RESULTS AND DISCUSSION
Hydroperoxide Measurements in Bee Pollen Samples
Lipid oxidation starts with the production of unstable intermediary compounds such as hydroperoxides. The variation in hydroperoxide contents in bee pollens during storage was determined (Fig. 1). The hydroperoxide level in the samples stored at 4C slightly increased with the time prolongation. Similar moderate trend was found in the 20C with higher hydroperoxide-formed speed. A significant increase (P < 0.05) was observed in the content of hydroperoxides. It indicated that the primary lipid oxidation occurrence at this condition proceeded faster than that at 4C cold storage. However, it is interesting to note that two stages were distinguished in the changes of hydroperoxide value during 3-month storage at 40C. The first 15 days of incubation resulted in a large rise from 2.73 to 6.20 µmoleq/kg. Then, an obvious steady decline in hydroperoxide values appeared after 30 days. This pattern could be explained by the balance between the opposing effects of the hydroperoxide formation and the degradation to secondary lipid oxidation products according to the classical kinetic scheme for the lipid auto-oxidation reported by Labuza (1971). High temperature (e.g., 40C) caused a high initial rate of hydroperoxide formation to a certain level. Afterward, the decomposition of the unstable hydroperoxides accelerated and finally resulted in the decrease of hydroperoxide content in the samples. This is also consistent with the results of Mortensen et al. (2002) who evaluated the change of hydroperoxide contents analyzed by different methods used for semihard cheeses during storage.