Research On The Processing Technology Of Clarified Jujube Juice Concentrate

Jujube contains a variety of compounds with nutritional function and biological activity.It is of great significance to conduct deep research in order to exploit and utilize the jujube resource in China. This paper studied the optimized extraction, clarification and concentration process conditions of jujube juice,as well as the effect of different processing technology on volatile flavor compounds of jujube juice. It was aimed mainly at providing the theoretical guidance for developing and utilizing jujube resource.In the process of jujube juice extraction, jujube was baked 1h at 60℃,and then baked30 min at 60℃.The jujube flesh was tight and exuded fragrance. Orthogonal design based on single factor experiments was performed. The optimal extraction conditions with pectinase were that pectinase concentration 0.3%(w/w) of dried jujube sample, 50 ℃ of extraction temperature, 5h of treatment time, 3.5 of pH and the water addition was 8 times(w/w) of the original dried jujube. The jujube juice content soluble solids were 9.5% and the extraction rate of soluble solids was 72.69%.Extracted jujube was clarified by pectinase, cellulose, bentonite, diatomite and chitosan.Through analyzed for light transmittance, I optimized its clarification process. The four clarification methods of optimization were compared by soluble solids content, light transmittance, turbidity, color and lustre, storage stability, vitamin C and total sugar content.The results showed cellulose had no obvious clarification effect of jujube juice. Pectinase concentration 0.2g/L and enzymatic hydrolysis 1.5h at 55℃, chitosan concentration 3%(v/v)and processing time 40 min at 30℃, bentonite concentration 3%(v/v)and processing time50 min at 35℃,and diatomite concentration 7%(v/v)and processing time 90 min at 40℃ had very good clarification effect of jujube juice. Chitosan clarification of jujube juice had highest transmittance values, the brightest color, the best storage stability and soluble solids content,total sugar and vitamin C could be preserved well in jujube juice.High concentration of jujube juice was prepared by the method of vacuum concentration.The effect of concentration multiple and concentrating temperature on the quality of jujube juice were studied. The results showed that the jujube juice was concentrated to 70% at 50℃.The concentrated jujube juice was not only clear and transparent, had less effect on reconstituted juice, but also had good storage stability. Freeze-concentration was used to concentrate Jujube juice. The final concentration degree was relatively low. But the concentrated jujube juice had less effect on content of total acid and vitamin C in jujubejuice.Using solid-phase microextraction and gas chromatography-mass spectrometer studied the effects of different clarification methods and concentration methods on the aroma components of jujube juice. The results showed different processing methods had different effects on the aroma components of jujube juice. Twenty-eight volatile compounds were identified in jujube juice. And the content of esters, acids and hydrocarbons were higher. Nine volatile compounds were identified in the clarified juice by pectinase. And the content of acids and ketones were higher. Nine volatile compounds were identified in the clarified juice by bentonite. And the content of ketones was higher. Four volatile compounds were identified in the clarified juice by diatomite. And the content of ketones was higher. Eleven volatile compounds were identified in the clarified juice by chitosan. And the content of ketones and esters were higher. Chitosan clarification juice could be better preserve the flavor of the original juice, and it produced propanoic acid, ethyl ester which did not appear in the other four kinds of red date juice. It can be used as a food flavor. And the pineapple flavor made the jujube juice with special flavor. In the concentration process, vacuum concentration makes the most serious loss of aroma components in jujube juice, and just seven volatile compounds were identified. The vacuum reconstituted juice just identified four volatile compounds. But freeze-thawing concentrated juice had twenty-three volatile compounds. A large number of new materials were detected. New material of 2-methyl-propanoic acid, hexanoic acid, methyl ester, 1-Octen-3-ol, eucalyptol, furfural, acetophenone and(E)-2-Octenal had a positive effect on the aroma components of freeze-thawing concentrated juice. The freeze-thawing reconstituted juice had eleven volatile compounds. It was less aroma components than concentrated juice. But it was better to preserve the main aroma components of acetophenone.