# The Potential of _Phaeodactylum_ as a Natural Source of Antioxidants for Fish Oil Stabilization
## 3 Results and Discussion
### Phaeodactylum Biomass Addition (Part I)
#### 3.1.4 Caroenoid Content  
Table 2 shows the results of the carotenoid characterization of the oil phase of the _Phaedactylum_ biomass-enriched fish oil system. It concerns the content of carotenoids after preparing the system (i.e., at the start of the storage experiment). Just like in the _Phaedactylum_ biomass, fucoxanthin was the most abundant carotenoid, followed by diatoxanthin and \(\beta\)-carotene. The fact that carotenoids were detected in the oil showed that during stirring, a certain carotenoid transfer from the _Phaedactylum_ biomass to the fish oil occurred, as no carotenoids were present in the pure fish oil. Based on the amount of fucoxanthin in the _Phaedactylum_ biomass (5.31 (\(\pm\)0.52) mg/g dry biomass), the amount of fucoxanthin in the oil phase in the case of full transfer would have been 133 (\(\pm\)13) \(\mu\)g/g, indicating that ca. 12 (\(\pm\)3)% of the fucoxanthin migrated. Although it could therefore be stated that the absence of antioxidant migration was not the reason for the lack of oxidation inhibition, it is still possible that the amount did not suffice for an antioxidative effect. [PERSON] et al. [27] reported carotenoid contents of ca. 20 \(\mu\)g \(\beta\)-carotene and ca. 6 \(\mu\)g lutein per g oil in their study that did describe an antioxidative effect of _Scenedesmus_ extract addition to virgin olive oil. These contents are comparable to the amount of fucoxanthin detected in the current research. Although the differences in set-up regarding raw materials (not containing n-3 LC-PUFA) and analysis methods (Rancimat) could again be remarked as possible reasons for different findings, the question remains why the microalgal antioxidants in the current research were not capable of keeping the n-3 LC-PUFA rich fish oil oxidatively stable while their role in doing so has been suggested for the n-3 LC-PUFA rich microalgal oil or biomass itself [16; 18].  
In trying to address this question, apart from only considering the carotenoid content itself, the amount relative to the amount of n-3 LC-PUFA (the compounds causing oxidative susceptibility) was also examined. Table 2 shows the ratio of carotenoid to n-3 LC-PUFA content of the oil phase, with the fucoxanthin to n-3 LC-PUFA ratio being 0.00007 (\(\pm\)0.00002). If this is compared with the pure _Phaeodactylum_ biomass having a fucoxanthin/n-3 LC-PUFA ratio calculated to be 0.27 (\(\pm\)0.03), the big difference in the order of magnitude is clear. Despite antioxidants being defined as compounds that delay or prevent oxidation when present at low concentrations compared with those of the oxidizable substrate [10], the observed concentrations in the oil phase may simply be too low. Investigating the amount that would suffice for stabilizing the fish oil could give more insight into the capacity of _Phaeodactylum_ as an antioxidant and forms the basis of the second part of the experimental set-up. The potential of _Phaeodactylum_ biomass addition will be returned at the end of Part II, taking into account its results.