Lipid oxidation and color degradation kinetics under different storage conditions of pollen

Abstract: Pollen is the male reproductive material of plants and rich in various nutrient and functional substances, including protein, lipid of pollen, polysaccharide, vitamins and mineral, which are benefit for human health. Because of its relatively high moisture content, and its sensitive to microbial spoilage and fermentation, fresh pollen has very short shelf-life. Drying is the most frequently used method for pollen preservation as it can prevent the growth and reproduction of microorganisms and minimize many of the moisture-mediated degradation reactions to enhance shelf-life. However, due to high lipid content of pollen, their oxidation and rancidity arise serious quality problems during unsuitable storage, such as undesirable color, odour, flavor, etc. Therefore, a quantitative investigation of the change kinetics of pollen quality during storage is critical for selecting proper package method and storage conditions. As one of the most important organoleptic evaluation indicators of most foods and agricultural products, unsuitable color changes affect the market value and sale quantity significantly. Yellowness value, as the trait color of pollen, was selected as one of the quality attributes in current research. Lipid oxidation is closely related to quality degradation and flavor of food. The peroxide value (POV) and thiobarbituric acid reactive substances value (TBArs) were used to evaluate the first-order and second-order lipid oxidation of pollen during storage, respectively. The higher the POV and TBArs values are, the more severe the oxidation of lipid is. In current work, effects of different package factors (illumination and oxygen) and storage temperatures (4, 20, and 30 ℃) on the changes of yellowness value (b* value), peroxide (peroxide value, POV) and thiobarbituric acid reactive substances (TBArs) were investigated during pollen storage. The aims of the study were: 1) to explore the impact of temperatures on color and lipid oxidation at vacuum and without illumination package; 2) to explore the impact of illumination on color and lipid oxidation at 4 ℃ with vacuum package; 3) to explore the impact of oxygen on color and lipid oxidation at 4 ℃ without illumination package; 4) to establish the kinetics model of b* value, POV and TBArs based on zero-order and first-order models during 30 d storage period. Results showed that, a higher b* value of pollen was obtained under storage temperature of 20 and 30 ℃ compared with 4 ℃ (P<0.05); no significant change(P＞0.05) was found for the POV value of pollen during storage at 4 ℃ for 30 days, while significant increasing (P<0.05) were observed for storage at temperature of 20 and 30 ℃, respectively. In addition, the effect of light on POV of pollen during storage was not significant. But, the illumination could enhance the acceleration of TBArs value, which increased 7.42 mg/kg after 30 days storage. Zero-order model could well predict the TBArs changes kinetics of pollen during storage, while the first-order model could well describe b* value and POV value variation. The results could provide a theoretical support for selecting of storage strategies and conditions, which are benefits for reducing the quality degradation and prolong the shelf-life of pollen.