HEAT TRANSFER RATES IN A CANNED FOOD MODEL AS INFLUENCED BY PROCESSING IN an END-OVER-END ROTARY STEAM/AIR RETORT

Abstract

The effect of various factors on the heat transfer rates of a canned food model (gelatinized starch) were evaluated during thermal processing in an agitating retort. Process variables were retort temperature (110–130C), rotation speed (10–20 rpm), can headspace (6.4–12.8 mm) and starch concentration (3–4%). Thermal process parameters (heating rate index, fh, and heating lag factor, jch) and the resulting process lethality, Fo and cook value, Co were obtained from time-temperature data obtained during processing for three consecutive runs. Rheological properties and color were experimentally evaluated both before and after each run. Overall heat transfer coefficient (Uo) was calculated from the heating rate index using a lumped capacity approach. the study indicated that fh, jch, Fo and Co were influenced (P<0.05) by all process variables except can headspace. Uo was related to retort temperature, rotation speed and initial apparent viscosity. the best dimensionless correlation for Uo was Nusselt number (logarithmic scale) versus specific apparent viscosity and Froude number (R2= 0.65).