Abstract
The primary aim of the research described in this thesis was to provide a characterisation of the phospholipid composition of eleven edible (kaimoana) shellfish species from New Zealand and the variation associated with species selection, collection season and sample location. The selected species were all traditional food sources for indigenous Māori in the region of the East Otago coast that is now the East Otago Taiāpure. The selected species comprised six bivalves (kuku/green-lipped mussel, Perna canaliculus; tio/oyster, Ostrea chilensis; toretore/blue mussel, Mytilus galloprovincialis; tūaki/cockle, Austrovenus stutchburyi; tuatua/surf clam, Paphies donacina; and pūkanikani/ribbed mussel, Aulacomya maoriana) and five gastropods (pāua, Haliotis iris; pūpū/catseye, Lunella smaragda; rori/duck’s bill limpet, Scutus breviculus; toitoi/Cook’s turban, Cookia sulcata; and whetiko/mudsnail, Amphibola crenata).
Phospholipids are emerging as a source of omega-3 polyunsaturated fatty acids (PUFA) with improved bioavailability compared to conventional fish oil supplements, which contain mainly triacylglycerols. To date, no study has searched for natural sources of highly bioavailable omega-3 PUFA. Shellfish, particularly kuku/green-lipped mussels, are a key New Zealand export, but outside of kuku/green-lipped mussels, few studies have characterised the lipids present in any shellfish species. Of the eleven species considered in this thesis, four had never been studied before and a further four had been included in two or fewer published works. This study provided detail of the phospholipid composition of all eleven shellfish species, reporting fatty acid profiles using gas chromatography-mass spectrometry and phospholipid class profiles using 31P nuclear magnetic resonance spectroscopy, and comparing the total phospholipid profiles using liquid chromatography-mass spectrometry.
The physical characteristics of the selected shellfish were described, along with the edible portion, lipid yield and phospholipid proportion for each species. It was found that the lipid yield per gram of shellfish edible tissue was similar between most species and was not affected by season or location, while the polar lipid (phospholipid) proportion was more variable between species and seasons. Phosphatidylcholine was found to be the predominant phospholipid class in almost every species, although every species contained a diverse range of phospholipid classes. Bivalves could be differentiated from gastropods by the presence of ceramide 2-aminoethylphosphonate (CAEP) in bivalve samples, and phosphoethanolamines were most associated with seasonal change, with an increase of its plasmanyl form in spring.
Bivalves were a better source of polar lipid-derived eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) than gastropods. In bivalves, some polar lipid-derived PUFA varied between seasons, while no seasonal trend was observed in gastropods. Analysis of the total phospholipid profile from each shellfish species indicated that EPA and DHA were widespread in phosphatidylcholine, lyso-phosphatidylcholine, phosphoethanolamine and CAEP structures, but not homogeneous throughout the phospholipid profile. Phospholipid profiles from gastropod species were found to be different to those from bivalve species. Both gastropod and bivalve samples had different phospholipid profiles in spring compared to other months. Overall, taxonomic class was found to be associated with most major changes in phospholipid composition, followed by season, and location (at both local and regional scale), which had more minor effects.
Characterising the phospholipid composition of eleven shellfish species deepens knowledge of species that had previously been studied, and expands the boundaries of marine lipid research to include four new species. Statistically comparing the phospholipid profiles of different species, and establishing the change associated with sampling season and location is progress towards better understanding factors that may affect phospholipid composition of shellfish species. The focus on phospholipids and omega-3 PUFA allows for future application to nutritional studies and study of species that may offer improved bioavailability compared to conventional omega-3 PUFA sources.