| Sweet potato belongs to the convolvulaceae,it is a kind of herbaceous root plant of annual or perennial.From Liaoning to Hainan,all of them are grown.They are important food ingredients,feed and industrial raw materials in China.The area under cultivation is mainly in Asia and Africa.Domestic and foreign research suggest that sweet potato contains anthocyanins,phenolic acids,flavonoids and other polyphenols and dietary fiber,?-carotene,glycoprotein and other functional ingredients,which have medicinal functions such as anti-cancer,antioxidant and so on.The sweet potato powder includes all the dry matter of the fresh sweet potato except the skin.It is widely used and can solve the difficult problems of storage and transportation.The sweet potato powder after rehydration can reflects the nutrition,flavor and taste and maintains its original physiological activity of the fresh sweet potato.And it can be applied in the field of baked food,breakfast food and baby food.It has great practical significance for improving people's diet structure.In this paper,12 varieties of sweet potato were made into two kinds of raw and cooked,and were dried by hot air drying and vacuum freeze-drying respectively.A total of 48 kinds of the sweet potato powder were analyzed and determined their sensory quality,physicochemical quality and functional quality.On the basis of optimizing the technological parameters of the combined phenol extraction,the free phenols,bound phenols and ?-carotene of the above 48 kinds of sweet potato powders were extracted and determined,and the DPPH free radical scavenging activity of their extracts was determined.The test result is as follows:The L* and b* values of the purple sweet potato powder were lower than those of the other two kinds of sweet potato powder,and the a* value was higher than that of the other two kinds of sweet potato powder.After the sweet potato was cooked,the L* value of the whole powder was reduced,but the a* value of the full-powder color index was increased.The whole-powder color saturation index b* of the sweet potato samples with apricot and light yellow color increased after cooked,and the purple sweet-fleshed varieties were sweet potatoes.After cooking,the full-powder color index b* decreased.From the six aspects of color,odor,taste,stickiness,rehydration,and graininess,total scores were used for sensory evaluation of different sweet potato powders.The purple meat variety No.3 Violet freeze dried whole powder and hot air dried ripe powder,apricot The meat color variety No.6 Liao potato 30 whole powder and hot air dry cooked whole powder,No.5 sweet potato 25 cooked whole powder and freeze-dried raw powder,all have higher ratings and are deeply loved.Violet variety No.3 sample Violet sweet potato powder was the highest(42.57%).Onthe whole,the total iodine blue values of all varieties of sweet potato are generally lower than that of cooked whole powder.The raw starch content of sweet potato is significantly higher than that of cooked whole powder.The content of reducing sugar is significantly lower than that of cooked whole powder,and the color of starch is light yellow.Compared with apricot yellow and purple varieties,the starch content was higher,but the apricot yellow sweet potato varieties had a higher reducing sugar content than the light yellow flesh and purple varieties.Among them,the raw and cooked iodine blue values of the sweet potato 33 and the No.1samples of the purple meat variety No.1 were all small,with the lowest values being 5.22 and5.54.The cell integrity was the best.The content of the whole powder starch in the light yellow flesh color variety No.10 was 78.44g/100 g,and the content of reducing sugar in the whole powder of Liao potato 30 was the highest,the highest value was 31.10.The overall perspective,all the powder,the highest transparency for the local red,the highest holding rate of the species is the potato 30;the highest water holding species for the sweet potato 5th.After the cooking,the whole powder has better paste ability and rehydration than the powder,but the freeze-thaw stability decreases.The freeze-dried whole powder is slightly higher than the hot water-dried whole powder rehydration ratio,and has better gelling properties and freeze-thaw stability.Freeze-dried whole powder emulsifying and emulsifying stability is slightly higher than that of hot air drying raw powder,but its cooked whole powder emulsifying property and emulsifying stability are slightly lower than that of hot air drying and cooked whole powder.Among them,the local red freeze-dried whole powder has the highest emulsifying properties,and the sweet and whole powder of the sweet potato No.5 has the best emulsifying stability.The sweet potato 25 freeze-dried whole powder and the Liao potato 20 freeze-dried cooked whole powder form the largest volume of the paste.The ratio of reconstituted raw water of the whole raw potato 30 was the highest.The whole powder of Liao potato 28 was the best in water,sugar liquid and salt solution.The freeze-thaw stability of Liao potato30 was the best.The optimum extraction parameters of phenolic acid hydrolysis were 21.33 h,62.67°C,34.67:1(mL/g),and the extraction rate was 0.22g/100 g.According to actual conditions,the process parameters were adjusted to extraction time 22 h,temperature 62°C,liquid to solid ratio 35:1(mL/g),and actual extraction amount was(0.212±0.004)g/100 g,reaching 96.36%of the predicted value.The content of free phenol and bound phenol between 12 different sweet potato varieties ranged from(0.14 to 1.63)g/100 g and(0.05 to 0.28)g/100 g.Purple sweet potato was generally superior in binding phenol content and free phenol content.Among non-purple varieties of sweet potato,the highest content of phenolic compounds was Liao potato 20 witha value of 1.63.The carotene content of the apricot yellow sweet flesh was greater than that of the purple sweet potato and the light yellow flesh sweet potato.The carotene content of the cooked sweet potato was lower than that of the raw sweet potato,and the carotene content of the local red and tobacco 25 was relatively higher in the 12 varieties of sweet potato.In the aspect of free radical scavenging rate,the DPPH clearance rate of free phenol extracts of sweet potato powder and cooked powder was generally higher than that of combined phenol extracts,and the clearance rate of cooked sweet potatoes was higher than that of fresh sweet potatoes.Among 12 varieties,the free phenol extract of No.2 variety Liao potato 33 had the highest DPPH clearance rate,with the highest value being 83.02%.The scavenging rate of DPPH in the No.3 variety violet combined with phenol extracts was the highest,with the highest value being 47.80%. |
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