Abstract
Three types of commercially available heat-treated milk (low temperature long time-treated milk (LTLT milk), high temperature short time-treated milk (HTST milk) and ultra-high temperature-treated milk (UHT milk)) were evaluated for their peptic digestibility using 16% SDS-polyacrylamide gel electrophoresis and Western blot analysis wish anti-bovine casein, anti-bovine β-lactoglobulin (β-LG) and antibovine α-lactalbumin (α-LA) antibodies. The digestion profile of casein was similar for all the types of milk, and the intact proteins of casein disappeared rapidly upon peptic digestion. α-LA in the LTLT and HTST milks was more resistant than casein to peptic digestion, and this resistance was also maintained in UHT milk, although to a lesser extent. Similarly, β-LG in the LTLT and HTST milks was resistant to peptic digestion, but this resistance was almost lost in UHT milk, so that β-LG in UHT milk was easily digested by pepsin, in a similar manner to casein. In rats, β-LG in UHT milk was digested more rapidly in the stomach than that in HTST milk. These results indicate that α-LA and β-LG differ in their peptic digestibility among different heat-treated milks, and that loss of resistance to peptic digestion of β-LG in UHT milk may have important consequences for reducing its allergenic properties.
