Lipid class and carbohydrate concentrations in marine colloids

Cross-flow filtration (CFF) was used to concentrate marine colloids (>10,000 Da) from microalgal cultures and surface seawater. Lipid classes in different size fractions were determined using the Iatroscan thin-layer chromatography with flame ionization detection method. Total carbohydrate concentrations were determined colorimetrically as hexose equivalents, using methyl benzothiazolinone hydrazone (MBTH) reagent, after dilute HCl hydrolysis. Colloidal lipid concentrations in microalgal cultures were 0.5–9.1 μM C, with triacylglycerol and polar lipids as the major lipid classes, while colloidal carbohydrate concentrations were ˜25 μM C. Concentrations of colloidal lipid and carbohydrates in Newfoundland coastal seawater were 0.05–0.51 μM C and ˜0.67 μM C respectively, with triacylglycerol, free fatty acids, and phospholipids as the major lipid classes. Data from algal cultures and seawater showed that marine colloids are characterized by having high proportions of free fatty acids, phospholipids and hydrocarbons by comparison with truly dissolved material. It is likely that the free fatty acids were produced by microbial degradation, the phospholipids derived from biological membranes, and the hydrocarbons preferentially adsorbed from the surrounding water onto the colloids.