Study On Belt Catalytic Infrared Dry Blanching Combined Drying Of Sweet Potato Slices Based On The Characteristics Of Peroxidase And Starch

Sweet potato is a kind of rhizome plant with high water content,short storage period and easy to rot.Dried sweet potato and sweet potato powder are the main processing products of sweet potato.At present,hot air drying is the main drying method of sweet potato.But the hot-air drying time is long,which leads to poor product quality.Compared with hot air drying,catalytic infrared drying has the advantages of fast drying efficiency,short drying time and energy saving.The main component of sweet potato is starch.There are many studies on the changes of color,texture and nutrients of sweet potato after drying,but few studies on the changes of starch structure and physicochemical properties of sweet potato after drying.Blanching pretreatment before drying can improve the quality of dried sweet potato.The traditional blanching method has the disadvantages of waste of water resources,environmental pollution and serious loss of nutrients.18-20 tons of hot water(above95?)is needed to produce 1 ton of dry sweet potato products.The emerging dry blanching technologies(microwave blanching and catalytic infrared blanching)have attracted much attention because they do not use water resources and reduce the loss of nutrients.Compared with microwave blanching and electric infrared blanching pretreatment,catalytic infrared blanching uses natural gas to produce energy directly,which has the advantages of uniform heating,energy saving and high energy conversion rate.Many scholars have done a lot of research on catalytic infrared blanching of small equipment.In this paper,the belt catalytic infrared device continues its advantages and uses the conveyor belt to achieve industrial scale.Therefore,it is necessary to explore a belt catalytic infrared"pretreatment+drying"process which can not only achieve the goal of green,environmental protection,water saving and high quality,but also be suitable for industrial production.In this paper,the blanching pretreatment and drying process of sweet potato slices were studied by using belt catalytic infrared device.Finally,a green,environment-friendly and water-saving belt catalytic infrared"pretreatment+drying"process was obtained,which can not only reduce POD activity but also improve the quality of dry products.The kinetic models of POD passivation and water drying of belt catalysis infrared blanched sweet potato slices were established,and the structure and physicochemical properties of sweet potato starch processed by"pretreatment+drying"were studied.The main contents and results of the study are as follows:(1)The effects of process parameters(slice thickness:3,5,7 mm,infrared irradiation distance:6,12,18 cm,conveyor speed:0.7,0.35,0.25,0.1 m/min,etc.)of belt catalytic infrared blanching on POD,moisture reduction,physicochemical properties and microstructure of sweet potato slices were studied.The effects of blanching pretreatment methods on the characteristics and quality of belt catalytic infrared drying sweet potato slices were studied the results showed that blanching pretreatment destroyed the tissue structure of sweet potato slices,led to the color change of sweet potato slices,electrolyte leakage,hardness reduction,vitamin C and total phenol content reduction.Compared with hot water blanching,belt catalytic infrared blanching not only inactivated 90%POD,but also removed 45.77-79.15%moisture of sweet potato slices.It can keep the cell structure well and reduce the leakage of electrolyte and the loss of vitamin C and total phenol content.The most appropriate technological parameters of belt catalytic infrared blanching were as follows:the slice thickness was 3 mm;the infrared irradiation distance was 12 cm and the irradiation time was 13 min.Under these conditions,the color change value of sweet potato slice?E(7.41)was the lowest,the retention rate of vitamin C(75.16%)was the highest,the retention rate of?-carotene(133.49%)was the highest,and the total phenol content was 1.03 mg/g.Belt catalytic infrared blanching-belt catalytic infrared blanching can obtain shorter drying time(60 min),lower color change value?E(19.47),lower hardness(3186.2 g)and smaller shrinkage(5.17%),and more complete microstructure.Finally,a green,environment-friendly and water-saving belt catalytic infrared"blanching(the slice thickness was 3 mm,the infrared irradiation distance was 12 cm and the time was 13 min)+drying(the infrared irradiation distance was 18 cm,the temperature was 60?and the time was 60 min)"process for sweet potato was obtained.(2)The kinetic models of POD passivation and moisture drying in the process of belt catalytic infrared blanching of sweet potato slices were established.First order,fractional transformation and Weibull distribution models were used to fit the POD inactivation of sweet potato slices during blanching,Lewis,page and Midilli models were used to fit the drying kinetics of sweet potato slices during blanching.The best fitting effect was obtained by determination coefficient(R²),chi square test(c²)and root mean square error(RSME).The results show that Weibull distribution model has higher R²,smallerc² and RSME.Page model has higher R² and smaller RSME.It is concluded that Weibull distribution model was the most suitable mathematical model to describe POD inactivation in the process of belt catalytic infrared blanching of sweet potato slices,Page model was the most suitable mathematical model to describe the moisture change in the process of belt catalytic infrared blanching of sweet potato slices.Through the establishment of the kinetic model,the basis for the prediction of the end point of belt catalytic infrared blanching of sweet potato slices was made,and the quality of sweet potato products was guaranteed.(3)The effects of belt catalytic infrared drying(BCIRD),belt catalytic infrared blanching-belt catalytic infrared drying(BCIRB-BCIRD)and water blanching-belt catalytic infrared drying(WB-BCIRD)on sweet potato starch were studied.Firstly,the structural characteristics of sweet potato starch were studied by scanning electron microscope,optical microscope,polarizing microscope,X-ray diffraction and Fourier transform infrared spectroscopy.Secondly,the function characteristics of sweet potato starch,such as solubility and swelling power,transparency,water and oil absorption capacity,freeze-thaw stability,thermal stability and so on,were studied.The results showe:1)that the starch content of sweet potato starch was 29.78-34.50%,and the amylose content was 23.22-43.46%.WB-BCIRD significantly reduced the starch content and amylose content of sweet potato starch(p<0.05),2)X-ray diffraction showed that the processed sweet potato starch showed A-type crystal structure,and the intensity of diffraction peak of WB-BCIRD sweet potato starch decreased,which may be due to the starch gelatinization and double helix movement during the thermal processing,resulting in the destruction of crystal structure.The morphology of BCIRD and BCIRB-BCIRD sweet potato starch granules remained intact.However,the surface of WB-BCIRD sweet potato starch granules ruptured or even collapsed,and the amorphous pattern of polarized cross appeared,which indicated that hot water blanching had more serious damage to sweet potato starch granules and crystal structure.Fourier transform infrared spectroscopy showed that the infrared absorption peak position of the processed sweet potato starch did not change,indicating that the chemical groups of the sweet potato starch would not be changed by thermal processing,but the O-H stretching vibration peak strength of WB-BCIRD sweet potato starch near3400 cm^-1 increased,3)the granule structure and crystal structure of BCIRB-BCIRD and WB-BCIRD sweet potato starches were destroyed,resulting in gelatinization of starches.The solubility,water absorption and oil absorption capacity of processed sweet potato starches increased,and the freeze-thaw stability,transparency and thermal stability decreased.It was concluded that the structure and crystallinity of sweet potato starch were changed by heat treatment,which affected the functional properties of sweet potato starch,BCIRB-BCIRD could maintain the structure and physicochemical properties of sweet potato starch,which was an alternative processing method of sweet potato starch.In summary,the belt catalytic blanching established in this study can effectively inactivate the POD activity of sweet potato while retaining more nutrients and saving water resources.Weibull distribution model was the most suitable mathematical model to describe the inactivation of POD in blanching process,and Page model was the most suitable mathematical model to describe the moisture change in blanching process.The belt catalytic infrared blanching-belt catalytic infrared drying can not only shorten the drying time,improve the quality of dried products,but also maintain the structural and functional properties of sweet potato starch.Finally,a green,environment-friendly and water-saving combination process of"blanching(the slice thickness was 3 mm,the infrared irradiation distance was 12 cm and the time was 13 min)+drying(the infrared irradiation distance was 18 cm,the temperature was 60?and the time was 60 min)"was provided.