Analysis On Quality Difference Of Rape Bee Pollen At Different Drying Methods

Bee pollen is produced by honeybees collecting pollen from plant sources with its secretions.Bee pollen is rich in nutrients and is a kind of food with a high potential of biological value,so it is called "the library of natural micro-nutrient".The different nutrients contained in bee pollen make bee pollen have therapeutic properties and potential for nutritional applications,which are beneficial to human health and have broad application prospects.In the process of drying bee pollen,the quality might be deteriorated.Therefore,this study explored the effect of 5 common drying methods on drying characteristics and quality of rape bee pollen and compared the difference among 5 different drying methods in lipid oxidation,antioxidant activity and volatile components of bee pollen.The result of this study can be used to obtain the most suitable drying method for rape bee pollen.The results of the study are as follows:1.Effect of different drying methods on the drying characteristics of rape bee pollenUsing fresh rape bee pollen as raw material,and dried by 5 drying methods.The results showed that the infrared radiation drying took the shortest time,which was 140 min,while freeze drying took 1380 min during the drying process.The infrared radiation drying was89.86% less than freeze drying in drying time.The drying stage of all drying methods is reduced-speed drying as a whole.Among these 5 drying methods,the infrared radiation drying rate had the fastest drying rate;the freeze drying was the slowest,and the drying rate of sun drying was dependent on natural environmental factors;the pulsed vacuum drying had a short-term stage of rising-speed drying in the initial stage of drying,followed by a falling-speed drying.2.Effect of different drying methods on the quality of rape bee pollenThe results showed that the color of rape bee pollen was significantly affected by different drying methods(p<0.05).The color of rape bee pollen became dark after drying,and the deterioration of the color caused by sun drying was the most serious.The rape bee pollen of pulsed vacuum drying had the minimum value of ΔE,while L*,a*,b* of the other 4 drying methods were significantly decreased(p<0.05).Compared with fresh rape bee pollen,the surface of pollen grains was broken by infrared radiation drying,and the microbial aggregation appeared on the surface of rape bee pollen at sun drying.After drying,the content of total free phenolic acid in rape bee pollen increased significantly(p<0.05),especially the chlorogenic acid,vanillic acid and sinapic acid.The content of p-coumaric acid in all dried samples had no significant change,while the content of gallic acid increased,which was insignificantly in statistical analysis.Compared with fresh rape bee pollen,the amino acid contents of the other 4 drying methods were decreased except the hot air drying,and the amino acid contents in infrared radiation drying,freeze drying and pulsed vacuum drying were decreased significantly(p<0.05).Except for freeze drying samples,the content of 3-DG and MGO in rape bee pollen were increased significantly(p<0.05),and the content of MGO were changed with the change of 3-DG.The content of 3,4-DGE in the sun drying bee pollen was significantly increased(p < 0.05)and was 0.4652 mg/kg DW,which was21.44 times of that in the hot air drying bee pollen.The content of 3,4-DGE in other 4 drying methods had no significantly difference.3.Effect of different drying methods on lipid oxidation and antioxidant activity of rape bee pollenThe content of malondialdehyde(MDA)in the sun drying rape bee pollen sample was38.86% higher than the hot air drying sample and significantly higher than other drying methods(p<0.05),but there was no statistically significant difference in the content of MDA among the other 4 drying methods.Compared with fresh rape bee pollen,the FRAP of all dried samples was significantly increased(p<0.05),and there was no statistically significant difference in the scavenging ability of DPPH free radicals.The pulsed vacuum drying rape bee pollen showed the strongest capability of FRAP,which was 1961.11 ± 4.42 mmol Trolox/g DW,which was 24.78% higher than that of fresh rape bee pollen.After drying,the volatile components were significantly different from those fresh rape bee pollen,especially the difference between the sun drying and the fresh rape bee pollen was the largest,with the similarity was about 50%.The volatile components of rape bee pollen samples were similar among the 4 drying methods,with the similarity was more than 85%.Contrast the difference among 5 drying methods,such as benzaldehyde,ethyl heptanoate were the characteristic aroma components of the sun drying rape bee pollen.Hexanal,heptanal,octanal,and n-nonanal were also rich in sun drying samples,while the several kinds of volatile components were less or not found in other drying methods.A large amount of ethyl acetate was found in the samples of pulsed vacuum drying and freeze drying.Acetoin,α-pinene and 3-methylbutanal were the most detected in freeze drying rape bee pollen samples,while 6-methyl-5-hepten-2-one and E-2-hexene-1-ol were the most detected in hot air drying rape bee pollen samples.