Occurrence of lysinoalanine in milk and dairy products

Lysinoalanine (LAL) is produced as an undesirable secondary product during alkaline treatment of proteins or the heating of foodstuffs containing proteins. Because of their closeness, dehydroalanine reacts with the lysine E-amino group. Since the reaction is quite irreversible, the value of the lysine content is almost completely or totally blocked. Due to an improvement in an analytical method, the LAL content of milk and various commercial dairy products was determined. UHT products (drink milk, full cream, coffee cream and condensed milk) analyzed by ALP generally did not contain traces of LAL. Only one UHT coffee cream showed higher levels of LAL. Moreover, cheese manufacture did not lead to any notable formation of LAL. The analyzed caseinates did not contain LAL, but different dried milk products as well as powdered food for children sometimes contained high levels of LAL. Moreover, milk powders with hydrolyzed milk proteins contained up to 2296 mg LAL/kg of proteins. LAL is used as indicator for heat treatment in the quality assurance of foodstuffs. If there is a high proportion of LAL in the sample, it means that the milk or the dairy product was exposed to too high temperatures at the time of treatment or treated during a too long period. The large fluctuation of the LAL contents in milk and dairy products is mainly due to different heat loads and duration of heating.