The above-described mechanism of pectin jelly applicable to agaropodobnyh substances. However, the nature of these gelling agents, their molecular structure and physicochemical properties require some features noted gelation process.
The molecular weight of pectin in 5 times higher than that of agar and 20 times greater than that of agaroid. Comparing the structure of the molecules of these substances, it is easy to see that in the molecules of agar and agaroid no carboxyl COOH groups, methyl groups OCH3So characteristic of the pectin molecule. The agar molecule (and possibly agaroid) sulfate group is present HS04. Hence, in a solution of magnitude of the potential on the surface of the agar and agaroid molecules will be much lower than the surface of pectin molecules. Accordingly, it will be small and the thickness of the diffusion layer. These characteristics of high-molecular ions, as noted above, determines the magnitude of the electrostatic repulsion forces at the molecular association.
From the functional groups of the molecules, it can also be concluded that the molecules of agar-like substances are less polar than the molecules of pectin; therefore, their aggregation can also occur with small amounts of sugar in the liquid phase. Even with a small concentration of hydrogen ions or potential-determining ions, barrier-free coagulation conditions are ensured. Apparently, for the molecules of agar-like substances, neutralization coagulation prevails in the solution, when the energy barrier is suppressed by the adsorption of potential ions HE ”, Ca++, Mg++ and etc.
The most important characteristic of agar and gels agaroidnyh determining their physico-chemical, structural, and mechanical properties, is the high value of the charge of the anion, which is caused by the number of sulfate groups per unit weight of gelling agents and cationic nature.
Introducing into a molecule or agar agaroid one or another cation can be known in advance to change the direction of the high amount of charge of the anion, and hence the physical and chemical properties of gelling agents.
SN Stavrova and FP Bounegru found that with an increase in the electrolytic dissociation of the cation, substituted agaroid samples, their viscosity increases in dilute solutions and the degree of swelling in water, but this decreases the ability to studneobrazovaniyu.
They have the best ability studneobrazuyuschey cation-exchanged samples Ba++ and Ca++-agaroida, ie just those molecules on the surface of which the solution will be a minimum potential.
When acidifying agar jelly masses, the concentration of potential-determining OH ions “in the liquid phase decreases, which causes a decrease in gel-forming ability. The previous interpretation of the hydrolyzing effect of acid on a molecule of agar-like substances must be considered erroneous.
The difference in the action of acids and their sodium salts on the strength of jellies is explained by various changes in the solubility of agar and agaroid. When organic acids that form insoluble or sparingly soluble salts with calcium are added to the jelly, the dissociation of molecules of partially released agar or agaric acid is largely suppressed by the acidic medium, and therefore no noticeable changes in the strength of the jelly are observed. With the introduction of sodium salts of these acids, which is often practiced in the production of jelly marmalades, agar (agaroid) is enriched in sodium, the solubility of its molecules increases, which increases the overall concentration at a given temperature and promotes the formation of stronger jellies.