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Title: Dynamic model for mass transfer of solutes in cucumber fermentation

item Fleming, Henry
item McFeeters, Roger

Submitted to: Journal of Food Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/2/2004
Publication Date: 9/1/2004
Citation: Passos, F.V., Felder, R.M., Fleming, H.P., McFeeters, R.F., Ollis, D.F. 2004. Dynamic model for mass transfer of solutes in cucumber fermentation. Journal of Food Engineering. 68:297-302.

Interpretive Summary: About 35% of the U.S. pickling cucumber crop is temporarily preserved by brining. During brine storage, sugars diffuse from the cucumbers into the brine where they are fermented by lactic acid bacteria to produce acids and other compounds, and salt diffuses from the brine into the cucumbers. Thus, the diffusion process is influential to fermentation and quality retention of the cucumbers. We developed a mathematical model to describe these solute changes. The model will be useful in developing a complete model of the cucumber fermentation process for potential application to methods for controlled fermentation of cucumbers for commercial use.

Technical Abstract: A mathematical model for the mass transfer of solutes between whole cucumbers and brine in cucumber fermentation has been developed that takes into account permeation of solutes through stomata in the cucumber skin and through the epidermal cells in the skin, as well as film diffusion through the surrounding brine boundary layer. The model was used to fit experimental data for the time-dependent concentrations of solutes that permeate into the cucumbers (glucose and malate) and out of them (lactic acid, acetic acid, ethanol, and sodium chloride). The rate of lactic acid transport through the stomata was found to be three orders of magnitude greater than that through the epidermis, and the permeabilities of lactic and acetic acids were effectively independent of the brine circulation rate. These results indicate that the rate of permeation of solutes into and out of cucumbers is controlled by mass transfer through the stomata, with neither film diffusion nor epidermal diffusion having a significant effect. The model differential equation for solute transfer combined with a set of rate equations for microbial growth will provide a good basis to establish a complete mechanistic model for the cucumber fermentation process.