| Sweet potato belongs to the convolvulaceae,it is a kind of herbaceous root plant of annual or perennial.In our country,the Planting amount and production output of sweet potato are very high.Sweet potato is an important food,feed and industrial raw materials in China.The research in China and abroad indicate that there are anthocyanins,phenolic acids,flavonoids and other polyphenols and dietary fiber,beta carotene,glycoprotein and other functional components in sweet potato,which have medicinal functions such as anti-cancer,anti-oxidation and so on.Study on the Selection of dried sweet potato varieties and the changes of its polyphenol content before and after drying is less now.In this study,16 varieties of sweet potato were used as raw materials,using the method of Hot air drying,vacuum freeze-drying,variable temperature and pressure difference puffing drying technology to dry them.Determine their sensory and physical and chemical indicators and screening out the suitable varieties of dry-processing.The correlation of each index between raw materials and finished products are analyzed and the material factors of affecting the quality of the product are confirmed.The effects of different drying techniques and parameters on the content of polyphenols were studied by determining polyphenols content in sweet potato under different drying conditions.The purpose of this research is to provide scientific basis for selecting suitable drying raw materials and guidance for selecting the appropriate processing methods and processing parameters,and reducing the loss of the functional components.of sweet potato polyphenol.The results are as follows:1.The physical and chemical components of different varieties of sweet potato are different.The moisture content,starch content and cellulose content of sample No.3 Shangshu19 are highest in the 16 varieties,they are 83.69%,67.57%,and 11.11%respectively,the content of reducing sugar of sample No.3 is 5.51%,which was lower than that of sample No.7 Violet(6.22%).Water content in the second place is sample No.15 Liaoshu No.30(77.50%),the lowest is sample No.8 No.868 sweet patato(61.97%).Starch content in the second place is No.2 Gaozhou sweet potato(57.03%),the lowest content is sample No.9 Local red(16.66%).The lowest content of reducing sugar is sample No.12 Liaoshu No.20(1.49%).Cellulose content in the second place is sample No.15 Liaoshu 30(9.98%),the lowest content was sample No.1 Vietnam pearl purple sweet potato(4.11%).Polyphenol oxidase activity of sample No.11 sweet potato No.1 is higher than the other of varieties of sweet potato,followed by sample No.2 Gaozhou sweet potato and sample No.7 Violet.The peroxidase activity of sample No.8 868 sweet patato is significantly higher than that of other varieties of sweet potato,followed by sample No.7 Violet and sample No.9 Local red.2.Hardness of hot air drying product is too large,puffing drying uneven.Vacuum freeze-drying of sweet potato products have good color,easy to maintain raw material structure shape,but the brittleness of the product is worse than the different temperature and pressure difference puffing drying.The products with different temperature and pressure difference were extruded with moderate hardness,the taste of the product is more crisp,the highest comprehensive evaluation of the three drying methods.Among the 16 varieties sweet potato,the average score of the yellow meat sample No.5 Yanshu25 is higher than that of the other varieties,and its color and texture of the product are the best.No.10 Yanshu 24 through the temperature difference pressure expansion after drying the product color is good,after drying to maintain the original color of raw materials,Moderate hardness taste crisp,uniform expansion,suitable for dry machining.Effect of dried product quality the quality of raw materials including moisture,starch content,cellulose content,polyphenol content,the starch content of raw material moisture content,chroma index b*of product value,rehydration ratio effect,starch content containing more water,chroma index b*value is small,the water than the smaller;the greater the polyphenol content of raw materials,products of greater hardness,the smaller the value of chroma index b*.3.In different varieties of sweet potato raw materials,the highest content of free polyphenols,flavonoids,phenolic acids and anthocyanins is sample No.16 Liaoshu3 3,the contents are 11.19mg/g,1.71mg/g,14.70mg/g,320?g/g respectively.The highest content of combined polyphenols,phenolic acids and anthocyanins is sample No.16 Liaoshu33,the contents are 5.28mg/g,13.03mg/g,60?tg/g,respectively;the highest content of combined flavonoids is sample No.12 Liaoshu20,the content is 0.27mg/g.The content of polyphenols and polyphenol content of different varieties of sweet potato are significantly different.Compare with the raw material,the content of polyphenols in dried sweet potato is significantly changed.Free polyphenols in 16 samples,in addition to No.8 868 sweet potato,No.12 Liaoshu20,No.16 Liaoshu33 content decreased,the content of other samples showed an upward trend.The content of combined polyphenol are only No.3 Shangshul 9,No.1 Liaoshu20 and No.16 Liaoshu33 increased,other samples showed a downward trend.Free flavonoids in 16 samples,in addition to No.1 Vietnam pearl purple sweet potato,No,3 Shangshul 9,No.4 Lonhshu9,No.9 Local red,No.10 Yanshu24 increase in content,other samples showed a downward trend,the content of combined flavonoids decreased.Free phenolic acids in 16 samples,in addition to the contents of samples No.7 Violet,No.12 Liaoshu20 and No.16 Liaoshu33 are down,the contents of other samples increased;the content of combined phenolic acids in the 16 samples are increased.Free anthocyanins in 16 samples,in addition to the sample No.3 Shangshul9 is increased,other samples are decreased.In addition to the addition of No.7 Violet,No.12 Liaoshu20,nd the number of samples(No.4),the binding status of anthocyanins is decreased and the content of other components in the samples are increased.4?To investigate the effects of different dry-process sweet potatoes on polyphenols.Sweet potato by different pretreatment and puffing drying conditions after different treatments,and the combination of free phenol phenol content changed,polyphenol,phenolic acid and flavonoid content change is obvious,anthocyanin content is relatively obvious.Select the appropriate blanching time(3min),pre drying time(8h)and the number of freeze-thaw cycles(1)can effectively reduce the loss of dried sweet potato polyphenol,and polyphenol content increased at variable temperature and pressure difference puffing drying temperature and residence time can promote the dried sweet potato.5.The content of phenolic acids monomer in different varieties of sweet potato is different.Sample No.16 Liaoshu33 four kinds of phenolic acid monomer content are the highest(chlorogenic acid is 3839.87ug/g,isochlorogenic acid A is 4524.80ug/g,isochlorogenic acid B is 555.66ug/g,isochlorogenic acid C is 258.56ug/g),followed by several varieties of high content from high to low ranking is No.12 Liaoshu20,No.7 Violet,No.5 Yanshu25.Sample No.8 868 sweet potato is not detected isochlorogenic acid B and isochlorogenic acid C.The content of phenolic acid monomer in purple sweet potato is higher than other color sweet potato. |
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