Liquid chromatographic enrichment ofN-acetylmethionine from casein hydrolysates for stable-isotope-ratio analysis of sulfur

Abstract

Key WardsColumn liquid chromatography Sulfur stable-isotope-ratio analysis Isotope-fractionation Casein N-Acetylmethionine SummaryA chromatographic method has been developed for enrichment of methionine-bouncl sulfur ~n casein, for stable-isotope analysis. Casein is precipitated from milk samples and cleaved by acid hydrolysis in 6 M hydrochloric acid at 95 ~ The amino acids released are converted into their N-acetyl derivatives by addition of acetic acid anhydride. After lyophihzation, N-ace@-methionine is separated from the accompanying components on octaclecylsilica by use of a gradient prepared from 0.02 M formic acid and methanol. The fractions containing N-ace@-methionine are pooled and freeze dried. Procedures for hydrolysis and clerivatization were optimized to furnish the highest yields. The influence of the abundance ratio on the chromatographic separation is shown and discussed. From 1.0 g casein 16.5 mg N-acetylmethionine were isolated.

Application of Multielement Stable Isotope Ratio Analysis to the Characterization of French, Italian, and Spanish Cheeses

“…Determination of δ 34 S was carried out on methionine separated from hydrolyzed casein according to the published protocols ( , ).…”

Chromatography of amino acids and short peptides. New advances

“…The isocratic mobile phase was water-methanol (9:1, v/v). It was indicated that the method can be applied for the authenticity and traceability tests of dairy products containing casein (Lamprecht and Haberhauer, 2001).…”