Changes in the stability of ultra-pasteurized lactose-free milk upon storage

Abstract

Lactose-free dairy products are a valued consumer option for lactose intolerant individuals. Short-term ultra-high pasteurization (UHT) allows the preparation of sterile milk products. Manufactures define the useful shelf life of UHT milk as 120 days. This study analyses lactose-free milk with low-fat content over 120 days of shelf storage. Milk composition, microbial presence, structure (micellar size and zeta potential), color, pH, and protein hydrolysis were examined. At 120 days of storage the pH decrease, change in particle size distribution, and significant browning of the milk were detected indicating meaningful changes in the milk structure. The changes occurring in the lactose-free milk are related to the introduction of a large number of reducing sugars as a result of delactosylation of the milk. Studied milk had no microbial contamination nor showed the presence of by-products contamination such as proteases (minimal hydrolysis after long time storage).