| Sweet potatoes（Ipomoea batatas）,also known as sweet potatoes,which have high yields,rich resources,and low prices.They are also rich in various nutrients and functional substances such as insoluble dietary fiber,trypsin inhibitors,anthocyanins and carotene.In this study,several sweet potatoes which was common in Chongqing was used as raw materials to brew vinegar.Firstly,the principal component analysis method was peformed to select sweet potato varieties suitable for vinegar processing.Secondly,three extract methods of purple potato anthocyanins and the acetic acid fermentation conditions were optimized by the response surface and orthogonal test method.Thirdly,the quality of different purple sweet potato vinegar were compared and analyzed.Finally,the volatile compounds of two vinegar products were investegated.The main results are as follows:（1）Index measurement of 5 kinds of raw sweet potatoes indicated that the content of protein and vc in sweet potatoes was not significantly different（protein content ranged from 1.54 to 3.89 g/100g,while vc content was 8.673 to 27.809 mg/100g）,but there were significant differences in TSS,moisture,total sugar,total acid,total phenol and total flavonoids among the five sweet potato varieties（p<0.05）.Meanwhile,the content of phenols and flavonoids in colored sweet potatoes were higher than the white.The content of total phenol in colored and whited sweet potatoest ranged from 2303.06to 3773.82 mg/100g and 358.83 to 518.96 mg/100g,while flavonoid content varied from 188.88 to 304.96 mg/100g and 72.22 to 159.64 mg/100g,separately.Besides,the content of starch in Yu 27 and Yu 19 were the highest and the lowest,22.785 and16.727%,respectively and there was no significant difference between the other varieties（p>0.05）.（2）Five sweet potatoes vinegar were brewed and its basic chemical indicators,active ingredients,color and antioxidant capacity were measured.At the same time,they were analyzed by principal component analysis.Three main components were extracted from 14 quality indicators,the first main component included total acid,total polyphenols,total flavonoids,the second main component was total ester,and the third main component was vitamine c.Simultaneously construct the score model as F=0.6220 F1+0.24448 F2+0.12166 F3.Accordingly,the comprehensive scores of five sweet potato vinegars were calculate and ranked as Yuzi 7>13-3-35>Yu15>Yu19>Yu27.Therefore,Yuzi 7 was selected as the acetic acid fermented raw material in this paper.（3）Combined single factor with response surface and orthogonal test method,the extraction conditions of purple potato anthocyanins performed by microwave,double enzyme and ultrasonic method were optimized and a method suitable for extracting anthocyanins from purple potato were selected.Optimized by response surface and orthogonal test methods,the optimal parameters of microwave assisted,double enzyme and ultrasonic assisted method for extracting anthocyanins from purple sweet potato were microwave time of 4.6 min,microwave power of 560 W,and liquid to material ratio of 22.8 mL/g;α-amylase:cellulase ratio of 1:2.5,and the amount of double enzyme addition of 0.5 mg/kg,enzymolysis time 1.5 h,and liquid to material ratio of30 mL/g;ultrasound power 480 W,liquid-to-material ratio of 30 mL/g,and ultrasonic time 80 min,respectively.Under their optimal conditions,its total anthocyanin yield was 92.78,83.28 and 85.43 mg/100g.Among three methods,the microwave-assisted method got the best results and was significantly different from the other method（p<0.05）.Therefore,the microwave-assisted method was selected as the method for extracting anthocyanins from purple potato in this paper.（4）The response surface method was performed to optimize the fermentation conditions of acetic acid of purple sweet potatoes,purple sweet potato vinegar and pigment vinegar were fermented under the optimal conditons.,At the same time,thirteen quality indicators（total acid,total sugar,total ester,vc,colour,total polyphenols,total flavonoids,anthocyanins,and antioxidant capacity）of two different vinegar were measured and compared.The optimal conditions for acetic acid fermentation of purple sweet potato were fermentation time 11 days,alcohol content of7.35%,and liquid volume of 28%.Under these conditions,the total acid content is6.92 g/100g.Compared with purple sweet potato vinegar,except that total sugar and vc content was lower than purple sweet potato pigment vinegar,total acid,total esters,total polyphenols,total flavonoids,anthocyanin content,and antioxidant capacity of it were higher it and had significant differences（p<0.05）.Comparing the loss of active ingredients with purple potato raw materials,the total polyphenols,total flavonoids,and anthocyanin content in purple potato vinegar lost 75.59,63.63,and 72.75%,respectively.The innovative fermentation process could reduce the loss rate by 10.34,15.61 and 42.93%,respectively.In general,the new fermentation process was propitious to the preservation of active ingredients in purple sweet potato.（5）The SDE-GC-MS technology were performed to analyze the two different purple sweet potato vinegar concentrates.114 volatile aroma components were detected,in which,esters was most,followed by acids and alcohols.There are 41 kinds of common compounds were determined in 2 kinds of vinegar,esters,acids,alcohols and aldehydes and ketones are the main types of compounds,and some components which had relatively higher contents including diethyl succinate,phenethyl acetate,ethyl palmitate,N-butyric acid,2-methylbutanoic acid,acetic acid,n-decanol,phenethyl alcohol,furfural,2-octanone and softwood ketone.There are 19 kinds of specific aroma components in purple sweet potato vinegar,including 3 acids:2-ethylbutanoic acid,capric acid,Linoleic acid;6 esters:ethyl propionate,ethyl3-hydroxybutyrate,isoamyl lactate,phenethyl isothiocyanate,ethyl undecanoate,isoamyl nonanoate;alcohols 2 species:furfuryl alcohol and cetyl alcohol;3 phenols:guaiacol,p-vinyl guaiacol and eugenol and 5 aldehydes and ketones:3-methyl-2-hexanone,4-methyl cyclohexanone,phenylacetaldehyde,rice aldehyde,and damascenone,and 14 kinds in purple sweet potato pigment,including 1 acid:octanoic acid;8 esters:cyclopentadecyllactone,isoamyl acetate,decyl propionate,dodecenyl acetate,ethyl stearate,dodecyl Isoamyl,methyl formate,pentyl formate;3alcohols:tert-butanol,1-undecyl alcohol,and neroli tertiary alcohol;2 aldehydes and ketones:1-phenyl-1,2-propanedione,cyclopentadecanone.The quantity of volatile components identified in the two types of purple sweet potato vinegar was not much different,but there was large differences in types.There were more aldehydes,ketones and phenols in purple sweet potato vinegar,while purple sweet potato pigment vinegar contained more alcohols and alkanes.Thus it can be seen that the extraction process of anthocyanins from purple potato could cause the loss of aldehydes,ketones and phenols which contributed to vinegar aroma. |
