Coupled Effects Of CO₂ And High Hydrostatic Pressure On Enzyme Inactivation And Quality Of Tomato Juice

High hydrostatic pressure(HHP)and dense phase carbon dioxide(DPCD)are two new types of non-thermal food processing technologies.They are mainly used for sterilizing,enzymes inactivation and improving quality in juice.HHP is highly efficient,instant,and uniform,and can preserve the original quality of juice to the greatest extent;however,it has poor passivation effect on some enzymes which cause food quality degradation,and even activates specific enzymes(for example,pectin methylesterase,PME);In addition,HHP(100-1000 MPa)requires so high equipment that equipment investments must increase.DPCD has better sterilization and passivation effects with lower treatment pressure(10-50 MPa);nonetheless,it takes a long time and the treated product needs to be aseptically packed again;the compressed gas not only has high energy consumption,but also produces a lot of heat,which is inferior to HHP in retaining the original ecological quality of food.In order to combine the advantages of HHP and DPCD,this work proposes the use of CO2 synergistic HHP(HHP+CO2),which can improve sterilization and passivation,reduce processing pressure,shorten processing time,and thus reduce food processing cost.It provides a theoretical basis and application reference for the application of HHP+CO2 in juice processing.The specific research content and results are as follows:(1)The activity of PME and polygalacturonase(PG)and the structure and properties of WSP(water soluble pectin)were studied by HHP+CO2 compared with HHP.The effect of HHP+CO2 treatment on the inactivation of PME and PG was significantly higher than that of HHP treatment(P<0.05).The changes of pectin content and esterification degree were closely related to the activity of PME and PG,but there was no significant change in WSP molecular mass distribution and infrared spectrum.(2)Effect of HHP+CO2 on the quality of tomato juice.HHP and HHP+CO2 had no significant effect on the pH value,total acid content and soluble solid content of tomato juice(P>0.05).Both the L and a value of the color parameter slightly increased,while the b value remained unchanged,and the total color difference AE was less than 2.HHP treatment increases the viscosity of tomato juice,and the addition of CO2 leads to a further increase in the viscosity.Vc and lycopene retention rate were both more than 90%.(3)The relationship between PME activity and its structure were studied by HHP+CO2.The secondary structure of PME,a-helix,?-sheet,p-turn and random coil,did not show apparent changes,and there was no relationship between its activity and secondary structure.However,the activity of PME is correlated with UV absorption value at 276 nm and thiol content.The addition of CO2 makes the densification of PME stronger,resulting in its decreased activity.(4)The relationship between PG activity and its structure were studied by HHP+CO2.PG activity was negatively correlated with ?-sheet content treated with HHP yet positively with HHP+CO2.but it was not a simple linear correlation.The UV spectra and sulfhydryl content analysis of the PG showed that the spatial conformation of the PG molecule indeed changed.The addition of CO2 resulted in an increase in UV absorption spectrum and thiol content of the PG.suggesting that the addition of CO2 makes this disruption more dramatic.