Exploring the digestion behaviour of goat and sheep milk

Exploring the digestion behaviour of goat and sheep milk

Dr Debashree Roy, Postdoctoral researcher, Riddet Institute. Contact: d.roy@massey.ac.nz

Goat milk and sheep milk are gaining strong consumer interest because of their perceived better nutrition and digestion properties. However, relatively little scientific research has been conducted to demonstrate how the digestion behaviour of goat and sheep milk differs from that of cow milk.

The overall digestibility of milk is expected to be similar regardless of the source or type of milk. However, different types of milk vary in composition and physicochemical properties (protein composition, casein micelle size, fat globule size), which may have implications in determining the rates of digestion of different nutrients in milk. Debashree Roy, a Riddet Institute researcher investigated the dynamics of digestion of cow, goat and sheep milk using an artificial stomach model (a human gastric simulator). She studied the phenomenon of curd formation in these milks in the stomach and explored the potential implications of curd structure in the delivery of nutrients to small intestine during digestion. She has shown that similar to cow milk, goat and sheep milk form a curd (coagulated caseins) and liquid phase (soluble nutrients such as whey) during digestion. The casein curd network is broken down slowly, whereas the soluble whey proteins are transferred rapidly to the small intestine. The curd formed entraps the majority of the fat globules that are gradually released by the breakdown and hydrolysis of the curd protein network by pepsin and mechanical shearing during digestion. This in turn influences the release of proteins and fats during digestion. Regardless of the species, the rates of fat release from the curd are directly correlated to the breakdown of the protein network of the curd. This work shows that the mechanisms of digestion in the stomach are similar for raw cow, goat, and sheep milk, but the relative amount of curds formed from milk from different species is dependent on their casein content, i.e. higher the casein content, the higher the amount of curd formed. Debashree has also conducted further studies to determine the impact of milk coagulation on gastric emptying of raw cow, goat, and sheep milk under physiological conditions using the bottle-fed suckled piglet as an animal model. The studies clearly show that the curd formation in the stomach is important in influencing the rates of nutrient delivery. The fundamental insights generated from these studies are a considerable step forward in providing new and improved understanding about the digestion behaviour of goat and sheep milk. Further studies are underway at the Riddet Institute as part of New Zealand Milk Means More (NZ3M) research programme (funded by Ministry of Business, Innovation and Employment Endeavour Fund). Under this programme, in-depth interdisciplinary research work is being carried out using advanced methodologies to understand the impact of different processing treatments on digestion behaviour of goat and sheep milk. The knowledge generated will help to develop value-added milk products with scientifically validated nutritional and health outcomes for different age groups.

Debashree Roy setting up of the artificial stomach (Human Gastric Simulator).

Picture of the internal compartment of the artificial stomach (human gastric simulator).

References Roy, D., Ye, A., Moughan, P. J., & Singh, H. (2020). Composition, structure, and digestive dynamics of milk from different species—A Review. Frontiers in Nutrition, 7(195) 10.3389/fnut.2020.577759. Roy, D., Ye, A., Moughan, P. J., & Singh, H. (2020). Gelation of milks of different species (dairy cattle, goat, sheep, red deer, and water buffalo) using glucono-δlactone and pepsin. Journal of Dairy Science, 103(7), 5844-5862. Roy, D., Ye, A., Moughan, P. J., & Singh, H. (2021). Structural changes in cow, goat and sheep skim milk during dynamic in vitro gastric digestion. Journal of Dairy Science, 104(2), 1394-1411. Roy, D., Ye, A., Moughan, P. J., & Singh, H. (2021). Impact of gastric coagulation on the kinetics of release of fat globules from milk of different species. Food & Function, 12(4), 1783-1802.

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