| Concentrated fruit juices are processed by processing fresh fruit,and removing part of the water in the juice.Finally a last product is obtained in which the moisture content is generally not less than 30%.The concentrated juice preserves the minerals,dietary fiber and active ingredients in fresh fruits,and has high nutritional value and healthcare functions,such as maintaining acid-base balance in the body,preventing anemia and cardiovascular disease,and improving immunity.So the concentrated juice has great potential to develop.In this study,concentrated juices that are commonly found on the market were selected as materials.The pigment components of 7 kinds of concentrated juices(grape?blueberry?strawberry?apple?orange?mango?white grape)and the changes of pigment components,color,and antioxidant capacity in concentrated juices during storage were investigated.The results were showed as following:(1)The soluble solids,pH value and color value parameters of the 7 concentrated juices were analyzed with the ranges of 54.8-72.0%of soluble solid,2.23-3.96 of pH,20.03-32.37 of L*,-1.70-4.43 of a*,4.43-19.07 of b*.The total phenolic content of the seven concentrated juices was measured by the Folin-Ciocalteu method with the range from 1.86 to 6.37 mg/g and sequence ranked as:grape>blueberry>orange>strawberry>mango>white grape>apple.Among the 7 kinds of concentrated juices,total flavonoids and total anthocyanins were only detected in grape and blueberry concentrated juices with 1.44 and 2.55 mg/g of the total flavonoid content,137.43 and 64.01 mg/100 mL of total anthocyanin content,respectively.The polyphenols and anthocyanins of the 7 concentrated juices were analyzed by HPLC.8 kinds of polyphenols were identified in the 7 concentrated juices.The grape concentrated juice contains gallic acid,3,4-dihydroxyphenylacetic acid,catechin,and propyl gallate.Blueberries concentrated juice contains 3,4-dihydroxyphenylacetic acid,catechin,epicatechin,syringic acid,and quercetin.Orange concentrated juice contains 4-hydroxyphenylacetic acid and quercetin.Mango concentrated juice contains gallic acid,3,4-hydroxyphenylacetic acid,catechin,4-hydroxyphenylacetic acid,epicatechin,and quercetin.White grapes contain gallic acid,catechins,and epicatechins.No peaks corresponding to these eight polyphenols were found in apple and strawberry concentrated juice.Among the identified polyphenols,catechin is the highest and the highest content of 1305.16?g/g was found in blueberry concentrated juice;and syringic acid,propyl gallate were only found in blueberry concentrated juice and in grape juice concentrate with the content of 1.97?g/g,7.82 ?g/g,respectively.Three kinds of anthocyanins i.e.,delphinium,cyanidin,and malvidin were identified in the concentrated juice of grape and blueberry by HPLC analysis.Delphinium,cyanidin and malvidin accounted for 8,10%,4.24%and 69.69%in the grape juice concentrate,respectively.And those in the blueberry juice concentrate were 18.32%,15.64%,42.62%,respectively.Calculated by external standard method,the content of delphinidin in these two kinds of concentrated juices was 2.93 and 1.24 mg/100g respectively,and the content of cyanidin was 1.05 and 0.80 mg/100g,respectively.The content of malvidin was 49.37 and 6.51 mg/100g,respectively.(2)7 kinds of concentrated juices were stored under-20?,4?,25?,and(25?+ light)conditions for 50 days.With the increasement of time,the color parameters of different concentrated juices changed little at-20 and 4? where the AE*was less than 2.Except the L*,the color parameters of concentrated juices stored at 25? and(25?+ light)were significantly changed(P<0.05).It is characterized by red reduction of grape,blueberry,strawberry,apple,orange and mango juice concentrate(a*);white grape juice concentrate red deepening(a*);grape,blueberry,orange juice yellow deepening(b*),strawberry,apple,mango,white grape juice concentrate blue deepening(b*).Under these two conditions,white grapes,oranges,apples,and mangoes had a ?E*greater than 2 after 50 days of storage.(3)The degradation of total phenols in the 7 concentrated juices at 25? and(25?+ light)was in accordance with the zero-order dynamic model.The half-life periods were 25.88-110.26 d at 25? and 24.52-98.86 d at 25?+light.The degradation of total anthocyanins in grape and blueberry juice concentrates at 4?,25? and 25?+ light was consistent with the first-order kinetic model.The half-life periods of total anthocyanins in grape and blueberry concentrates were 182.41 and 288.81 d at 4?;for 25.40,35.73 d at 25?;24.15,25.39 d at 25?+light;respectively.When the temperature increased,the degradation rate constant of pigments increased as well,the half-life decreased.The degradation rate of the pigments is greater under light conditions and the half-life is shorter.(4)In grape and blueberry juice concentrate,total phenol,total anthocyanin,the contents of delphinium,cyanidin and malvidin decreased significantly with time(P<0.05).The total phenolic concentration of strawberry,apple,orange,mango and white grape juice concentrate decreased significantly with time(P<0.05).After storage for 50 days under different conditions,the content of those discussed above was ranked as-20?>-4?>25?>25?+light.Correlation analysis between total phenol,total anthocyanin,delphinium,cyanidin,malvidin contents and color value parameters of concentrated juice under Different storage conditions showed a strong correlation at 25? and 25?+light,Degradation of anthocyanins leads to a decrease in a*value and an increase in b*value,while the degradation of polyphenols has different effects on the a*and b*values of different concentrated juices.Through multivariate regression analysis,it was found that the fitted equations of concentrated polyphenols,total anthocyanin content and color value parameters(R>0.9)stored at 25 ? and 25 ?+light were better than-20 and 4 ?.(5)By measuring the DPPH,ABTS and ORAC antioxidant capacity of the seven concentrated juices,the DPPH radical scavenging capacity value ranged from 0.56 to 2.90 mg GAE/g,and ABTS antioxidant activity value ranged from 10.59 to 51.09?mol TE/g.The ORAC value ranged from 168.79-458.26 ?mol TE/g.The order of DPPH and ABTS antioxidant capacity ranked as:grape>blueberry>orange>strawberry>mango>white grape>apple.The ORAC antioxidant capacity ranked as:blueberry>grape>strawberry>orange>white grape>mango>apple.According to the comprehensive evaluation method,the antioxidant capacity of concentrated juices ranked as follows:grape>strawberry>blueberry>orange>white grape>mango>apple.Correlation analysis showed that there was a significant positive correlation between the content of total polyphenols,total anthocyanins,delphinium,cyanidin,malvidin in the concentrated juice under various storage conditions(P<0.05).In grape and blueberry juice concentrates,total anthocyanins,total polyphenols,and malvidin contribute significantly to the three antioxidant capacities.Under the storage conditions of 50 d,the three antioxidant capacities showed a decreasing trend with time,and the retention rates of the three antioxidants at-20? and 4 ? were higher than those at 25? and 25?+light.After storage for 50 days,the retention rates of the three antioxidants of strawberry,apple,orange,mango and white grape juice concentrate were all below 50%,so storage should be avoided for more than 50 days at temperatures above 25?.The highest retention rate was stored at-20?.The DPPH antioxidant ability retention rates of the 7 concentrated juices ranged from 75.00 to 97.41%;the ABTS antioxidant ability retention rate ranged from 83.87 to 95.35%;and the ORAC antioxidant ability retention rate ranged from 58.27 to 81.63%. |
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