Doctoral thesis (Dissertations and theses)
DEVELOPMENT OF ANALYTICAL TOOLS FOR THE DETERMINATION OF MARKERS OF LIPID ALTERATION IN FOOD
Douny, Caroline
2017
 

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Abstract :
[en] It is now well-known that n-3 polyunsaturated fatty acids (omega-3 PUFA) have beneficial effects on health but are also rapidly oxidized in potentially toxic compounds, which means that healthy food products, rich in n-3 PUFA, can become toxic for the consumer if not stored or processed appropriately. The main objective of this work was to develop new analytical tools to study markers of lipids alteration in food, in order to allow an adequate monitoring of possible toxic compounds in n-3 PUFA rich food products. The first chapter of this PhD thesis is a literature review about fatty acids, their oxidation and the different oxidation products generated. The different analytical techniques used to study the oxidative stability of polyunsaturated fatty acids and their degradation products in food are also described. Chapter 2 describes the development of a gas chromatography coupled to mass spectrometry (GC-MS) method to analyze the fatty acids in food. The method was applied to eggs and pork (both standard and n-3 enriched) submitted to various cooking processes and storage conditions. This study confirmed that the fat of standard eggs or pork from the Belgian market cannot be considered as a source ofn-3 PUFA.. Indeed, in this work, we measured no n-3 PUFA in meat or only around 2 % for eggs, while the fat of both enriched eggs and pork contained about 10 % of n-3 fatty acids. After storage or cooking without culinary fat no change of the fatty acid profile was observed, in standard eggs or pork. We made the same observation for n-3 enriched products, except for some cooking processes (pan-frying and oven cooking), which induced a slight but significant loss of n-3 fatty acids in n-3 enriched eggs or pork. The fairly stable behavior of the fatty acids after various cooking and storage experiments indicates that the fatty acid profile is not a good marker of lipid alteration. As a consequence, this work was oriented to the development of analytical tools to evaluate the presence of toxic aldehydes in food and feed as secondary oxidation products coming from polyunsaturated fatty acids. Chapter 3 is dedicated to the study of the oxidative stability of linseed oil, an oil rich in n-3 fatty acids. Section 3.1 describes the development of a liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS) method to evaluate the aldehyde content in linseed oil. After optimisation of the extraction, derivation, detection and quantification steps, the method was validated according to guidelines from the European legislation as well as the recommendations of the AFNOR protocol NF V 03-110 (AFNOR, 2010). The evaluated parameters included specificity/selectivity, recovery, precision, accuracy, uncertainty, limits of detection and quantification, determined using the concept of accuracy profiles. When the method was applied to first pressure linseed oil stored for several days at 60 °C according to the Schaal oven test, it was shown that 4-hydroxy-2E-hexenal (4-HHE) was the most produced aldehyde. In Section 3.2, the different patterns of oxidation of linseed oil in real-time and accelerated aging assays were investigated, in order to verify the hypothesis commonly accepted for vegetal oil that one day aging at 60 °C is equivalent to one month real time aging at room temperature. Oxidation was evaluated with the peroxide value and para-anisidine value, as well as the content in conjugated dienes and aldehydes. All four indicators of oxidation showed very different kinetic behaviours at 20 and 60 °C, showing that the hypothesis (1 day at 60 °C = 1 month at 20 °C) is not valid for linseed oil. Chapter 4 describes the adaptation and the validation of a LC-MS/MS method to determine aldehydes in animal feed samples. Indeed, as animal feed is often enriched with linseed to increase the human intake of n-3 fatty acids through the consumption of food from animal origin, the study of the oxidative stability of n-3 enriched animal feed is also of interest. To achieve that goal, the LC-MS/MS method previously developed for linseed oil was adapted to include more aldehydes and was validated using the same guidelines as in section 3.1. Finally, chapter 5 presents the discussion and conclusions about the developed methods and the results obtained as well as their comparison with literature. Future prospects to improve the evaluation of and the exposure to the markers of lipid alteration in food are proposed.
Research center :
FARAH - Fundamental and Applied Research for Animals and Health - ULiège
Disciplines :
Food science
Author, co-author :
Douny, Caroline  ;  Université de Liège > Département de sciences des denrées alimentaires (DDA) > Analyse des denrées alimentaires
Language :
English
Title :
DEVELOPMENT OF ANALYTICAL TOOLS FOR THE DETERMINATION OF MARKERS OF LIPID ALTERATION IN FOOD
Alternative titles :
[en] DEVELOPPEMENT D’OUTILS ANALYTIQUES POUR LA DETERMINATION DE MARQUEURS DE L’ALTERATION DES LIPIDES ALIMENTAIRES
Defense date :
2017
Institution :
ULiège - Université de Liège
Degree :
DOCTEUR EN SCIENCES VETERINAIRES
Promotor :
Scippo, Marie-Louise  ;  Université de Liège - ULiège > Fundamental and Applied Research for Animals and Health (FARAH) > FARAH: Santé publique vétérinaire
Maghuin-Rogister, Guy ;  Université de Liège - ULiège > Département de sciences des denrées alimentaires (DDA)
President :
Dewals, Benjamin G  ;  Université de Liège - ULiège > Fundamental and Applied Research for Animals and Health (FARAH) > FARAH: Santé publique vétérinaire
Jury member :
Clinquart, Antoine ;  Université de Liège - ULiège > Fundamental and Applied Research for Animals and Health (FARAH) > FARAH: Productions animales durables
Larondelle, Yvan
Dufrasne, Isabelle  ;  Université de Liège - ULiège > Fundamental and Applied Research for Animals and Health (FARAH) > FARAH: Productions animales durables
Eppe, Gauthier  ;  Université de Liège - ULiège > Molecular Systems (MolSys)
Hubert, Philippe  ;  Université de Liège - ULiège > Unités de recherche interfacultaires > Centre Interdisciplinaire de Recherche sur le Médicament (CIRM)
Gustin, Pascal ;  Université de Liège - ULiège > Fundamental and Applied Research for Animals and Health (FARAH) > FARAH: Médecine vétérinaire comparée
Bast, Aalt
De Smet, Stefaan
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since 13 January 2017

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