Changes And Control Of Nitrate In Carrot Juice During Processing And Storage

Carrot?Daucus carrot L.?has the reputation of‘small ginseng'with unique nutritional value.Its industry is one of the important vegetable industries in China.Carrot was processed carrot juice and carrot pulp,which are the main export products of carrot.Nitrate can be converted into nitrite in vivo and in vitro,which has potential health risks to human body.Vegetables are the main source of nitrate intake in human body.Carrot is easy to enrich nitrate,and its carrot juice has high nitrate content,which has become an important factor affecting the safety and quality of its products and domestic and foreign markets.Carrot juice was used as raw material to study the change of nitrate and nitrite in carrot juice during processing and storage,effect of ion exchange resin on the removal of nitrate and the quality of carrot juice,and the mechanism of removal of nitrate by resin was discussed.The main results and conclusions were as follows:1.Changes of nitrate and nitrite in carrot juice during processing and storage:Carrot juice was used as raw material,and the content of nitrate and nitrite were analyzed by spectrophotometric method.The changes of nitrate and nitrite during process of carrot juice peeling,blanching,enzymolysis and sterilization,and the effects of different blanching and sterilization methods on nitrate were studied.The changes of nitrate,nitrite and nitrate reductase activity of fresh carrot juice were stored at 4?and 25?for one week.The results showed that the contents of nitrate and nitrite were significantly decreased in the peeling and blanching process,and the water bath blanching is more conducive to reducing the nitrate and nitrite content.The nitrate content in carrot juice decreased with the storage time,and the rate of storage at room temperature decreased faster than cold storage,and nitrite content increased.The activity of nitrate reductase increased first and then decreased with the prolongation of storage time,and the nitrate reductase activity peaked at 5 day and 3 day respectively at room temperature and cold storage.2.Effect of ion exchange resin on the removal of nitrate and the quality of carrot juice:Carrot juice was used as raw material,and effects of nitrate concentration,resin dosage,treatment time and treatment temperature on nitrate removal rate,a*,b*,soluble solids content and?-carotene content were studied.The results showed that ion exchange resin could be used for the adsorption and removal of nitrate in carrot juice.Nitrate concentration,treatment time and resin dosage significantly affected nitrate removal rate,but treatment temperature had no significant effect on nitrate removal rate.There was a significant negative correlation between nitrate removal rate and a*,b*,soluble solids content and?-carotene content under the conditions of resin dosage and treatment time.The response surface test and verification results showed that in the carrot juice with nitrate concentration of 2481.39mg·kg^-1,the removal rate of nitrate was 80.77%,a*was 6.36,b*was 31.15,and the nitrate content was less than 500mg kg^-1when the resin was added 7.21%and the treatment time was3 h.3.The mechanism of removal of nitrate by resin:The kinetics of adsorption of three resins?LX-13,LX-12,and HZ-222?in aqueous solution and carrot juice was studied,quasi-first-order kinetic equations and pseudo-second-order kinetic equations were used to fit the liquid film diffusion,and liquid film diffusion dynamic mode,intro-traparticle diffusion dynamic mode,and chemical reaction dynamic mode was analyzed for the mechanism of kinetic rate control.The results showed that the adsorption kinetics of the three resins conformed to the pseudo-second-order kinetics model;the correlation coefficient R² fitted by intro-traparticle diffusion dynamic mode was above 0.9 and 0.8 in both aqueous solution and carrot juice,and the adsorption rate of nitrate by the three resins is mainly controlled by intro-traparticle diffusion dynamic mode.