Ultra High-pressure (UHP) Treatment Of Dangshan Pear Juices And Enhancement Methods

The effect of ultra-high pressure processing on the microflora, mold and yeast, E.Coli, polyphenoloxidase (PPO) and peroxidase (POD) in Chinese Dangshan pear juices (pH5) under the pressure of 0.1--500MPa and the temperature of 19—60℃) was investigated. The effect of ultra-high pressure processing on Bacillus subtilis AS 1.140 and horseradish peroxidase (HRP) was investigated, and all experiments were designed and optimized with Box-Behnken concept of RSM. The effect of ultra high pressure processing combined with mild temperature on the microorganisms and the enzymes and combined with Nisin on the microorganisms was investigated. The effect of ultra-high pressure processing on the microstructure of B. subtilis AS 1.140 was investigated, and the inactivation mechanism of its vegetative form and spore was discussed. The horseradish peroxidase (HRP) activity and its secondary structure before and after decompression were studied by the measurement of circular dichroic (CD) spectra.1 )Secondary bonds of maintaining the conformation of enzymes are weakened by UHP. Microbial cell walls and membranes are destroyed and their intracellular physiological functions become to dysfunction and lose. So enzyme and microorganism are inactivated by UHP, and the preservation processing to pear juice can put into practice by it.2) The effect of UHP to fruit juice is influenced not only by intrinsic factors of processing goals such as the types of microorganism and enzyme, its chemical compositions, pH and so on; also by extrinsic factors such as pressure, dwell time, temperature, additives and so on. If synergizing effect between the factors is exerted, the pressure of effectively UHP to fruit juice will be reduced.3) A study was made of the effect of ultra high pressure (0.1—500MPa) / mild temperature (19—58℃) treatments on the microflora, mold and yeast and E.Coli in Chinese Dangshan pear juices (pH5) with the dwell time 10min. Results showed that the residual microflora was 50 cfu/mL under 19 ℃ (environmental temperature), dwell time 10min. and 500MPa; the residual molds and yeasts were 10cfu/mL under 400MPa; however, the E.Coli was completely sterilized under 19 ℃, dwell time 10min. and 400MPa. On the other hand, results show that the residual microflora was 70cfu/mL under 450MPa, dwell time 10min. and ≥29℃, and the residual molds and yeasts were completely sterilized under the same conditions; the E.Coli were completely sterilized under 450MPa, dwell time lOmin. and 19℃.4) Ultra high pressure processing to B. subtilis was investigated, and all experiments were designed and optimized with Box-Behnken concept of RSM. Results showed that: ? The pressure, temperature and dwelling time are believed to be the significant factors for ultra high pressure sterilizing to B. subtilis, and their significant order is pressure > temperature > dwelling time; (D The regression equation (model) for UHPP to B. subtilis was established, and also verified with additive samples experiments; d) The range of variable factors to sterilize B. subtilis Of 6 log cycles is as pressure (343.8MPa~ 475.8MPa), temperature (27.5°C ~57.4°C), pressure holding time (14.1min~ 19.7min), and the process parameter of 10 groups were optimized .5) Ultra high pressure processing(UHPP) combined with Nisin to B. subtilis AS 1.140 was investigated, and all experiments were designed and optimized with Pentagonal concept of RSM. Results showed that: the pressure and Nisin concentration are believed to be the significant factors for ultra high pressure sterilizing to B. subtilis, and their significant order is pressure > Nisin concentration; The regression equation (model) for UHPP to B. subtilis was established, and also verified to be good for prediction in the range of experimental conditions; Nisin can be more effective to synergize sterilization of UHPP to B. subtilis than temperature; The increase of sterilizing rate(the change of log-circles) is higher in Nisin concentration of 0.00~0.05mg/mL than in that of 0.50~0.15mg/mL.6) The effect of ultra-high pressure processing on the microstructure of B. subtilis AS 1.140 was investigated, and the inactivation mechanism of its vegetative form and spore was discussed. Before/after UHPP (500MPaX601C X 20min), their microstructures were observed by a transmission electron microscope, and were analyzed and compared with. Results showed the vegetative cell wall of B. subtilis shrinked and breached, cytoplasm leaked out, the layer structure of cytoplasm disappeared, and the large electron transmission area appeared after compression; the outer coat of its spore breached, the layer structure of spores inclusion disordered, its inclusion leaked out, and the partial electron transmission area appeared after compression.7) A study was made of the effect of high hydrostatic pressure treatment (0.1~500MPa) combined with mild heat treatment (20~60'C) under dwell time of lOmin on polyphenoloxidase (PPO) and peroxidase (POD) activity of Chinese Dangshan pear juice with different pH values (3.0~7.0). Results showed that both enzymes were activated when the high pressure treatment on the pear juice was carried out under the temperature 50V, the dwell time lOmin, the pH 5 and the pressure between 200~300 MPa for PPO and between 150—250 MPa for POD,and their activities were the maximal level, and then they decreased along with increasing of pressure. At 500MPa, PPO and POD activity decreased respectively to 75.3% and 75%. The temperature of above 40°C could synergized high pressure to inactivate PPO and POD, and their activities decreased respectively to 72.3% and 77.0% under the treatment of 400MPaX60°C X lOmin. The both enzymes residual activity was the maximal level and the most pressure-resistant under pH6.8) Effect of three main factors(pressure, temperature and dwell time) in UHP treatment on HRP activity was investigated, and all experiments were designed and optimized with Box-Behnken concept of RSM. Results showed that: (D The pressure, temperature and dwelling time are believed to be significant factors for UHP treatment of inactivating HRP, and their significant level is pressure > temperature; Dwelling time is not significant factor in the range oflO~20min. ? The regression equation (model) for UHP treatment to HRP was established, and also could predict HRP residual activity in this experimental conditions. (3) The range of independent variable factors to inactivated 80% HRP activity of the normal one is as pressure of 410.3MPa~499.9MPa and temperature of 27.5°C~ 57.5"C and dwell time of 14.1min~ 19.7min, and the treatment parameters of 10 groups were optimized.9) A study was carried out about the effect of high hydrostatic pressure treatment (0.1~500 MPa) under temperature (20~60°C) and dwell time lOmin and pH7.0 of the enzymatic solution on horseradish peroxidase (HRP) activity and its secondary structure, which was studied by the measurement of circular dichroic(CD) spectra. Results showed that: ? There is tightly correlation between HRP activity and the content of p-sheet conformation. The percentage rate content of p-sheet conformation decreases after compression, and HRP activity descends. Both descend rapidly after compression synergizing with mild temperature.?The effect of compression is significant on HRP activity under the treatment temperature 40"C and dwell time lOmin and pH7.0; HRP activity increases abnormally in treatment of about lOOMPa, and decreases slowly above 400MPa. ? HRP activity decreases slowly under temperature of less than 40 "C at the pressure of 500MPa and dwell time of lOmin and pH7.0; and decreases rapidly with increase of temperature above 40 °C .