Study On Extraction Process And Properties Of A New Thermal Gel

Curdlan also known as gelatin,has unique thermogelation and physiological functions,and has broad application infood,life and medicine.The present research focused on the fermentation and extraction of curdlan.There are few studies on the improvement of curdlan properties.In this study,the precipitation of curdlan fermentation was used as raw material,and xanthan gum was added during the alkali-soluble treatment of acid and alkali extraction process,in order to obtain a new thermal gel based curdlan with stable structure and excellent properties,which lays the foundation for the realization of industrialized production of perfect thermal gel.The main contents and results are as follows:Firstly,the fermentation strategy of the curdlan was studied at the level of 7 L fermenter.The effects of different pH control strategies,high-density fermentation strategy and natural pH drop combined with high-density fermentation on the fermentation of the curdlan were compared.Using the natural pH drop strategy,the final yield of fermentation is 42.38 g·L^-1,the total fermentation time is 96 h,the curdlan production rate is 0.58 g·L^-1·h^-1.The final yield of fermentation is 40.6 g·L^-11 by high-density fermentation strategy,the total fermentation time is 67 h,and the gel production rate is 0.812 g·L^-1·h^-1.pH natural decline combined with high-density fermentation strategy,and the final gel yield of fermentation is52.8 g·L^-1.The total fermentation time was 67 h,and the final gel production rate was 1.05g·L^-1·h^-1.Secondly,the new thermal gel extraction process was optimized.The precipitation of curdlan fermentation was used as raw material,and xanthan gum was added during the alkali-soluble treatment of acid and alkali extraction process.A new thermal gel extraction process was established.Taking the rheological and texture properties as the indicators,the best extraction process was determined by single factor experiment:the ratio of curdlanand xanthan gum was 4:1,the alkali concentration was 0.2⁰.4 mol·L^-1,stirring time was 10 h.Compared with the single curdlan,the new thermal gel obtained by the best extraction process has a 1.8-fold increase in hardness,a 3.6-fold increase in viscosity,less elastic lift,and a greater chewiness,cohesiveness and recovery.Dynamic frequency sweeping indicated the new thermal gel had a higher storage modulus G?and loss modulus G??,showingsuperior viscoelasticity.Then the physicochemical properties and molecular structure analysis of the new thermal gel obtained by the optimal extraction process were characterized.The peak temperature of curdlan and the new thermal gel were 48.48?and 60?,respectively,and the thermal enthalpy values??were 0.3359 J·g^-11 and 0.4764 J·g^-11 respectively,which indicated that the new thermal gel showed higher thermal stability.The new thermal gel has no significant functional group generation and disappearance,but curdlan molecule and xanthan gum molecule can generated network structure and the content of hydrogen bonds increased.This structural feature was consistent with the results of texture and rheological properties.The effects of temperature,ionic strength and pH on the rheology and texture properties of the new thermal gel were then investigated.The results showed that the new thermal gel also had hot gelation property,but the gelation temperatures of the new thermal gel and curdlan were 80?and 65?,respectively;A certain concentration of K⁺can enhance the texture and structure of the new thermal gel.The presence of K⁺weakened the texture and rheological properties of the curdlans,but enhanced that of the new thermal gel.,which indicated that the salt-tolerant stability of the new thermal gel was better than that of curdlan.The texture and rheological properties of the new thermal gel were enhanced under acidic and basic conditions,but the texture and rheological properties of curdlan was more suitable under neutral conditions.Finally,the effects of the new thermal gel and curdlan on the dehydration amount and rheological properties of whey protein during freeze-thaw cycle were determined.The results showed that the blank group?without adding the new thermal gel and curdlan?had the highest syneresis of 22.24%after the first freeze-thaw cycle,while the addition of curdlan and the new thermal gel can reduce the the amount of syneresis.,The addition of 0.5%(w·v^-1)curdlan and the new thermal gel of can reduce the syneresis rate to 2.89%and 0.46%,respectively.After five freeze-thaw cycles,the total dehydration amounts of blank group,curdlan group and the new thermal gel group were 44.23%,25.82%and 3.28%,respectively.The storage modulus G?of blank group,whey protein:curdlan?5:0.5?group and whey protein:the new thermal gel?5:0.5?group before the freeze-thaw cycle were 5,90 and 499 Pa,respectively.After five freeze-thaw cycles,the of blank group changed most,while the group with adding curdlan and the new thermal gel changed little,especially the storage modulus G?of adding the new thermal gel group was almost unchanged during five freeze-thaw cycles.