Extending the Shelf Life of Fresh Seafood

An ongoing effort by the purveyors of fresh seafood is the opening of inland markets. This can be done by speedier transportation, but this turns out to be costly and sometimes hard to arrange if these products are to enter ordinary marketing channels. This business objective can also be advanced by improving the holding technologies for fresh seafood products (4). With such technologies the product can come through shipping and handling and still be desirable to the consumer. Perhaps the most common of these technologies is refrigeration, but this too has limits, which still leaves large markets untapped.

Two emerging technologies have application here: modified atmosphere packaging and the use of a sorbate dip on the product. With modified atmosphere packaging, the product is enclosed by a barrier material and the atmosphere over the product is replaced by one without oxygen. The permeability of the barrier material to oxygen is a controllable variable—the packaging material must be chosen (and paid for) by the seafood seller. The sorbate dip technology requires that the product be coated with a sorbate solution of variable concentration. Because these two technologies can be used simultaneously, a reasonable question is, what combination of both would be most beneficial to the seafood seller?

This was investigated by gradient search methods. Consumer response data were taken by asking consumers to taste and then to rate the sample tasted as acceptable or unacceptable. (Other data were taken as well.) The purpose was to determine the consumer response to applications of combinations of these technologies by estimating the acceptor set size over time. The system was constrained by the limits on the sorbate concentration that seemed acceptable and by available barrier materials. The acceptor set size function was assumed to be differentiable and the data taken were used to estimate the gradient of this function. The gradient of any differentiable function has the property that it points in the direction of the steepest ascent of the function. Thus, after each completed test, new information was available that indicated what adjustment in the technologies could be made to make the combined application better. This approach is an example of a gradient search method and is a decision-making tool that is broadly applied in optimization, often as part of a computer algorithm. The novelty here is that data collection must be done before each iteration of the algorithm, making the whole procedure considerably slower than most algorithms.

A starting permeability of the barrier film and concentration of sorbate is chosen. Tests are run for higher and lower permeabilities at this sorbate concentration and for higher and lower sorbate concentrations at this permeability. The resulting data allows the estimation of the gradient vector at the starting point. If the gradient vector is at or near zero, little improvement is possible, otherwise a step in the direction of the gradient will improve the performance of the combined technologies. New values for permeability and concentration are chosen and the test is repeated.

The application of this procedure portrayed consumer response through time to different combinations of technologies. An important question not addressed is, is the extra expense of implementing and using the technology worth the resulting extension in shelf life? Addressing this question would mean a more complicated model would have to be developed and perhaps different computational methods would be required.

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