Structural changes in milk of different species during digestion : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy (Food Technology), Massey University, Manawatū, New Zealand

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Massey University
Cow milk is the most abundant type of mammalian milk produced in the world. It has been widely explored industrially as well as academically. However, non-cow milk (e.g. water buffalo, goat, and sheep milk) consumption is significant and forms an important nutritional source for people in many countries. The interest in non-cow milks has increased because of several anecdotal experiences reported about the nutritional and digestive benefits of these milks. However, there is very little scientifically validated information available. The overall objective of this PhD study was to investigate how some of the non-cow milks (such as goat and sheep milk) are structurally different (or similar) to cow milk, especially in their coagulation behaviour under the gastric environment. The potential implications of structural changes on the delivery of nutrients under dynamic gastric digestion conditions were also explored. Dynamic in vitro and in vivo gastric digestion models were employed for this study. It was found that milk from different species vary in their natural macronutrient composition, structure, and acid-gelation behaviour. The fundamental mechanism of coagulation of proteins under the dynamic in vitro gastric digestion conditions was found to be similar for different species milk. The in vivo gastric digestion studies revealed comparable results, although goat and sheep milk curds had relatively lower rates of strengthening and relatively more open microstructure. Both the dynamic in vitro and in vivo studies revealed that the release of fat globules from the coagulated curd was directly proportional to the breakdown (or hydrolysis) of the protein in the curd during gastric digestion. The studies clearly showed that the curd formation and its disintegration in the stomach is a key factor influencing the rate of delivery of macronutrients to the small intestine. The results from this thesis contribute to the knowledge of how composition along with structure impact the release of nutrients at various stages of gastric digestion of different mammalian milks. The information gained from this study might have important consequences for developing dairy products with improved structures for controlled delivery or release of nutrients to meet the special dietary needs of consumers.
Figures 2.2, 2.3 & 2.4 are re-used with permission, and Figure 2.5 is re-used for non-commercial purposes under an Elsevier user license.
Milk, Composition, Digestion, Animal models in research