Mild Heat Combined With Pulsed Electric Field Technology And Its Application On Forzen Concentrated Watermelon Juice

During storage at-18℃,due to the presence of osmophilic yeast in the frozen concentrated watermelon juice,it will produce large amounts of gas leading to the deterioration of the watermelon juice.Therefore,the method of bacterial isolation and identification of osmophilic yeast in the frozen concentrated watermelon juice,and the use of reasonable sterilization measures to control the frozen concentrated watermelon juice and long-term storage are essential.In this paper,the homology of the 16S rRNA sequence was analyzed by the Bergey’s Bacteria Identification Manual,and W-1 was identified as Pichia anomala by qualitative identification and ITS sequence comparison of the resistant yeast strain.Pulsed electric field is one of the emerging non-thermal technologies.It has the advantages of short processing time,small temperature rise,good sterilization effect and low energy consumption,through which food can maintain original quality,color and nutrients to the largest extent.But it also has its shortcomings,the enzyme activity of PEF is poor.The current domestic and international laboratory design of the pulsed electric field processing chamber is too small.If increasing the diameter,it will weaken its sterilization effect,which will limit the flow of liquid food and be difficult to achieve industrialization..In this paper,the material immersed in the water bath through the stainless steel tube quickly preheated to 40℃,the warm-up time of about 24s;then went through the PEF with 4 continuous processing rooms,which would rise temperature by 15℃.The experimental results showed that the material preheating temperature T was 40℃ and t was 24s.For treatment chamber,the diameter was 10mm,electrode plate distance was 1cm,electric field strength E was 12kV,flow rate was 200mL/min,pulsed electric field treatment time was 200us,the pulse width of 3us,f was 300Hz.The results showed that Mild heat with PEF could not only effectively inactivate the enzyme activity of watermelon juice,but also solve the shortcomings of processing chamber size and sterilization effect for large flow,which made the heat-sensitive fruit juice industrialization..The mathematical relationship between the electric field strength(E)and the pulse time(t)and the survival rate of microbes was established by the function fitting.The results showed the resistant ability of osmophilic yeast and background bacteria in the frozen watermelon juice.The experimental data showed that the resistance of osmophilic yeast EC was 0.2143kV/cm<background bacteria EC was 0.2351kV/cm;and the size of the regression coefficient was higher than that of osmophilic yeast k was 1.6339>background bacteria k was 1.5378.This indicated that the resistant ability of background bacteria was higher than that of osmophilic yeast by mild heat combine with PEF.And compared with the previous study of the effect of PEF on orange juice showed that the frozen concentrated watermelon juice sterilization critical field strength value was lower than that of orange juice,yeast was more sensitive to mild heat combine with PEF in frozen concentration watermelon Juice.The determination of total sugar,pH,soluble solids,vitamin C,color value L*,a*,b*,physical and chemical indexes of frozen concentrated watermelon juice during the storage period were studied.The determination of POD,PME and PPO activity changes in frozen concentrated watermelon juice were studied and compared with the untreated original sample.The result showed that pH value,soluble solids and total sugar content of the frozen concentrated watermelon juice decreased significantly with storage period.While Vc content showed a significant decrease trend.The L*、b*values changed slightly,the a*value showed a downward trend.Mild heat combine with PEF could effectively inhibit the activity of POD,PPO and PEM in frozen concentrated watermelon juice.