Investigation into the protein modification of nutritional powder : a thesis presented in partial fulfillment of the requirements for the degree of Master of Food Technology at Massey University, Manawatu, New Zealand

Abstract

Infant milk formula (IF) is a manufactured food that is fortified with nutrients to meet the composition of human mother’s milk at the first 0-6 months postpartum. The common ingredients include bovine milk and/or whey as protein sources, lactose, vegetable oils, vitamins, and minerals. Unlike human milk, infant formula uses high- heat treatments to ensure microbiological safety and stability of the final product. These heat treatments are potentially detrimental to the nutrients by lowering the nutritional quality of the IF and can be seen as unnatural. Of particular interest is the effect of heating on proteins that contain the essential amino acids which supports the infant growth. The complex reaction between the proteins and lactose called glycation, measured as Furosine, is known to impair nutritional quality and protein digestibility. Hence, some infant formula manufacturers consider less heat treatment as a marker of naturalness. Furosine was used as chemical marker in this study because it is known to be abundant in infant formula. The objective was to investigate if an IF that used a liquid skim had less modification as shown by furosine concentration, than an IF that used a Skimmed Milk Powder. Skimmed Milk Powder is produced by heating and dehydration and is usually rehydrated before it proceeds to the IF manufacture. Therefore, it experiences a double heat-treatment potentially resulting in a greater protein modification. The study showed that the commercial IFs with fresh Skimmed Milk had significantly lower modified proteins than an IF with Skimmed Milk Powder. The results suggested that the cumulative extent of modification found in the IF was greatest during spray drying. Additionally, it was shown that whey ingredients were responsible for the significant protein modification found in the batch tank. It was likely that the batch-to-batch variations of furosine observed in the commercial IFs were dominated by variations in the whey ingredients. The milk quality and the rigors of the subsequent whey protein production will be variable between factories, particularly those that use liquid whey. Therefore, the use of both liquid skim and liquid whey will minimize the contribution of the ingredients to the final IF. The glycation and other parameters (denaturation and aggregation and lactulose) measured in this study gave insights to the possible differences of heat treatment and ingredients used between manufacturers. Lactulose content was analysed along with the total whey protein and β-lactoglobulin (β-LG) to gain information about the heat treatment history of the infant formula. The outcome of this work can be used to guide manufacturers to decrease the protein modification in the commercial infant formula.