Gel in Food Products Structure
Gels are an essential part of the structure of many food products. Almost all semi-solid foods have a gel-like structure. These structures can either be water-based (hydrogel) or oil-based (oleogel). Gel structures are highly dependent on the characteristics of the molecules that make them up, the type of molecular interactions, and the chemical properties of the gel-forming environment, particularly ion concentration (oleogels and reducing saturated fats).
Gel Structure Response to Temperature
One of the most important parameters in food formulations is the gel structure response to food temperature. During the formulation phase, the molding and packaging processes are heavily reliant on the gel’s setting temperature and the solidification of its structure. From a sensory perspective, if a product does not melt at body temperature, it will be less appealing (importance of sensory evaluation in market development). Temperature changes during distribution and shelf life can affect the gel structure and alter the product’s shape and integrity. In processes like 3D printing, the thermal behavior of the gel plays a crucial role in designing the printing material fluid (potential of 3D printers in the food industry).
ThermoReversible Gels
Gel structures are formed by a transition from a sol to a gel. In most cases, a sol structure at a temperature above the gel formation temperature, containing high-energy molecules with a random molecular shape, will, upon cooling, reduce the energy within the entire system. Under the right conditions, the molecules will organize into a network. However, once the gel structure is formed, it will not necessarily break down with an increase in temperature above the gel formation temperature, even several degrees higher.
It’s important to note that this refers to temperatures below the boiling point of water; when temperatures rise above 100°C, due to the system’s higher energy, different behaviors may be observed. Thus, the concept of thermal reversibility of a gel applies primarily to the temperatures encountered during the packaging, storage, and consumption stages of food. Thermo-reversible gels offer great flexibility for formulations, although in some cases, non-reversible gels are also needed. Most thermo-reversible gels are formed from gel structures based on ionic bonds and active groups. It should also be noted that the gel setting temperature and the gel melting temperature are different, and processes such as packaging depend on the gel setting temperature.
Gelatin
Gelatin is likely the most well-known hydrocolloid with thermo-reversible properties. More importantly, the melting temperature of gelatin gel is close to the human body temperature, which creates a pleasant mouthfeel when it melts during consumption. This feature, along with its soft gel structure, makes gelatin an unrivaled choice in various products, especially gummy candies.
Agar
Agar is a hydrocolloid extracted from algae and is quite expensive. Due to its ability to form thermo-reversible gels and its strong gel structure, agar is used in various food products. Although agar forms a thermo-reversible gel, its melting point is typically higher than 80°C under standard conditions. This temperature range is significant for baked goods that undergo high-temperature processes.
Kappa and Iota Carrageenan
Kappa and iota carrageenan are among the most widely used hydrocolloids in food products, especially dairy and meat items. These hydrocolloids also exhibit thermo-reversible gel properties. The melting temperature of Kappa carrageenan gel is around 60°C, while Iota carrageenan melts at approximately 50°C. This feature allows for re-melting of formulations for packaging purposes.
Low Methoxyl Pectin
Low methoxyl pectin is a hydrocolloid used to form soft gels that require acidic conditions and of calcium ions at optimal concentrations. The gel formed by low methoxyl pectin transforms from a sol to a gel at approximately 60°C.
Modified Starch
Modified waxy starches, treated with amylomaltase, possess thermo-reversible properties and provide a suitable mouth-feel similar to gelatin in products such as yogurt (why waxy starches are widely used).
