Nancy Katherine Rubio, Marlene Janes, Zhimin Xu and Witoon Prinyawiwatkul

Chitosan, a natural substance created from the shells of shrimp and other crustaceans, has gained popularity as a dietary supplement. LSU AgCenter researchers are studying another use for the natural biopolymer. They are researching whether this abundant natural resource may be used as a food preservative or coating material to help keep foods safe and prevent them from spoiling.

Chitosan has received increased attention for its commercial applications in the biomedical, food and chemical industries. The use of chitosan in the food industry is growing because of its distinctive biological activities and functional properties. The market need for chitosan is projected to grow at a compound annual growth rate of 17.7% to 2020, at which point it is expected to reach $4.2 billion. Additionally, the market for antimicrobial coatings for food should grow at a compound annual growth rate of 9% until 2020, reaching $5 billion.

The antimicrobial activity and film-forming property of chitosan make it a potential source for a food preservative or coating material of natural origin that can be used to improve the storability of perishable foods and potentially prevent illness from spoiled foods.

The enormous amount of crustacean shell waste from Louisiana shrimp, crab and crawfish processing can be used to produce chitosan, which would help reduce costs for handling shell waste and also reduce environmental pollution. Chitosan can be produced with various molecular weights, which determine whether it is water soluble. Molecular weight affects the functionality and end usage of chitosan. For example, compared with low-molecular-weight chitosan, the high-molecular-weight chitosan exhibits better tensile strength and elongation properties when used as a functional film. However, the poor water solubility of high-molecular-weight chitosan limits its applications.

LSU AgCenter researchers invented a simple preparation procedure for fast-dissolving high-molecular-weight chitosan without any chemical modifications, eliminating its pungent acid odor. Also, the fast dissolving and redissolving time for the freshly prepared high-molecular-weight chitosan solution or the dried high-molecular-weight chitosan powder will reduce the cost of production. Additionally, much higher concentrations of water-soluble high-molecular-weight chitosan solutions can be obtained, which is not possible with the current technology.

AgCenter food microbiologists applied water-soluble high-molecular-weight chitosan solutions as coatings and dipping solutions. To analyze the antimicrobial activity of these high-molecular-weight chitosan coatings, this chitosan was coated onto the surface of ready-to-eat chicken, raw catfish and shucked oysters that were inoculated with different foodborne pathogens. Then the food products were stored at refrigerated temperatures. The bacterial counts of samples were enumerated during the shelf life study. The results demonstrated that high-molecular-weight chitosan coatings were effective against some foodborne pathogens. The antibacterial activity of high-molecular-weight chitosan differed depending on the concentration of chitosan solution, the solvent used to dissolve the chitosan, the bacteria tested and the product that was tested. More research is being conducted.

Nancy Katherine Rubio, a former graduate student in the School of Nutrition and Food Sciences, inoculates seafood with L. monocytogenes. Photo provided by Nancy Katherine Rubio

These oysters have been dipped in chitosan solutions. Photo by Nancy Katherine Rubio

A beaker of chitosan in the lab. Photo by Nancy Katherine Rubio