Microstructure, rheological and geometrical properties of fat globules of milk from different animal species

Abstract

The variation between different Egyptian milk species (cows, buffaloes, sheep, goat and camel) in microstructure, shape, size and volume distribution as well as rheological properties, of fat globules was determined. Milk samples were scanned with SEM. The electron micrographs obtained were analyzed using an image analysis computer program. Results showed fat globules of different milk species as an oval shape in a regularity of spatial arrangement and encased in a lipoprotein membrane. Fat globules of different species vary considerably in diameter from those <1 µm to ~18 µm. Buffalo’s globules were the greatest in size (8.7 µm), whereas close size values were found between cow and sheep globules (3.78 and 3.76 µm) as well as goat and camel globules (3.2 and 2.99 µm). On the contrary, the size of buffalo fat globules ranging from 0.1–4.0 µm was obviously less (23.0%) than that of camel (80.6%), goat (73.3%), cow (68.4%) and sheep (55.3%). Fat globules exhibited different patterns according to their sizes and milk type. Small globules, as in camel’s milk, were less spherical than the large ones, as in buffalo’s milk (at a=0.05). An inverse proportional relationship (r=-0.8) was found between spherical diameter and compactness. Most of the fat globules in buffalo’s, cow’s and goat’s milks oriented with obtuse angle, while those for sheep’s and camel’s milks oriented with acute angles. Changes in distribution of fat globules volume, perimeter, surface area, width and length were similar to that of size and significantly (p<0.001) affected by milk species.