The influence of ingredients or lipophilized antioxidants on the oxidative stability of fish oil enriched

261 Pages·2011·1.89 MB·English

The influence of ingredients or
lipophilized antioxidants on the
oxidative stability of fish oil
enriched food systems
Ann-Dorit Moltke Sørensen
PhD Thesis
2010

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PREFACE

PREFACE
The present thesis entitled ”The influence of ingredients or lipophilized antioxidants on the
oxidative stability of fish oil enriched food systems” concludes my PhD project carried out
at the National Food Institute (DTU Food), Technical University of Denmark (former
National Institute of Aquatic Resources (DTU Aqua) and Danish Institute for Fisheries
Research). My PhD was under supervision of Senior Researcher Charlotte Jacobsen
(main supervisor), Section leader for Aquatic lipids and Oxidation and Senior Researcher
Nina Skall Nielsen (co-supervisor).

The project began August 1, 2006 and continued until March 31, 2010, but was interrupted
by a 2 months leave due to another project assignment. Additional 5 months extension
was due to project delay from a collaboration partner at Aarhus University (Denmark). In
these 5 months I worked on other project assignments.

This PhD project constituted part of the project “Nutritious and tasty n-3 PUFA rich food
products for a slim and healthy population (Nu3Health)”, which was financed by the Danish
Council for Strategic Research (Programme committee for food, nutrition and health) and
the Directorate for Food, Fisheries and Agri Business. A travel grant awarded from LMC
(Centre for Advanced Food Studies) supported my research stay abroad at the
Department of Food Science, University of Massachusetts, Amherst, USA. The duration of
the research stay was 3 months (September 10, 2008 until December 7, 2008). An Young
scientist award supported participation in the 25th Nordic Lipid Symposium 2009 (Elsinore,
Denmark) and an European student travel award supported participation in the 2010
American Oil Chemists’ Society (AOCS) annual meeting and expo in Phoenix, Arizona,
USA.

March 31, 2010
Kgs. Lyngby, Denmark

Ann-Dorit Moltke Sørensen

I

ACKNOWLEDGMENTS

ACKNOWLEDGEMENTS
I am very grateful to my supervisor Senior Researcher Charlotte Jacobsen for her great
support, for continuously encouraging me, for all the discussions and advice I have had
throughout the project and for always being there and finding time when I needed it. I am
also grateful to my co-supervisor Senior Researcher Nina Skall Nielsen for sharing her
knowledge on sensory evaluation, valuable discussions and for her always positive and
supportive attitude. I sincerely thank Dr. Eric A. Decker for letting me work in his lab at the
Department of Food Science and for valuable discussions of obtained results during my
research stay. I sincerely thank Trang Vu for her excellent and invaluable work in the
laboratory. I am also grateful for the experimental work carried out by Lien Nguyen
(Laboratory technician student), Sara de Diego (PhD guest student) and Lone Kirsten
Petersen (M.Sc. student). I want to thank all my colleagues at DTU Food and colleagues
at the Department of Food Science, where I spent time as a guest researcher.

Many people have helped with this project in some way and deserve my sincere thanks:
Gråsten Salater for producing mayonnaise salads and mayonnaises for my
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experiments - Especially thanks to Camilla Bang and Lene Søndergaard.
Xuebing Xu, Flemming Vang Sparso (Danisco), Mette Bruni Let and Zhiyoung Yang for
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valuable discussions at our project meetings as well as the other members of the
Nu3Health project group.
Zhiyoung Yang, Mette Bruni Let, Bena-Marie Lue and Xuebing Xu are also thanked for
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producing the lipophilized antioxidants.
Grethe Hyldig, Rie Sørensen and Jeanette Unger Møller are thanked for carrying out
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the sensory evaluations on one of the experiments.
Nancy Kjøbæk and Jean Alamed are thanked for their assistance and instruction on
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the use of instruments.
Mette Bruni Let, Bena-Marie Lue and Caroline P. Baron for good advice and critical
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reading of this thesis or parts of it - Thank you for your time and efforts!
Finally, I would like to thank my mum Ingermarie, my brother Brian and my sister-in-law
Christina for their encouragement and for always being there for me when I needed it.
Especially thanks to the Lipid group, it has been invaluable to be a part of this group!

III

SUMMARY

SUMMARY

The relatively low intake of fish and the health beneficial n-3 polyunsaturated fatty acids (PUFAs) in
the Western countries has created a growing market for n-3 PUFA enriched food products e.g.
products enriched with eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) from fish oil.
EPA and DHA are more susceptible to lipid oxidation than PUFAs from vegetable oils due to their
highly polyunsaturated nature and it is therefore necessary to develop methods to protect these
PUFAs.

The main objective of this PhD work was to expand current knowledge on oxidative stabilization of
fish oil enriched food systems. This included an evaluation of the effects of adding modified
antioxidants to the food products and the influence of ingredients on the oxidative stability of
emulsions and food products.

Vegetables in fish oil enriched mayonnaise based shrimp and tuna salads did not improve the
overall oxidative stability compared to pure fish oil enriched mayonnaise. The findings indicated
that asparagus in shrimp salad had an antioxidative effect, but this effect was neutralized by the
prooxidative effect caused by the shrimps. In tuna salads, the high level of volatiles was suggested
to be due to the natural volatiles from the different vegetables. Replacing egg yolk with a milk
protein based emulsifier did not reduce the lipid oxidation in fish oil enriched light mayonnaise and
this finding was explained by the initial low quality of the milk protein based emulsifier.

The results obtained from fish oil enriched mayonnaise salads and light mayonnaise showed that
fish oil can be added without further addition of antioxidants as long as the storage temperature
and time were controlled. Thus, fish oil enrichment of mayonnaise based shrimp and tuna salads
results in acceptable products when the storage at 2°C is maximum 6 weeks. It was possible to
enrich the light mayonnaise with 4% fish oil when stored at 2°C for 113 days as concluded from the
concentration of secondary oxidation products.

Studies on protection of o/w and w/o emulsions by ascorbic acid derivatives with different polarities
indicated that ascorbic acid acted as a better antioxidant in w/o emulsion than o/w emulsion. This
was explained by the higher concentration of ascorbic acid in the aqueous phase in a w/o emulsion
and thereby closer location of ascorbic acid to the oil-water interface.

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SUMMARY

Evaluation of the effect of lipophilization of selected phenolic antioxidants revealed that in general,
the lipophilized dihydrocaffeic acid and rutin increased the oxidative stability of o/w emulsions and
fish oil enriched milk compared with their parent hydrophilic compound. The results supported a
cut-off effect in relation to the acyl chain length of the alcohol esterified to the phenolic compound.
Octyl dihydrocaffeate (C8 acyl chain) was a stronger antioxidant than oleyl dihydrocaffeate (C18
acyl chain) and rutin laurate (C12 acyl chain) was a stronger antioxidant than rutin palmitate (C16
acyl chain). Interestingly, it seemed that the cut-off effect was not only specific for the individual
lipophilized phenolic compounds, but that it also depended on the emulsion system, i.e. the optimal
chain length seems to vary between different emulsion systems.

Based on the results it was concluded that addition of dry spices (oregano, thyme or rosemary) or
spice extracts (rosemary or green tea) improved the oxidative stability of fish oil enriched tuna
salads and milk. However, these spices and extracts are not appropriate due to their contribution to
an off-flavor of the spices or green tea in the final products. A tasteless oregano-based extract did
not improve the oxidative stability of fish oil enriched tuna salads. It was concluded that the
changes in the type of oil used for the mayonnaise from soy oil to rapeseed oil reduced the lipid
oxidation and thereby resulted in the unclear effect of origanox.

Overall, the PhD work has contributed with interesting findings regarding oxidative stabilization of
fish oil enriched food systems. Amongst the alternatives investigated, the most promising way to
reduce lipid oxidation of fish oil enriched food emulsions seems to be addition of lipophilized
antioxidants and spice extracts, as long as they do not add additional flavor to the product.

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