Structural characteristics of triacylglycerols contribute to the distinct in vitro gastric digestibility of sheep and cow milk fat prior to and after homogenisation

Abstract

The regiodistribution of fatty acids (FAs) in triacylglycerols (TAGs) is highly correlated to the digestion and absorption of dietary fats. During in vitro gastric digestion, medium-long-medium/short chain triacylglycerols (MLM) showed the fastest digestibility among 105 TAG molecular species, for both raw and homogenised milk, resulting from the higher activity of gastric lipase towards medium-chain fatty acids (MCFAs) than towards long-chain fatty acids (LCFAs). After 60 min of in vitro gastric digestion, the percentage of digestion of each MLM was 16.6-31.2% and 12.3-18.6% respectively in raw sheep and cow milk, and it reached 33.4-45.5% and 23.0-38.9% respectively, after homogenisation. Sheep milk TAGs were digested faster than cow milk TAGs in raw milk (16.1% and 12.4%, respectively) as well as after homogenisation (24.1% and 20.3%, respectively). This is due to the higher percentages of MCFAs esterified on the sn-1/3 positions of sheep milk TAGs (48.3-67.3% and 11.9-51.5% respectively for sheep and cow milk prior to and after homogenisation). Homogenisation favoured TAG lipolysis due to the increased fat globule surface area; however, it did not affect lipase regiospecificity towards TAG molecular species.

Keywords: Lipid metabolism; Lipolysis; Processed milk; Ruminant milk fat; Structured triacylglycerols; Triglycerides.