The Stability Of Carotenoids In Pumpkin Slices During Microwave Vaccum Drying

Pumpkin is rich in some functional carotenoids,which is a natural health food resource needing exploitation.The traditional vacuum drying time is long,and microwave drying is easy to cause the degradation of heat-sensitive components in pumpkin.However,as a new drying method,microwave vacuum brings together the advantages of microwave drying and vacuum drying,which can quickly dry the material at lower temperature,and obtain high quality of dried products.Therefore,in this paper,the content changes of carotenoid in pumpkin(cultivar Miben)during microwave vacuum drying was investigated.The reaction kinetic model of the main trans carotenoid was established and the relationship between the microwave power and drying time and carotenoid was quantified.Meanwhile,the effect of starch pretreatment on the carotenoid retention rate of pumpkin slices was studied.The results will provide theoretical basis and technical support for the production of high value-added pumpkin slices.The results are as following:1.A total of 8 trans carotenoids and 6 cis carotenoids were identified in different dried pumpkin slices by C30-HPLC-DAD-APCI/MS/MS,among which lutein,a-carotene and?-carotene were the main component.Compared to Vacuum freeze dried sample,9-cis-lutein and 5,6-epoxy-?-carotene were identified in hot air dried and microwave vacuum dried sample.The content of total carotenoids and total trans carotenoid in hot air drying and microwave vacuum dried pumpkin slices were significantly lower than that of vacuum freeze dried sample(P<0.05),while the loss of carotenoids in microwave vacuum dried was smaller.At the same time,the color parameters of microwave vacuum dried pumpkin slices were superior to that of hot air drying.2.The parameters of microwave vacuum drying had some effect on the carotenoid content of pumpkin slices,in which the microwave power were more obvious.Meanwhile,increasing vacuum degree or slice thickness was beneficial to retain carotenoids,but too high microwave intensity resulted in decreased content of carotenoids.When microwave power was 5 W/g,vacuum degree was 90 kPa and slice thickness was 10 mm,the retention rate of carotenoids content was the highest.Lutein,?-carotene and ?-carotene content decreased gradually with increasing drying time during microwave vacuum drying process.Changes of three carotenoid content followed the first-order degradation kinetics model,and the correlation coefficient was between 0.8280 and 0.9942.Increasing of microwave power resulted in increasing of the degradation rate constant k,on the contrary,decreasing the half-life t1/a and D value,while the influence of vacuum degree and slice thickness on them is relatively small.In addition,the degradation of the color L*×b*and the total color difference ?E of pumpkin slices during microwave vacuum drying process accorded with the first-order and zero-order reaction kinetic models,respectively.There was a certain correlation between the L*×b*value and the three trans carotenoids of the pumpkin,and the correlation coefficient ranged from 0.8283 to 0.9952.Then the content of carotenoids in pumpkin slices can be predicted by L*×b*value.3.Corn starch,potato starch and corn starch phosphate double.coating treatment could improve the retention rate of carotenoids in pumpkin slices and VA activity,especially in the 1%corn distarch phosphate.The colour parameters L*and H value increased,but a*value decreased significantly(P<0.05).The correlation analysis showed that lutein had highly significant positive correlated with L*values and negative correlation with ?E,while ?-carotene and ?-carotene had highly significant positive correlated with L*values and significant negative correlation with ?E.