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Bioavailability of Lysine in Maillard Browned Protein as Determined by Plasma Lysine Response in Rainbow Trout (Salmo gairdneri)¹

Department of Fisheries, Aquaculture and Pathology ^* Department of Food Science and Nutrition, University of Rhode Island, Kingston, RI 02881

The bioavailability of lysine in Maillard browned protein was investigated by plasma lysine response in rainbow trout (Salmo gairdnerl). The concentrations of free lysine in the plasma were measured after feeding control and browned protein diets supplemented with graded levels of lysine. Bioavailability of lysine was estimated based on the amounts of supplemental lysine in the diets that resulted in rapid increases in plasma lysine. An approximately 80% loss in bioavailable lysine content was determined by this method in a fish protein isolate subjected to the Mail-lard browning reaction under mild conditions (40 d incubation at 37°C). The nutritional damage to lysine determined by plasma lysine response was similar to that estimated in vitro by enzymatic hydrolysis and fluorodinitrobenzene reagent, but was underestimated by acid hydrolysis and trinitrobenzene sulfonic acid reagent. Rainbow trout are similar to other animals in their inability to utilize the deoxyketosyl (Amadori) compound of lysine formed in early Maillard reaction, and in their plasma response to dietary levels of essential amino acids.

KEY WORDS: • lysine bioavailability • Maillard browning reaction • plasma lysine • rainbow trout

¹ Funded by Grant No. NA81AA-D-00073, Office of Sea Grant, National Oceanic and Atmospheric Administration, U.S. Department of Commerce.

² Present address: Fishery Research Branch, Food and Drug Administration, P. O. Box 158, Dauphin Island, AL 36528.

Manuscript received 21 May 1987. Revision accepted 10 September 1987.