Julie Anderson Lively and Evelyn Watts

Keeping the fresh look of shrimp straight out of the water faces a major challenge: melanosis or black spot. Black spot occurs when the shell on the shrimp begins turning black within hours or days after harvesting. This darkening is due to an enzyme process causing oxidation in the shrimp, just like in cut apples. It’s not harmful or indicative of spoilage, but it’s not attractive. This can create a problem for fishermen and processors because black spot can result in a loss of quality during inspection or simply rejection by buyers. However, black spot is preventable.

For years, fishermen have used sulfite powders, often on the boat right after harvest, to stop the blackening of the shell. However, sulfite use comes with some risks.

First, it is known to cause hypersensitivity reactions, which are especially harmful to those with asthma, and it is required to be labeled on the ingredient list for any product that includes sulfite at any point in the harvest or processing chain. Additionally, more buyers are requesting sulfite-free shrimp.

Second, it must be handled correctly. Most often, fishermen or docks will create a liquid dip for the shrimp. If the dip is not mixed to the proper concentration or the shrimp is dipped too long, shrimp could have a sulfite residue over 100 parts per million, the legal limit set by the U.S. Food and Drug Administration. Additionally, using too much powder can be hazardous for workers because hydrogen sulfite gas can be given off.

New products for black spot prevention have entered the market, but none were developed with Louisiana shrimp in mind. These new products use a 4-hexylresorcinol (4HR) formulation, a compound originally derived from kiwifruit that does not require a statement on the package label. However, before these products could be recommended to the Louisiana shrimp industry, they needed to be tested for effectiveness, ease of use and overall quality.

LSU AgCenter and Louisiana Sea Grant researchers began working with shrimp fishermen to test two new products, EverFresh and Prawnfresh, beginning with the manufacturers’ recommendations. Both products were developed for shrimp or prawn fisheries in other parts of the world and designed to be integrated easily into those fisheries. That did not mean they would work with Louisiana shrimp or climate. For example, Prawnfresh recommends a dip time 10 times longer than for sulfite (10 minutes versus one minute) and in freezing-cold, full-salinity seawater, something easy to find off the coast of the United Kingdom where the company is located but not common off the coast of Louisiana.

To test effectiveness in Louisiana, fresh shrimp were treated with these compounds and compared with sulfite-treated and untreated shrimp over 10 days to see what levels of black spot developed. Variations of the manufacturers’ recommendations were also tested so the products could be swapped seamlessly into current Louisiana shrimp harvest processes. At the end of the testing, not only are the 4HR products effective, they are more effective and safer than using sulfite. While sulfite will delay melanosis three to five days, 4HR-treated shrimp looked fresh 12 days after harvest. Researchers also tested the texture and color of the shrimp, and no differences were found.

The alternative products using 4HR can create a higher-quality shrimp product that does not contain sulfite and can be sold for higher prices and longer times by extending the shelf life. The outcome of the work is being shared directly with commercial fishermen through the Louisiana Fisheries Forward program with fact sheets, workshops and direct partnering. Consumers can now find sulfite-free Louisiana shrimp in the market. The AgCenter and Sea Grant are now working to improve the process of incorporating these products into brine- and plate-frozen shrimp.

Julie Anderson Lively is an associate professor and a marine fisheries specialist in the School of Renewable Natural Resources and Louisiana Sea Grant, and Evelyn Watts is an assistant professor in the School of Nutrition and Food Sciences and Louisiana Sea Grant.

(This article appears in the fall 2018 issue of Louisiana Agriculture.)

Watch the video (1 min. 21 sec) on how food scientists are finding ways to enhance the quality of seafood and extend its shelf life.

The shrimp at left have developed black spot, which can occur within hours or days of harvesting due to an enzyme process causing oxidation, just like in cut apples. It’s not harmful or indicative of spoilage, but it’s not attractive. Black spot is preventable using a compound derived from kiwifruit. LSU AgCenter and Louisiana Sea Grant researchers are working to develop products and procedures using this compound appropriate for the Louisiana seafood industry. Photo by Nick Haddad

Graduate student Nick Haddad submerges a basket of fresh shrimp into a solution containing EverFresh, a product that uses a compound derived from kiwifruit that prevents black spot. Photo by Olivia McClure

Looking over a tray of fresh shrimp at Randol’s restaurant in Lafayette are, from left, graduate student Nick Haddad; Evelyn Watts, an assistant professor with the LSU AgCenter School of Nutrition and Food Sciences and Louisiana Sea Grant; and Thomas Hymel, an agent with the AgCenter and Sea Grant. They are developing ways to better package shrimp in trays sealed with plastic film using the equipment in the background. Photo by Olivia McClure