| dc.description.abstract | <div id="_mcePaste" style="position: absolute; left: -10000px; top: 0px; width: 1px; height: 1px; overflow: hidden;">Lipid autoxidation is an unwanted process that affects the quality of food and has impact on</div>
<div id="_mcePaste" style="position: absolute; left: -10000px; top: 0px; width: 1px; height: 1px; overflow: hidden;">human health. Lipid oxidation has been studied extensively, but oxidation during digestion</div>
<div id="_mcePaste" style="position: absolute; left: -10000px; top: 0px; width: 1px; height: 1px; overflow: hidden;">has largely been ignored. Formation of oxidized lipids increases rapidly when protective</div>
<div id="_mcePaste" style="position: absolute; left: -10000px; top: 0px; width: 1px; height: 1px; overflow: hidden;">antioxidants are exhausted. On the other hand, the nature of antioxidants can lead to problems</div>
<div id="_mcePaste" style="position: absolute; left: -10000px; top: 0px; width: 1px; height: 1px; overflow: hidden;">when fortifying foods with too much antioxidants. Pro-oxidative effects of several</div>
<div id="_mcePaste" style="position: absolute; left: -10000px; top: 0px; width: 1px; height: 1px; overflow: hidden;">antioxidants have been observed when used in excessive amounts.</div>
<div id="_mcePaste" style="position: absolute; left: -10000px; top: 0px; width: 1px; height: 1px; overflow: hidden;">Methods for studying lipid oxidation are numerous. Among them are unspecific titrimetric</div>
<div id="_mcePaste" style="position: absolute; left: -10000px; top: 0px; width: 1px; height: 1px; overflow: hidden;">methods and highly specialized chromatographic and mass spectrometric methods. Nuclear</div>
<div id="_mcePaste" style="position: absolute; left: -10000px; top: 0px; width: 1px; height: 1px; overflow: hidden;">magnetic resonance (NMR) spectroscopy, especially the proton (1H) NMR, is a promising</div>
<div id="_mcePaste" style="position: absolute; left: -10000px; top: 0px; width: 1px; height: 1px; overflow: hidden;">technique for fast screening of lipid samples as it is non-destructive and because of the large</div>
<div id="_mcePaste" style="position: absolute; left: -10000px; top: 0px; width: 1px; height: 1px; overflow: hidden;">dynamic scale of the technique. Drawbacks of NMR are that relatively large amount of</div>
<div id="_mcePaste" style="position: absolute; left: -10000px; top: 0px; width: 1px; height: 1px; overflow: hidden;">sample is required for the analysis and that specific molecular structures may be difficult to</div>
<div id="_mcePaste" style="position: absolute; left: -10000px; top: 0px; width: 1px; height: 1px; overflow: hidden;">identify from complex spectrum. This thesis focuses on the study of in vitro lipid oxidation by</div>
<div id="_mcePaste" style="position: absolute; left: -10000px; top: 0px; width: 1px; height: 1px; overflow: hidden;">different chromatographic, mass spectrometric and nuclear magnetic resonance spectroscopic</div>
<div id="_mcePaste" style="position: absolute; left: -10000px; top: 0px; width: 1px; height: 1px; overflow: hidden;">methods.</div>
<div id="_mcePaste" style="position: absolute; left: -10000px; top: 0px; width: 1px; height: 1px; overflow: hidden;">The most significant findings of the studies in this thesis centre around oxidation, hydrolysis,</div>
<div id="_mcePaste" style="position: absolute; left: -10000px; top: 0px; width: 1px; height: 1px; overflow: hidden;">and behaviour of lipids in an artificial digestion model used in the studies. The model</div>
<div id="_mcePaste" style="position: absolute; left: -10000px; top: 0px; width: 1px; height: 1px; overflow: hidden;">simulates the digestion processes of human and can be used to study lipid oxidation in vitro.</div>
<div id="_mcePaste" style="position: absolute; left: -10000px; top: 0px; width: 1px; height: 1px; overflow: hidden;">Also of importance, are the lipid analysis techniques developed for the experiments, as the</div>
<div id="_mcePaste" style="position: absolute; left: -10000px; top: 0px; width: 1px; height: 1px; overflow: hidden;">techniques can be adopted to other fields of scientific studies as well for industrial uses.</div>
<div id="_mcePaste" style="position: absolute; left: -10000px; top: 0px; width: 1px; height: 1px; overflow: hidden;">Four major studies were conducted in this thesis: first an in vitro digestion model was adopted</div>
<div id="_mcePaste" style="position: absolute; left: -10000px; top: 0px; width: 1px; height: 1px; overflow: hidden;">to study the behaviour of differently oxidized rapeseed oils. Simultaneously, a novel HPLC–</div>
<div id="_mcePaste" style="position: absolute; left: -10000px; top: 0px; width: 1px; height: 1px; overflow: hidden;">evaporative light scattering detector–MS analysis technique was developed, which enabled</div>
<div id="_mcePaste" style="position: absolute; left: -10000px; top: 0px; width: 1px; height: 1px; overflow: hidden;">the analysis of native and oxidized free fatty acids, monoacylglycerols, diacylglycerols, and</div>
<div id="_mcePaste" style="position: absolute; left: -10000px; top: 0px; width: 1px; height: 1px; overflow: hidden;">triacylglycerols in the chyme produced by the digestion model. The main findings of the study</div>
<div id="_mcePaste" style="position: absolute; left: -10000px; top: 0px; width: 1px; height: 1px; overflow: hidden;">were that thermally oxidized rapeseed oil, chemically oxidized rapeseed oil and unoxidized</div>
<div id="_mcePaste" style="position: absolute; left: -10000px; top: 0px; width: 1px; height: 1px; overflow: hidden;">rapeseed oil were hydrolyzed in a similar manner. No hydroperoxides were detected in the</div>
<div id="_mcePaste" style="position: absolute; left: -10000px; top: 0px; width: 1px; height: 1px; overflow: hidden;">digested samples, even though they were present in the undigested oils. Also, the finding of</div>
<div id="_mcePaste" style="position: absolute; left: -10000px; top: 0px; width: 1px; height: 1px; overflow: hidden;">Abstract vii</div>
<div id="_mcePaste" style="position: absolute; left: -10000px; top: 0px; width: 1px; height: 1px; overflow: hidden;">large amounts of sn-1(3) monoacylglycerols was surprising, questioning the long believed</div>
<div id="_mcePaste" style="position: absolute; left: -10000px; top: 0px; width: 1px; height: 1px; overflow: hidden;">mechanism of triacylglycerol digestion and absorption.</div>
<div id="_mcePaste" style="position: absolute; left: -10000px; top: 0px; width: 1px; height: 1px; overflow: hidden;">In the second study, an ultra-high performance liquid chromatography (UHPLC) analysis</div>
<div id="_mcePaste" style="position: absolute; left: -10000px; top: 0px; width: 1px; height: 1px; overflow: hidden;">technique was developed to replace the previous HPLC method. Analysis time was reduced</div>
<div id="_mcePaste" style="position: absolute; left: -10000px; top: 0px; width: 1px; height: 1px; overflow: hidden;">by a factor of 5.5 without the loss of chromatographic resolution or detection sensitivity. Over</div>
<div id="_mcePaste" style="position: absolute; left: -10000px; top: 0px; width: 1px; height: 1px; overflow: hidden;">150 compounds were detected from digested and undigested oxidized rapeseed oils with the</div>
<div id="_mcePaste" style="position: absolute; left: -10000px; top: 0px; width: 1px; height: 1px; overflow: hidden;">method. Most significant finding was that toxic core aldehydes present in the undigested</div>
<div id="_mcePaste" style="position: absolute; left: -10000px; top: 0px; width: 1px; height: 1px; overflow: hidden;">oxidized oils were not detected in the extracted chyme. This implies that the aldehydic</div>
<div id="_mcePaste" style="position: absolute; left: -10000px; top: 0px; width: 1px; height: 1px; overflow: hidden;">functions were either lost during the hydrolysis of lipids or that the compounds formed</div>
<div id="_mcePaste" style="position: absolute; left: -10000px; top: 0px; width: 1px; height: 1px; overflow: hidden;">various complexes with other components of the chyme and were not detectable by the</div>
<div id="_mcePaste" style="position: absolute; left: -10000px; top: 0px; width: 1px; height: 1px; overflow: hidden;">analysis technique used.</div>
<div id="_mcePaste" style="position: absolute; left: -10000px; top: 0px; width: 1px; height: 1px; overflow: hidden;">In the third study, a series of antioxidants were assessed for the effects in the artificial</div>
<div id="_mcePaste" style="position: absolute; left: -10000px; top: 0px; width: 1px; height: 1px; overflow: hidden;">digestion model. An improved UHPLC–ESI–MS analysis method was developed, which used</div>
<div id="_mcePaste" style="position: absolute; left: -10000px; top: 0px; width: 1px; height: 1px; overflow: hidden;">lithium salt to greatly enhance the ionization and therefore the detection limits of the low level</div>
<div id="_mcePaste" style="position: absolute; left: -10000px; top: 0px; width: 1px; height: 1px; overflow: hidden;">analytes in electrospray ionization–mass spectrometry. The main findings were that native</div>
<div id="_mcePaste" style="position: absolute; left: -10000px; top: 0px; width: 1px; height: 1px; overflow: hidden;">(unoxidized) rapeseed oil can be oxidized during the digestion processes and that none of the</div>
<div id="_mcePaste" style="position: absolute; left: -10000px; top: 0px; width: 1px; height: 1px; overflow: hidden;">used antioxidants could completely prevent this oxidation. L-ascorbic acid, 6-palmitoyl-O-Lascorbic</div>
<div id="_mcePaste" style="position: absolute; left: -10000px; top: 0px; width: 1px; height: 1px; overflow: hidden;">acid, 3,5-di-tert-butyl-4-hydroxytoluene (BHT), DL-α-tocopherol, and DL-α-</div>
<div id="_mcePaste" style="position: absolute; left: -10000px; top: 0px; width: 1px; height: 1px; overflow: hidden;">tocopheryl acetate had different kinds of effects against this oxidation, as measured by the</div>
<div id="_mcePaste" style="position: absolute; left: -10000px; top: 0px; width: 1px; height: 1px; overflow: hidden;">concentration of oxidized lipids in the samples.</div>
<div id="_mcePaste" style="position: absolute; left: -10000px; top: 0px; width: 1px; height: 1px; overflow: hidden;">The findings of our second study were supported by the fourth study in where 1H NMR</div>
<div id="_mcePaste" style="position: absolute; left: -10000px; top: 0px; width: 1px; height: 1px; overflow: hidden;">spectroscopy was used along UHPLC–ESI–MS analyses to study the behaviour of core</div>
<div id="_mcePaste" style="position: absolute; left: -10000px; top: 0px; width: 1px; height: 1px; overflow: hidden;">aldehyde-rich oils in the artificial digestion model. Again, no compounds with aldehydic</div>
<div id="_mcePaste" style="position: absolute; left: -10000px; top: 0px; width: 1px; height: 1px; overflow: hidden;">functions were detected by UHPLC–ESI–MS analyses of the digested oils even when high</div>
<div id="_mcePaste" style="position: absolute; left: -10000px; top: 0px; width: 1px; height: 1px; overflow: hidden;">amounts of core aldehydes were present in the original oil. However, 1H NMR analyses of</div>
<div id="_mcePaste" style="position: absolute; left: -10000px; top: 0px; width: 1px; height: 1px; overflow: hidden;">several samples revealed that there were some remaining carbonyl functions in the digested</div>
<div id="_mcePaste" style="position: absolute; left: -10000px; top: 0px; width: 1px; height: 1px; overflow: hidden;">samples. The combined results of these analyses techniques strongly hinted that Schiff bases</div>
<div id="_mcePaste" style="position: absolute; left: -10000px; top: 0px; width: 1px; height: 1px; overflow: hidden;">and Michael addition products were formed in the digestion mixture. Overall, the scientific</div>
<div id="_mcePaste" style="position: absolute; left: -10000px; top: 0px; width: 1px; height: 1px; overflow: hidden;">studies conducted in this thesis have increased the knowledge of lipid oxidation and especially</div>
<div id="_mcePaste" style="position: absolute; left: -10000px; top: 0px; width: 1px; height: 1px; overflow: hidden;">provided more detailed information on possible oxidation during lipid digestion. The findings</div>
<div id="_mcePaste" style="position: absolute; left: -10000px; top: 0px; width: 1px; height: 1px; overflow: hidden;">merit for more research in the fieLipid autoxidation is an unwanted process that affects the quality of food and has impact on human health. Lipid oxidation has been studied extensively, but oxidation during digestion has largely been ignored. Formation of oxidized lipids increases rapidly when protective antioxidants are exhausted. On the other hand, the nature of antioxidants can lead to problems when fortifying foods with too much antioxidants. Pro-oxidative effects of several antioxidants have been observed when used in excessive amounts.</div>
<div>Methods for studying lipid oxidation are numerous. Among them are unspecific titrimetric methods and highly specialized chromatographic and mass spectrometric methods. Nuclear magnetic resonance (NMR) spectroscopy, especially the proton (1H) NMR, is a promising technique for fast screening of lipid samples as it is non-destructive and because of the large dynamic scale of the technique. Drawbacks of NMR are that relatively large amount of sample is required for the analysis and that specific molecular structures may be difficult to identify from complex spectrum. This thesis focuses on the study of in vitro lipid oxidation by different chromatographic, mass spectrometric and nuclear magnetic resonance spectroscopic methods.</div>
<div>The most significant findings of the studies in this thesis centre around oxidation, hydrolysis, and behaviour of lipids in an artificial digestion model used in the studies. The model simulates the digestion processes of human and can be used to study lipid oxidation in vitro. Also of importance, are the lipid analysis techniques developed for the experiments, as the techniques can be adopted to other fields of scientific studies as well for industrial uses.</div>
<div>Four major studies were conducted in this thesis: first an in vitro digestion model was adopted to study the behaviour of differently oxidized rapeseed oils. Simultaneously, a novel HPLC–evaporative light scattering detector–MS analysis technique was developed, which enabled the analysis of native and oxidized free fatty acids, monoacylglycerols, diacylglycerols, and triacylglycerols in the chyme produced by the digestion model. The main findings of the study were that thermally oxidized rapeseed oil, chemically oxidized rapeseed oil and unoxidized rapeseed oil were hydrolyzed in a similar manner. No hydroperoxides were detected in the digested samples, even though they were present in the undigested oils. Also, the finding of large amounts of sn-1(3) monoacylglycerols was surprising, questioning the long believed mechanism of triacylglycerol digestion and absorption.</div>
<div>In the second study, an ultra-high performance liquid chromatography (UHPLC) analysis technique was developed to replace the previous HPLC method. Analysis time was reduced by a factor of 5.5 without the loss of chromatographic resolution or detection sensitivity. Over 150 compounds were detected from digested and undigested oxidized rapeseed oils with the method. Most significant finding was that toxic core aldehydes present in the undigested oxidized oils were not detected in the extracted chyme. This implies that the aldehydic functions were either lost during the hydrolysis of lipids or that the compounds formed various complexes with other components of the chyme and were not detectable by the analysis technique used.</div>
<div>In the third study, a series of antioxidants were assessed for the effects in the artificial digestion model. An improved UHPLC–ESI–MS analysis method was developed, which used lithium salt to greatly enhance the ionization and therefore the detection limits of the low level analytes in electrospray ionization–mass spectrometry. The main findings were that native (unoxidized) rapeseed oil can be oxidized during the digestion processes and that none of the used antioxidants could completely prevent this oxidation. L-ascorbic acid, 6-palmitoyl-O-Lascorbic acid, 3,5-di-tert-butyl-4-hydroxytoluene (BHT), DL-α-tocopherol, and DL-α-tocopheryl acetate had different kinds of effects against this oxidation, as measured by the concentration of oxidized lipids in the samples.</div>
<div>The findings of our second study were supported by the fourth study in where 1H NMR spectroscopy was used along UHPLC–ESI–MS analyses to study the behaviour of core aldehyde-rich oils in the artificial digestion model. Again, no compounds with aldehydic functions were detected by UHPLC–ESI–MS analyses of the digested oils even when high amounts of core aldehydes were present in the original oil. However, 1H NMR analyses of several samples revealed that there were some remaining carbonyl functions in the digested samples. The combined results of these analyses techniques strongly hinted that Schiff bases and Michael addition products were formed in the digestion mixture. Overall, the scientific studies conducted in this thesis have increased the knowledge of lipid oxidation and especially provided more detailed information on possible oxidation during lipid digestion. The findings merit for more research in the field.</div>
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