Protein-Lipid Interactions in Concentrated Infant Formula

Abstract

Radiolabeled milk proteins ([carbon-14] beta-lactoglobulin or [carbon-14] kappa-casein) were added to raw skim milk used to prepare concentrated humanized infant formula. Ultracentrifugation of the sterilized product allowed separation of three fractions: lipids and the proteins associated with them; free casein micelles and other dense particles; and the fluid phase. Distribution of radiolabeled tracer proteins or of protein measured by chemical methods among these three phases varied significantly with differences in processing conditions (time and temperature of sterilization) or amount of certain additives (potassium hydroxide or urea). In the range of 0 to 8 meq/L of potassium hydroxide added to the formula after homogenization but before sterilization, the lipid layer content of carbon-14 from [carbon-14] kappa-casein in the sterilized product decreased by 4.7% for each 1 meq/L of added potassium hydroxide. Lipid layer content of protein decreased by 2 g/L (of a total of 32 g/L) for each 1 meq/L potassium hydroxide. Such differences in the structure of the product, related to interactions of protein with lipid, protein, or calcium phosphate, may correlate with physical properties and stability of milk-based lipid-rich products.

Effects of Sterilization, Packaging, and Storage on Vitamin C Degradation, Protein Denaturation, and Glycation in Fortified Milks

“…In particular, the role of vitamin C degradation products on the development of the Maillard reaction (Leclère et al, 2002) and radical reactions initiated by the ironvitamin C mixture (Stadtman, 1991;Almaas et al, 1997) have been reported. The loss of protein digestibility (Rowley and Richardson, 1985;Jelen and Rattray, 1995), the decrease in the bioavailability of several essential amino acids (particularly lysine and tryptophan), and formation of undesirable compounds such as carboxymethyllysine (Birlouez-Aragon et al, 2004) could be explained by vitamin C-derived Maillard reaction (Leclère et al, 2002;Puscasu and Birlouez-Aragon, 2002).…”

Solubility and Digestibility of Milk Proteins in Infant Formulas Exposed to Different Heat Treatments

“…1,1992 termeyer and Reimerdes (10), however, observed a significant change in protein digestibility in vitro after heat treatment at 70-80°C. Differences between the digestibility and bioavailability of essential amino acids from different forms of IF were shown by Sarwar et al (18,19). They attributed their findings not to physicochemical interactions of proteins and lipids, but rather to chemical changes due to Maillard reactions.…”