Study On The Preparation Of Cross-linked Inulin With Different Degrees Of Polymerization And Its Application In Set Yogurt

Inulin,a natural fructose polymer,has exhibited many bioactivities such as intestinal prebiotics,promotion of mineral absorption,antioxidant property and so on,along with the ability to add texture and improve rheological characteristics and nutritional properties of food.Inulin has been increasingly used in various of foods due to its beneficial nutritional properties.Considering that the modified inulin could have some extra properties besides the original biodegradability,renewability and non-toxicity of native inulin,the modified inulin would be applied in many fields.In this paper,inulins with low and medium degree of polymerization(DP)were obtained by alcohol precipitation method with natural inulin as raw material.The preparation of cross-linked inulin was optimized by the response surface method with the cross-linking degree as an index.The cross-linked inulins with different DP which crosslinked by inulins with low and medium DP and untreated inulin were characterized.On this basis,different kinds of inulin as a stabilizer used in set yogurt,which will provide basic data and beneficial references for practical application of cross-linked inulin in set yogurt.The main results are as follows:(1)In order to find optimal conditions for the preparation of cross-linked inulin,the effects of inulin concentration,cross-linking agent dosage,pH value,reaction temperature and reaction time on the degree of cross-linking were investigated using single factor experiment.The preparation conditions of the cross-linked inulin were optimized according to central-composite design principles and response surface analysis.The result showed that the concentration of inulin,cross-linking agent dosage,pH and reaction time had significant effects on cross-linking degree of cross-linked inulin.The optimal conditions were the concentration of inulin 4.63%(w/w),cross-linking agent dosage12.04%(w/w),pH10.19 and reaction time 3.59 h.Under the optimum conditions,the cross-linking degree of cross-linked inulin was 0.0137±0.0012,which was well consistent with the predicted value of 0.013939.(2)The inulins with average DP of 4.30 and 11.37 were abtioned by alcohol precipitation method.The results of physicochemical properties of inulin with different DP showed that with the increase of DP,the intrinsic viscosity of inulin was increased significantly,thermal stability and acid stability were improved,and the solubility,moisture absorption and retention showed a decreasing trend.With the increase of DP,the gel properties were also improved,such as the size of gel particle,the VGI and gel strength were increased,and gel formation time was reduced.(3)The results of physicochemical properties of cross-linked inulin showed that the average DP of cross-linked inulin increased and cross-linked inulin has higher viscosity,lower solubility,better moisture absorption,thermal stability and acid stability compared with natural inulin.Cross-linked inulin also showed better gel properties compared with inulin,such as higher VGI,better gel water holding and freeze-thaw stability,shorter gel formation time.The trend of the physicochemical properties of the cross-linked inulin with DP was the same as that of natural inulin.(4)The results of different kinds of inulin on the quality of set yogurt showed that the addition of all kinds of inulin improved the quality of set yogurt at a certain level,especially inulin with medium DP and cross-linked inulin with medium DP.When the adding amount was 1%~2.5%,the sensory characteristics and the water holding of set yogurt can be significantly improved,the acidity,viscosity and the hardness of the yogurt can be appropriate increased.Compared the inulin with medium DP,cross-linked inulin with medium DP showed better effect on improving the water-holding capacity,hardness and viscosity of set yogurt.The microstructure observation of inulin yogurt showed that compared with control group,protein network of inulin yogurt had harder structure,more protein branch,smaller hole size due to the addition of inulin.Cross-linked inulin further increased the degree of protein crosslinking to make yogurt structure denser and more uniform.