| The dry stems of Dendrobium officinale Kimura et Migo is rare traditional Chinese medicinal materials in our country,has anti-aging,anti-tumor,reduce blood sugar and improve immune efficacy.The fresh Dendrobium officinale Kimura et Migo are usually processed into dryed.Exploring high quality,high efficiency,better drying method,are problems of Dendrobium officinale Kimura et Migo drying needs to solve currently.In order to provide a reference for exploring the high efficiency and high quality drying method of Dendrobium officinale Kimura et Migo,this paper used Microwave drying technologies to study the effect of different microwave irradiation on the quality of Dendrobium officinale Kimura et Migo,establish its microwave drying dynamic model and investigate its polyphenol oxidase(PPO)enzymes inactivation.The main research methods and results are as follows:Methods :1.The influence of different drying methods on the quality: In order to investigate different drying methods on the influence of Dendrobium officinale Kimura et Migo drying quality.This paper applicated different drying methods(105? hot air drying,80?hot air drying after steam 30 min,far-infrared drying and microwave drying)to dry Dendrobium officinale Kimura et Migo which are origined from zhejiang,guangxi and yunnan,and respectively using Sulfuric acid-phenol method,the forint phenol method,high performance liquid chromatography to determinated total polysaccharides,total polyphenol and naringenin content of Dendrobium officinale Kimura et Migo.2.Drying dynamics research: In order to provided a theory basis of Dendrobium officinale Kimura et Migo drying process supervision and drying quality control,this paper through stem weight fastly by timing to establish the dryness curve and the drying rate curve of Dendrobium officinale Kimura et Migo which was changed by the drying time andscreen the optimum drying model of its drying process by using Origin 8.0 software to fit its dryness curve with three commonly used drying model.3.Effect of microwave irradiation on quality: The aim of this chapter was to provid the basis for the optimization of Dendrobium officinale Kimura et Migo drying process,so we have designed the experimentalas the following three aspects.1)By controlling the microwave power and microwave time to study the effect of microwave radiation on the chemical constituents of Dendrobium officinale Kimura et Migo.2)To explore the microwave variable power drying on the quality of Dendrobium officinale Kimura et Migo,we have set three variable power Microwave drying process which the microwave conversion point was set at 80%±5%,60%±5%,40%±5% and 20%±5% of the initial total mass respectively on the basis of the microwave drying dynamic curve.3)The effect of microwave intermittent drying on the drying quality of Dendrobium officinale Kimura et Migo was discussed by controlling the intermittent ratio of microwave drying under different power,which were microwave 30 s then intermittent 1,3,5,7 min.4.Polyphenol oxidase(PPO)Character and Passivation: By controlling the polyphenol oxidase(PPO)reaction substrate concentration,temperature,pH,enzyme dosage,PVP amount to investigate the enzymatic properties of Dendrobium officinale Kimura et Migo PPO for enzyme inhibition and passivation provide the basis;The activity of PPO in Dendrobium officinale Kimura et Migo was induced by different heating methods,and the dynamic curve of PPO activity was established.Which can provide evidence for the in-depth study of the appearance of Dendrobium officinale Kimura et Migo and its phenolic acid content change.Results:1.The dryness results of Dendrobium officinale Kimura et Migo by different drying methods showed that: 1)Total polysaccharides is calculated by glucose meter,its had good linear relationship with absorbance of a value during concentration range(0.611 ~ 13.057g/mL),the content of total polysaccharides in different regions of Dendrobium officinale Kimura et Migo were different and the effect of different drying methods on the content of total polysaccharides in its was significant,each origin Dendrobium officinale Kimura etMigo all had the highest total polysaccharide content after microwave drying.2)Total polyphenols is calculated by ferulic acid,its had good linear relationship with absorbance of a value during concentration range(0.806~12.096 ?g/mL),the dryness of different drying methods had a great effect on the total polyphenol content in Dendrobium officinale Kimura et Migo,in which the microwave drying was the highest and the hot air drying was the lowest.3)Naringenin had good linear relationship with peak area during concentration range(0.017~0.170 ?g),the average sample recovery rate was 98.03%,RSD was 1.80%,this method has the advantages of precision,stability and reproducibility,and can be used for the determination of naringenin in Dendrobium officinale Kimura et Migo.The effects of different drying methods on the content of naringenin in Dendrobium officinale Kimura et Migo were different,the microwave drying and drying at 105? after steam 30 min were best.2.Drying kinetics results showed that: The results showed that: Dendrobium drying characteristics exhibit a rule of fast followed by slow.Compared with the far-infrared drying and hot air drying,microwave drying can significantly shorten the drying time,and with the increase of microwave power,the drying time of Dendrobium officinale Kimura et Migo was shortened,the initial drying rate increased and the drying curve became more steep.In the three commonly used dry models,the Logairthmic model had a good fitting effect on the drying curves of Dendrobium officinale Kimura et Migo,which the R2 values were above 0.99,the RMSE and X~2 values were the smallest.3.The results of microwave irradiation showed that: 1)Compared with hot air drying,the microwave drying of Dendrobium officinale Kimura et Migohad had good dry quality at microwave 600 W and 3 min drying time,which the total polysaccharide,the total polyphenol,naringenin and the content of alcohol soluble leachate were 51.220%,1.069%,0.234 mg/g,12% respectively,and had the highest comprehensive evaluation.2)There was no significant difference in the dry quality of Dendrobium officinale Kimura et Migo(P>0.05)between three variable power microwave drying,but it was better than microwave drying and hot air drying.3)Microwave intermittent time had little effection on the total polysaccharides and alcohol-soluble of Dendrobium officinale Kimura et Migo whenextracted at different power,but it had great impaction of phenolic compounds,which had the highest comprehensive evaluation when microwave 600 W intermittent 3 min.4.The results of polyphenol oxidase of Dendrobium officinale Kimura et Migo showed that: 1)The activity of PPO in Dendrobium officinale Kimura et Migo was the highest when 0.30 mL of 60 mmol / L of pyrogallic acid was added into 0.1 mmol / L citric acid-disodium hydrogen phosphate buffer solution(pH = 6.8)at 40?,and the enzymatic reaction kinetics conforms to the Michaelis-Menten equation,the kinetic constant Km was58.83 mmol / L and the maximum reaction rate Vmax was 3725.78 U / min.The addition of0.20 g PVP could effectively increase the activity of PPO in Dendrobium officinale Kimura et Migo.2)The passivation rule of PPO in Dendrobium officinale Kimura et Migo was not consistent with the heating method.Compared with steaming for 30 min and hot air heating,microwave heating could significantly reduce the passivation time of PPO enzyme,and with the increase of microwave power,the time required for 80% passivation was shortened. |
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