Liquid gels are viscous solutions that display similar properties to those of strong gels when low shear speeds are applied and act as liquids when high shear speeds are applied. The possibility of creating certain textures and the unique rheological properties of gellan gels have led to the production of liquid gels utilized in the food industry. Because gellan gels prevent particle sedimentation, they are used in fruit pulp juice or liquid foods containing cocoa, fibers, or insoluble minerals. The particles are captured in the gel structure.
The methods for producing liquid gels using gellan gum gels are the following:
gellan heating at 70-95 ºC, followed by gradual cooling and stirring;
solution heating and sudden cooling; gellan dissolution in cold water and gel formation by adding ions and stirring. The factors that influence gel formation comprise temperature, gellan concentration, cations concentration, cations type, stirring, and shear stress applied.
Any change in these factors leads to different rheological properties for a product that has a constant composition, resulting in elastic gels or fluids. The mentioned gels are considered physical gels because the connection points are formed by physical bonds, such as hydrogen bonds, hydrophobic bonds, and butt joints using cations. There have been numerous studies on the use of gellan gels. In this regard, gellan was used to stabilize Doogh, a drink produced by milk fermentation containing peppermint particles or wheat insoluble fiber. In all studies, the use of gellan liquid gel prevented the phase separation of Doogh, with changes of the rheological properties. Thus, an appropriate texture for the traditional Iranian drink was developed. The addition of gellan and fiber changed the rheological properties of Doogh from a Newtonian behavior to a pseudoplastic one. Interactions between milk proteins and gellan during the pasteurization process also led to a change of rheological properties.
Researches have been made for developing a gel used as food ingredient. This gel was formed from a deacetylated and acetylated gellan mixture to help structure the stomach content and thus, have an effect on satiety. The gellan mixture based gel is composed of separate phases, and DSC analysis shows separate conformational transitions for the two gellan variations at neutral pH. An acid pH affects the gelling properties and the structure of the mixture becomes a semi-interpenetrated network. In obtaining such a gel, the ratio between the biopolymer quantities is of major importance. Acetylated gellan is used in a proportion of about 60%.
The storage conditions of these gels can affect their properties. Supplementary studies are needed before using them as satiety increasing food agents.Mixed gels obtained from many hydrocolloids, used in the food industry, have been investigated as well.
The results have shown that food containing mixed gels exhibits superior features and a gel mixture is much more efficient than using a single hydrocolloid.These gels can provide economic and health benefits as they are used to obtain functional foods.
Oxidized cellulose, along with other gelling agents, reduces cholesterol in functional foods.The studies performed on the nutritional gels with carrot pulp proved that they can be prepared with gellan.Soumya Banerjee et al. have studied the properties of a nutritional gel based on agar, gellan, and carrot juice. For gel preparation, equal amounts of hydrocolloid solution (1%), carrot juice, and an amount of sucrose, which ranged from 7.5% to 15%, were used.Alginate gels with carrot juice showed that gel strength decreases with an increase of carrot pulp concentration and increases when a higher polymer concentration is used.Tear strength, compression energy, and syneresis of the gel increase due to carrot juice pectin.
Agar gel has a breaking tension smaller than that of the gellan gel and has no effect in the presence of pectin. Mixing the two polymers results in the formation of a more brittle gel. Sucrose improves the formed gel cohesion. These gels are healthy because they are rich in β-carotene and they also seem profitable for marketers.
