Project

The effects of additional β-CN on the structure and behavior of casein micelle and on digestibility in bovine milk

Breast-feeding is considered as the optimal feeding mode to support the growth and development of infants. Although infant formula is designed to be a simulation of human milk, its nutritional composition and functionality are still significantly different from human milk. Therefore it is very relevant to understand and improve the digestive function of infant formula.

Human milk proteins are categorized into three classes: casein (CN), whey protein, and milk fat globule membrane (MFGM) protein (Lonnerdal B, et al. 2017). Caseins and whey proteins dominate the milk proteins quantitatively. At present, bovine milk is the primary milk source for infant formula as the alternative of human milk. The composition (especially protein composition) and digestive behaviors of bovine and human milk, are quite different. Therefore, in order to mimic the 60:40 ratio of human milk, usually the infant formulas are made by removing casein from bovine milk (Goedhart A C, et al. 1994). Thompkinson et al., found that infant formula with adjusted whey : casein ratio (60 : 40) could form a softer curd during the gastric phase, leading to faster and easier gastro-intestinal (GI) digestion (Thompkinson, et al. 2007).

Among which the β-CN is the predominant casein in human milk, accounting for approximately 68% of the casein in human milk. However, β-CN only accounts for approximately 36% of casein in bovine milk (Kunz C, et al. 1992). Therefore, to mimic human milk, one could adjust the proportion of β-CN in infant formula by increasing the content of β-CN. Therefore, more comprehensive studies on how the proportion of β-CN would impact the casein structure and impact the protein digestive behavior are needed.

Aim
The aim of this research is to investigate the effects of additional β-CN in bovine milk on the structure and behavior of casein micelles, such as micelles structure, digestibility, and coagulating properties of the proteins in digestion models. The amount of additional β-CN should be adjusted in such a way that it could mimic human milk as much as possible. Further, this research also aims to compare the concentration of peptides during in vitro digestion to observe common characteristics of peptidome between β-CN-adjusted bovine milk and human milk.

Approach
1 Set up sample models and focus on the impact of β-CN on the casein micelles.Compare the impact of additional β-CN on coagulum formation under different digestion conditions. To start with, we could design the experiment by setting different β-CN addition/dosing levels.

2 After digestion, the apparent and internal structures of the samples can be compared separately. We will also measure the size of the micelles and their stability in each sample.

3 After determining the optimal amount of β-CN, we could determine what factors are important and relevant to improve the digestibility of infant formula in order to achieve optimal human digestion.

Future research
Choose an optimal addition ratio of β-casein to make its digestibility and other characteristics closer to breast milk.

References

  1. Lonnerdal B, Erdmann P, Thakkar S K, et al. Longitudinal evolution of true protein, amino acids and bioactive proteins in breast milk: a developmental perspective [J]. Journal of Nutritional Biochemistry, 2017, 41: 1-11.
  2. Goedhart A C, Bindels J G. The composition of human milk as a model for the design of infant formulas: recent findings and possible applications [J]. Nutr Res Rev, 1994, 7(1): 1-23.
  3. Thompkinson D K, Kharb S. Aspects of infant food formulation [J]. Comprehensive Reviews in Food Science and Food Safety, 2007, 6(4): 79-102.
  4. Kunz C, Lonnerdal B. REEVALUATION OF THE WHEY-PROTEIN CASEIN RATIO OF HUMAN-MILK [J]. Acta Paediatrica, 1992, 81(2):107-112.