Figure 3. GAS CHROMATOGRAPHY-MASS SPECTROMETRY CHROMATOGRAM FOR THE VOLATILE COMPOUNDS FROM LOTUS BEE POLLEN STORED AT 40C
All these compounds represented groups of characteristic secondary lipid oxidation products derived from oxidized oleic, linoleic and linolenic acids. Table 2 showed that the dominant fatty acids in lipid of lotus bee pollen were palmitic acid (16:0), stearic acid (18:0), oleic acid (18:l) and linoleic acid (18:2). The saturated fatty acids (SFAs) were accounted for approximately 70% of total fatty acids in bee pollen oil. The monounsaturated fatty acids consisted of small quantities of palmitoleic and oleic acids while the total percentage of polyunsaturated fatty acids was about 10% in FAMEs. Linoleic acid oxidation would produce 9-hydroperoxide and 13-hydroperoxide, which were responsible for the production of hexanal and 2,4-heptadienal (Frankel 1998). Octanal and nonanal, in addition, were produced by decomposition of the most oleic acid hydroperoxides (Varlet et al. 2007). The fatty acid composition can well explain the formation of aldehydes in the sample, which is the main source of off-flavors in bee pollen products. Because of the high content of SFA, the amount of second lipid oxidation products remained low in lotus bee pollen. For this reason, the discoloration in the pollen sample seems to be more accurate to reflect the lipid oxidation than stale flavor formation.