Changes during storage of lactose hydrolysed extended shelf life (ESL) milk.

摘要

The effect of lactose hydrolysis and/or reduction of carbohydrate content of extended shelf life (ESL) milk on proteolysis and the formation of furosine was studied during 8 wk of storage at 8 degrees C. The reduction of carbohydrate content was carried out by ultrafiltration. The proteolysis was distinct in all test milk samples as analysed by SDS-PAGE and measurement of the free tyrosine equivalent content. The proteolysis was weakest in milk with a reduced carbohydrate content and hydrolysed lactose probably due to the inactivation of plasmin during the production process. Proteolytic side activities of lactase were less significant than other proteolytic activities during storage. Furosine concn. increased linearly during storage in unhydrolysed, hydrolysed and carbohydrate-reduced & hydrolysed milk from 0.19, 0.34 and 0.26 mg/g, respectively, on day 0 to 0.23, 0.48 and 0.38 mg/g protein, respectively, on day 56. The rate of early Maillard reaction during the ESL heat treatment and storage was clearly decreased by the reduction of carbohydrate content in lactose hydrolysed milk. The estimated lysine blockage was nutritionally insignificant in all test milk samples.