Isolation and Characterization of Fatty Acid Content of Shrimp Shell Chitin

Biomarkers are biologically produced organic compounds that can be used to identify sources of organic matter in geologic materials (soils, sediments, rocks). This information allows scientists to track important environmental and ecological changes over time and space. Some of the most commonly used biomarkers are a class of lipids called fatty acids. These compounds resist degradation and are diverse in structure, making them valuable indicators of carbon sources. 1 Most fatty acids can be extracted from sediments using organic solvents. However, a significant fraction cannot be extracted in this way and must first be liberated by hydrolysis of ester or amide bonds. 2 The understanding of the sources of these " bound lipids " is limited, but multiple studies have speculated about a relationship between fatty acids and chitin, a biopolymer found in arthropods and fungi. Analyses of chitin from several sources (Red crab shells, 3 commercial chitin standard 4) have indicated that there are fatty acids associated with the material. However, it is not known how this association occurs, or whether it is natural or an artifact of the chitin preparation process. As a member of Neal Blair's organic geochemistry lab, this summer I am interested in investigating this property of chitin and gaining valuable research experience. Therefore, the purpose of this study is to attempt a new method for the isolation of chitin in order to determine if fatty acids are naturally associated with it. Chitin is the second most abundant biopolymer on earth. 5 It is a-1,4 linked polymer of N-acetylglucosamine, and is found mainly in arthropod exoskeletons and fungal cell walls (Fig. 1). 6 Chitin is an insoluble, high molecular weight polymer with an extensive hydrogen bonding network, and it is naturally strengthened and functionalized by associated minerals and proteins. This makes it a challenge to purify without compromising the polymer structure, and it is thus difficult to analyze natural fatty acid content. 7 Preliminary analyses in our lab indicated that a chitin standard from Sigma Aldrich chemical company contained bound fatty acids. The use of the methylating reagent tetramethyl ammonium hydroxide (TMAH) with Gas Chromatography/Mass Spectroscopy (GCMS) identified the presence of C16 and C18 fatty acids in the chitin (Fig. 2). 4 Even though this chitin was intended for laboratory use, the bound fatty acid content was most likely not considered in purity analyses. Due to this, it is uncertain as to whether the fatty …