Study On The Vegetable Juices--Cloudy Pumpkin Juices And Cloudy Carrot Juices

There are the most vegetable yields and varieties in China, but many of them are not made full use. Fresh vegetables produced to natural, healthy cloudy vegetable juices are beneficial to promote the development of beverage industry and exert the advantage of vegetable resource. In order to improve the qualities of cloudy vegetable juices and resolve the critical technologies restricted the quick development of juice market, the systemic study on the processing and the qualities of cloudy vegetable juices is very essential. The objective of this dissertation was to develop multiple enzymatic liquefaction for processing cloudy pumpkin and carrot juices, investigate the juice concentrates and their cloud stability, color stability and flavor. The main results were as follows. The effects of different enzymatic preparations on pumpkin purees, pulp cells and cloudy juices were determined. The combination of cellulytic and pectolytic preparations had a desirable effect on the yield and quality of pumpkin juices. An appropriate enzymatic formulation containing both PU and JC could increase the juice yield by 20% and improve the color and cloud stability substantially. The key of terminal control of enzymatic liquefaction was master of the extent of pectin hydrolysis. It related to the different raw materials, the varieties, combinations and dosages of enzymatic preparations and the conditions of enzymatic reaction.The mechanism of effect of multiple enzymatic liquefaction was investigated. The synergistic effect of pectinase, polygalacturonases, cellulase and xylanase was due to cooperative enzymatic hydrolysis of pectin, cellulose and hemicellulose coexisting in the primary wall and in the middle lamella of pumpkin pulp cell walls. By controlling the dosages of enzymatic preparations, pectin was broken down to such an extent that the viscosity decreased but not totally clarified. Other polysaccharides and cell-substances were partially or completely disintegrated. Thus, the soluble solid, beta-carotene content, pigment and other components were increased in pumpkin juices. This resulted in good color and cloud stability of pumpkin juices.Processing technology of cloudy carrot juices was established. After peeling in 4g/dL NaOH at 95℃ for 1min, carrots were blanched in 0.6g/dL citric acid at 95℃ for 6min. The optimal processing of multiple enzymatic liquefaction was added 0.0035g/dL PU and 0.16g/dL JC into the carrot purees and reacted at 50℃ for 2 hours. The juice yield was increased 10% than the method of pressing. The resulting cloudy carrot juices had high nutritional components, good cloud stability, vivid color and favorable flavor.Cloudy pumpkin and carrot juice concentrates and their cloud stability during storage were studied. They behaved as non-Newtonian fluids (shear thinning). The 47° Brix pumpkin juiceconcentrates, The 55°Brix pumpkin juice concentrates without gums and with guar/xanthan gums appeared a pseudoplasticity;the over 55°Brix pumpkin juice concentrates with carboxymethyl cellulose (CMC), 63°Brix pumpkin juice concentrates without gums and with guar/xanthan gums and 55°Brix carrot juice concentrates with or without flaxseed gums exhibited a thixotropic property;juice concentrates over 55°Brix presented a static yield stress. The results of rheological behaviors and ultrastructures of pumpkin juice concentrates indicated that a weak three-dimension network was formed in the system by the macromolecular interaction and the small particles aggregation with each other. Furthermore, the juice concentrates had high viscosity. So they had good cloud stability during storage. The juice concentrates had better storage stability in low temperature.The particle size distribution and z-potential of cloudy juices were researched. When the average size of suspended particles in pumpkin juices was 2~3um, the cloud stability was good. Homogenization could control the size of suspended particles. Different z-potential was due to different components in different cloudy vegetable juices. Cloudy carrot juices had low z-potential and its cloud stability involved in steric macromolecular repulsion. Cloudy pumpkin juices had high z-potential and its cloud stability involved in steric and electrostatic repulsive forces. Different concentrations and varieties hydrocolloids had different effects on cloud stability of cloudy carrot juices. Guar gum was the most thickening effect, and flaxseed gum possessed a little emulsification. By accelerated storage tests at 30, 35 and 40°C, the activation energies of the suspension stability and relative viscosity in cloudy pumpkin juices were 50-85 kJ/mol. The shelf life of cloudy pumpkin juices was over one year at ambient temperature.According to the results of the main components of cloudy pumpkin juice, sedimentation, crude protein and the analysis of soluble protein and pectin by DEAE Sepharose CL-6B ion exchange chromatography, IR, SDS-PAGE, P -expunction reaction, HPGFC and NMR, the mechanism of cloud stability of cloudy pumpkin juices was discussed. The macromolecular substances, cell fragments and other suspended particles in cloudy pumpkin juices were resulted in turbidity. At the beginning, the bigger particles formed the sedimentation due to the action of gravity. During storage part of steady particles were aggregated together and grown up to form more sediments. Stability of other clouds was depended on the steric and electrostatic repulsive effects among smaller different particles including macromolecular substances and suspended cell substances.The results of storage tests at different storage temperature indicated that the cloudy carrot and pumpkin juices had good color stability during storage. The processing condition was more effect on the color change than storage condition. Non-enzymatic browning of cloudy carrot juices was less than that of pumpkin juices. The main carotenoids rich in cloudy carrot and pumpkin juices was 3 -carotene. And the carotenoids were oxidized and isomerized during storage. But the changes of carotenoids were not aroused the worse color. The volatile compounds of carrot and pumpkin juices during processing were concentrated by SPME, separated and identified by GC-MS. 48 kinds of compounds were identified in volatilefraction of fresh and blanching carrots, and the main components were terpene. 59 and 66 kinds of compounds were identified in volatile fraction of original and single strength carrot juices, and the main components were benzene, aldehyde, ketone and terpene. 44, 33 and 53 kinds of compounds were identified in volatile fraction of fresh and blanching pumpkins and cloudy pumpkin juices, and the main components were alcohol, aldehyde and ketone. The results indicated that carrot and pumpkin juices retained the main aroma components of fresh carrot and pumpkin after processing. However, the heat treatment made many of cooking aroma such as furfural, pyridine and furan. The carotenoids broke down aldehyde, ketone and ionone.