Study On The Stability Of Anthocyanins And The Changes Of Antioxidant Activity In Red Raspberry And Mulberry Juice During Storage

Compositions of the major anthocyanins and flavonoids in red raspberry and mulberry were identified by ultraviolet-visible spectrophotometer and high-performance liquid chromatography with electrospray ionization-mass spectrometry?HPLC-ESI-MS?.We compared and analyzed the effect of three different sterilization methods,including pasteurization,boiling sterilization and microwave sterilization,on the anthocyanins,major flavonoids and other physicochemical properties of red raspberry and mulberry juice.Moreover,fluctuations of active constituent and antioxidant activities as well as their correlations during storage were also studied.Eventually,the degradation pathways of anthocyanins in the juice system were explored.The results were shown as follows:1.The structural identification of main anthocyanins and flavonoids in red raspberry and mulberry fruitThe main anthocyanins of red raspberry are cyanidin-3-sophoroside and cyanidin-3-glucoside,whereas the main flavonoids are kaempferol glycosides.On the other hand,the main anthocyanins of mulberry are cyanidin-3-glucoside and cyanidin-3-rutinoside,while the main flavonoids are quercetin and kaempferol glycosides.2.The influence of different sterilization treatments on the quality of the red raspberry and mulberry juicesThe parameters of 3 sterilization methods namely pasteurization?80^°C,20 min?,boiling sterilization?100^°C,5 min?,microwave sterilization?7 w/mL,2 min?were determined based on the germicidal efficacy.Compared with the untreated juice,three sterilization methods reduced the total anthocyanins,single anthocyanins,and total phenols contents of red raspberry and mulberry juice in different levels.Although,the microwave sterilization treatment showed the feeblest effects;however,no significance?p>0.05?in the levels of H₂O₂of the two treated juices was observed among different sterilization methods.Taken together,microwave sterilization treatment could efficiency reserve the nutritional quality of red raspberry and mulberry juices.3.Changes in quality and antioxidant activities of red raspberry and mulberry juice as well as their correlations during storage?1?The contents of active components,such as total anthocyanins,single anthocyanins,total phenol,flavonoids and Vc,and the quality parameters including absorbance,browning degree,and transmittance of red raspberry and mulberry juices were decreased in different levels during storage of 30 d at 37°C.?2?The color changes of red raspberry and mulberry juices were mainly caused by anthocyanins content changes during storage.?3?The fluctuations in the anthocyanins content had a more significant effect on the antioxidant capacity of juice than that of flavonoids,total phenols,and Vc.In addition,the degradations of active compounds did not necessarily reduce the antioxidant capacity of the juice.4.Study on the kinetic parameters and the degradation mechanism of anthocyanins in red raspberry and mulberry juice during storageThe degradation kinetics of anthocyanins in the model system and real juice system matched with the first-order kinetic model.The half-life of anthocyanins in the model system was greater than that of the juice system,indicating that the coexisting components in the juice could accelerate the anthocyanins degradation.In addition,anthocyanins of both systems followed the same and similar degradation pathways.However,there are two degradation pathways are identified.The first one was summarized as:the cyanidin glycosides firstly were hydrolyzed to produce anthocyanins,subsequently to form a chalcone by opening the ring,and finally degraded to produce the protocatechuic acid.The second pathway was recognized as follow:the cyanidin glycosides were firstly formed the chalcone glycoside by opening ring,then de-glycosylated to produce a chalcone,and eventually to shape the degradation products like protocatechuic acid.