Final Examination for the Degree of PhD Food Science - REED NICHOLSON

Examining Committee
Dr. Massimo Marcone, Chair
Dr. Alejandro Marangoni, Advisor
Dr. Erica Pensini, Advisory Committee Member
Dr. Donald Mercer, Department Member
Dr. Patrick Ruhs, External Examiner

TITLE: STRUCTURING LIPIDS THROUGH GLYCEROLYSIS

ABSTRACT: This thesis covers an investigation into the potential use of enzymatic glycerolysis to convert liquid oils into structural fats through the production of partial acylglycerols, without altering the fatty acid composition of the native oil. Glycerolysis reaction conditions were shown to affect production of mono- and diacylglycerols (MAGs and DAGs) in a cottonseed oil system. Overall production of MAGs and DAGs was time dependent, while the relative ratios of partial acylglycerols was affected by the glycerol content present in the reaction. These conditions factored into the physical properties of the glycerolysis reaction products. Total MAG and DAG contents influenced the crystallization behaviour, solid fat content (SFC) at 5 °C, and the oil holding capabilities of the glycerolysis reaction products. While production of specific MAGs, namely monopalmitin and monoolein, were maximised in cottonseed oil with a 1:1 glycerol:triacylglycerol molar ratio. Elevated monopalmitin and monoolein contents increased the crystallization onset temperature, producing a crystal network containing smaller, more numerous fat crystals with a more homogenous distribution, as demonstrated by the fractal dimension. This increased the oil binding capabilities of the system from that that would be expected from the SFC of the glycerolysis-structured system alone. Glycerolysis reactions were performed for 48 h in the presence of a 1:1 glycerol:triacylglycerol molar ratio with a variety of vegetable oils. Saturated fatty acid and oleic acid contents both contributed to the SFC of the glycerolysis reaction products at 5 °C. Furthermore, a more substantial drop in SFC, at low temperatures (5-20 °C), was observed for systems structured mainly by partial acylglycerols containing oleic acid compared to those structured predominantly by saturated fatty acids. The highest SFC following glycerolysis was achieved with tigernut oil (34%). This glycerolysisstructured system was subsequently used to produce a margarine with plasticity similar to commercial products. Additional analysis of the crystallization and melting behaviour of binary mixtures of MAGs and DAGs provided an improved understanding of the interactions that occur between these molecules. This research has demonstrated that glycerolysis is an effective means of structuring liquid oils and offers a healthful and sustainable means to replace high saturated
fat sources.