The measurement of available lysine in textured soy protein

Although soy protein is considered to be an excellent source of lysine, the effect of extrusion on lysine availability in commercial textured soy protein of the hamburger extender type had not been reported. The purpose of this research was to determine the effect of extruder processing on the lysine availability in textured soy protein.

York soy and three brands of textured soy protein were studied, Protein content of defatted, dehulled York soy measured 43%, while the protein content of the three textured products was 51, 54, and 49%, Available lysine was measured using the methods of Kakade and Liener (1969 ). Molar absorptivity of ε -TNP-L-lysine HCl was 1.5 x 10⁴M^-1 cm^-1, a value which compared favorably to values reported in the literature. When soy samples were analyzed, no significant difference between the available lysine content of the samples was observed, although processed products had slightly lower available lysine values than did the unprocessed soybeans. The Kakade and Liener (1969) TNBS procedure provided a quick reproducible measure of lysine availability. The results of this study indicated that lysine availability in textured soy protein was not altered significantly during processing.