Gel Firmness Research Articles

A New Biopolymer for High-Temperature Profile Control: Part 1—Laboratory Testing

Summary An extracellular polysaccharide produced by Alcaligenes bacteria has been crosslinked to form firm gels that are stable for long periods at elevated temperatures. The biopolymer can be gelled with multivalent ions such as Cr+3; it can also be gelled at the 2, 000-to-4, 000-ppm level without Cr+3 in high-salinity [∼20% total dissolved solids (TDS)] brines. Gel samples have been stable for 2 years at 74 and 93°C. Gels could be formed over a wide pH range, but best long-term stability was achieved in the pH range of 7 to 8. A flow test of Alcaligenes biopolymer gel in Berea sandstone at 74 °C showed that the gel gave a brine permeability reduction factor of 320.

High-purity isolation of bullfrog hair bundles and subcellular and topological localization of constituent proteins.

The small number of hair cells in auditory and vestibular organs severely impedes the biochemical characterization of the proteins involved in mechano-electrical transduction. By developing an efficient and clean "twist-off" method of hair bundle isolation, and by devising a sensitive, nonradioactive method to detect minute quantities of protein, we have partially overcome this limitation and have extensively classified the proteins of the bundles. To isolate hair bundles, we glue the saccular macula of the bullfrog to a glass coverslip, expose the tissue to a molten agarose solution, and allow the agarose to solidify to a firm gel. By rotating the gel disk with respect to the fixed macula, we isolate the hair bundles by shearing them at their mechanically weak bases. The plasma membranes of at least 80% of the stereocilia reseal. To visualize the proteins of the hair bundle, we covalently label them with biotin, separate them by SDS-PAGE, and transfer them to a charged nylon membrane. We can detect less than 500 fg of protein by probing the membrane with streptavidin-alkaline phosphatase and detecting the chemiluminescent product from the hydrolysis of the substrate 3-(4-methoxyspiro-(1,2-dioxetane-3,2'-tricyclo-[3.3.1. 1(3.7)]decan)-4-yl) phenyl phosphate (AMPPD). These techniques reveal a distinct constellation of proteins in and associated with hair bundles. Several proteins, such as calmodulin, calbindin, actin, tubulin, and fimbrin, have previously been described. A second class of proteins in the preparation appears to be derived from extracellular sources. Finally, several heretofore undescribed bundle proteins are identified and characterized by their membrane topology, subcellular localization, and glycosidase and protease sensitivities.

Surface Tension, Spinnability, and Gelation of Denatured Carp Actomyosin Preparation.

Actomyosin preparation was treated by denaturating agents. When NH2C(=NH)NH2HSCN was added to actomyosin preparation in water or 0.6M KCl, surface tension and spinnability showed the maximum around 3M, decreased at 6M and decreased farther at 8M. When CO(NH2)2 was added to actomyosin preparation, surface tension and spinnability showed the maxima at 2M and around 8M. It was suggested from the great changes of surface tension and spinnability that structure change (unfolding) of actomyosin was induced with the treatments by these denaturating agents. When actomyosin preparation in water or 0.6M KCl was treated by NH2C(=NH)NH2HSCN or CO(NH2)2 and dialysed against water to remove the denaturating agent, 6M-treatment pro-duced firm gel, 4M-treatment produced medium gel, and 8M-treatment produced soft gel. It was concluded that the local unfolding of actomyosin molecule by 6M-treatment was more favoured for the gelation of actomyosin than the complete unfolding by 8M-treatment. When actomyosin preparation was treated by NH2C(=NH)NH2HSCN and dialysed against 0.6M KCl in place of water, the gel made by 6M-treatment was softer than the gels made by 4M- and 8M-treatments.

A Computerized Curd Firmness Meter

The curd firmness meter was interfaced with an Apple IIe computer to increase both the efficiency of the instrument and the accuracy of the instrumental measurements. The computerization allows for collection of real-time data, graphical analysis, and maintenance of results in a data base capable of generating reports. The newly modified curd firmness meter can measure the firmness of cheeses and gels. The mean, lowest, and highest firmness points are obtained from the computer-generated, force-time curve. The mean firmness values distinguish among samples, and the low and high firmness points give information on variability within samples.

Reduction of postoperative adhesions in the rat uterine hornmodel with poloxamer 407

Adjuvants shown to have significant adhesion prevention capabilities have been based on barrier separation of deperitonealized surfaces. We investigated the adhesion prevention properties of poloxamer 407. This polyol, in the proper concentration, is fluid at room temperature and becomes a firm gel at body temperature. The prevention of postoperative adhesions was evaluated in the rat uterine horn model. Twenty-two rats underwent bilateral surgical injury to the uterine horn and the parietal peritoneum. A random side was treated with a 30% solution of poloxamer 407. Twenty-one days later the animals were sacrificed and evaluated for the presence of adhesions. A highly significant reduction in adhesion formation was documented on the treated side.

An improved formulation and method of preparation of crystal violet pectate medium for detection of pectolytic erwinia

An improved procedure for the preparation of CVP medium is described on which pectolytic erwinia rapidly develop deep, localised pits. The medium can be prepared quickly and easily and forms a smooth, firm gel suitable for streaking.

Characteristics of Bovine Plasma Gels as Affected by pH Sodium Chloride, and Sodium Tripolyphosphate

ABSTRACTA model system, which simulated the pH, sodium chloride (NaCl), and alkaline phosphate (STP) levels of typical processed meat products, was used to determine the effect of NaCl, STP and pH on firmness and percent cooked yield of bovine plasma gels. Bovine plasma gel firmness increased with increasing plasma pH, whereas percent cooked yield was not affected. In contrast, when the pH, of the plasma solutions, was adjusted to a constant 5.6 to simulate the pH and buffering of meat, percent cooked yield was affected; gel firmness was not affected. With increased levels of NaCl and STP, the percent cooked plasma gel yield increased.

Properties of Mixed and Filled‐type Dairy Gels

ABSTRACTSkim milk powder (SMP), a whey protein concentrate (WPC) and fat globules with modified membranes were used for the fabrication of mixed and filled dairy gels. Firmness and syneresis of pure gels varied broadly with pH and total solids (TS). Mixing SMP and WPC at 10% TS showed synergistic effects on gel firmness, particularly for 50:50 blends, and addition of fat provided further reinforcement. Syneresis of gels and their appearance changed from high and clear to low and turbid, respectively, as the WPC content was increased. Microstructural studies revealed the porous structure of the parent gels, compatability between both protein sources and between fat globules and the protein matrix.

Chickpea, mungbean, cowpea and peanuts as substitutes for soybean curds

SummaryAcceptable beancurds could not be formed from chickpea, mungbean, cowpea and peanuts, when using the standard procedure used to make soybean curds. Firmness (rigidity) of the curd was proportional to the protein content; inversely proportional to the square of the starch content; and negatively correlated with the square of the fat content. Firmness also improved the taste of the curds. Satisfactory curds could be formed from legume sources other than soybean only after the partial removal of starch (in chickpea, mungbean and cowpea) or oil (in peanuts). Calcium sulphate was the best coagulant; optimum concentrations were 0.3% (0.02 M) of the milk; and optimal heating time was 15 min at 95°C. Stirring during coagulation aided formation of firmer gels. The rigidity moduli of the various curds were: soybean 51 000 N m−2; peanuts 2200 N m−2; chickpea 6000 N m−2; mungbean 11 000 N m−2; and, cowpea 29 000 N m−2. Chickpea and mungbean curds were rated as liked (2.0 and 1.8 respectively), almost as well as soybean curds (1.5); cowpea (3.1) and peanut (4.2) curds were less preferred.

Effects of Polysaccharides on Rennet Coagulation of Skim Milk Proteins

The effects of commercially available polysaccharides on rennet coagulation of milk were investigated. Polysaccharide material from a slimy strain of Lactococcus lactis was examined. Clotting time was measured using a rolling bottle method and a Formagraph. The Formagraph also indicated the rate of curd firming and final curd firmness. Clotting time was reduced, curd formation rate increased, and curd firmness reached a maximum with addition of low methoxyl pectin. Xanthan reduced curd formation rate and decreased gel firmness. The polysaccharide from L. lactis produced results similar to low methoxyl pectin.

Functional Properties of Cryocasein

Functional properties of casein isolated by UF and cryodestabilization as compared with commercial caseinates were assessed. Cryocasein was readily resuspended in water by the application of agitation and mild heat. Solubility profiles of cryocasein suggested a partial disintegration of micellar structure by the changes in pH and ionic strength. In spite of its resuspendibility, the emulsifying properties of cryocasein were not as good as those of commercial caseinates. Cryocasein retained the ability of native casein micelles in milk to form a curd upon rennet addition. It formed a firmer gel with a lower syneresis than sodium caseinate and calcium caseinate with added CaCl2.

Gel-Forming Characteristics of Milk Proteins. 1. Effect of Heat Treatment

Skim milk with or without preheating (60 to 80°C for 30min) were acid coagulated at 60 to 80°C for 1h with glucono-delta-lactone. Preheating below 70°C has no effect on gel firmness and water-holding capacity. When coagulated below 70°C, the gels were weak and had low water-holding capacity. When coagulated at 80°C, the gels were solid and had high water-holding capacity. Gels prepared from skim milks preheated to above 80°C had a different quality: when coagulated at less than 70°C, gel firmness increased slightly, and when coagulated at 80°C, gel firmness decreased sharply. Change in the accessibility of sulfhydryl groups in milk protein caused by heating, was also measured using Ellman's reagent. Changes in the gel-forming property of milk protein, caused by the heat treatment, were closely related to increase in available sulfhydryl groups in milk proteins, and also were related to heat denaturation of whey protein or the formation of β-lactoglobulin/κ-casein complex.

Gel-Forming Characteristics of Milk Proteins, 2. Roles of Sulfhydryl Groups and Disulfide Bonds

The gel-forming characteristics of milk proteins were investigated by employing skim milk either nonpreheated or preheated at 80°C, and coagulating them at 70 or 80°C with glucono-delta-lactone. The solubility of each gel in the phosphate buffer (pH 7.0) containing urea and 2- mercaptoethanol was examined. The disulfide bonds played a more important role in the gel coagulated at 80°C from skim milk preheated at 80°C than in the gel coagulated at 70°C from nonpreheated skim milk.The effect of the reduction treatment with 2-mercaptoethanol was more pronounced on preheated skim milk than on nonpreheated skim milk. Sulfhydryl groups and disulfide bonds, which were buried in the molecules of whey proteins in their native state, were rendered accessible following heat treatment at 80°C.The gel prepared from skim milk pretreated with oxidizing agent, hydrogen peroxide (i.e., skim milk has no accessible sulfhydryl groups as a result), or the gel prepared from skim milk pretreated with reducing agent, 2-mercaptoethanol, (i.e., skim milk has few disulfide bonds as a result), displayed weak gel formation. But the gel prepared from the mixture of these skim milks with appropriate ratio displayed higher gel firmness. These findings suggest that intermolecular disulfide bonds are formed by the exchange reaction between sulfhydryl groups and disulfide bonds during gel formation.

The influence of cation and gelling agent concentrations on vitrification of apple cultivars in vitro

Shoot tips of ‘York’ and ‘Vermont Spur Delicious’ apples (Malus domestica Borkh.) were cultured in vitro to test the influence of K+, Mg++ and gelling agent concentrations on vitrification. These concentrations were 20.05, 14.05 and 8.05 mM K+, 1.5 and 3.0 mM Mg++, 7.0 g/l Difco Bacto agar and 1.0, 1.5 and 2.0 g/l Gelrite. The lowest K+ level produced a higher percentage of vitrified shoots, affected tissue appearance, reduced shoot number and shoot elongation and apparently altered shoot metabolic activity. Gelrite consistently produced vitrified leaves and stems, even though media gelled with 1.5 g/l Gelrite presented the same apparent gel firmness as using 7 g/l Difco Bacto agar, which did not induce vitrification. Less shoot elongation, fewer total shoots, and more usable shoots of ‘York’ were obtained on Bacto-agar, while similar but less noticeable effects were obtained with ‘Vermont Spur Delicious’. The results presented here show that vitrification can be studied in a standardized system in which the only change is substitution of one gelling agent for another.

Curdlan Gel Formed by Neutralizing Its Alkaline Solution

When an aqueous alkaline solution of curdlan in the stationary state was neutralized with carbon dioxide, it became a firm gel with slight syneresis, the resultant gel showing high syneresis when freeze-thawed. This gel behavior differed from that of the gels obtained by heating an aqueous suspension of curdlan at high temperatures. The dried matter obtained by pressing the unheated gel to remove the water could be regenerated into a gel by soaking it in water. Curdlan powder, which was obtained by crushing the dried matter, was found to be a good material to form a gel. However, curdlan powder obtained from gels that were formed by heating an aqueous suspension of curdlan could not produce a good gel. An electron microscopic study showed no significant difference between the preparations of original curdlan and the gels formed by neutralizing its alkaline solution.

The kinetics of milk coagulation: IV. The kinetics of the gel‐firming process

A mechanistic kinetic model of gel firmness development during milk gel formation is presented. The model correctly accounts for the influence of enzymatic kappa-casein hydrolysis on the rate of firmness development in renneted milk gels. The model used is based on two first-order reactions occurring in series. The first reaction is enzymatically controlled and corresponds to the formation of gel crosslink sites by kappa-casein hydrolysis. The second reaction is nonenzymatic and corresponds to the process of crosslink formation and depletion of active sites. The model successfully predicts gel firmness development in the temperature range 31-45 degrees C for a variety of initial enzyme concentrations.

Curdlan gel formed by neutralizing its alkaline solution.

When an aqueous alkaline solution of curdlan in the stationary state was neutralized with carbon dioxide, it became a firm gel with slight syneresis, the resultant gel showing high syneresis when freeze-thawed. This gel behavior differed from that of the gels obtained by heating an aqueous suspension of curdlan at high temperatures. The dried matter obtained by pressing the unheated gel to remove the water could be regenerated into a gel by soaking it in water. Curdlan powder, which was obtained by crushing the dried matter, was found to be a good material to form a gel. However, curdlan powder obtained from gels that were formed by heating an aqueous suspension of curdlan could not produce a good gel. An electron microscopic study showed no significant difference between the preparations of original curdlan and the gels formed by neutralizing its alkaline solution.

The physicochemical properties and the process of pyrogel formation of IgD pyroglobulin

The extremely rare IgD pyroglobulin caused opalescence, lost its antigenicity and acquired more negative charge when heated for 30 min at 56°C. Exposure to 60°C for 60 min produced a firm gel. The thermoprecipitability was abolished by the treatment with guanidine, urea and sodium dodecyl sulfate, but not by 2-mercaptoethanol or neuraminidase, and required the presence of both heavy and light chains. However, amino acid analysis showed abnormalities only in the heavy chain. We hypothesize that the irreversible heat-induced aggregation of IgD pyroglobulin is the result of a conformational change, triggered by light chain, which increases the molecular hydrophobicity.

Contribution of Paramyosin to Marine Meat Gel Characteristics

ABSTRACTThe properties of the paramyosin‐natural actomyosin system gels were considerably improved by paramyosin, and a strong and firm gel was formed. This effect of paramyosin on gel properties was large at relatively low paramyosin contents. Paramyosin considerably altered the characteristic texture of the marine meat gel products made from invertebrate meats. Two‐step heating, including the low temperature setting, was effective in increasing the gel strength for the paramyosinnatural actomyosin system gels. The strengthening effect of setting on the gel strength became larger on increasing the paramyosin content.

Gelation Mechanism of Protein Solution by Transglutaminase

Transglutaminase catalyzes the formation of e-(γ-glutamyl)lysyl cross-links within and between protein molecules. Therefore, transglutaminase polymerizes proteins through the formation of isopeptide bonds. We have reported that several high-concentration protein solutions formed firm gels when they were incubated with transglutaminase. This paper presents unambiguous evidence that αs1-casein solution is gelled by the formation of e-(γ-glutamyl)lysyl cross-links. Gelation of αs1-casein was effected by the amount of transglutaminase and pH value, and αs1-casein gel was not dissolved by various denaturants. Succinylated αs1-casein, in which e-amino groups of lysine residues are blocked, was not gelled by transglutaminase. Therefore, it is confirmed that αs1-casein is formed by the action of transglutaminase.