Effects of different pretreatments on the pore structure of Chinese yam during microwave freeze drying

In order to explore the effects of different pretreatments on the pore structure of Chinese yam during Microwave Freeze Drying(MFD),the samples were treated by typical drying pretreatments including osmosis,blanching and ultrasound,and compared with the untreated samples.The results showed that the pretreatment had significant impacts on the porosity of MFD Chinese yam.Ultrasonic pretreatment could obtain the highest open porosity,and the internal pore network structure of the material showed a uniform sponge shape.The shape of pores obtained by blanching pretreatment was the most irregular.The pore network structure obtained by different pretreatments could result in various product texture and rehydration,which implied that pretreatment methods should be carefully selected according to actual requirements.All these pretreatments could improve the open porosity of MFD Chinese yam,which result in a better rehydration capability.Among them,ultrasonic treatment is worth further investigating.

Drying curve simulation and LF-NMR online monitor of water state in ursolic acid loaded chitosan nanoparticles during microwave freeze drying

The changes in various states of water in ursolic acid(UA)loaded chitosan nanoparticles were assessed using lowfield nuclear magnetic resonance(LF-NMR)during microwave freeze drying(MFD)process,and six thin-layer models were applied to simulate the drying kinetics.UA nanoparticles were dried at different microwave power densities(1 W/g,2 W/g and 4 W/g).The results showed that three water fractions with different transverse relaxation times(T_(2))were detected in fresh UA nanoparticles.The T_(2)relaxation time of water decreased significantly with drying time at different microwave power densities.And the mutual migration and transformation of water in different states during the drying process of chitosan nanoparticles occurred.Furthermore,mathematical model analysis showed that the Page model provided the best description during the process of UA nanoparticle dried by MFD.The Page model can better simulate the drying kinetics of chitosan nanoparticles dried by MFD,and LF-NMR technology can monitor the changes in water status of UA nanoparticles.The results revealed that LF-NMR can monitor the changes of water in UA nanoparticles during the drying process.

Evolution of pore structure during microwave freeze-drying of Chinese yam

In order to reduce the energy consumption of freeze drying(FD),microwave freeze drying(MFD)can be used to dry Chinese yam.Porosity is a critical factor influencing transport mechanism,and can be considered as an important index to reflect the changes of structure of MFD foods.In this study,the changes of pore structure during the process of MFD Chinese yam were investigated by SEM and mercury porosimetry.The results showed that some closed pores could transform to open pores in drying process,and the open porosity showed a rising trend throughout the drying process.The pore size distribution range was about 10 nm to 10^(6) nm throughout the drying process.In the early stage of drying,the pore size was mainly in the range of 10-10^(4) nm,and then the pore size and the number of pores reduced.In the middle and late drying stages,the size of large pores increased again.

Effects of hot air drying temperature and tempering time on the properties of maize starch

Yellow maize as raw materials,hot air drying was used to reduce moisture content,and the tempering was implemented after drying.This study aimed to investigate the effects of hot air drying temperature and tempering time on the properties of maize starch.The wet milling was used to extract maize starch.Starch yield,protein content,amylose and amylopectin content,transparency and coagulation,solubility index and swelling power,color,pasting properties,and gelatinization properties were researched.The results showed that when the hot air temperature increased,the properties such as starch yield,amylopectin content,transparency,solubility,swelling power,whiteness decreased,and properties such as protein content and amylose content,coagulation,gelatinization temperature increased.Compared to drying temperature,tempering time has a less remarkable effect on the maize starch properties.The maize starch with better whiteness,solubility,swelling power could be obtained by adjusting tempering time.