Study on the structural characteristics and in-vitro digestion behaviours of NZ goat and sheep milk Dr Siqi Li (Postdoctoral Fellow), Riddet Institute, Massey University
New Zealand’s goat and sheep milk industries have seen rapid growth over the past years, playing an increasingly important role in diversifying the NZ dairy export portfolio. Ruminant milks from different species have different compositions and consumer perceptions of their health benefits, providing opportunities for innovation and development of high-value products for global consumers. Beyond the bulk composition of milk, the structural assemblies of milk components, such as the casein micelles and fat globules, play important roles in the technological and nutritional properties of milk and milk products. These milk structures vary naturally between the ruminant species, breeds and seasons. For example, goat milk has smaller fat globules and larger casein micelles than cow milk. Besides natural variations, processing technologies used in the dairy industry can alter these structures of milk. Recent research has shown that the digestion behaviour and nutritional outcomes of foods can be modulated by altering food structures.
Schematic illustration of the Human Gastric Simulator (Guo et al. 2015)
Our research aims to provide a better understanding of the natural differences in the compositional and structural characteristics of NZ ruminant milks (cow, sheep and goat), and how these characteristics change under common industrial processing treatments. We have studied the digestion behaviours of these processed milks from different species in a dynamic in vitro digestion system, the Human Gastric Simulator (HGS). The most common method for studying food digestion in vitro employs a “static” system, where the food and the simulated digestive fluids and enzymes are added into a closed vessel, adjusted to a fixed pH value and mixed by shaking or stirring. In such systems, the simulation of the physical movements of the stomach is oversimplified and the structural changes of ingested foods during digestion are not simulated well. The dynamic HGS utilised in our research however, was designed to simulate the peristaltic movement of the stomach based on the amplitude and frequency of contraction reported in humans. This is vital to gastric digestion and absent in “static” systems. This makes the HGS much closer to a ‘real life’ gastric system. In the HGS, a latex vessel serves as the stomach chamber. The continuous contraction of stomach walls is simulated by a series of moving rollers, controlled by motors on four sides of the stomach chamber (as shown in the photograph).
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Goat & Sheep Milk NZ - Issue 5 | February 2022
References: Guo, Q., Ye, A., Lad, M., Ferrua, M., Dalgleish, D., & Singh, H. (2015). Disintegration kinetics of food gels during gastric digestion and its role on gastric emptying: An in vitro analysis. Food and Function. Li, S., Pan, Z., Ye, A., Cui, J., Dave, A., & Singh, H. (2022). Structural and rheological properties of the clots formed by ruminant milks during dynamic in vitro gastric digestion: Effects of processing and species. Food Hydrocolloids.
