UTILIZATION OF THE COLORIMETRIC METHOD OF MCCARTHY AND SULLIVAN FOR THE DETERMINATION OF BIOAVAILABLE METHIONINE IN BEAN PROTEINS (PHASEOLUS-VULGARIS L)

The colorimetric method developed by McCarthy & Sullivan (1941), based on the reaction of methionine with sodium nitroprusside in presence o f a strong hydroxide solution and later acidification to give the best colour yield, and the modifications of this procedure proposed by sev eral authors (Hess & Sullivan, 1943; Horn et al, 1946; Tannenbaum et a l, 1969; Sorbier & Abello, 1973) were tested in order to verify the in terferences from other aminoacids. According to our results, the inter ference from histidine cannot be totally eliminated and it is necessar y to prepare a protein blank, where methionine residues had been oxidi zed, to determine the colour formation due to histidine or other possi ble interferences. The enzymatic hydrolysis of bean proteins and deter mination of methionine in the hydrolysates gives an estimate of its av ailability, as oxidized forms (sulphone, sulphoxide) do not participat e in this reaction. However, the absolute Values of bioavailability ar e intimately related to the enzymes used for the digestion of the prot ein.