MISSISSIPPI STATE -- Giving a food product a longer shelf life means increased quality and often opens new markets.

Foods that stay fresh longer have greater consumer appeal. They also can survive the transport time needed to reach distant markets, or can be stored fresh and used when needed to maintain a steady supply.

Dr. Doug Marshall, food microbiologist with the Mississippi Agricultural and Forestry Experiment Station, is working on ways to increase the shelf life of fish and shellfish. He is focusing his research at the Mississippi State University Food Science and Technology Department on ways to decontaminate products and rapidly detect the quality of seafoods.

"Consumers expect the food supply to be high quality and wholesome," Marshall said. "The quality of seafoods you buy at the retail level can be poor, and it is a severe damage to the industry to have low quality products on the market."

While all meats have a limited shelf life, fish and shell fish are vulnerable to spoilage more quickly than beef, pork or chicken. The reason, Marshall said, is that the microorganisms on the meat of warm-blooded animals are suited to warm temperatures. Placing this meat in cold storage greatly slows the multiplication of these spoilage organisms.

Fish and shell fish, however, are cold blooded and assume the temperature of the water. Since the water is often cool, these microorganisms can survive more easily in cold storage.

One approach to extending the shelf life of fish and shelf fish is to remove or inactivate the organisms on the surfaces of the food. Marshall is trying to develop biological, chemical and physical methods to do this.

"The overall objective is to offer processors a broader range of possibilities of inventory control," Marshall said. "When you have an extensive delay between the processor and the consumer, the product will be of a poor quality before it ever reaches the consumer."

Marshall is studying a biological method to control contamination by dipping the meat in a bath of beneficial bacteria that restricts spoilage organisms. A chemical control under investigation provides a longer shelf life by using phosphates and organic acids to kill and remove spoilage organisms from the surface of fish.

The third decontamination method uses a rapid heat process to physically inactivate microorganisms from the surface of the meat. Marshall said the ongoing project with the U.S. Department of Agriculture Agricultural Research Service steam pasteurizes catfish before skinning and fileting the meat.

"If we can reduce the levels of microorganisms on the skin surface, we will have fewer microorganisms to contaminate the meat," Marshall said.

Related to extending the shelf life of a meat product is checking its quality. Marshall said the current standard is a sniff test. Nationwide, there are three registered noses whose pronouncements of quality are legally binding, although subjective.

"We need an objective method to determine the freshness or spoilage of seafood that anyone can use," Marshall said. "It needs to be quick and easy and not require highly trained people to do it."

There is a computerized machine that can test multiple samples at once and provide freshness information within seven minutes. Marshall developed the standards for this machine to use to determine the freshness and quality of shellfish.

His and other research at MSU's Food Science and Technology Department offers new opportunities to extend the shelf life of food and then detect the quality of that meat.

"If you have an extended shelf life product, you can open up new markets for that product and also assist in inventory control. A company can run a plant on a constant basis, stockpiling the excess inventory and using the extended shelf life product when demand is high," Marshall said.

Dr. Juan Silva, MAFES food engineer in MSU's Food Science and Technology Department, is studying the value of using ozone and hydrogen peroxide to kill microorganisms on catfish fillets. Roberto Chamul, research assistant, explained the work.

"We're trying to see what effect ozone and hydrogen peroxide have on selected microorganisms that may be on the fish and see if we can improve the shelf life of catfish," Chamul said.

Varying concentrations of ozone and hydrogen peroxide were added to the chiller water catfish are dipped in at processing plants. High concentrations remove all microorganisms but destroy the appearance of the fillets.

"We found there are always some microorganisms resistant to treatment, but this does lower their numbers," Chamul said. "We're trying to find the ideal concentrations so as not to affect the sensory quality of the fillet."

This research was conducted in response to industry needs as some Delta processors are considering buying expensive ozonators to treat the fillets. Results of the research and consumer taste panels have established procedures that allow processors to correctly treat the fillets.

Contact: Dr. Doug Marshall, (662) 325-8722