The increase in the &tryptophan' content of heated samples was confirmed by UV spectroscopy; A
280 (after correcting for increased turbidity at A 400) increased with the duration of heating at 1403C, indicating that some compound(s) was formed during heating which interfered with the determination of tryptophan. The wavelength of maximum absorbance (280 nm) was not shifted by heating, even for the sample heated at 1403C for 60 min.