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The influence of ingredients or lipophilized antioxidants on the oxidative stability of fish oil enriched food systemsAnn-Dorit Moltke Srensen PhD Thesis 2010
The influence of ingredients or lipophilized antioxidants on the oxidative stability of fish oil enriched food systems
Ann-Dorit Moltke Srensen PhD Thesis
Technical University of Denmark National Food Institute, Division of Seafood Research March 2010
PREFACEThe 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 Srensen
ACKNOWLEDGEMENTSI 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: o Grsten Salater for producing mayonnaise salads and mayonnaises for my experiments - Especially thanks to Camilla Bang and Lene Sndergaard. o Xuebing Xu, Flemming Vang Sparso (Danisco), Mette Bruni Let and Zhiyoung Yang for valuable discussions at our project meetings as well as the other members of the Nu3Health project group. o Zhiyoung Yang, Mette Bruni Let, Bena-Marie Lue and Xuebing Xu are also thanked for producing the lipophilized antioxidants. o Grethe Hyldig, Rie Srensen and Jeanette Unger Mller are thanked for carrying out the sensory evaluations on one of the experiments. o Nancy Kjbk and Jean Alamed are thanked for their assistance and instruction on the use of instruments. o Mette Bruni Let, Bena-Marie Lue and Caroline P. Baron for good advice and critical 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!
SUMMARYThe 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 2C is maximum 6 weeks. It was possible to enrich the light mayonnaise with 4% fish oil when stored at 2C 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.
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.
SAMMENFATNINGEt lavt indtag af de gavnlige n-3 langkdede polyumttede fedtsyrer (PUFA) i de vestlige lande, har skabt et marked for n-3 berigede fdevarer dvs. produkter beriget med eicosapentaensyre (EPA) og docosahexaensyre (DHA) fra eksempelvis fiskeolie. EPA og DHA er mere flsomme overfor oxidation sammenlignet med PUFA fra vegetabilske olier p grund af deres hjere grad af umttethed. Det er derfor ndvendigt at finde metoder til at beskytte disse fedtsyrer mod oxidation, sledes at der ikke udvikles en fiskesmag i produkter beriget med fiskeolie.
Det overordnede forml med dette Ph.d. projekt var at forge den viden der findes omkring oxidativ stabilitet af fiskeolieberigede fdevare produkter. Dette inkluderede undersgelse af ingrediensernes indflydelse p den oxidative stabilitet af fdevareprodukter samt effekten af at tilstte modificerede antioxidanter til simple model emulsioner svel som mere komplek