ISOLATION AND CHARACTERIZATION OF BOVINE MILK LIPIDS

Abstract

Bovine milk is a complex physiological fluid with multifaceted functionality for the nourishment of its young as well as a vital source of nutrition for humans of all ages. Milk composition is dynamic in nature and varies due to a number of factors such as breed, feeding strategies, season and lactation stage. Of different components, lipids are the most variable constituent, for instance, with increase in total fat, average size of the milk fat globules (MFG) increases but ratio of phospholipids and cholesterol to Triacylglycerols decreases. Although milk has evolved as a natural food under selective pressure to meet nutritional needs of different species, there is limited knowledge to acknowledge the significance of different endogenous (e.g. cow vs. buffalo) and exogenous factors (e.g. season) on its altered composition. Thus, the aims of the present study were designed to isolate and characterize milk lipids available freely as fatty acids and on fat globules. Microstructure analysis of MFG was performed to investigate breed (e.g. Jafarabadi buffalo vs. Holstein Friesian cow) and physiological (e.g. healthy vs. disease) specific differences. Comparison of globules from healthy (native) and mastitis (impaired), the most infectious disease in dairy cow, using exogenous phospholipids showed non-homogenous distribution of membrane phospholipids including significant variation in globules size not only amongst breeds but also between healthy and mastitic samples. Similarly, zeta potential showed significant difference between the breeds as well as demonstrated its specificity between localized and systemic infection. Furthermore, interaction of globules with bacteria demonstrated higher affinity for native compared to impaired globules highlighting the influence of membrane integrity in adhesive preference of bacteria. Secondly, a functionalized membrane based process was developed to selectively enrich MFG rich in phospholipids directly from milk compared to cream thereby minimizing loss due to higher processing time. Finally, lipids expression across breeds and season using mass spectrometry (MS) confidently identified 221 lipids including saturation levels, for example, higher unsaturated fatty acids were observed in winter compared to summer. This lipidomic study supports the use of MS as a robust discovery tool and such results provide a foundation for future studies to design strategies for increasing desirable lipids for their potential usage in dairy industries including identification of specific lipids to differentiate between local and/or systemic diseases.