Influence of seasonal variation and ultra high temperature processing on lipid profile and fat globule structure of Swedish cow milk

•Higher PL, FFA, 1-2 DAG, UFAs and lower TAG and SFAs were found in both UHT-processed and raw milk.•Difference between lipid profiles from different months was found in raw and UHT-processed milk samples.•The distribution of TAG, PL and some FAs in final UHT milk was altered under commercial UHT processing.•Smaller fat droplets and thinner globule membrane were observed in UHT milk.•Higher PL and UFAs in summer UHT milk were plausibly caused by interaction of sampling month and process.

To investigate the effects of seasonal variations and processing on cow milk fat, raw milk collected in six individual months and corresponding ultra high temperature (UHT) milk were analyzed. Similar seasonal variations in lipid classes and fatty acid composition were found in raw and UHT milk.Under commercial processing, lipid content was standardized to approximately 1.5% in UHT milk. Decreased diameter of fat droplets (around 1 µm) and thinner globule membranes were observed, as revealed using confocal laser scanning microscopy (CLSM). The distribution of lipid classes was modified with a decreased proportion of triacylglycerol accompanied by the increase of phospholipids and free fatty acids. Saturated fatty acids C12:0 and C14:0, trans-fatty acids including conjugated linoleic acid (CLA), polyunsaturated fatty acids C18:2(n-6) and C18:3(n-3), showed increased proportions in UHT milk.These results provide an indication of the effect of UHT processing on milk lipid properties.