Study On Centrifugal Dewatering Ability And Quality Of Carrot Cubes Synergized By Ultrasound And Microwave

In the pre-processing of central kitchen,blanching and centrifugal dewatering are the important pre-processing links of vegetable intensive and deep processing.The traditional centrifugal dewatering pretreatment of vegetables has the problems of low dewatering efficiency and large nutrient loss.In order to solve the above problems,a platform of ultrasound and microwave-assisted centrifugal dewatering was set up to study the effect,mechanism and quality influence of carrot pre-dewatering in the central kitchen.The main research contents are as follows:Firstly,the traditional method of hot water blanching assisted centrifugal dewatering(HWB-CD)was improved by ultrasound.In order to determine the best ultrasonic frequency,the changes of dewatering effect in the centrifugal dewatering and quality of carrots treated with HWB were analyzed.Under different ultrasonic frequencies,the ultrasonic frequency of45 k Hz showed a higher dewatering rate.With the increase of ultrasonic frequency,the cell structure would be damaged and the quality of dehydrated carrot would be affected.Although the centrifugation for a long time was more beneficial to improve the dewatering rate,considering that the treatment for a short time was more beneficial to retain the nutrients of carrot,the operating conditions of ultrasonic frequency of 45 k Hz and centrifugation time of frequency conversion of 10 min were selected as the subsequent experiments.Under these conditions,the dewatering rate of carrot was 37.63% higher than that of the traditional HWB-CD method,and the reducing power of carrot was 3.40% higher.The total phenol content,flavonoid content and ?-carotenoid retention rate were increased by 33.89%,48.51%and 26.71%,respectively.Then,traditional HWB-CD was used as the control group to study the dewatering ability and mechanism of ultrasound combined with microwave in centrifugal dewatering of carrot.The dewatering rate,water content,water distribution and migration,the change of pectin composition in cell wall and the damage of cell membrane of centrifugal carrot were analyzed.Compared with HWB,ultrasound combined with 915 MHz low-frequency microwave blanching(US-LFMB)and ultrasound combined with 2450 MHz high-frequency microwave blanching(US-HFMB)increased the dewatering rate of carrot by 43.39% and 40.51%,respectively.The degree of methylesterification(DM)of different bleaching methods was HWB>LFMB>HFMB>LFMB>US-HFMB.After centrifugal dewatering(CD),the DM value of HWB-CD did not change significantly before and after centrifugal dewatering,indicating that the pectin of HWB sample was reduced less during the process.Under the synergistic effect of ultrasound and microwave,US-LFMB and US-HFMB caused less cell damage than HWB,but US-HFMB caused less cell membrane damage than US-LFMB.Therefore,the higher dewatering effect of US-LFMB-CD may be related to the greater water loss in cells.Finally,the effects of ultrasound and microwave on the quality and energy consumption of carrot centrifugal dewatering were evaluated.Carrots were treated with LFMB-CD,HFMB-CD,US-LFMB-CD and US-HFMB-CD,respectively.The effects of different treatment methods on the changes of mineral elements,impedance characteristics,dielectric characteristics,relative conductivity,color difference,texture characteristics,DPPH inhibition rate,iron reduction antioxidant capacity,total phenol content,flavonoid content,ascorbic acid content and carotenoid content of carrot were compared.The results showed that the changes of mineral elements were great under HWB treatment.Compared with HFMB,the elements of Na,Mg,K,Ca,Mn,Fe and Cu in LFMB are lower than those in HFMB.The changes of elements caused by the thermal effect of LFMB are more obvious,which may be because the water evaporation rate caused by LFMB is higher than that of HFMB,and the cells are subjected to greater swelling force,which leads to partial cell damage and the reduction of ions in the matrix.The thermal effect of LFMB and HFMB resulted in the decrease of water added to US,the increase of conductive medium concentration,and the decrease of impedance values of US-LFMB and US-HFMB.After CD treatment,the removal of water leads to an increase in the concentration of conductive medium.At the same time,the cell membrane was superimposed by centrifugal force,and the phase Angle increases,resulting in an increase in the impedance value.US-HFMB-CD could remove more water on carrot surface,resulting in lower L value.The hardness,brittleness and elasticity of HWB-CD are lower than those of LFMB-CD,HFMB-CD,US-LFMB-CD and US-HFMB-CD.The contents of total phenols,flavonoids and carotenoids were in the order of US-HFMB>US-LFMB>HWB,and the changes were consistent with those after centrifugation.The main reason was that HWB caused the loss of nutrients in water.The content of ascorbic acid was the highest retained by HFMB-CD,mainly due to the dual thermal effect of US-LFMB and US-HFMB,which increased the thermal loss of ascorbic acid.Therefore,the inhibition rate of DPPH and iron reduction antioxidant capacity of carrots treated with US-HLMB and US-HFMB were higher than those treated with HWB.For different pretreatment technologies,the water consumption of HFMB was 18.92% less than that of LFMB,and the energy saving was 27.87%,and the water consumption of US-HFMB-CD was 91.80% less than that of US-LFMB-CD,and the energy saving was66.67%.Considering the effects of dewatering effect,quality change and energy consumption,the pre-dewatering technology of US-HFMB-CD was better for the pretreatment of carrot.