The electrokinetic properties of phospholipid stabilized fat emulsions. V. The effect of amino acids on emulsion stability

Abstract

This study investigates the effect of amino acids, as commercial intravenous mixtures, on the flocculation of a parenteral fat emulsion (Intralipid 20%) by calcium ions. Flocculation was studied both by turbidimetry in dilute solutions, and by measurement of cream dimensions. The amino acid solutions stabilised the emulsion/electrolyte mixtures to a considerable degree; two separate influences were apparent in the flocculation profile. The peak flocculation rate (or maximum cream depth) of the mixtures was depressed by the addition of amino acids, suggesting that the interdroplet Hamaker constant was changed in the systems. In addition, amino acids ionized into the predominantly negative form acted as complexing agents for calcium, shifting the flocculation curve to higher calcium concentrations. The effect of calcium binding was only marked at high pH (8–9) and suggests that amino acids, like glucose, stabilize TPN mixtures primarily by decreasing the attractive component of the interdroplet force.