Thermal effect in foods during quasi-adiabatic pressure treatments

Abstract

Large pressure shifts are a part of the emerging high-pressure food treatments. Pressure treatments count among their advantages vs. thermal processes the lack of the undesirable effects associated with temperature changes and a better cost-efficient ratio. Nevertheless, any pressure variation has with it an associated temperature change, whose effect, if not conveniently considered, can alter the product, increase costs by introducing the need of thermoregulation or, at the very least, become an error source in hydrostatic pressure treatment studies. In this article, water and fatty foods are used as models and the thermal changes originated by pressure variations are studied. The range 20-65°C and 0.1-350 MPa was considered, as it is the most interesting for food applications. Results were compared, where possible, to theoretically calculated values and a sufficiently good agreement with them was found. The fatty foods studied (milk fat and cream) yielded negative temperature changes, much higher than that of water, upon quasi-adiabatic expansions of the same magnitude. The absolute value of this temperature change decreased with increasing temperatures and pressures, in opposite sense to the water case. A delay of the thermal effect over its causing pressure shift was consistently found. © 2000 Elsevier Science Ltd. All rights reserved.