Determination of lysinoalanine in foods containing milk protein by high-performance chromatography after derivatisation with dansyl chloride

A modified RP-HPLC method for the determination of lysinoalanine (LAL) with dansyl chloride derivatisation without solid-phase extraction is presented. The method was applied to market samples of liquid milk (n = 54) and cheese (n = 32) as well as to human milk from healthy volunteers (n = 12). Additional liquid milk samples were obtained from model experiments on falling stream heating (FSH) high-pasteurisation (n = 40). In raw milk, pasteurised and FSH high-pasteurised milk products LAL was quantified for the first time. The LAL contents analysed in raw and pasteurised milk ranged from 4 to 24 and 17 to 69 mg kg(-1) crude protein, respectively. Compared to that, UHT-treated milk and sterilised milk showed higher LAL levels up to 186 and 653 mg kg(-1) crude protein, respectively. Among all of the dairy samples, LAL was proven to be a suitable and sensitive indicator to assess the heat treatment intensity given to milk which was heated without and with the addition of dairy-based substitutes,like caseinates. (C) 2000 Elsevier Science Ltd. All rights reserved.