Improving The Colour And Anthocyanin Stability Of Blueberry Juice By Blanching And Copigmentation

Blueberry belongs to the genus Vaccinium and family Ericaceae.Blueberry fruit contains abundant sugar,organic acids,vitamins,minerals and bioactive compounds,including anthocyanins,flavonoids and phenolic acids.In recent years,with the increase of production year by year,blueberry processing research has become a hot spot.Blueberry juice is increasingly promoted and consumed for its nutritional,health benefits and easily processing.Anthocyanins are the main polyphenols in blueberry juice and exhibit a very positive effect,including antioxidant capacity,antiinflammatory,anticarcinogenic properties and potent cardioprotective.However,anthocyanins are unstable and easily degraded because of many factors during processing and storage.Blanching pretreatment or intermolecular copigmentation not only could remarkably enhance the anthocyanins contents,but also improve the stability of blueberry juice.The rabbiteye blueberry cultivar ‘Baldwin' was as raw material,we studied the effects of different blanched pretreatment or copigmentation on the anthocyanins,color,total phenol and antioxidant capacity of blueberry juice.The findings are as follows:(1)We compareded the effects of boiled(95°C)or steamed pretreatment on the juice yields,total phenols,total anthocyanins and antioxidant capacity of blueberry juice and optimized the time parameters.The results showed that blanched pretreatment could significantly increased the content of anthocyanins and total phenols in blueberry juice,but the increase in juice yield was not significant.Steam-blanching for 3 min resulted in total phenols(1403.17mg/L)and total anthocyanins(579.51 mg/L)values were 1.53 times and 4.75 times as many as control,respectively.(2)UPLC-DAD-ESI/MS was used to identify anthocyanins from different blanched pretreatment blueberry juices.The results of the study showed there are eight,ten and eleven anthocyanin compounds were detected in the control,boiled(95°C,5 min)and steamed(3 min)pretreatment juice,respectively.Individual anthocyanin contents of the different blueberry juices(control,boiling and steaming pretreatments)were analyzed by UPLC system.We observed that peonidin glucoside(Pnd)was the major anthocyanin in all juices.Morever,the content of each individual anthocyanin were higher in the juice from the steamed berries than in the juice from boiled and control berries.The effects of different blanched pretreatments on the stability of blueberry juice were compared.The retention rate of anthocyanins in blueberry juice prepared by 3 min steam blanching was 1.54 times of that of the untreated group at 40°C for 10 days.The results also showed the blueberry juice produced via 3 min steam-blanching had better color stability and higher antioxidant capacity.(3)We compared the effects of tea polyphenols(TP),epigallocatechin gallate(EGCG),gallic acid(GA)and p-coumaric acid(PCA)on the stability of blueberry anthocyanins,and the addition of copigments GA presented a most significantly stabilized effect on blueberry anthocyanins.Further,we studied the effects of GA on anthocyanin and antioxidant capacity of blueberry juice storage at 40°C.At a molar anthocyanins/gallic acid ratio of 1:5,the anthocyanins(%,of initial),peonidin-3-glucoside,petunidin-3-galactoside,and malvidin-3-arabinoside contents of blueberry juice were higher than juice without copigment(49.40%,43.16%,49.45% and 46.47% respectively)after storage for 20 d.The DPPH and FRAP of blueberry juice at a molar anthocyanins/gallic acid ratio of 1:5 were 3.10 and 2.09 times that of control sample.(4)We also investigated the copigmentation effect of gallic acid on the stability of anthocyanins in blueberry juice during storage for 4°C and 25°C.Anthocyanins in blueberry juice are more stable,and copigments GA presented a most significantly stabilized effect on blueberry anthocyanins during 4°C storage.The anthocyanins(%,of initial)of blueberry juice with GA during storage for 4°C and 25°C were 68.32% and 14.72%.However,the anthocyanins(%,of initial)of control juice during storage for 4°C and 25 °C were 54.48% and 6.39%.