Carbohydrate-binding and agglutinating lectins in raw and processed soybean meals

Abstract

Total N-acetyl- d-galactosamine binding and functional brush border agglutinating lectins were measured in raw defatted soybean meal, in 11 samples of soybean meals obtained from various processing plants using conventional desolventising and toasting, and one sample of meal from a plant using a `flash' desolventising system. Agglutination activity of the affinity purified lectins was measured with brush border vesicles prepared from the small intestine of 4-week-old broiler chickens. Raw soybean meal contained 2.3 mg of N-acetyl- d-galactosamine binding and 2.3 mg of brush border agglutinating lectin protein/g. As such all of the lectin in the raw soybean meal retained functional brush border agglutinating activity. Of the 11 samples of conventionally-processed soybean meal, three had 20–30%, six had 10–20%, and two had 3–10%, of the concentration of carbohydrate-binding lectin obtained per gram of raw soybean meal. All the 11 samples had agglutinating lectin levels of less than 10% and eight had agglutinating levels of less than 3% of the level found in raw soybean meal. The flash desolventised sample had a carbohydrate binding lectin level in excess of that obtained with raw soybean meal and an agglutinating lectin level that was 38% of that obtained with the raw meal. This study indicates that conventionally-processed soybean meals can retain significant levels of carbohydrate-binding lectin but that the functional capacity of the lectins to induce agglutination of the intestinal brush border membrane is mostly destroyed during processing. The finding of substantial carbohydrate-binding lectin in some of the conventionally-processed samples, and of substantial carbohydrate-binding and brush border agglutinating lectin in the flash desolventised sample suggests that soybean meals can, on occasion, retain functional lectins at levels that may be detrimental to the animal's health and productivity.