Study And Application Of Inhibitory Effect Of Wheat Gluten And Coexisting Mannitol On Moisture Absorption Of Freeze-dried Jujube Powder

Jujube powder is a powdered dry product obtained by drying and crushing concentrated jujube juice or jujube slices.It is usually added as an ingredient to various foods to enhance and improve the nutritional value,flavor and function of the products.However,the application of jujube powder is affected by its hygroscopicity and adhesion during storage.In this paper,the effects of wheat gluten and mannitol on the hygroscopicity of freeze-dried jujube powder were investigated by means of hygroscopicity curve,surface wettability,hygroscopicity isothermal curve and low field nuclear magnetic field.The effects of wheat gluten and mannitol on the properties of freeze-dried jujube powder were investigated by bulk density,angle of rerest,water solubility index,water holding capacity/oil capacity and rehydration.Finally,wheat gluten and mannitol were applied to Ganmai Dazao Decoction,and a low hygroscopicity freeze-dried jujube powder product was developed.The research work provides a safe new strategy for moisture-proof and anti-caking of hygroscopic foods.The main conclusions are as follows:1.The effects of wheat gluten（WG）on hygroscopicity and powder properties of freeze-dried jujube powder were studied.Under the condition of 25℃and 75%humidity,the equilibrium moisture content（EMC）of jujube with a mass ratio WG of 10:0 was30.78%.The EMC of 7:3,5:5,3:7 and 0:10 decreased to 24.15%,20.02%,16.42%and13.03%,and the initial moisture absorption rate decreased from 0.3537 g/h to 0.2509 g/h,0.2169 g/h and 0.1778 g/h respectively.The results showed that WG could significantly reduce the equilibrium moisture content and moisture absorption rate of freeze-dried jujube powder.GAB and Peleg models can describe the hygroscopic behavior of freeze-dried jujube powder at different temperatures.The hygroscopic isotherms of 10:0,7:3,5:5and 3:7 samples belong to"J"type,while the hygroscopic isotherms of 0:10 belong to"S"type,indicating that the addition of WG does not change the isothermal adsorption type of freeze-dried jujube powder.The increase of WG ratio can weaken the surface wettability of freeze-dried jujube powder and reduce the degree of water migration from low degree of freedom to high degree of freedom,which is beneficial to alleviate the occurrence of caking.By comparing the powder properties of 10:0 and 7:3,it can be seen that the addition of WG can improve the fluidity and bulk density of freeze-dried jujube powder,but reduce its water solubility,rehydration and color and other powder properties.2.In view of the decrease of color and solubility of jujube powder caused by WG addition,the hygroscopicity and powder properties of D-mannitol（DM）partially replaced wheat gluten were investigated.The results showed that the addition of DM could further reduce the equilibrium moisture content of freeze-dried jujube powder.The Ferro-Fontan model could better describe the hygroscopic behavior of jujube,WG and DM at 7:2:1,7:1:2 and 7:0:3,and the hygroscopic isotherms were"J"type,indicating that the addition of DM could not change the isothermal adsorption type of freeze-dried jujube powder.When the ambient humidity was constant,the T₂ relaxation time of the three samples was significantly greater than 7:3,and showed an increasing trend with the increase of DM content.The macroscopic and scanning electron microscope images showed that the addition of DM did not significantly improve the agglomeration of jujube powder.However,partial substitution of WG with DM can help to maintain the color of jujube powder,and significantly improve the fluidity,water solubility index,water holding capacity,oil holding capacity and rehydration of the system.The results showed that the combination of WG and DM did not significantly inhibit the hygroscopicity and adhesion of jujube powder,but significantly improved its powder properties.3.The effects of WG and DM on the hygroscopicity and powder properties of Ganmai Dazao powder were studied.Compared with adding WG alone,the combined application of the two can further reduce the equilibrium moisture content of Ganmai Dazao powder.The hygroscopic isotherms of different proportions of Ganmai Dazao powder can still be fitted by the Ferro-Fontan model,and the hygroscopic isotherms also belong to the"J"type.However,only adding DM will aggravate the agglomeration of Ganmai Dazao powder,enhance its surface wettability,and promote the migration of water in the system to water that is not easy to flow,resulting in powder particles sticking together and deterioration of the overall state.In terms of powder properties,adding DM alone is more helpful to improve the fluidity,water solubility and rehydration of Ganmai Dazao powder.It was found that when WG/DM mass ratio was 1:2,Ganmei Dazao powder had lower equilibrium water content at high humidity,relatively light agglomerating phenomenon,relatively less water with high degrees of freedom,and the powder had better fluidity,water solubility and rehydration,so it had the most potential application.