Effects Of Mild Heat Combined With High-voltage Pulsed Electric Field Treatment On The Quality Of Frozen Concentrated Bayberry Juic

Bayberry is the specialty fruit in southern China,which has a long history of cultivation.Fujian is one of the biggest bayberry industrial province.Bayberry not only has unique flavor,sweet and sour taste,but also has antibacterial,anti-constipation and promote appetite and other effects.It has been popular to consumers for its high nutritional and economic value.Dongkui bayberry has the biggest shape and weight among all baberries.It is the biggest baberry at home and abroad.It is a good raw material of fruit juice processing for the high moisture content and juice rate.PEF is a new non-thermal processing technology.It can maximum to maintain the color,flavor and nutritional components of food after killed the microorganisms.In this paper,the freeze concentrated bayberry juice was prepared from dongkui bayberry as raw material by freeze-enrichment technology.First,the lethal and sublethal phenomenons of Escherichia coli and the best lethal process for total colony count were studied after Wild Heat comined with PEF treatment(MH-PEF).Then,raw freeze-concentrated bayberry juice,MH-PEF treatment and pasteurization treatment bayberry juice were stored at different temperatures.The comparison of microbial indexes and physical and chemical properties of the three kinds of bayberry juice were determined.Finally,the effects of the antibacterial and antioxidant capacities of the three kinds of bayberry juice were measured.At first,the lethal and sublethal phenomenons of Escherichia coli in freeze concentrated bayberry juice were studied by different electric field strengths of PEF(2 kV/cm,4 kV/cm,6 kV/cm,8 kV/cm,10 kV/cm),different treatment times(20 μs,40 μs,60 μs,80 μs,100 μs)and inlet temperatures of PEF(35℃,40℃,45℃,50℃,55℃).The results showed that the lethal logarithm values increased with the increase of electric field strengths and treatment temperatures.But the logarithm values of sub-lethal were opposite.And the lethal and sub-lethal logarithm values were not affected by the treatment times.Secondly,the lethal effect of total number of colonies in freeze-concentrated bayberry juice was studied by different electric field strengths of PEF(2 kV/cm,4 kV/cm,6 kV/cm,8 kV/cm,10 kV/cm),different treatment times(20 μs,40 μs,60 μs,80 μs,100 μs)and inlet temperatures of PEF(35℃,40℃,45℃,50℃,55℃).There was a good mathematical relationship between the treatment conditions of PEF and the lethal logarithm values of the total number of colonies of bayberry juice.The logarithm values of the total number of colonies of bayberry juice increased significantly with the increase of electric field strengths and treatment temperatures.But it was not affected by the treatment times.The optimal processing parameters of PEF were as follows:electric field strength was 10 kV/cm,the inlet temperature of PEF was 45℃,treatment time was 80 μs,and the lethal logarithm value was 2.15.Thirdly,the raw freeze concentrated bayberry juice,MH-PEF treatment and pasteurization treatment bayberry juices were stored at 4℃,8℃ and-18℃ for 60 days.The comparation of microbial indicators and important physical and chemical properties were determined every 6 days.The results were described that MH-PEF treatment had better bactericidal effect and storage performance than pasteurization treatment during storage.The pH,°Brix and electrical conductivity were not affected by the different temperatures and treatments.The anthocyanin and phenolic substances had the lowest loss rate and the color was closer to the raw freeze concentrated bayberry juice by MH-PEF treatment.And the best temperature was stored at-18℃.Finally,the antibacterial and antioxidation capacities of freeze concentrated bayberry juice,MH-PEF treatment and pasteurized treatment bayberry juices were studied.The results showed no significant inhibitory effect on S.Aureus in the range of experimental concentration.But it had obvious inhibitory effect on Listeria monocytogenes,Escherichia coli,Purple bacillus and Salmonella.Furthermore,the inhibitory effect of three kinds of bayberry juice on Listeria monocytogenes reached 12 mm,14 mm and 13 mm,respectively.The antibacterial effect by MH-PEF treatment was better than by the other two treatments.Three kinds of bayberry juice were found to have the strongest inhibitory effect on Purple bacillus by the minimum inhibitory concentration test.Therefore,the three kinds of bayberry juice had obvious inhibitory effect on Listeria monocytogenes and Purple bacillus.There was no significant difference in DPPH free radical scavenging ability between MH-PEF treatment and pasteurized treatment after the study of antioxidant capacity.While the scavenged superoxide anion free radical,hydroxyl free radical scavenging ability and SOD activity by MH-PEF treatment was higher than the raw bayberry juice and pasteurized treatment.The results showed that MH-PEF treatment could maintain the antimicrobial and antioxidant capacity of bayberry juice better than the raw bayberry juice.It showed that MH-PEF technology is an ideal non-thermal processing technology,which can be applied and popularized in practical processing.