Study On Effect Of Instantaneous High Pressure Treatment On Conformation Of Plyphenol Oxidase

The paper studied the effect of Instantaneous High Pressure(IHP)treatment on chemical quality of pear juice through Ascorbic acid,amino nitrogen,total sugar and total acid of four aspects.The results indicated that;Processed under pressures from 80MPa to 180MPa of 6 gradients for one time,Ascorbic acid loss percentage was 13.14% under 80MPa and 14.85% under 180MPa.Ascorbic acid loss percentage reduced unobvious; amino nitrogen content reduced slightly,from 24.25 mg/100mL under 0MPa to 23.41 mg/100mL under 180MPa; the content of total sugar and total acid remained invariable,maintaining about 8.0% and 0.079g/100mL separately. Processed respectively under the above pressures for three times,Ascorbic acid lost a lot after treating one time,with the most loss percentage of 20.41% under 160MPa, while Ascorbic acid loss percentage reduced slightly after treatment of twice and three times,with the most Ascorbic acid loss percentage of 29.01% under 140MPa; Amino nitrogen content assumed the even reducing tendency with treatment times increasing.It reduced most under 100MPa,from 21.63 mg/100mL to 17.47 mg/100mL; The content of total sugar had a slight reduction with treatment times increasing.It reduced the most under 100MPa,from 8.28% to 7.68%.The decrement was 0.072%;The content of total acid remained nearly invariable with treatment times increasing,maintaining about 0.09g/100mL.Characters of PPO from Zao Su pear were studied,including reaction kinetics using pyrocatechol as its substrate and effect of temperature,pH and substrate concentrations on activity of PPO.The results indicated that the absorptive wavelength of enzymatic reactive product was 416nm.When pyrocatechol as the substrate,the Vmax and Km were 0.289ΔA/min and 0.502mol/L respectively.The optimal reaction temperature of PPO was 48℃and the optimal pH value of PPO was 4.5.Treated under the pressures of 80MPa,100MPa,120MPa,140MPa,160MPa and 180MPa for one time respectively,the activity of PPO from pear juice increased with pressure increasing,from 110.36% under the pressure of 80MPa to 169.90% under the pressure of 180MPa.When treated under the pressures of 120MPa,140MPa and 160MPa for three times respectively,the activity of PPO from pear juice increased with treatment times increasing.After treatment under the pressures of 120MPa,140MPa and 160MPa for one time,the activity of PPO increased by 53.35%, 94.58% and 128.57% respectively,while the activity of PPO increased slowly when treated for 2 and 3 times.Treated under the.pressures of 120MPa,140MPa and 160MPa for one time at the materiel temperature of 25℃,35℃and 45℃respectively, the activity of PPO increased with the materiel temperature increasing.Effect of Instantaneous High Pressure treatment on the activity and conformational changes of Mushroom PPO was studied by means of UV spectrophotometer,far-UV circular dichroism,fluorescence emission spectra,UV absorption spectra and sulphydryl groups detection.The results indicated that, treated under the pressures of 90MPa,110MPa,130MPa and 150MPa one time respectively,the activity of Mushroom PPO increased for every sample.The highest relative activity of 110.74% was showed at the pressure of 110Mpa and the relative activity decreased to 104.13% at the pressure of 150MPa.The percentages ofα-helix decreased.Trp and Tyr residues in Mushroom PPO were more or less exposed to solvent.New free SH residues were created and,consequently,new S-S bondings were formed.Treated three times under the pressure of 150MPa,the relative activity of Mushroom PPO increased with more treatment times and the relative activity was 111.57% after treated three times.With treatment times increasing,the percentages ofα-helix had an obvious reduction and the percentages ofα-helix was 29.4% after treated three times.Trp and Tyr residues in Mushroom PPO were gradually exposed to solvent.New free SH residues were gradually created and,consequently,more new S-S bondings were formed.