MASS TRANSFER AND SOLUTE DIFFUSION IN BRINED CUCUMBERS

Authors: Fasina, Oladiran; Fleming, Henry; Thompson, Roger

Submitted to: Journal of Food Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/12/2001
Publication Date: 1/1/2002
Citation: Fasina, O.O., Fleming, H.P., Thompson, R.L. 2002. Mass transfer and solute diffusion in brined cucumbers. Journal of Food Science. 67:181-187.

Interpretive Summary: In the preservation of pickling cucumbers by fermentation in brine, salt and other brine additions diffuse into the fruit, where they act to prevent softening of the tissue. Sugars diffuse out of the fruit into the surrounding brine where they are fermented to acids. Factors affecting diffusion can greatly influence the quality of the fermented fruit. In this study we developed mathematical models to describe these diffusion processes. We determined that salt and other additives move into the cucumbers faster than sugars and other compounds move out of the cucumbers. Diffusion was faster in smaller than larger fruit. The mathematical models developed should be useful in designing brining methods to reduce the amount of salt necessary to preserve the cucumbers. This information may be useful to commercial pickle processors in their efforts to reduce the concentration of salt used for preservation and avoid problems related to disposal of excess salt, which has become an important environmental issue.

Technical Abstract: Brine fermentation is one of the methods used to preserve cucumbers. Modeling of the fermentation process will require the choice of an appropriate equation to describe the movement of solutes in and out of the brined cucumber fruit. The exchange of malic acid, lactic acid, NaCl, and sugar between cucumber and cover brine were monitored over a course of 16 days for 5 sizes of cucumbers. Experimental results showed that sugar exchange between cucumbers and cover brine was the slowest in comparison to other solute transport. The diffusion coefficient of sugar (estimated by the inverse theory optimization method) in the brined cucumbers varied from 1.80 x 10-9 to 9.18 x 10-9 m2/s. Based on the estimated diffusion coefficient, it was found that the exponential (first-order) or lumped- type model, as opposed to a distributed model (Ficks diffusion equation), better describes the movement of solutes during the brine fermentation of cucumbers. Solute sorption rate (k) from the exponential model varied from 0.0204 to 0.233 h-1 and decreased with increase in cucumber size.