| Sweet potato taste sweet and has high nutritional value,and is recognized as one of the healthiest food.Sweet potato is rich in polysaccharide,mucous protein,v itamin C,?-carotene,folic acid,flavonoid,phenolic acid and other natural active ingr edients.It is helpful for hypolipidemic,hypoglycemic,anti-oxidation,anti-aging,anti-m utation and immune regulation.The fresh sweet potato juice were directly process ed with sweet potato only.No additives added which better kept the nutrients and flavors of sweet potato,thus it has a broad market prospects.This study can prov ide a new way for the deep processing of sweet potato and provide some theore tical basis for the development of fresh sweet potato juice.The most suitable varietie for fresh juice processing was selected through thest udy of the comprehensive quality of different sweet potato varieties.The technolo gical conditions of fresh sweet potato juice and sweet potato enzymatic juice we re optimized.At the same time,the nutrition and sensory of two sweet potato ju ices were compared and analyzed.The in-depth study of antioxidant capacity and the changes of quality indexes of sweet potato enzymatic juice duringstorage wer e investigated.The main conclusions were as follows:(1)The processing quality(juice yield)and nutritional quality(polysaccharide s,vitamin C and?-carotene)of different sweet potato varieties were significantly different(P<0.05).eight varieties of sweet potato were clustered into 4 categor ies by cluster analysis,and combined with the fuzzy comprehensive evaluation me thod,the final order of the sensory quality of fresh sweet potato juices as follo ws:Yushu 17>Hechuan>15-14-5JY>15-17-2JY>15-14-4Y>Shangshu 19>Yushu27>15-14-2H.In general,Yushu 17 was the most suitable varietie for fresh juic e processing,followed by Hechuan sweet potato.(2)The single-factor and orthogonal experiments were used to optimize the fr esh sweet potato juice processing,it was concluded that sweet potatoes were finel y crushed with screw extrusion and centrifuged at 5000 r/min for 20 min,the sup ernatants were inactivated at 90?for 40 s,and the tinplate cans were sterilized at 115?for 20 minutes after hot filling.The results of the heat preservation te st showed that the canned foods were required for commercial sterilization.(3)The parameters of fine crushing,inactivation and sterilizztion in sweet pota to enzymatic juice were consistent with that of the fresh sweet potato juice.Base d on the single-factor tests,the liquefaction and saccharification process conditions of sweet potato enzymatic juice were optimized by the method of DE value an d reducing sugar content.The regression model was R(DE)=14.99+0.65A+0.32B+0.75C+0.17AB+0.12AC-0.038BC-1.07A~2-1.00B~2-0.62C~2.The best liquefaction technic al parameters were the addition amount of?-amylase 0.33 mL/kg,hydrolysis temp erature 63?and hydrolysis time 3.0 h,the DE value in the final solution was 15.34%.While the regression model was R(reducing sugar)=18.90+0.66A+0.18B+0.32C+0.015AB+0.22AC+0.18BC-1.53A~2-1.30B~2-1.29C~2,was used to determined the b est saccharification technology:the addition amount of composite glucoamylase w as 0.40 mL/kg,saccharification temperature 61?,hydrolysis time 2.0 h,the reducin g sugar content in the final solution was 18.97%.(4)By analyzinging the quality indicators of fresh sweet potato juice and sweet potato enzymatic juice,the results showed that compared with fresh sweet potato juice,the transmittance of sweet potato enzymatic juice increased by 28.21%,the content of pectin decreased by 67.12%,the viscosity decreased by 39.12%and the content of flavonoids increased by 12.39%.The contents of vitamin C,?-carotene and total phenol were significantly lower than those of fresh sweet potato juice(P<0.05).There was a significant difference in the free amino acid content between two sweet potato juices(P<0.05).The content of total amino acid in sweet potato enzymatic juice was about23.20%lower than that of fresh sweet potato juice,of which the sweet taste amino acid increased by 24.28%,while the sour and bitter taste amino acids decreased by 34.89%and 36.46%.The sensory evaluation score is higher than that of fresh sweet potato juice.The comprehensive evaluation showed that the quality of sweet potato enzymatic juice was better than fresh sweet potato juice.(5)The survival test and biochemical indicator test of drosophila melanogaster were adopted to identify the antioxidant activity of sweet potato enzymatic juice.The results showed that comparing with the negative group,the average life span and maximum life span of drosophila melanogaster in the different dose groups were significantly increased(P<0.05 or P<0.01),exhibiting a dosage effect.The activities of SOD and T-AOC in the low,middle and high dose groups were significantly increased(P<0.05 or P<0.01)meanwhile the MDA content in the middle and high dose groups were decreased(P<0.05 or P<0.01).The high-dose group(0.20 mg/mL)extended average life span by 16.00%for male flies and 17.93%for females,the activity of SOD in drosophila melanogaster increased by about 35.04%~92.54%,and T-AOC activity increased by about 1.54~1.80 times,while the content of MDA decreased by about 31.20%~37.14%.(6)The results of the study on the quality changes of sweet potato enzymati c juice during storage(6 months)showed that:With the extension of storage time,the values of L*and a*in juice showed a general downtrend while the values of b*and?E showed a general uptrend,and the value of?E in juice at 25?was significantly higher than that at 4?(P<0.05).There was no significant diffe rence in the content of soluble solids in juice after storage at 4?and 25?(P>0.05),but the total sugar and reducing sugar contents were significantly different f rom those at 0 d storage(P<0.05).The preservation rates of vitamin C and?-ca rotene in juice after storage at 4?were 53.37%and 66.72%,which were signific antly higher than those at 25?(P<0.05).Under the two storage conditions,The c hanges of total phenolic content in juice were basically the same,that was,it rised first then declined slightly,while the changes of flavonoid content decreased slo wly.The contents of browning index and 5-HMF in juice after storage at 25?w ere increased by 0.61 and 15.67 times,which were significantly higher than those at 4?(P<0.05).Based on the results obtained from the comprehensive evaluati on:4?was the best storage condition to maintainthe nutritional quality of sweet potato enzymatic juice. |
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