| There are rich konjac resources in our country,in which konjac glucomannan is the main functional factor.It has excellent gelling,thickening,film-forming and other physicochemical properties as well as functional effects such as reducing blood glucose and lipid,regulating intestine and enhancing immunity.However,there exist some disadvantages that limit its applications in food industry,such as lower purity,long time of complete dissolving and easy occurrence of encapsulated block during swelling process.Therefore,it is important to improve the purity of KGM and develop gel products.Single KGM gel has some shortcomings,such as lack of hydrophobicity,high viscosity,low solubility and unstable property.Compounding of natural hydrocolloids is an easy and effective method for overcoming the deficiency of a single gel.In this study,KGM was purified with ethanol precipitation which was assisted by ultrasonic wave-microwave,using konjac flour as the raw material.Then,composite gel was prepared by KGM and GA.Changes of gel properties as well as the synergy between KGM and GA were analyzed.Further,the impact of?-cyclodextrin on KGM/GA composite gel was studied.Finally,the optimal process of KGM/GA sol was determined.The main contents and results of our experiment are as following:(1)KGM was purified by ethanol precipitation assisted by ultrasonic wave-microwave.The optimal process parameters which were determined by single factor test and response surface methodology are as following: ethanol concentration70%,material to liquid ratio 1: 120,ultrasonic power 300 w,ultrasonic time 33 min,microwave power 300 w,and microwave time 10 min.Under these conditions,KGM purity can reach 96.87%.(2)Composite gel was prepared by KGM and GA.The results of water solubility,water absorption,texture,rheology,Fourier transform infrared and scanning electron microscope are as following: The addition of GA can improve water solubility and water absorption of gels.When GA concentration is lower(0?2.0%),with the increase of GA,hardness and springiness of gels decline,but cohesiveness increases;gel strength decreases and network structures become looser.However,when GA increases from 2.0% to 4.0%,hardness and springiness increase,but cohesiveness decreases;gel strength increases and network structures become denser.KGM/GA composite gel is a physical gel,with shear thinning property.Non-covalent linkages mainly involve hydrogen bonding and hydrophobic interaction,in which hydrogen bonding is dominant.KGM and GA have antagonistic effect at low GA concentrations and synergistic effect at high GA concentrations.(3)The effect of ?-cyclodextrin on KGM/GA gel was studied.The results of water solubility,water absorption,texture,rheology,Fourier transform infrared and scanning electron microscope are as following: Water solubility and water absorption of gels both increase with ?-CD.When ?-CD increases from 1.0% to 2.0%,hardness and springiness of gels increase,but cohesiveness decreases.When ?-CD increases from 2.0% to 3.0%,the trends are opposite.?-CD can promote hydrogen bonding and hydrophobic interaction,resulting in higher gel strength and denser network structures.However,it does not alter the non-Newtonian pseudoplastic property and anti-thixotropy of gels.An appropriate amount of ?-CD can improve properties of KGM/GA gel.(4)KGM/GA composite sol was prepared according to the interaction between KGM and GA.The viscosity of KGM is exponentially related to concentration.The antagonistic effect is strongest when the ratio of KGM to GA is about 7: 3.The optimal conditions of KGM/GA sol which were determined by single factor test and quadratic regression orthogonal experiment are as following: KGM concentration1.75%,GA concentration 1.02%,?-CD concentration 0.6% and stirring time 50 min.At this time,the sol viscosity can reach 49.11 Pa·s. |
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