Assessment of whey protein nitrogen index as an indicator of heat treatment for UHT milk and milk powder

Abstract

During heat treatment of dairy products it is possible to occur several chemical modifications which whey protein denaturation is quite evident and studied. This phenomenon can cause gelation in UHT milk and some problems in reconstitution of milk powder, two major dairy products widely used in dairy foods and by consumer. The whey protein nitrogen index (WPNI) can be an useful tool to assess the degree of severity that milk was submitted, and therefore inferred from the occurrence of possible defects associated with protein denaturation. This study presents the
evaluation of the non-denaturated whey protein contents as a heat treatment indicator for ultrapasteurization and drying milk processing. Commercial samples of UHT milk and milk powdershowed WPNI confidence interval of (2.39 ± 1.41) mgWPN.mL-1 and (2.63 ± 1.38) mgWPN.mL-1, respectively. According to the statistical analysis of variance, all samples differed with a p-value < 0.001; and 90% of UHT milk and 67% milk powder samples were classified as medium heat treatment. It was possible to infer the severity of the heat treatment associated with each kind of product analyzed.
The results were able to demonstrate the lack of standardization of heat treatment processes on the samples studied, a fact that may result in the growth of undesirable
characteristics in the products during the storage or commercia lization.