Effect of lactose hydrolysis on furosine and available lysine in UHT skim milk

The effect of enzymatic lactose hydrolysis on the formation of furosine and blockage of lysine was studied in direct UHT processed skim milk. Enzymatic hydrolysis was performed either before or after the UHT-treatment and milk samples during 12 weeks storage at 4 different temperatures were compared to those of unhydrolysed skim milk. The storage temperature had a significantly greater effect on furosine formation than the order of hydrolysis and UHT-treatment especially at elevated storage temperatures of 22, 30 and 45 degrees C. Colour measurement was used to follow the advanced Maillard reaction in milk. The colour change correlated well with the furosine change during the storage (r(2)=0.926, n=36). Monosaccharide levels in hydrolysed milks were at the same level in all milks except in those stored at 45 degrees C, where their levels were clearly lower due to the Maillard reaction.