Study Of Carrot Dices Dry-blanching And Drying Technologies

The production of dehydrated vegetables mainly includes two stages of blanching and drying.But traditional methods such as hot water blanching and hot air have many disadvantages,including low energy efficiency,low utilization ratio and quality deterioration.So it is indispensable to establish new blanching and drying technologies to improve the product quality and promote the development of dehydration vegetable industry.Firstly,new drying technologies were used to discuss the feasibility of obtained high quality carrot dices without blanching.Secondly,used a infrared dry-blanching,which could reduce costs,improve product quality and reduce subsequent drying load.Then selected several new drying technology which based on hot air drying,built a new technical method which can complete the high efficiency,high quality dehydrated carrot production.(1)Experiments were conducted to investigate three drying technology for drying fresh carrot dices,included combined infrared and hot air drying,pulsed vacuum drying,staged temperature and humidity control dying.Carrot dices' drying characteristics that included wet base moisture content,dehydration rate and effective moisture diffusion coefficient were investigated.It obtained the best parameters of the three drying technology respectively,combined infrared and hot air drying temperature was 70?,wind speed was 1.22~1.69m/s drying time was 9.5h,pulsed vacuum drying temperature was 70?,vacuum time/atmospheric time was 15min/5min drying time was 8.22 h,staged temperature and humidity control dying temperature was 70?,relative humidity was 50% maintain time was 10 min drying time was 9h.The effective moisture diffusion coefficient of pulsed vacuum drying,staged temperature and humidity control dying,combined infrared and hot air drying were 9.02×10-10m2/s,9.04×10-10m2/s,8.01×10-10m2/s respectively.Pulsed vacuum drying could get better quality compared with staged temperature and humidity control dying and combined infrared and hot air drying.But the carrot dices quality were not good by all of this three drying methods,concrete problems were bad color,the color change vale over 20,obviously white change,low beta carotene content,obviously surface structure shrinkage,and low rehydration rate,the methods only could use for low quality carrot dices production.(2)Experiments were conducted to investigate a technology of simultaneous catalytic infrared dry-blanching and dehydration for producing dehydrated carrot dices.The investigated parameters were radiation distances,dice thickness and processing time.A three-factor factorial experiment was conducted to determine the influence of parameters on surface temperature,center temperature,moisture rate(MR),drying rate,peroxidase(POD)residual enzyme activity,surface color change,retention of VC and retention of ?-carotene.Models were established for describing the moisture distribution and POD inactivation.It analyzed the cost of the two kinds of blanching methods.The experiments proved that shorter radiation distances,thin dices had higher product temperature,and quicker POD inactivation,the processing time was between 5min to 11.17 min,resulted in moisture reductions of 40%~69.7%.The surface color change,retention of VC and retention of ?-carotene of carrot dices under SIRDBD were better than traditional industrial water blanching.Infrared dry-blanching and hot water blanching took 0.11yuan/kg and 0.13yuan/kg respectively.Infrared dry-blanching took lower costs and could help improve the drying rate during drying compared with hot water blanching.The Midilli model performed well for describing drying behavior during SIRDBD.The Fractional conversion model fitted well for POD inactivation curves.(3)Experiments were conducted to study and compare carrot drying characteristics and quality with infrared dry-blanching and four drying methods,included combined hot air drying,pulsed vacuum drying,staged temperature and humidity control hot air dying and traditional hot air drying.The experiment proved that(1)After infrared dry-blanching,the effective moisture diffusion coefficient of the four above drying methods were 9.75×10-10,8.91×10-10,9.48×10-10 and 12.6×10-10m2/s respectively.The combined infrared and hot air drying,traditional hot air drying had higher value of maximum dehydration rate,the infrared dry-blanching coupling hot air drying needed shorter time.(2)After infrared dry-blanching,pulsed vacuum drying could get the highest comprehensive quality such as: smaller color change value,better reconstitution properties,higher VC and ?-carotene retention rate,more complete surface microstructure,next were staged temperature and humidity control hot air dying and combined infrared and hot air drying,the quality of the traditional hot air drying was slightly poor.The infrared dry-blanching-pulsed vacuum drying method could be used for high quality carrot dices production.(3)In term of both drying rate and quality,infrared dry-blanching-combined infrared and hot air drying was the most suitable way for dehydrated carrot dices within the range of this study.This way solved the disadvantages of traditional hot water blanching and hot air drying,regarded as a kind of dehydrated carrot dices production technology,which were energy conservation,environment protection,high produce quality and could significantly improve the efficiency of drying.