Vacuum Pulsed Drying Characteristics And Quality Of Lotus Pollen

Drying is a critical step during bee pollen processing. Traditionally, pollen is usually dried by natural open sun drying method or hot air drying in ovens. However, these methods exhibitshort comings such as long time consuming, instability of products quality, heavily loss of nutrition and susceptible to the variety and unpredictability of the weather, Vacuum pulsed drying (VPD) is an innovative drying technology. During the drying process of VPD, the chamber pressure is alternating between vacuum and normal atmosphere condition, which breaks the balance condition of water vapor partial pressure between material surface and the drying medium, by thus enhancing drying rate extensively Meanwhile, as the VPD process occurs at lower pressure, the boiling point of the water is depressed, and therefore moisture evaporation can take place at lower temperature. In this paper, the effect of vacuum pulsed drying technology on lotus pollen drying characterization and nutritional quality were investigated. The vacuum pulsed drying processes of bee pollen were performed at different drying temperatures (45,50,55,60, and 65℃) and different vacuum keeping time (3,6,9,12, and 15 min) and their effect on drying kinetics were compared. Additionally, total SOD content, color and microstructure of the dried bee pollen were detected. Meanwhile, the polysaccharide structure and activation were compared between hot air drying method and vacuum pulsed drying method.The pulsed vacuum drying kinetics of lotus pollen indicated that both drying temperature and vacuum keeping time had significant influence on drying time with p value less than 0.05. The drying time of bee pollen decreased with increasing of the drying temperature. And drying time would decrease or increase as the increasing the vacuum keeping time. The Fick’s second law of diffusion was used to calculate the moisture effective diffusivity of vacuum pulsed drying process of bee pollen, which ranged from 0.8094×10-9 to 1.7962×10-9 m2/s. In addition, the moisture effective diffusivity increased as drying temperature increment and increased then decreased with vacuum keeping time increment. The drying activation was calculated to be 25.96 kJ/mol when vacuum keeping time was 12 min and normal keeping time was 3 min.The 9 popular agricultural products thin drying models were used to describe the drying processof pollen. Coefficient of determination(R2), root mean square error (RMSE) and chi-square test value (χ2) were used to evaluate and analyze the fitting. Results indicated that the Weibull model and logarithmic model fitted well with the drying data. The regression analysis between the model parameters and drying parameters (drying temperature and vacuum keeping time) was carried out, the new model were developed to describe the pulse vacuum drying of lotus pollen.The study of total SOD content and color value of dried bee pollen indicated that drying temperature had significant influence on total SOD content with p value less than 0.05. Total SOD content appeared decreased gradually as drying temperature increased. When drying temperature was 65℃, the content declined obvisously, which showed significant difference compared with the sample of drying temperature 45℃. Drying temperature as well as vacuum keeping time had obvious effects on AE* value. With drying temperature incresment, AE* value seemed to rise up continuously. Additionally, when drying temperature of 45℃, vacuum keeping time of 12 min and normal pressure keeping time of 3 min, the AE* value was not significant different from fresh sample. Besides, the total SOD content was higher than fresh sample.The microstructure investigation of bee pollen showed that the miscrostructure of bee pollen grain was very tight with nearly no holes and thepollen grain looked like aspherical ball. The dried bee pollen cells with cacuum plused drying technology came into being different holes structure. With drying temperature increased the bee pollen density decresed and developed more holes. The bee pollen microstructure appeared the tendecty of approximately globose to ellipsoid transformation. At the same time, the bee pollen structure collapsed. When it was dried at 65 ℃, the drying temperature not only increased the pollen structure deformation, but also led to structure fracture. Besides, the bee pollen structure changes may contribute to internal material release.In current work, the effects of lotus bee pollen polysaccharides (LP) extracted from Lotus Bee Pollen dried by different drying methods on structure and activity were also investigated. The results showed that the LP significantly improved intestinal propelling rates and shorten of colon. LP combined with 5-Fu were both extended significantly colon lengths (p<0.05). Hematoxylin and eosin (HE) stained results showed that LP significantly reduced colonic mucosa epithelium goblet cell loss, inflammatory cells infiltration and crypt depth shallow induced by 5-Fu. In addition, LP significantly increased the area of peyer patchs (PPs) (p<0.01 or p<0.05). Those results suggested that LP could ameliorate intestinal mucosal damage, improve the intestine transit function and protect intestine oxidative damage in mice induced by 5-Fu.