3 Results
3.1 Selection of Favors
The pAV of flavored fish oils were consistently higher than the pAV of the unflavored control oil. However, the magnitude of this pAV difference varied (Fig. 1). Among all the flavors screened, chocolate-vanilla and lemon flavors caused the greatest change in pAV. Therefore, these flavors were selected for further analysis.
3.2 Compound Identification in Chocolate-Vanilla and Lemon Flavors
Although there were only six compounds identified in chocolate-vanilla flavor with peak areas > 1% of the internal standard (Table 1), three of them (p -anisaldehyde, piperonal, and vanillin) were aldehydes that have a great potential to condense with the p -anisidine reagent and increase the pAV. Among the six identified compounds, the three aldehydes also had the highest area relative to the internal standard (ARIS), with p -anisaldehyde, piperonal, and vanillin at 4.7%, 24.5%, and 90.7%, respectively. A small amount of trimethylpyrazine, ethyl caprylate, and ethyl caprate were also identified. On the other hand, 15 compounds were identified in lemon flavor, but there were still only three aldehydes (decanal, β-citral, and α-citral) that had potential to react withp -anisidine. Decanal, β-citral, and α-citral had ARIS of 2.1%, 19.2%, and 29.6%, respectively. Total ARIS of the three aldehydes in the chocolate-vanilla flavor was much larger than the three aldehydes in lemon flavor. Besides aldehydes, a large amount of terpenes was also identified in the lemon flavor. Limonene and β-pinene had ARIS of 824.5% and 123.0% respectively.
3.3 Oxidation of Chocolate-Vanilla and Lemon Flavored Fish Oils
The pAV of all the fish oil samples increased over the course of the 20-day study at 40°C (Fig. 2). In chocolate-vanilla flavored oils, a significant difference in pAV was found between FBO and FAO samples on Day 20. In lemon flavored oils, a significant difference in pAV occurred between FBO and FAO since Day 12. According to regression analysis, an exponential model was best fitted to the pAV data of each treatment (R2 = 0.961 - 0.975). In both chocolate-vanilla and lemon flavored oils, A (stable interfering aldehydes) was significantly higher in FBO and FAO than in UFO (Table 2). No differences were detected in B (changing aldehydes). In the chocolate-vanilla flavored fish oils, FBO samples had a significantly lower k (rate constant) than UFO. In lemon flavored oils, no significant difference was detected in the k of UFO, FBO, and FAO.