Study On The Changes Of Flavor And Quality In Hami Melon Juice By Ultra-high Pressure Technology

This study was adopted the Ultra-high Pressure Technology,and the fresh hami melon was used as the material to study the changes of the reduced Vc,TSS,color, turbid, browning degree,the particle size in hami melon juice before and after treatment of UHP and at during the storage time;And the sugars and organic acids content,the fatty acid, aroma compounds in the hami juice were determined by HPLC,GC and SPME/GC/MS respectively,and found the change regular;Meanwhile,the total amounts and mold and yeast counts and the key enzymes LOX activity in the Hami melon juice were studied before and after UHP treatment and storage at 4℃;In this study with the heat treatment and pH value synergistic UHP processing as contrast.To find out a more appropriate high pressure treatment experimental parameters of Hami melon juice treatment, providing the high pressure non-thermal sterilization technology that is still in the initial phase for a theoretical and experimental basis. The main conclusions are as follows:(1) The reduced Vc in melon juice has little lose by high pressure, its save rate is still up to 84.8% when the pressure reached 500Mpa. at normal temperature. High pressure treatment improved the juice color,L was increased to 0.65, the browning reduced;the particle size increased to 132.4μm,reduced to 52.24μm after heat treated;and turbidity. Increased, to147.3NTU and the stability increased to 6.4%,;the pH and TSS have no obviously change.The low pH had evident effect on part index:The reduced Vc was kept above 91%;The turbidity. Increased obviously above 50%;the stability reduced and L disincreased to 0.6;the particle size was deviated smaller.The quality of the treated samples throughout the storage period has significant improved after treated by the UHP and the UHP combined pH value,and extended the storage period of melon juice.(2) Organic acids have no significant change with the different pH value of sample; the tartaric acid content increased after high pressure treatment to 0.8mg/mL;The Vc reduced to 0.21mg/mL;sucrose concentration Sucrose increased to 33.533mg/mL and Fructose reduced to 20.4% at 300Mpa,the glucose has no significantly chang. when pH value of Melon juice changes (P<0.05); The major fatty acids in melon juice were not significantly changed both High pressure and High pressure combined pH value treated (P>0.05);The organic acids and soluble sugar content in melon juice were more stable throughout the storage period after the high pressure and high pressure combined pH value treatment.(3) Hami melon juice was a pseudoplastic fluid.The Pressure and temperature,of high pressure processing which were the main factors affect the rheological properties and pectin content of Hami melon juice and the K increased to 31% and 52.9%,its flow characteristics of consistency coefficient,viscosity and pectin were change most significant as 0.0253mpa.s",3.22mpa.s与0.172μg/g respectively when pH= 3.The viscosity gradually increased,flow behavior index decreases consistency increased,Pectin content decreased in melon juice with time of storage conditions at 4℃.However, the degree of change the index above of melon juice decreased significantly after high pressure treatment.The present study found that the viscosity value size of melon juice may be closely related with pectin.(4) The LOX activity and microbial residue remaining in Hami melon juice decreased after high pressure and heat and adjust the pH value treatment.LOX was most difficult to be inactivated at 30℃-35℃,When the temperature reaches to 55℃, the residual activity reduced to 0.56 under the 400Mpa, 10min conditions;LOX activity decreased more significant under the heat treated,it reduced.to 0.296 under the 85℃,10min condition.Compared to the pure UHP and heat treatment,the UHP combined pH value treatment has more effective function on LOX passivation and microbial killing in the melon juice.The melon juice can more long-term preservation after high pressure and temperature treatment.The main volatile components in Hami melon juice as aldehydes were 61.7%-28.61%,esters were 6.87%-16.3%,alcohols were 35.09%-2.77% and ketones were 1.74%-0.13%.The main esters in melon juice as acetic acid esters, propionate, butyrate, adipic acid esters has little effect by high pressure treatment, and loss more severe after heat treatment;The 2,6-Nonadienal, (E,Z)-and 2-Nonenal, (E)-changed particularly significant by heat treatment, the 6-Nonenal, (Z)-increased dramatically after heat treatment;The total alcohol content showed a significant increase in Hami melon juice after treated,6-Nonenol,(Z)-and (E,Z)-3,6-Nonadienol is particularly affected by the treatment conditions.Changes of Hami melon juice aroma components as aldehydes, esters and ketones may be related to the effect on the microbial and LOX activity in the melon juice by the treatment condition.(5) Integrated all the experimental results can be found, melon juice can achieve better sterilization, and keep its quality less affected.Ultra High when the Pressure was 300Mpa-400Mpa, temperature was 45℃,the treatment time was 10min, combined the conditions as pH=5.