Investigation of the migration of the least heating zone of clarified apple juice during heat treatment

Abstract

When developing modes of food products thermal sterilization, it is necessary to determine the conditions for microorganisms test cultures and their spores guaranteed death in the least heating zone. The location of this zone is a critical parameter in thermal processes. At present, there are conflicting ideas about the localization and possible migration of the zone of least heating in the process of thermal sterilization of products with convective heat transfer. The kinetics of localization of the zone of least heating in the medium volume with convective heat transfer during heat treatment in conjunction with rheological properties was studied in the work. The clarified apple juice for baby food of domestic production was used as the object of study. The probe was placed so that the thermocouple was located on the vertical axis of the can at a geometric height of 3, 6, 9, 12, 18 and 24 mm. At each height value of the thermocouple, the jar with the sample was thermostated for 20 minutes, and then quickly cooled for 10 minutes. Heating was carried out at a thermostat temperature of 75, 80, 85, 90, and 95°C. The dynamics of rheological properties under isothermal conditions at temperatures of 30, 35, 40, 45, 50, 55, and 60°C and a range of shear rates from 0 to 700 s – 1 were also studied in the samples. As a result of the studies carried out, the presence of the migration of the zone of least heating during the heat treatment of single-phase media with convective heat transfer was determined experimentally, its kinetics was studied, the non-linear and reversible nature of the migration of the zone of least heating was established. The mechanism of the process of migration of the zone of least heating was proposed taking into account the dynamics of the rheology of the heated medium and the convective flows interaction.