Author
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Fasina, Oladiran |
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Fleming, Henry |
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Submitted to: Journal of Food Engineering
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 7/14/2000 Publication Date: 1/1/2001 Citation: Fasina, O.O., Fleming, H.P. 2001. Heat transfer characteristics of cucumbers during blanching. J. Food Eng. 47:203-210. Interpretive Summary: Pickling cucumbers preserved by fermentation require high salt levels to ensure microbial and textural stability of the pickles. Many of the pickle companies cannot meet the EPA requirement of 230 ppm of chloride limit in the wastewater obtained when the preserved pickles are desalted during processing into finished products. Preliminary experiments in our laboratory indicate that the high salt levels presently used can be reduced by heating the cucumbers before brining and controlling the fermentation process. The optimum heat process necessary to adequately preserve cucumbers brined at low salt levels has not been established. The first step towards this goal was the focus of this manuscript, which involved investigating the rate at which cucumber fruit increase in temperature during rapid water blanching. Equations that can be used to predict the heat transfer process were also developed, and the appropriateness of the equations was verified with experimental data on temperature. If successful, the rapid blanching-controlled fermentation approach to preservation of pickled cucumbers can be extended to other pickled fruits and vegetables. This will contribute to the reduction in wastes and resultant environmental problems associated with the pickle industry. It is hoped, in addition, that the proposed process will enhance the farm value and improve the quality of vegetables grown for pickling in the U.S. The results from this study will also provide fundamental and basic knowledge into thermal process optimization of vegetable in the area of food processing, food engineering, and food safety. Technical Abstract: The possible use of blanching in combination with controlled fermentation is being considered as a means to reduce the salt levels needed in the storage of brined cucumbers. To be commercially feasible, the use of heat should be optimized for economic and product quality considerations. This study reports basic information on the heat transfer characteristics of cucumbers needed to optimize the blanching process. Two-dimensional (cylindrical coordinates) heat diffusion equations were used to simulate the heat transfer characteristics of cucumbers during rapid water heating (blanching). The equations were solved by the explicit form of the finite difference method. Thermo-physical (thermal conductivity, specific heat and density) properties of cucumbers needed to solve the heat transfer equation were also measured. Temperature (20 to 95 deg C) did not significantly affect the thermal conductivity (average value of 0.61 W/m K) and specific heat (4.04 kJ/kg K) of cucumbers. The maximum standard error of simulated temperatures of the cucumbers from experimental data was 4.5 deg C. There was no significant change in the moisture level of the cucumbers during blanching. Simulation results showed that heat transfer coefficient between 500 and 6,000 W/m2 K had no effect on the average temperature change of cucumbers during blanching. |
