Dissertation defence (Food Development): MSc Qizhu Zhao
MSc Qizhu Zhao defends the dissertation in Food Development titled “Triacylglycerol and glycerophospholipid regioisomerism in natural fats and oils” at the University of Turku on 23 September 2026 at 12.00 (University of Turku, Pharmacity, Auditorium Pha 1, Turku).
Opponent: Professor Filip Van Bockstaele (Ghent University, Belgium)
Custos: Professor Baoru Yang (University of Turku)
Summary of the Doctoral Dissertation:
We eat fats every day, but the nutritional effects of fats depend on more than just their fatty acid compositions. The digestion, absorption, and metabolism of fatty acids are also influenced by where they are located within lipid molecules. In nature, fatty acids are not arranged randomly. Their positions in triacylglycerols and glycerophospholipids are determined by species-specific lipid biosynthesis pathways, which are influenced by available fatty acids and the selectivity of lipid-producing enzymes.
For this reason, studying regioisomers, which are lipids that contain the same fatty acids but differ in their positions on the glycerol backbone, is particularly important when we want to link lipid structure to nutritional and physicochemical properties.
This doctoral thesis comprehensively analyzed the regioisomeric composition of triacylglycerols in eighteen commercial plant oils and of both triacylglycerols and glycerophospholipids in milk from eight mammalian species using advanced analytical tools. Overall, this thesis examined over 200 triacylglycerol regioisomers in plant oils, nearly 1,000 triacylglycerol regioisomers, and over 100 phosphatidylcholine regioisomers in milk samples.
The regioisomeric compositions of plant oils were relatively consistent, reflecting similarities in their triacylglycerol biosynthesis. However, milk samples from different mammalian species showed distinct patterns, reflecting differences in their digestive physiology. The regioisomeric compositions of both triacylglycerols and phosphatidylcholines in ruminants (cow, goat, and sheep) differed from those in non-ruminants (dog, horse, human, and pig). The pseudo-ruminant camel was positioned between these two groups while showing greater similarity to ruminants. These differences were particularly evident in lipids containing palmitic acid (16:0). In non-ruminants, palmitic acid was more frequently located at the middle (sn-2) position of the glycerol backbone than in ruminants.
The study also revealed major structural differences between plant oils and milk fats. In plant oils, the middle position was more commonly occupied by unsaturated fatty acids, whereas in milk fats it was more often occupied by saturated fatty acids. Importantly, commonly used ingredients in human milk fat substitute formulations, including cow milk fat, sunflower oil, and rapeseed oil, exhibited regioisomeric compositions that differed substantially from those of human milk fat. These findings highlight the importance of considering not only fatty acid composition but also fatty acid position when designing nutritionally functional lipid ingredients.
The comprehensive regioisomeric profiles obtained in this thesis also offer opportunities for practical applications. Selected triacylglycerol regioisomers could serve as markers for the rapid detection of oil adulteration, while regioisomeric compositions in plant oils may be linked to physicochemical properties and food texture. In addition, the species-specific distribution of fatty acids in triacylglycerols and phosphatidylcholines provides structural information for developing improved human milk fat substitutes that better mimic the lipid structure of human milk. Furthermore, phosphatidylcholine regioisomeric profiles may provide insights into membrane properties and the nutritional functions of milk lipids, supporting the development of nutritionally optimized foods.
