Study Of Of Pulsed Electric Field Processing On Microbial Popution And Quality Characteristic Of Carrot Juice

Non-thermal food processing technology was an interesting topic in the field of food processing. Pulse electric field (PEF) was one of the mostly studied technologies in the field.The effect of PEF processing on microorganism was investigated in the paper.Introduced the theory of the thermal death time called F-value into Pulsed Electric Field (PEF),establishment of F-value theory of PEF whice took Escherichia coli, Saccharomyces cerevisiae as the target microorganism.A comparative analysis of PEF to thermal treatments concernin gquality characteristic,nutrient components, stored-stability and volatile aroma compounds of carrot juice were also conducted. The studied results were as follows:1.Effects of PEF intensity and treatment time and temperature on inactivation of microbe were investigated by analysis of Box-Benhnken model of Response surface methodology. Intensity and treatment time and temperature were significant factors to PEF inactivation of microbe with the order of intensity >treatment time > temperature. Ten group of PEF processing parameters were obtained to inactivate microbe lower than 2 lg in the study.2. Sterilizing effect of PEF treated to Escherichia coli and Saccharomycs increased as intensity and treamtment time increased.And the linear relation between sterilizing effect and treamtment time was significant.When intensity was 33.33kV/cm and treamtment time was 684μs,counts of Escherichia coli reduced 7.4 lg and Saccharomyces cerevisiae were not detected.3.The study referenced the theory of the thermal death time called F-value, established F-value theory of PEF which took Escherichia coli, Saccharomyces cerevisiae as the target microorganism, and the decimal reduction time (D) and the PEF resistance constant (Z) of microorganisms were obtained. The results showed that the D and Z value of Escherichia coli were lager than those of Saccharomycs which meaned Escherichia coli was more endurable than Saccharomyces cerevisiae to PEF treatment.Based LR=10^E-Er/Z,with 33.33 kV/cm as the referenced intensity, the death time of Escherichia coli, Saccharomyces cerevisiae were 726.35μs and 344.17μs respectively,which were longer than actual death time 696.19μs and 342.47μs.From food safety point of view,that the theory death time slightly larger than actual value was reasonable,so as to ensure the food safety in a greater degree.4.PEF processing didn't cause significant changes in pH,conductivity,0Brix,and L*.But a*decreased and b* increased. The viscosity of carrot juice didn't change when the intensity was 18.52 kV/cm while increased with PEF treatment of 33.33 kV/cm.And showed the property of cutting-diluted.The content of total sugar and carotenoid increased while the content of Vc decreased after PEF treatment. And the conten tof total sugar and carotenoid and Vc were 108.3%,119.8% and 92% respectively,compared to original,when intensity was 33.33 kV/cm amd treatment time was 680μs.The increased content of total sugar and carotenoid by PEF was probably caused by the combination of cell membrane rupture, loss of cytoplasm. The results of storage experiment showed PEF treatment could bring the carrot juice longer shelf life,especially synergistic with low temperature storage, which could bring a shelf life up to 40 days.At the same time,the color and turbidity decreased during the storage.5.Compared to thermal treatment,PEF processing can better maintain the volatile components of carrot juice.And PEF processing of carrot juice tasted better than the heat treatment.