Thermophysical properties and thermal behavior of leafy vegetables packaged in clamshells
Bergeron Quirion, S., Villeneuve, S., Leblanc, D.I., Delaquis, P. (2012). Thermophysical properties and thermal behavior of leafy vegetables packaged in clamshells, 113(1), 27-32. http://dx.doi.org/10.1016/j.jfoodeng.2012.05.032
Little is known about the thermophysical properties of fresh-cut lettuce other than heat of respiration. Empirical correlations based on food composition remain the only way to estimate the thermophysical properties of fresh-cut lettuce. The objectives of this study were (i) to determine the thermophysical properties of several baby-leaf lettuce and brassica greens and (ii) to verify the measured thermophysical properties by using them in a heat transfer model and comparing the predicted product temperatures with measured product temperatures in a simulated interruption of a cold chain. Density, leaf thickness, thermal conductivity, specific heat and water activity from nine varieties of baby-leaf lettuce and brassica greens were measured. A broken cold chain was simulated in a low temperature incubator set at 10 °C for a length of time before readjustment at 2 °C. Results showed that density (1078-1112 kg m -3), leaf thickness (0.18-0.54 mm), thermal conductivity (0.55-0.70 W (m °C) -1) and specific heat (3.1-4.3 kJ (kg °C) -1) varied significantly (P < 0.05) between varieties. However, no significant differences were observed for water activity (0.959 ± 0.006). Using thermophysical properties as input in the heat transfer model, experimental and calculated temperatures were well correlated (R 2 = 0.98) with a root mean square error of 0.57 °C over the 10-40 mg CO 2 (kg h) -1 range of respiration rate. The measured thermophysical properties adequately predicted the temperature of the baby-leaf greens during simulated broken cold chains. A sensitivity analysis performed with the heat transfer model showed that the thermal conductivity, the specific heat and the density were relatively more important on the thermal behaviour of the baby-leaf greens than the heat of respiration.© 2012 Elsevier B.V. All rights reserved.
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