Temperature gelation

Agar, which is low in metabolizable or inhibitory substances, debris, and thermoduric spores, is ideal for the propagation and pure culture of yeasts, molds, and bacteria. Agar also meets the other requirements of ready solubiUty, good gel firmness and clarity, and a gelation temperature of 35—40°C and a gel melting temperature of 75—85°C. A clarified and purified form of the bacterial polysaccharide, geUan gum, is the only known satisfactory substitute. 

Chatterjee S., Bohidar H.B. 2005. Effect of cationic size on gelation temperature and properties of gelatin hydrogels. International Journal of Biological Macromolecules 35, 81-88. 

Effect of Different TEOS/H2O Mole Ratios, pH, and Gelation Temperature... 

AND GELATION TEMPERATURE ON STRUCTURE AND PROPERTIES OF THE HYBRID COMPOSITES... 

The gelling temperature is an important factor for the characterization and application of pectins. The pectin consumer wants a pectin fulfilling his special requirements, this can mean either working with or without pregelation. Pregelation, the weakening of gel structure, occurs when pectin preparations are stressed below their gelation temperature so that the mechanical treatment leads to an irreversible destruction of the three-dimensional network. 

Rgure 2.39. Evolution of the wetting transition temperature T (c) for macroscopic interfaces and gelation temperature Tg(c) of emulsions of various droplet sizes. (Adapted from [113].)... 

While gelation temperature Is usually considered a characteristic property of a given protein system, the heating conditions required for gel formation may be Interrelated to all of the previously mentioned factors. It has been observed that WPG dispersions In 0.2 M NaCl will gel at 75 C while a temperature of 90 C Is required to gel WPG dispersions In distilled water (1). Heating time, at a specific temperature, required to form a protein gel structure Is generally considered to decrease with Increased protein concentration. Alteration of heat treatment conditions affects the gel s macroscopic and microscopic structural attributes. This has been dramatically shown by Tombs (A) with electromlcroscoplc evaluation of bovine serum albumin gels. 

The present article first provided the brief overview of the synthetic methods of the porous carbons. In order to prepare the microporous carbons with high surface area, the physical/chemical activation methods have been widely used for a long time.18"35 Recently, the meso/macroporous carbons with various pore structures are prepared by templating methods by using various templates and changing sol-gel reaction conditions, e.g., pH, amount of template, and gelation temperature.17,36 55... 

Fig, 7.—Upward shift of the gelation temperature of starch granules under the influence of high pressure (from Ref. 58). 

Walter, R. H., and Sherman, R. M. (1986). Rheology of high-methoxyl pectin jelly sols prepared above and below the gelation temperature. Lebensm. Wiss. Technol. 19 95-100. 

Methylcellulose solutions generally form gels at higher temperatures. The gelation temperature is increased when hydroxyethyl or hydroxypropyl groups are introduced into the methylcellulose (cf. Section 9.6.2). Hy-droxyethylmethylcellulose and hydroxypropylmethylcellulose are prepared industrially by the reaction of alkali cellulose first with ethylene oxide or propylene oxide and then with methyl chloride. Similarly, hydroxyethyl-ethylcellulose is prepared by consecutive ethylene oxide and ethyl chloride treatments. Cellulose ethers with both methyl and ethyl groups have also been manufactured. 

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