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Trypsin inhibitors in soy products: modification of the standard analytical procedure

Hamerstrand, G.E., Black, L.T., Glover, J.D.
Cereal chemistry 1981 v.58 no.1 pp. 42
soybeans, food composition, trypsin inhibitors, chemical analysis, food analysis, enzyme inhibition, trypsin, enzymatic hydrolysis, spectroscopy, enzyme substrates, soybean products
The standard AACC (American Association of Cereal Chemists) method for determining trypsin inhibitor in soy products, based on the tryptic hydrolysis of a synthetic substrate, benzoyl-DL-arginine-p-nitroanalide hydrochloride, produced data in the nonlinear portion of the absorbance-sample size curve (above 60% inhibition of trypsin). These values, when converted to trypsin inhibitor units/ml and extrapolated to zero concentration, tended to give erroneously high values for trypsin inhibitor content. To obviate these problems, the trypsin inhibitor was determined from a single dilution of a sample extract that inhibited at least 40 but no more than 60% of the trypsin. The inhibitor content was calculated from the differential absorbance readings and reported in pure or absolute units as mg of trypsin inhibitor/g of sample. Values obtained by the modified procedure, although approximately 20% lower than those obtained by the standard method, were considered a more accurate representation of the trypsin inhibitor actually contained in the sample. Based on 18 replicate sets of data on the same soy sample, the modified procedure was more reproducible, giving a SD of .+-. 2.4 units vs. .+-. 4.2 units for the standard method.