超高压下Ca^(2+)与Na^+离子对甜菜果胶结构及流变性质的影响

Effects of Ca^(2+) and Na^+ Ions on the Structure and Rheological Property of Sugar Beet Pectin Under High Hydrostatic Pressure

[目的]研究超高压下不同浓度Ca2+与Na+对甜菜果胶结构及流变性质的影响,为甜菜果胶在食品中的应用提供理论依据。[方法]甜菜果胶用浓度0.05 mol·L-1的Tris-HCl溶液溶解,添加不同浓度Ca2+(2、12和20mmol·L-1)和Na+(0.05、0.1和0.6 mol·L-1),配制成1%(w/v)甜菜果胶溶液后进行超高压处理,然后分别对甜菜果胶分子量、微观结构、黏度和动态粘弹性进行测定。[结果]与常压下相比,在450 MPa条件下处理不同时间(10、20、30和50 min)后,甜菜果胶在1 550 cm-1处均出现新的吸收峰,甜菜果胶溶液的屈服应力σ0显著增加,但不同超高压处理时间之间无显著差异。添加不同浓度Ca2+或Na+的甜菜果胶在450 MPa条件下处理30 min,其结构及流变性的变化有所不同。相对于未添加Ca2+或Na+的甜菜果胶,添加2 mmol·L-1 Ca2+离子使甜菜果胶溶液屈服应力σ0、储能模量G’和损耗模量G"均明显增加,当Ca2+浓度增加到12 mmol·L-1和20 mmol·L-1时,果胶的流变性质变化不显著;添加2 mmol·L-1 Ca2+使甜菜果胶分子发生明显的交联。果胶分子量由只高压处理的2.25×105 Da显著增加到6.07×105 Da,Ca2+的添加浓度增加到20 mmol·L-1,果胶的分子量变为5.99×105 Da,与添加2mmol·L-1 Ca2+时没有显著差异,其流变性质变化亦不显著。相对于未添加Ca2+或Na+的甜菜果胶,添加0.05 mol·L-1 Na+也使甜菜果胶的屈服应力σ0显著增加,并且随着Na+浓度的持续增加,果胶的屈服应力σ0显著增加;而只有当Na+浓度增加到0.6 mol·L-1时,甜菜果胶储能模量G’和损耗模量G"才发生明显增加。添加0.1 mmol·L-1 Na+的甜菜果胶,其果胶分子链相互交联成网状,果胶分子发生明显聚集,果胶分子量显著增加到11.95×105 Da;而当Na+浓度增加到0.6 mol·L-1时,果胶链呈棒状结构,果胶分子量显著降低到5.53×105 Da。[结论]超高压下Ca2+与Na+可能与甜菜果胶分子结合使其结构发生改变,进而影响甜菜果胶的结构及流变性质。

[Objective] This study was in order to discuss the influence of metal ions（Ca^2＋ and Na^＋） sodium on the structure and rheological properties of sugar beet pectin under high hydrostatic pressure（HHP）,and to provide theoretical basis for the application of sugar beet pectin in food.[Method] 1%（w/v） sugar beet pectin solution which was prepared by 0.05 mol·L^-1Tris-HCl solution with adding different concentrations of Ca^2＋（2,12 and 20 mmol·L^-1） and Na^＋（0.05,0.1 and 0.6 mol·L^-1）,was treated under HHP,and the molecular weight,microstructure,viscosity and dynamic viscoelasticity of sugar beet pectin were investigated.[Result] Compared with the control one,new peaks were shown at 1 550 cm^-1 and the yield stress σ0 increased significantly for sugar beet pectin treated at 450 MPa for 10,20,30 and 50 min,but there were little changes between the different treatment time.Sugar beet pectin with adding different concentrations of calcium or sodium ions was treated under 450 MPa for 30 min;the changes of its structure and rheological property were different.Relative to no add calcium or sodium ions,the σ0,G＇ and G＂ of sugar beet pectin increased significantly when adding 2 mmol·L^-1calcium ions,when the concentration of calcium ions increased to 12 mol·L^-1 and 20 mol·L^-1 ,there was little change compared with add 2 mmol·L^-1calcium;adding 2 calcium ions in the sugar beet pectin made the pectin crosslinking,and the molecular weight of sugar beet pectin was increased from 2.25 × 10^5 Da to 6.07 × 10^5 Da;with the concentrations of calcium ions was increased to 20 mmol·L^-1,the molecular weight of pectin into 5.99 × 10^5 Da,and there was no significant differences with the sugar beet pectin add 2 mmol·L^-1,calcium ions,and also its rheological properties.Relative to no add calcium or sodium ions,add 0.05 mol·L^-1,sodium ions also made the yield stress σ0 of sugar beet pectin increase significantly,and with the increase of sodium ion concentration,yield stress σ0 of pectin was increased significantly.when the concentration of sodium ion was increased to 0.6 mol·L^-1,the G＇ and G＂ of sugar beet pectin was increased obviously.After adding 0.1 mol·L^-1,sodium ions,sugar beet pectin chains formed reticular by crosslinking with molecular weight significantly increased to 11.95 × 10^5 Da.However,when added 0.6 mol·L^-1 sodium ion,the molecular weight of pectin was decreased to 5.53×10^5 Da with virgate structure.[Conclusion] The calcium and sodium ions might change the structure of sugar beet pectin under HHP treatment,thus affect its structure and rheological properties.