implemented with the commercial COMSOL Multiphysics CFD program. This includes a main equation for heat transfer (internal conduction and external convection) and takes into account vegetal physico-chemical properties (humidity, density, thermal conductivity), as well as the thermoresistance of basic quality properties (polyphenol oxidase activity and greenness) considering their first order Arrhenius behaviour. Three systems where the heating-cooling takes place have been simulated, implemented with different heat convective coefficients(h_heating=500, 170 and 40 Wm^-2 K^-1, and h_cooling=5000 and 170 Wm^-2 K^-1). 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). There are differences of up to 45 minutes among the various systems studied to achieve the same degree of pasteurization with the same temperature set point. Using the least thermically effective treatment, a greater deactivation of the PPO enzyme can be achieved if the process is carried out at less than 72 °C. The colour retention associated with each equivalent time-temperature combination shows an optimum between 82 and 95 °C for the different systems tested.