Characterization of the lipid and protein membrane components of the natural emulsifier of coconut (Cocos nucifera L.) milk

The natural emulsifier of coconut milk referred to as coconut oil globule (COGM) was prepared using Brunner's method with modifications. The COGM was fractionated and the protein and lipid membrane fractions were analyzed and characterized. The protein recovered consisted of a soluble and insoluble fraction, based on their solubility in 0.02 m sodium chloride. The soluble fraction contained 0.37 percent nitrogen, 2.31 percent protein and 0.11 percent sulfur, while the insoluble fraction contained 0.68 percent nitrogen, 4.25 percent protein and traces of phosphorus and sulfur, with isoelectric point of 4.54-5.0. Both fractions were negative in Molisch and Fehling solutions after heating at 80 deg C. Higher lipase activity was detected in soluble than in insoluble protein fraction. Amino acid composition of the insoluble fraction showed the predominance of acidic amino acid but lower in sulfur containing amino acid. SDS-PAGE analysis of soluble and insoluble fraction revealed same number of subunits with estimated molecular weights of 18,000, 17,200, 15,700 and 19,600, 17,200, 15,400 Daltons. The following lipid classes were identified as components of membrane lipids: triglyceride mixture, mono, diglycerides, phospholipids and unesterified fatty acid. Ion exchange chromatography of phospholipid fractions showed the presence of lecithin, lysophosphatidyl, choline and Sphingomyelin in equal proportions (52.38 percent), phosphatidyl ethanolamine (28.57 percent), phosphatidyl serine (19.05) and traces of simple lipid. Fatty acid composition of the membrane lipid fraction showed relatively large quantities of lauric acid (25.82 percent); the phospholipid fraction contained higher amounts of unsaturated fatty acid and oleic acid, but lower amount of lauric acid. Similarities in the chromatographic elution characteristics between the membrane lipid fraction and the high melting glyceride fraction (HMG) suggest that the membrane lipid is composed principally of HMG