Chemical modifications of casein occurring during industrial manufacturing of milk protein powders

The effect of milk acidification at different pH levels applied during the processing of various types of milk protein powders was first evaluated in the experimental samples of caseins, caseinates and milk protein concentrates. The absence of inorganic colloidal phosphorus was detected when milk was acidified to pH 4.60, whereas low levels (0.36–0.72 g/100 g of protein) were detected when mild milk acidification occurred. The extent of protein glycation and the occurrence of protein cross-linking were assessed in the same samples by measuring their furosine (5.7–427 mg/100 g of protein) and lysinoalanine (0.4–35.2 mg/100 g of protein) levels, respectively. In addition to heat treatments, the contents of these markers strictly depend on the presence of lactose and consequently on the effectiveness of the washing step applied during processing before drying to remove non-protein soluble components. The determination of these chemical markers in the samples permitted the identification of different technological conditions applied in the manufacturing of commercial milk protein powders with the same class.