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

The effect of various factors on the heat transfer rates of a canned f ood model (gelatinized,starch) were evaluated during thermal processin g in an agitating retort. Process variables were retort temperature (1 10-130C), rotation speed (10-20 rpm), can headspace (6.4-12.8 mm) and starch concentration (3-4%). Thermal process parameters (heating rate index, f(h), and heating lag factor, j(ch)) and the resulting process lethalily, F(o) and cook value, C(o) were obtained, from time-temperat ure data obtained during processing for three consecutive runs. Rheolo gical properties and color were experimentally evaluated both before a nd after each run. Overall heat transfer coefficient (U(o)) was calcul ated from the heating rate index using a lumped capacity approach. The study indicated that f(h), j(ch), F(o) and C(o) were influenced (p < 0.05) by all process variables except can headspace. U(o) was related to retort temperature, rotation speed and initial apparent viscosity. The best dimensionless correlation for U(o) was Nusselt number (logari thmic scale) versus specific apparent viscosity and Froude number (R2 = 0.65).