Problems in the determination of FDNB‐available lysine

Publisher Website
Google Scholar
Abstract
Methods that use FDNB Abbreviations used: FDNB, 2,4‐dinitrofluorobenzene; for the determination of available lysine need a correction for loss. The correction procedure has been studied, especially for vegetable materials.DNP‐L† was adsorbed by residues. To minimise loss of DNP‐L, hydrolysates were filtered hot and residues washed thoroughly. Hydrolysis of dinitrophenylated protein was incomplete after 16 h reflux in 5.8 M‐HCl, the yield of DNP‐L being improved by a second hydrolysis of residues. The effect of obtaining higher values after hydrolysis in a large volume of add (dilute hydrolysis) has been largely eliminated. Although DNP‐L added to dinitrophenylated materials (Carpenter's procedure)1 was partly destroyed during acid digestion, DNP‐L in protein (indigenous DNP‐L) was diminished less. DNP‐protein was therefore tried as recovery agent instead of DNP‐L.A modified Carpenter method is described in the Appendix. The estimated coefficient of variation was 3.8%. Various materials were assayed by this method and by TLMI† (the Silcock methody)2. The two values were closer for animal than for vegetable materials, and for undamaged than for heat, damaged materials. The loss of indigenous DNP‐L during an assay (the criterion being comparison with TLMI) was about half that predicted from the recovery of added DNP‐L, but about equal to that predicted from recovery from DNP‐protein. Less DNP‐L was lost during acid digestion in presence of animal than of vegetable protein.The use of the new, smaller, correction factor is discussed.