Lipase-catalyzed acidolysis of algal oils with a medium-chain fatty acid, capric acid

Hamam, Fayez (2003) Lipase-catalyzed acidolysis of algal oils with a medium-chain fatty acid, capric acid. Masters thesis, Memorial University of Newfoundland.

[English] PDF (Migrated (PDF/A Conversion) from original format: (application/pdf)) - Accepted Version Available under License - The author retains copyright ownership and moral rights in this thesis. Neither the thesis nor substantial extracts from it may be printed or otherwise reproduced without the author's permission. Download (3MB) [English] PDF - Accepted Version Available under License - The author retains copyright ownership and moral rights in this thesis. Neither the thesis nor substantial extracts from it may be printed or otherwise reproduced without the author's permission. (Original Version)

Abstract

Lipase-assisted acidolysis of algal oils with a medium-chain fatty acid (capric acid) was studied. Five commercially available lipase preparations from Candida antarctica, Mucor miehei, Pseudomonas sp., Aspergillus niger and Candida rugosa were initially used as biocatalysts for the incorporation of capric acid (CA) into selected algal oils. The algal oils of interest were arachidoinc acid single cell oil (ARASCO), docosahexaenoic acid single cell oil (DHASCO) and single cell oil rich in docosahexaenoic acid (DHA) and docosapentaenoic acid (DP A) (OMEGA-GOLD). Among the lipases examined, Pseudomonas sp. was the most efficient. -- Effects of various reaction variables, namely the mole ratio of substrates, enzyme amount, time course, temperature and the amount of added water were examined for Pseudomonas sp. Response surface methodology was used to obtain a maximum incorporation of CA into algal oils. The process variables studied were the amount of enzyme (2-12 %), reaction temperature (25-55°C) and incubation time (12-48h). All experiments were conducted according to a face-centred cube design. Under optimum conditions (12.3 % of enzyme; 45°C; 29.4 h), the incorporation of CA was 20.0 % into ARASCO. Optimization of acidolysis of DHASCO with CA gave rise to a maximum of 22.6 % at 4.2 % enzyme amount, and a reaction temperature of 43.3°C and reaction time of 27.1 h. Similarly, the maximum incorporation of CA into the OMEGA-GOLD oil was obtained when enzyme amounts, reaction temperature and time were 2.5 %, 46.6°C and 25.2 h, respectively. -- Stereospecific analysis was performed to establish positional distribution of fatty acids on the glycerol backbone of modified ARASCO, DHASCO and the OMEGA-GOLD oil. In all oils examined CA was mainly located at the sn-1 and sn-3 positions of the triacylglycerol (TAG) molecules. In ARASCO-based SL, arachidonic acid (ARA) was mostly esterified at the sn-2 position of the glycerol backbone. In DHASCO-based SL, DHA was concentrated in the sn-2 position, but also present in the sn-1,3 positions. DHA or DP A were preferentially esterified at the sn-2 position of the modified OMEGA-GOLD oil. -- The oxidative stabilities of enzymatically modified oils as well as their unmodified counterparts were assessed under Schaal oven conditions at 60°C over a 72 h storage period. Conjugated dienes (CD), and 2-thiobarbituric acid reactive substances (TBARS) were used to follow the primary and secondary products of oxidation, respectively. Among the oils tested, the structured lipids (SL) of ARASCO, DHASCO, and the OMEGA-GOLD oil had higher conjugated dienes than those of their unmodified counterparts. TBARS values of modified DHASCO were significantly higher than their origin oil at all times. TBARS values of both modified and unmodified ARASCO increased gradually over the entire storage period. TBARS values of the OMEGA-GOLD-based SL increased steadily with increasing storage time. The results presented in this study suggest that enzymatically modified oils are more susceptible to oxidation than their unmodified counterparts. However, when the three oils (ARASCO, DHASCO and the OMEGA-GOLD) were subjected to the same procedure steps, the stabilities of the oils were adversely affected to a large extent. This observation might possibly be due to the loss of natural antioxidants during the reaction work up.

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