Effect of milk protein composition of a model infant formula on the physicochemical properties of in vivo gastric digestates.

We investigated the effect of protein composition and, in particular, the presence of whey proteins or ß-casein on the digestion behavior of a model infant formula using an in vivo piglet model. Three isocaloric diets optimized for piglets were prepared with the same concentrations of protein. For protein source, 1 diet contained only whey proteins and 2 contained a casein:whey protein ratio of 40:60 but differed in the amount of ß-casein. To obtain the desired protein compositions, skim milk was microfiltered at 7 or 22°C, and retentates and permeates were combined with whey protein isolate. The diets were optimized to the nutritional needs of the piglets and fed to 24 newborn piglets for 18 d. Eight piglets were also fed ad libitum with sow milk and considered only as reference (not included in the statistical analysis). The study was carried out in 2 blocks, killing the animals 60 and 120 min after the last meal. All gastric contents, regardless of diet, showed a wide range of pH. Postprandial time did not affect the pH or physical properties of the gastric digesta. The digesta from whey protein-casein formulas showed significantly higher viscosity, a higher storage modulus, and a denser microstructure than digesta obtained from piglets fed whey protein formula. The ß-casein:total casein ratio at the level used in this study did not significantly affect the physical and chemical properties of the stomach digestate. Although caseins showed extensive gastric hydrolysis, whey proteins remained largely intact at both postprandial times. The results indicate that the presence of different concentrations of milk proteins can be critical to the digestion properties of the food matrix and may affect the nutritional properties of the components.

Short communication: determination of inulin in milk using high-performance liquid chromatography with evaporative light scattering detection.

The objective of this study was to develop an HPLC method for the determination of inulin in a dairy matrix. Inulin is often added to dairy products to act as a source of dietary fiber as well as to provide technological functionality (e.g., water-holding or fat-replacing functions). The method includes hydrolysis of inulin with inulinase enzyme and determination of released fructose and glucose by HPLC coupled with evaporative light scattering detection, using water as the mobile phase. The effect of the milk background was investigated, preparing standards in milk, whey, or permeate and subjecting them to inulinase treatment. The developed method showed satisfactory linearity (R(2)=0.98 for glucose and 0.99 for fructose), good repeatability (relative standard deviation, RSD, ranging from 2.2 to 7.3% for glucose and from 0.6 to 2.3% for fructose), satisfactory reproducibility (RSD from 8.1 to 12.9% for glucose and from 3.1 to 4.9% for fructose), and good recovery (98.4 to 103.6%).