Protein quality of milk-cereal based foods for infants and children in relation to processing methods and composition of the products*

Summary The protein quality of milk-cereal based infant foods, i.e. gruel and porridge powders prepared by different industrial processing methods, was assayed biologically. Net protein utilization (NPU) determinations were made in order to elucidate causes of previously observed wide variations in the protein quality of marketed products and to permit recommendations for improvement of processing methods and formulations. In a pre-mix of a milk-cereal based gruel with about 58% of the total protein content derived from milk, the NPU varied between 15 and 85, depending on the method of roller-drying and on the type of sugar added to the mixture before drying. Heat treatment of porridge powder products was found to reduce the availability of lysine. Thus when the wheat flour was roller-dried and the milk spraydried, the NPU value was 78. When wheat flour, glucose and milk were all present on the drum, the NPU decreased to 40. The presence of reducing sugars, e.g. glucose and fructose, on the drum invariably seemed to result in protein destruction. The advantages and disadvantages of changing sucrose to fructose, glucose or lactose in baby foods are discussed.