该文研究商业酸提法所得紫色百香果皮果胶(passion fruit pectin,PFP)的单糖组成、分子特征以及Ca2+和Zn2+致流变特性的变化, 以了解其在特殊流质食品应用的潜力。结果显示,PFP含有80.5%总糖醛酸, 酯化度75.2%, 单糖组成中半乳糖醛酸占78.5% (同质半乳糖醛酸聚糖占74.3%), 单糖组成近似商业柑橘高甲氧基果胶,其重均分子质量(Mw)为190.5 kDa; 固有黏度[η]为6.09 dL/g, 马克-霍温-樱田(Mark-Houwink-Sakurada)关系式([η]=K×Mwa)指数α为0.875; 环动半径Rg为44.5 nm, 水合动态半径Rh为25.6 nm, Rg/Rh为1.74。稳剪切测定结果显示,0.01~0.05 mol/L Ca2+或Zn2+可显著提高PFP溶液的剪切应力、表观黏度, 并提高稠度系数K和降低流体行为指数n (即提高剪切稀化现象), 在 0.05 mol/L Ca2+或0.02~0.05 mol/L Zn2+时效果最大,且Ca2+效果大于Zn2+。综合而言, Ca2+与 Zn2+添加可促使PFP溶液产生高屈服应力、高表观黏度及高K值-低n值。该研究结果可作为百香果皮果胶在特殊流质食品应用的重要依据。
The aim of this study was to identify the monosaccharide composition, molecular characteristics, and Ca2+ and Zn2+ induced rheological changes of passion fruit pectin (PFP) prepared by commercial acid extraction in order to understand the possibility of PFP applications in special fluid foods. The results indicated that PFP contained 80.5% uronic acids, degree of esterification=75.2%, and 78.5% galacturonic acid (where 74.3% homogalacturonans) in its monosaccharide composition. The monosaccharide compositions were very similar to those of commercial citrus high methoxy pectin. PFP showed, in average, a weight-averaged molecular weight=190.5 kDa; intrinsic viscosity [η]=6.09 dL/g; Mark-Houwink-Sakurada exponent a=0.875; gyration of radius (Rg)=44.5 nm; hydrodynamic radius (Rh)=25.6 nm; and Rg/Rh ratio=1.74. The results of steady-shear viscosity measurements displayed that the shear stress and apparent viscosity of PFP solution enhanced significantly in the presence of 0.01-0.05 mol/L Ca2+ or Zn2+, which accompanied with the increased consistency constant K and lessened flow behavior index n, greater shear-thinning behavior. The cation effects were greatest at 0.05 mol/L Ca2+ or 0.02-0.05 mol/L Zn2+; and Ca2+ > Zn2+. Conclusively, the addition of Ca2+ and Zn2+ improved the PFP solution of high yield stress, high apparent viscosity, and high K-low n combination. The results of this study could be an important basis for PFP applications in special fluid foods.
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