Study On Inhibition Of Fructose Hygroscopicity By Wheat Gluten And Its Main Components

The strong hygroscopicity of small-molecule sugars usually limits its processing applications.The development of methods to reduce hygroscopicity,agglomeration and deliquescence is of great value for the storage of small-molecule sugars and related products.This paper firstly compared the hygroscopicity of three common small molecule sugars(sucrose,glucose and fructose)and,on this basis,investigated the effect of wheat gluten on the hygroscopicity of freeze-dried fructose,taking fructose,the most hygroscopic sugar,as the object of study.Finally,the effect of two main components of wheat gluten,gliadin and glutenin on the hygroscopic properties of freeze-dried fructose was investigated.This study revealed the effect of wheat gluten on the hygroscopicity of freeze-dried fructose and grasped its law,which can provide data support for inhibiting the hygroscopicity of high sugar foods.The main results are as follows:1.The hygroscopicity of sucrose,glucose and fructose was compared under the same environment.Comparing the moisture absorption data,it was found that the equilibrium moisture content(EMC)of fructose was significantly higher than that of sucrose and glucose,and the gap increased with the increase of relative humidity.At 75%relative humidity,the EMC of sucrose,glucose and fructose were 0.07%,0.86%and 31.61%respectively.And the Peleg model was the best fit for the adsorption data and was the best hygroscopic isotherm model.The hygroscopic isotherms of sucrose,glucose and fructose all had a typical“J”shape and belonged to the Brunauer classification of type III isotherm.The macroscopic images showed that the degree of agglomeration was positively correlated with the hygroscopic time,with fructose>glucose>sucrose in the order of the three sugars.Differential scanning calorimetry,XRD and contact angle revealed the reasons for the obvious difference of hygroscopic properties of the three small molecular sugars from the glass transition temperature,crystallinity and hydrophilicity.The low-field NMR results showed that the main water in both fructose and glucose changed from bound water to less mobile water during the hygroscopic process,and the fructose had a higher proportion of high free water,while the water in sucrose was mainly maintained in the bound water state,explaining the phenomenon that sucrose maintained better stability during the hygroscopic process.In addition,the total peak area of fructose was significantly higher than that of glucose and sucrose(p<0.05),indicating that fructose has a stronger water absorption.2.The effect law of adding different ratios of wheat gluten(Fru:WG=0:10,Fru:WG=2:8,Fru:WG=3:7,Fru:WG=10:0)to regulate the moisture absorption of fructose freeze-dried products was studied.The results of the hygroscopic curves showed that the addition of wheat gluten had a very significant inhibitory effect on the hygroscopic absorption of fructose,and the inhibition effect of Fru:WG=2:8 was better in environments with relative humidity above 43%.At 25℃and 75%relative humidity,the EMC of freeze-dried samples with fructose and gluten ratio of 3:7 and 2:8 decreased to16.00%and 14.61%respectively.Seven classical models were used to fit the hygroscopic data and the appropriate model to describe the hygroscopic isotherm of fructose freeze-dried products was determined by R~2to be the GAB model.At 25°C,the addition of wheat gluten shifted the type of the hygroscopic isotherm of freeze-dried fructose from type III to type II of Brunauer’s classification,and at 35°C,the proportion of wheat gluten greater than 70%had an effect on the sorption characteristics of fructose.The macroscopic and microscopic morphological pictures of freeze-dried fructose showed that the increase in wheat gluten content helped to reduce the moisture absorption and caking of the powder.The addition of wheat gluten significantly enhanced the hydrophobicity of the sample surface;and restricted the migration of water to higher degrees of freedom in the freeze-dried fructose,reducing the water absorption capacity of the fructose.3.The inhibition of the hygroscopicity of freeze-dried fructose by gliadin and glutenin was investigated.The results showed that the equilibrium moisture content of the samples with glutenin was lower than that of the samples with gliadin in the system with a fructose:gliadin/glutenin ratio of 3:7,and at 69%relative humidity,the difference between the two was higher.When the mass ratio of fructose to the two proteins was 2:8,there was no significant difference in the equilibrium moisture absorption rate of the two systems.So glutenin had a better moisture inhibition effect in the system with a higher percentage of fructose.The Peleg and GAB models were more descriptive of the fructose samples,with the Peleg model fitting the best and predicting the equilibrium moisture uptake rate more accurately.All freeze-dried samples shifted to type II isotherms,except for the 3:7 fructose to glutenin ratio which still exhibited type III isotherms.Macroscopic and microscopic images of the samples at hygroscopic equilibrium showed that both gliadin and glutenin could reduce their hygroscopicity,but glutenin was more effective,which may be related to the greater hydrophobicity of glutenin.In addition,the addition of gliadin and glutenin was able to influence the state of water in the samples,reducing water uptake and reducing the degree of water migration towards higher degrees of freedom,with glutenin having a more effective effect on reducing water freedom compared to gliadin.