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ALPHA-LINOLENIC ACID Postprandial Lipid Metabolism and Enzymatic Interesterification of Triacylgylcerols

Author

  • Julia Svensson

Summary, in English

An important indicator of the metabolic capacity of humans is the ability to

regulate plasma triacylglycerol levels and to clear triacylglycerol-rich lipoproteins

(TRLs) from the circulation after a meal. This is crucial since most of the day is

spent in the postprandial state. High concentrations and long circulation times of

TRL remnants may be detrimental since these are considered to be highly

atherogenic.



Postprandial effects of alpha-linolenic acid (ALA) in men and women are poorly

characterized. A new ALA-rich oil was produced from rapeseed and linseed oil by

enzymatic interesterification. The postprandial effects of 3 meals containing 35 g

of this new ALA-rich oil, olive oil, or butter were compared in two randomized

crossover studies (26 men and 19 premenopausal women). Blood samples were

drawn at regular intervals up to 7 h after the meals. We hypothesized that the

postprandial lipid response might be attenuated by a preferential oxidation of ALA

compared to other long chain dietary fatty acids.



Premenopausal women showed lower postprandial lipemia and were less sensitive

to variations in dietary fat than men. Butter resulted in lower postprandial lipemia

than the oils in men, whereas no such difference was seen in the women. The ALA

oil and olive oil meals induced similar plasma triacylglycerol concentrations.

Women showed significantly lower NEFA responses after the olive oil and butter

meals than men. The ALA-rich oil had significant effects on the different plasma

lipid fractions and decreased the n-6:n-3 ratio in plasma several hours

postprandially.



ALA levels remained high in plasma triacylglycerols and NEFA even after 5-7 h.

This late high concentration of ALA in NEFA is indicative of spill-over NEFA

and/or preferential release of ALA by the adipose tissue into the circulation.

In summary we did thus not find evidence that ALA has a beneficial effect on

postprandial lipids by a selective partitioning to oxidation. This does not exclude

the possibility that ALA over a longer time period may have health effects not

only as precursor of longer chain n-3 fatty, primarily docosahexaenoic acid, but

also because it is sorted out for oxidation.





The enzymatic interesterification of triacylglycerols using immobilized

Thermomyces lanuginosus lipase (Lipozyme TL IM) as catalyst has also been

investigated. Three different reaction systems were studied: rapeseed oil + butter,

rapeseed oil + linseed oil (ALA oil), and trilaurin + 1,3-palmitin-2-olein. The ALA

oil (35% ALA) was the same as that used in the meal studies. All reactions were

followed by reversed-phase HPLC and the triacylglycerol peaks were tentatively

identified by calculating equivalent carbon numbers. The triacylglycerols in the

rapeseed oil + butter mixture and products were also identified by HPLC-electrospray

tandem mass spectrometry.



In ideal sn-1,3-specific lipase-catalyzed interesterification, the fatty acid

composition in the sn-2 position remains constant. In practice, however, slight

changes are observed in the sn-2 position and, under certain conditions, a

completely randomized fatty acid distribution can be obtained. Randomization is

slower than interesterification. Uncontrolled hydrolysis should, however, be

avoided as it lowers the TAG yield. Different triacylglycerol mixtures, i.e.

products originating from 1,3-specific interesterification as well as totally or

partially randomized products, can be produced by varying the reaction time.

Enzymatic interesterification could be used as a method of designing dietary oils

with new properties regarding fatty acid composition, susceptibility to oxidation

and effects on blood lipids. The future of enzymatic processes relies on efficient,

flexible, and easy-to-use systems that ensure high stability of the enzyme

preparation and stable output of high-quality products at a reasonable cost.

Department/s

Publishing year

2011

Language

English

Document type

Dissertation

Topic

  • Industrial Biotechnology

Keywords

  • alpha-linolenic acid
  • triacylglycerol
  • postprandial lipemia
  • Lipozyme TL IM
  • interesterification

Status

Published

Project

  • ANTIDIABETIC FOOD CENTRE

ISBN/ISSN/Other

  • ISBN: 978-91-89627-71-0

Defence date

26 May 2011

Defence time

10:30

Defence place

Lecture hall C, Center of Chemistry and Chemical Engineering, Sölvegatan 39, Lund University Faculty of Engineering

Opponent

  • Tom Sanders (Professor)