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To establish the effect of the presence of milk serum proteins on heat-induced changes to lactoferrin, lactoferrin alone, and lactoferrin mixed with either milk serum or β-lactoglobulin was heated at 65 °C, 70 °C and 75 °C for 30 min. After heating, the effect of milk serum proteins on aggregation of lactoferrin was characterized, after which the effect of such aggregation on digestion and bacteriostatic capacity of lactoferrin were determined. The presence of milk serum proteins accelerated the aggregation of lactoferrin during heating through thiol/disulphide interchange. Lactoferrin also formed disulphide-linked aggregates when it was heated with β-lactoglobulin. Protein aggregates formed at 75 °C were much more resistant to infant digestion, causing decreased peptide release from lactoferrin. Heating lactoferrin and milk serum proteins together accelerated the loss of bacteriostatic activity upon heating. In conclusion, heat-induced aggregation of lactoferrin with milk serum proteins affected both its digestion and its bacteriostatic activity.

In present study, 198, 169, 213 and 128 proteins were identified and quantified in human, cow, goat and yak milk serum respectively by using proteomics techniques. Large variations were observed between human and ruminant milk proteins. Human milk contained higher concentration of mucosal immune response, complement proteins and regulators. The concentration of bactericidal proteins were relatively higher in ruminants milk. Human milk exclusively expressed proteins important for delivery or utilization of nutrients. Peptidase inhibitors prevent the bioactive proteins/peptides in human milk from gastral-intestinal digestion. Protein composition among ruminants milk was similar but with variations. Goat milk contained high level of complement proteins but low level of corresponding regulators. In addition, the acute phase proteins were significantly higher in goat milk. Of note, osteopontin in yak milk was enriched, which could offer an alternative source for producing osteopontin and revealed possible nutritional value of yak milk.

This study investigated the effects of heating skim milk with soluble calcium salts, calcium chloride, calcium lactate, calcium gluconate and calcium lactobionate, on the physico-chemical and rheological properties of milk. Regardless of the type of salt added, the amount of casein in milk serum decreased and the amount of calcium in centrifuge sediment increased along with the serum calcium. The amount of calcium salt required for gelation and the gel firmness (G') varied depending on the salt. The aCa2+ order in milk was calcium chloride>calcium lactate>calcium gluconate>calcium lactobionate. With the same amount of added calcium salt, the final G' of milk gel followed the same order. The findings from this study suggest that the different association constants and formation of an intermediate calcium complex with hydroxycarboylate groups affected the calcium ion activity, which may influence the gelation properties in milk.

This study mainly investigated changes in milk serum proteins by simulating the industrial processing of whole milk powder using a label-free proteomic approach. A total of 391 proteins were identified, 89 of which were quantified in all groups. Compared with raw milk, the milk subjected to the heating pasteurization process showed significantly decreased the serum protein profile, whereas that subjected to vacuum concentration and spray-drying showed minimal changes. The LC-MS/MS results were further confirmed by determining the activity of bioactive xanthine oxidase and retention of lactoferrin and immunoglobulins. The data showed that 70%-85% of lactoferrin and immunoglobulins were retained in vacuum-concentrated or spray-dried milk but were hardly identifiable in heat-pasteurized milk or whole milk powders. These findings indicate the need for improving the current milk powder-manufacturing techniques to allow the retention of active milk proteins.

The ability of buttermilk to carry and stabilise a preparation of curcuminoids was examined. The quenching of intrinsic protein fluorescence confirmed that the curcuminoids interacted with proteins in buttermilk. The Stern-Volmer quenching constant was ≥ 9.4 × 10³ M⁻¹. The apparent binding constant of curcuminoids to whole buttermilk was ≥ 2.2 × 10⁴ M⁻¹. Centrifugation of buttermilk (5% total solids, TS)--curcuminoid mixtures demonstrated that curcuminoids were partitioned into the cream (18.0%w/w, 0.64% TS), milk serum (73.3%w/w, 2.86% TS) and the casein-rich precipitate (6.76% w/w, 1.87% TS) fractions in the ratio of 1:3.7:3.5. The interaction of curcuminoids with components in the buttermilk improved its stability, as evidenced by the faster degradation of curcuminoids in phosphate buffer (pH=6.8) than in buttermilk. The ability of buttermilk to carry and stabilise curcuminoids has the potential to enable the delivery of these components into functional foods.