Improvement Of Comprehensive Quality In Cloudy Ponkan Juice Based On High Pressure Homogenization Technology

China is a great producer of Mandarin(Citrus reticulata),with a long cultivation history and traditional fresh eating habits.To a certain extent,developing Mandarin juice products can alleviate the urgent demand of the imbalance between supply and demand of citrus industry in China.The cloud of Mandarin juice was unstable,and it was easy to precipitate in layers during storage.Traditional stabilization process either lost the natural flavor and taste of fruit juice,or the stabilization effect was limited,so it was difficult to achieve the expected results.With the concept of food clean label(FCL)widely recognized,the application of physical processing technology to improve the juice cloud stability has great application prospects.Based on different homogenization pressures,high pressure homogenization(HPH)technology is used to meet the different requirements of stabilization and / or preservation technology in the process of fruit juice processing.It has unique advantages in improving the turbidity stability of fruit juice,reducing microbial load and maintaining nutritional quality.Based on the quality characteristics of Mandarin juice and the potential advantages of high-pressure homogenization technology,this study selected cloudy Ponkan juice as raw material to maintain its nutritional quality and improve its cloud stability at same time.Firstly,the mechanism of thermal inactivation of pectin methylesterase(PME)in cloudy Ponkan juice and change of relative cloud value in juice were studied.Then the physical sta bilization process of filtration combined with standard homogenization(SH)to improve the cloud stability of cloudy Ponkan juice was optimized.Based on response surface methodology(RSM),the potential of HPH technology applied to the sterilization of cloudy Ponkan juice,and to improve cloud stability and maintain the nutritional quality of cloudy Ponkan juice was studied.Finally,the physical stabilization technology was combined with pasteurization(TP)and high pressure processing(HPP),and the HPH sterilization technology was compared to clarify its effect on the quality stability of cloudy Ponkan juice during storage.The specific conclusions are as follows:1.Cloudy Ponkan juice are at least three kinds of PME isozymes,one of which is heat tolerance isozyme,the other is heat sensitive isozyme.Heat sensitive fraction of PME can be inactivated rapidly when the heating temperature is not lower than 70 ℃.71.7%of PME inactivation occurred in the temperature come up time(CUT),and the inactivation rate was 96.3% at 95 ℃ for 75 s.The cloud value of cloudy Ponkan juice was determined.It was found that the inactivation rate of PME had less relationship with the cloud stability of cloudy Ponkan juice under the traditional heating conditions.Prolonging CUT resulted in obvious stratification of cloudy Ponkan juice and enhanced granular sense of micro particle morphology.Increasing temperature and prolonging CUT were not conducive to the cloud retention of cloudy Ponkan juice,and the enzymatic reaction of PME was not the only factor leading to the stratification of cloudy Ponkan juice.2.The traditional filtration process is combined with SH.When the filtration process removed the large particles suspension of cloudy Ponkan juice,the results showed that the average particle size,viscosity,centrifugation sedimentation rate and PME activity of the juice all decreased,while the turbidity increased,which was beneficial to maintain the cloud stability of the juice.After 100 mesh,the color of juice became dark and leads low sensory quality.The content of sugar and organic acid had no significant effect on the filtration process.However,the content of Vc,free phenols and bound phenols decreased,the intensity of aroma decreased,resulting in the decrease of the overall flavor of the juice.SH treatment decreased the particle size,viscosity and centrifugation sedimentation rate of the juice,increased the cloud value,and had no significant effect on PME activity.After homogenization,the color of the juice became brighter,and the saturation increased,the content of sugar,organic acid and aroma intensity had no significant change,the content of Vc and bound phenol decreased,and the bound phenol was released into free phenol,which increased the content of some individual free phenol.Then,partial least squares(PLS)were used to study the correlation between filtration mesh(homogenization pressure)and the comprehensive quality in cloudy Ponkan juice.It was found that increasing filtration mesh was not conducive to the retention of color and flavor of cloudy Ponkan juice.Homogenization could improve the cloud stability of cloudy Ponkan juice,and had little effect on the nutritional quality of cloudy Ponkan juice.The results showed that the stabilization technology of cloudy Ponkan juice was as follows: 100 mesh filter and 20 MPa homogeneous pressure.3.Exploration of the effect of HPH sterilization on the comprehensive quality of cloudy Ponkan juice represented by microbial load,PME activity,Vc content and color saturation(C*),the effects of homogenization pressure,homogenization conditions and inlet temperature on the comprehensive score of HPH cloudy Ponkan juice were investigated by single factor experiment.On the basis of this optimization,the response surface optimization experiment was used to obtain the optimal process parameters as follows: homogenization pressure 150 MPa,homogenization times 3 times,inlet temperature 31 ℃,resulting in the total lethal rate of microorganisms was 2.92 lg CFU /m L,residual PME activity rate was 31.94%,Vc loss rate was 15.19%,and C* value increased by 3.74%.The results showed that the microorganisms load in cloudy Ponkan juice decreased to the national health standard,the activity of PME decreased significantly,the color of the juice improved,and the loss of Vc was relatively low,which indicated that HPH technology was suitable for the sterilization of cloudy Ponkan juice.4.The effects of physical stabilization technology combined with thermal pasteurization(SH-TP),high pressure processing(SH-HPP)and HPH sterilization on the storage quality of cloudy Ponkan juice were evaluated,the results showed that SH-TP,SH-HPP and HPH could improve the cloud stability of cloudy Ponkan juice and reduce the total bacterial count to the national health standard.The three processing methods had no significant effect on the content of sugar and organic acid in cloudy Ponkan juice.The effect of SH-TP treatment on Vc content of cloudy Ponkan juice was higher than that of SH-HPP and HPH.All the three processing methods could transform part of the bound phenols into free phenols.SH-TP treatment can cause serious degradation of polyphenols in fruit juice,SH-HPP has little effect on bound phenols,and HPH can significantly increase the ratio of bound phenols to free phenols.During storage at 4 ℃,the cloud of SH-HPP juice was unstable,and it was easy to precipitate layer by layer;SH-TP and HPH juice maintained better cloud stability during storage.During storage,the sucrose content of treatment cloudy Ponkan juice gradually decreased,while the glucose and fructose content increased,and the organic acid content had no significant change.Vc content of SH-TP juice was seriously lost during storage.The content of free protocatechuic acid in the processed cloudy Ponkan juice increased with the prolongation of storage time,the other individual phenols decreased gradually,and the content of bound phenols increased.The loss of polyphenols in SH-HPP juice was slight,but the conversion of free phenols to bound phenols was faster;and the loss of polyphenols in SH-TP juice was serious.Hesperidin and naringin in cloudy Ponkan juice may be the main polyphenols involved in precipitation.Partial least squares discriminant analysis(PLS-DA)model can significantly distinguish the SH-TP,SH-HPP,HPH and fresh juice samples(F)at the beginning and end of storage(0 and 35 days).The results showed that the stability of storage quality of HPH juice was better;the cloud stability and bactericidal activity of SH-TP juice were better,but the sensory and nutritional quality were lower;the cloud stability of SH-HPP juice was lower,and the nutrients were easy to precipitate.Furthermore,PLS analysis was conducted on the quality changes of SH-TP,SH-HPP and HPH juice during storage,and the marked quality indexes that changed significantly during storage were screened out.The most significant quality indexes affected by storage time were Vc,polyphenol content and color value;the most significant indexes affected by processing methods were average particle size,viscosity and centrifugal sedimentation rate.The results showed that the influence of different processing methods on the quality index of cloudy Ponkan juice was as follows: SH-TP > SH-HPP > HPH.