Preparation Of Low Methoxyl Pectin De-esterified By Different Methods And Its Stabilization Effect On Soybean Protein Solution

Pectin is a complex heterogeneous polysaccharide existing in middle lamella of plants cell walls and has been widely used in food industry as a stabilizer and thickener for its high safety.Pectin with different structure features presents various physical and chemical properties,which determines its industrial applications.Currently,researches on the relationship between pectin structure and its properties are insufficient,and mainly focus on the differences of the rheological properties between pectins extracted from different resources without systematic and practical guidance.In the presented work,commercial citrus pectin was de-esterified by alkaline and PME to prepare pectins with various DM(degree of methoxylation)values and molecular weight,and its reduced viscosity and the conditions of macroscopic gel were tested.Moreover,the stabilization effect of pectin with different structural features on soybean protein solution and soybean protein-oil emulsion was investigated,respectively,which was of the significance in practical manufacture and application of pectin.Firstly,alkaline de-esterification(4? and 20?)and enzymatic de-esterification were implemented in terms of DM values.The result showed that DM value was decreased to below 50% at the condition of pH 11.0 for 5 h under 4?,and then remained at around 15% at pH 12.0.In the same process,it took much less time to achieve lower DM values under 20?.During the enzymatic de-esterification,the DM value of pectin was negatively correlated with the amount of enzyme and reaction time,and the lower limit of DM was about 15%.In addition,the molecular chains were also degraded in some extent during the de-esterification.The molecular weight results show that the degradation strength of de-esterification methods was 20? alkaline > 4? alkaline > enzymatic method.Secondly,gelling properties and reduced viscosity of the pectin prepared by different methods were evaluated.Alkaline de-esterified pectin with lower DM(9.36%)was more likely to form macroscopic gel.The gelation of enzymatic de-esterified pectin was better than alkaline de-esterified pectin,because of the lower degradation of molecular chain.At the same time,the experimental results showed different decrease of the reduced viscosity(?red)and the intrinsic viscosity([?])of pectin samples prepared by three different methods,compared to those of the high methoxyl pectin(HMP).The [?] of HMP was about 1400 m L/g,and the ?red and [?] of the alkaline de-esterified pectin were reduced by about 50%,while the viscosity of the enzymatic de-esterified samples were close to that of HMP,indicating that the viscosity of the dilute solution was higher with the more extended molecular chain.In addition,?red and [?] all rebounded with the decrease of DM,indicating that the decrease of DM value was favorable for the extension of pectin in dilute solution,so as to improve its dilute solution viscosity.The [?] of LMP3-4(DM 14.67 ± 0.89%)de-esterified by PME even exceeded HMP to 1700 mL/g.Finally,the stabilization effect of pectin with different structural features on the soybean protein solution and emulsion system was investigated,respectively.The results showed that pectin had a better stabilization effect on soybean protein with lower DM value and longer molecular chain.Thus,LMP3-4 had the best effect on stability of soybean protein solution.The sedimentation rate decreased from 83.97±2.49% to 32.56±2.73%,and the Zeta-potential decreased from-30.7 m V to-41.9 mV.The range of particle size distribution was also reduced significantly.In addition,similar experimental results showed that the emulsion system also got a good stability with LMP3-4.