Study On Vacuum Pulsation Drying Characteristics And Process Optimization Of Daylily

The daylily is rich in nutrients,including protein,vitamins,polysaccharides,carbohydrates,flavonoids,anthraquinones and other functional ingredients,but the fresh daylily after picking still maintains strong respiration and transpiration,and is not resistant to storage.Therefore,selecting appropriate drying methods and optimizing process conditions to reduce water content to a safe wet basis while maximizing the retention of the flavor,nutrients,and product rehydration of daylily has become the focus of research on daylily drying.This article studies the effects of different drying methods on the flavor and quality of daylily,establishes a vacuum pulsation drying model,and optimizes the vacuum pulsation drying process conditions,in order to provide theoretical basis and technical support for the improvement of daylily drying methods and the development of daylily industry.Study on the effect of drying methods on flavor substances of daylily.Using headspace solid-phase microextraction technology and gas chromatography-mass spectrometry(GC-MS)technology to identify and analyze the volatile substances in daylily,the effects of natural drying,hot air drying,and vacuum pulsation drying on the flavor substances of daylily were studied.Multiple statistical analysis methods such as aroma activity value(OAV),partial least squares discriminant analysis(PLS-DA),and principal component analysis(PCA)were used for analysis.The results showed that 49,40,and 44 species were detected in natural drying,hot air drying,and vacuum pulsation drying,respectively.Meanwhile,3-furan formaldehyde,3-octen-2-one,hexadecane,and acetic acid were identified as natural drying characteristic flavor substances;(E)-2-methyl-2-butenal,3-oct-2-one,and hexadecane are characteristic flavor substances for hot air drying;(E)2-methyl-2-butenal β-Laurene was a characteristic flavor substance of vacuum pulsation drying.Therefore,from the perspective of obtaining good flavor,vacuum pulsation drying is the preferred drying method.A study on the effect of drying methods on the quality of daylily.The effects of three different drying methods(natural drying,hot air drying,and vacuum pulsation drying)on soluble protein,flavonoids,total sugar,color,texture,and microstructure of daylily were compared.The results showed that the protein content,shear force,and hardness of vacuum pulsation drying of daylily were significantly higher than those of natural drying and hot air drying(P<0.05),while the flavonoid content was significantly higher than that of natural drying(P<0.05)and slightly higher than that of hot air drying(P>0.05).The b*value was significantly higher than that of hot air drying(P<0.05)and slightly higher than that of natural drying(P>0.05).In addition,natural drying was better than vacuum pulsation drying in terms of microstructure,but from the perspective of obtaining good nutritional quality and physical properties(color,texture),vacuum pulsation drying was the preferred drying method.Vacuum pulsation drying characteristics and model establishment of daylily.Study the effects of different drying temperatures,vacuum holding time,and atmospheric pressure holding time on the moisture ratio,drying rate,activation energy,and water diffusion coefficient of daylily drying.Based on this,select five commonly used thin layer drying models for fitting and screening the best model suitable for vacuum pulsation drying of daylily.The results showed that under different vacuum pulsation drying conditions,the drying process had obvious stages of increasing and decreasing speed,but no constant speed stage,which was a typical internal water diffusion control characteristic.Meanwhile,under different drying temperatures,the Ea of daylily was 29.20 kJ/mol,and under different atmospheric and vacuum holding times,the Ea was less than 12.70 kJ/mol.The Page model has the highest R2,χ2 and RSS are the lowest,and the MR values obtained from the experiment after fitting and solving had a good fit with the predicted MR values of the model,making it the most suitable model for vacuum pulsation drying of daylily.Study on the effect of temperature on the quality of vacuum pulsation drying of daylily.Comparative study was conducted on the effects of different temperatures(natural drying,65℃,70℃,75℃,80℃,85℃)on the color,free amino acid content,flavor,protein secondary structure,and thermal stability of vacuum pulsation dried daylily.Partial least squares discriminant analysis combined with principal component analysis was used to characterize free amino acids and flavor substances.The results showed that the b*value of dried daylily at PVD drying temperature was significantly higher than that of natural drying(P<0.05),with the highest L*value at PVD75℃(35.96)and significantly lower free amino acid content than that of natural drying(P<0.05).However,as the PVD drying temperature increased,the free amino acid content gradually decreased.PVD65℃ can effectively retain flavor substances such as inorganic sulfides,nitrogen oxides,and terpenoids.In the sample of daylily at PVD70℃ β-fold and α-the highest helix content.At PVD75℃ β-fold and α-the content of both spirals was second only to PVD70℃.Therefore,based on the content of chapter 4,it can be further determined that PVD75℃ was the optimal drying temperature range for vacuum pulse drying.Optimization of vacuum pulsation drying process of daylily.Explored the effects of drying temperature,vacuum holding time,and atmospheric pressure holding time on the flavonoid content,rehydration rate,and overall sensory perception of daylily,and calculated the comprehensive value of daylily using membership comprehensive score and principal component analysis.The results showed that the drying temperature had a significant impact on the rehydration rate and flavonoid content of daylily(P<0.05),with the highest rehydration rate at PVD65℃ and the highest flavonoid content at PVD75℃.The normal pressure holding time has a significant impact on the rehydration rate and flavonoid content(P<0.05),with the rehydration rate and flavonoid content being the highest when the normal pressure holding time was 5 minutes;The vacuum holding time had a significant impact on the rehydration rate and flavonoid content(P<0.05).The rehydration rate was highest at 15 minutes of vacuum holding time,and the flavonoid content was highest at 10 minutes.Meanwhile,the optimal process parameters for vacuum pulsation drying of daylily were further determined:drying temperature 77℃,vacuum holding time 10 minutes,and atmospheric pressure holding time 5 minutes.Therefore,Under these conditions,three repeated experiments were conducted to obtain a comprehensive evaluation value of about 0.710 of daylily.