Conversely, the ability of ruminant b-lactoglobulin to bind fatty acids in vitro, the presence of fatty acids physiologically bound to the protein in milk , its ability to increase the activity of pregastric lipase, and its capacity to enhance the uptake of fatty acids, suggest that ruminant b-lactoglobulin could participate in milk fatty acid metabolism in the newborn.
Most fatty acids present in milk are found as triglycerides which form the fat globule. Most of the retinol in milk is found esterified with fatty acids. However, during gastric digestion of milk lipids, the triglycerides and retinol esters are hydrolyzed by preduodenal lipases, greatly increasing the amount of free fatty acids. Under these conditions, b-lactoglobulin would probably bind a large amount of fatty acids which would therefore displace the retinol eventualy bound to b-lactoglobulin. These observations suggest that the biological role of ruminant b-lactoglobulin is probably more closely related to milk fatty acids metabolism than to retinol transport.
However, the lack of interaction between equine and porcine b-lactoglobulins with fatty acids indicates that the biological function of b-lactoglobulin in these species is not related to fatty acid metabolism.ĘThis fact could be due to the low homology existing between ruminant with horse and pig b-lactoglobulins that could lead to the existence of functional differences among species.