Study On The Quality Of Artichoke Powder With Different Drying Technology

Artichoke is worthy of further study due to it is rich in polyphenols,protein,cellulose and mineral elements,and has the functions of anti-oxidation,reducing blood fat,anti-aging,anti-tumor,reducing blood pressure,tonifying kidney and so on.The production of artichoke powder was obtained by cleaning,enzyme killing pretreatment,drying and powdering of artichoke.In this study,the inhibition effect of different pretreatment methods on enzymatic browning of artichoke was studied,and the effects of four drying methods(hot air drying,vacuum drying,vacuum freeze-drying,microwave drying)on the nutritional composition,processing characteristics,oxidation resistance and aroma components of artichoke powder were compared and analyzed,to provide a theoretical basis for the development and utilization of artichoke.The results are as follows:(1)The effects of three pretreatment methods(microwave treatment,blanching treatment,steam treatment)on the activity of polyphenol oxidase(PPO)in artichoke were studied.The optimal conditions of each group were obtained: steam treatment for 160 s,blanching treatment for 100 ?/20 s,microwave treatment for 700 w/40 s,taking the total phenol retention and color of artichoke powder as the evaluation index.The results of the determination of total phenol,total flavone and the color of the samples obtained by three optimum pretreatment conditions showed that total phenols and flavonoids in pretreated samples were higher than that in untreated samples.The total phenols of 33.92 mg/g and flavonoids of 66.71 mg/g were obtained in the 700 w/40 s,which were significantly different from those in the other three groups(P<0.05),and the color protection effect was better.The microwave treatment of 700 w/40 s was the best condition.(2)The effects of four drying methods on the basic components,color,processing characteristics,particle size and microstructure of artichoke powder were investigated.In terms of basic components,the highest crude fiber content of 15.18 g/100 g and crude protein content of 23.05 g/100 g were obtained in freeze-dried group,which was significantly different from other three groups(P<0.05).The highest crude fat content of 0.76 g/100 g was obtained in microwave group.The order of total sugar content was hot air group(30.44)>microwave group(26.94)>Vacuum group(25.52)>freeze-dried group(24.75 g/100g);It can be seen from the drying curve that the shortest drying time was obtained in microwaveXII group,and the longest drying time was obtained in freeze-drying group with the highest L *value of 87.76;The bulk density of 0.62 g / ml was obtained in microwave group,which was higher than that of the other three groups.There was no significant difference between hot air group and vacuum group(P > 0.05);The microwave group displayed the best water holding capacity and oil holding capacity with value 15.77 and 4.50 m L/g,respectively,but its freeze-thaw stability was poor.The maximum solubility of 9.46 mg/100 m L and minimum caking degree of 40.36% were obtained in vacuum group.The best freeze-thaw stability of8.91% was obtained in hot air group.And the lowest moisture absorption rate of 7.24% was obtained in freeze-drying group.The order of water recovery rate was vacuum group>hot air group>microwave group>freeze-drying group;As for the particle size and microstructure,the smaller particle size of 645.8 nm and 615.6 nm were obtained in freeze-drying group and microwave group,respectively,and the lower dispersion coefficient indicated that the particles were more uniform.The sample in freeze-drying group were was loose sponge shape and the sample particles in microwave group was smooth and flat,which indicated that the two drying methods had better protective effect on the morphology of artichoke powder.(3)The effects of four drying methods on the content of phenols and antioxidation of artichoke powder were investigated.The highest free phenol content of 29.03 mg/g and binding phenol content of 3.70 mg/g were obtained in microwave group,but free phenol was no significant difference with freeze-drying group(P > 0.05).The order of total phenol content was microwave group(32.73)>freeze-dried group(31.70)>Vacuum group(28.84)> hot air group(27.63mg/g);The highest free flavone content of microwave group was78.75mg/g,which was significantly different from the other three groups(P < 0.05).The highest combined flavone content of 3.21mg/g was obtained in hot air group;In the comparison of antioxidant capacity of free phenols from different drying methods,the antioxidant capacity showed a linear trend with the increase of extract concentration.The four evaluation systems showed that the strongest of antioxidant capacity was obtained in microwave group.And the sequence of antioxidant capacity was microwave group >freeze-drying group>Vacuum group>hot air group,which was consistent with the results of antioxidant capacity of combined phenols.There was a good linear relationship between the content of phenols and antioxidant capacity.(4)The volatile aroma components in samples with different drying methods were detected by HS-SPME-GC-MS.There were 107 kinds of aroma components in fresh samples and 4 groups of dried powders,including 16 kinds of terpenoids,22 kinds of aldehydes,21 kinds of alcohols,24 kinds of alkanes,12 kinds of esters and 12 kinds of other substances.Itcan be concluded that the main aroma components were terpenoids,aldehydes and alcohols.The volatile aroma components of 40,58,52,43 and 52 were detected from fresh samples,hot air group,vacuum group,freeze-drying group and microwave group,respectively.The main components in fresh samples were(+)-?-apine,heptadiene,?-caryophyllene,n-hexanal,2-hexenal,n-hexanol,(s)-3-ethyl-4-methylpentanol and(9z,12 z,15z)-9,12,15-octadecatriene-1-ol.The volatile matter and content of the four drying groups were different.With the increase of aroma substances,the change or content of main aroma substances increased,making the aroma components of artichoke more abundant.In conclusion,the best protection of basic nutrients and color was obtained in freeze-drying group.The microwave group had the best retention effect of phenolic substances and the strongest antioxidant capacity.Both of them showed the increase of aroma substances.They can be used in the development and utilization of artichoke powder alone or in combination.