Solubilization of nutritional lipids from three coastal and estuarine primary producers using sodium taurocholate as a model surfactant to mimic typical consumer gut-fluids

Coastal and estuarine food webs receive large inputs of both autochthonous and allochthonous detritus, which serves as an important dietary input for a variety of detritivorous and omnivorous organisms. Surfactants, which aid digestion by solubilizing hydrophobic lipids, are found in the gut-fluids of many fish and invertebrate consumers. To develop a biomimetic assay to explore how source of primary production and age may affect the bioavailability of nutritional lipids from detrital food sources, we assessed the capacity of a model surfactant, sodium taurocholate (STC), to solubilize fatty acids from three primary producers, a haptophyte (Isochrysis galbana), a rock-weed (Ascophyllum nodosum), and a marsh grass (Spartina alterniflora). Comparing lipids solubilized by a constant concentration of STC to traditional Folch-extracted yields, we assessed relative bioavailability of nutritional lipids from fresh and decayed material of each primary producer. We focused on the solubilization of storage triacylglycerols (TAG) and the fatty acid constituents of all lipids (FA). With a temperature of 5 ?C, 28.7 mM STC solubilized 44 +/- 12% of total FA from S. alterniflora and about half that fraction for I. galbana and A. nodosum after 15 h in the dark unstirred. In the form of TAG, STC solubilized 53 +/- 19% of pure triolein as a reference and similar proportions from S. alterniflora (56 +/- 19%) and I. galbana (48 +/- 2%) but only 9 +/- 3% from A. nodosum. Both approaches (TAG and FA) thus show significant differences in bioavailability among these three sources. Two months of decay had inconsistent effects on overall lipid yields but substantial effects on composition. Degradation led to decreased total phospholipids and long-chain polyunsaturated FA and increased break-down products (free FA and diacylglycerols), saturated and monounsaturated FA, and bacterial FA. Lower FA bioavailability and reduced degradation rates in A. nodosum may be due to its higher polyphenol and alginate concentrations. Although we mimicked only one component of the digestion process of lipids, this study represents a first step in developing a biomimetic assay to assess the relative bioavailability of nutritional lipids.

Automated summary

Coastal and estuarine food webs receive significant inputs of detritus, which serves as an important dietary source for detritivorous and omnivorous organisms. This study assessed the ability of a model surfactant, sodium taurocholate, to solubilize fatty acids from different primary producers and found significant differences in the bioavailability of nutritional lipids. Decay had inconsistent effects on lipid yields but substantial effects on composition.