Sawitri Chuntranuluck

Prediction of chilling times of foods in situations where evaporative cooling is significant : Part 1. Method development

Abstract The finite difference method was used to simulate the unsteady state cooling of spheres, infinite slabs and infinite cylinders of food materials subject to both convection and evaporation at the product surface. Simulations were conducted across wide ranges of air temperature, surface heat transfer coefficient, product initial temperature, surface water activity and air relative humidity. Algebraic equations are proposed for finding three parameters—the product equilibrium temperature as time → ∞, a slope parameter of semi-log plots relating unaccomplished temperature change to time and an intercept parameter of the same plots. The first of these equations is based on psychrometric theory and the other two were derived by using non-linear regression to curve-fit the numerically simulated cooling rates. These equations allow the numerically simulated cooling times to be predicted within about ±5%. In Part 2 the accuracy of these equations as a simple chilling time prediction method is tested experimentally for model food systems. In Part 3 their application to real foods is considered.

Prediction of chilling times of foods in situations where evaporative cooling is significant—Part 2. Experimental testing

Abstract The algebraic model developed in Part 1 for prediction of chilling times, where cooling at the product surface is by evaporation as well as convection, was tested. Experimental measurements were made by chilling cylindrical test samples constructed of a food analogue in an air chiller. During chilling, the surface of each sample was continually wetted by a wetting agent of known water activity and the relative humidity of the air was controlled. Over the 30 trials, the proposed method predicted measured equilibrium temperature, intercept and slope parameters of semi-log unaccomplished temperature change vs time plots as accurately as could reasonably be expected taking into account data uncertainties (agreement largely within ± 6%, but at worst ± 10%). Chilling times were also predicted sufficiently accurately for many industrial applications. The simple model can be used with confidence for most chilling conditions likely to be encountered in industrial practice and including a w values below 1.0. Part 3 considers applications to food materials in which surface water activity may not be constant.

Prediction of chilling times of foods in situations where evaporative cooling is significant : Part 3. Applications

Abstract Heuristics (rules of thumb) are proposed for extending the chilling time prediction method proposed in Part 1 and tested for model substances in Part 2 to real foods with non-unity water activity. Guidance is given for selecting three water activity values—one representing the maximally wetted starting condition, one representing the mean value during the active chilling phase, and the third describing the surface condition in the quasi-equilibrium state reached at the end of chilling. Chilling times of a product retaining a well-wetted surface during chilling (peeled carrots) were predicted to within approx. − 10 to + 15% of measured values. At least part of this difference can be attributed to experimental error. For a product not retaining a well-wetted surface due to skin resistance (unpeeled carrots) predictions of only slightly lower accuracy were achieved. Accurate prediction of chilling time across a wide range of conditions by a simple algebraic prediction method is possible in spite of the complexity introduced by evaporative cooling at the product surface with water activity less than 1.

An in vitro study of the bioefficacy of essential oil blends against Aedes aegypti (Linn.) and Anopheles dirus (Peyton and Harrison) by using membrane feeding apparatus

Nutthanun Auysawasdi, Sawitri Chuntranuluck, Vichien Keeratinijakal, Siriporn Phasomkusolsil, Silas A Davidson Department of Biotechnology, Faculty of Agro-Industry, Kasetsart University, 50 Ngam Wong Wan Road, Ladyaow, Chatuchak, Bangkok 10900, Thailand Department of Agronomy, Faculty of Agriculture, Kasetsart University, 50 Ngam Wong Wan Road, Ladyaow, Chatuchak, Bangkok 10900, Thailand Department of Entomology, Armed Forces Research Institute of Medical Science, Bangkok 10400, Thailand Journal of Coastal Life Medicine 2017; 5(2): 82-87