Structure formation in sugar containing pectin gels - influence of tartaric acid content (pH) and cooling rate on the gelation of high-methoxylated pectin.
The aim of the study was the application of a recently published method, using structuring parameters calculated from dG'/dt, for the characterisation of the pectin sugar acid gelation process. The influence of cooling rate and pH on structure formation of HM pectin gels containing 65 wt.% sucrose were investigated. The results show that the structure formation process as well as the properties of the final gels strongly depended on both parameters. With increasing cooling rates from 0.5 to 1.0 K/min the initial structuring temperature slightly decreased and the maximum structuring velocity increased. The lower the cooling rates, the firmer and more elastic were the final gels. With increasing acid content (decreasing pH from 2.5-2.0) the initial structuring temperatures were nearly constant. The final gel properties varied visibly but not systematically. Gels with the lowest and highest pH were less elastic and weaker compared to those with medium acid concentrations.
The Gelation Of Proteins
Publisher Summary This chapter describes the process of the gelation of proteins. Gelation is a phenomenon; therefore, its definition and that of its product, a gel, is dependent on the perspective of the observer and the technique(s) used to observe it. For example, gels may be defined by their ability to immobilize a liquid, their macromolecular structure, or their textural or rheological properties. The chapter reviews a variety of protein gel systems with a broad perspective stressing similarities between them, yet not without mentioning the important differences that make each unique. It describes the multicomponent protein gels. The rheological and optical properties of thermally irreversible gels are the outcome of two events. First, a change in protein structure is needed that permits protein–protein interactions. The subsequent aggregation process, which is highly influenced by the solvent environment, may produce the gel microstructure, which is responsible for the optical and rheological properties. The physical integrity of a gel is maintained by counterbalancing forces of attraction and repulsion among polymer molecules and between the polymer network and the surrounding solvent
Relationship of Disulfide Bond Formation to Altered Rheological Properties of Oleic Acid Modified Egg White
Egg white modification with oleic acid (OEW) had no effect on disulfide bond formation during the thermal gelation process. Lower transition temperatures were seen for oleic acid treated egg white (70°C) relative to native egg white (EW) (74°C). Torsional failure testing showed increases of 60 and 100% for shear stress and strain at failure, respectively, of OEW over EW. Dialysis, pH-adjustment, and treatment with N-ethylmaleimide (NEM) lowered stress values while shear strain Was affected only by pH-adjustment. Scanning electron micrographs indicated a more dense structure for OEW than that of EW. No visible structural change was apparent due to treatment with NEM.