Ms. M. Birundha1, Dr. Suresh Kumar. P2*, Ms. Pushpavalli.S1
Research Scholar1, Principal Scientist2
ICAR-National Research Centre for Banana, Tiruchirappalli.
*e-mail: [email protected]
INTRODUCTION
In recent times, edible materials like polysaccharides have gained attention because of their distinct characteristics, especially gelling properties. Polysaccharides are biopolymers categorized within the carbohydrate class. These compounds are widely present in nature and are characterized by their low-cost production, non-toxicity, biocompatibility, biodegradability, bioactivity, and water solubility. Edible gels derived from polysaccharides (PEGs) can be categorized into hydrogels, oleo gels, bigels, aerogels, cryogels, and xerogels, each serving distinct purposes. Hydrogels are hydrophilic where the primary phase is water combined with one or more biopolymers composites.
Lipids are the main component of oleo gels for forming a 3d network, entrapped in oleogelators, which can be emulsifiers or biopolymers. A combination of hydrogel and oleo gels together forms bigels containing both water and oil as the predominant phases. Aerogels are created by a 3-dimensional biopolymer chain that preserves the network structure observed in the wet state (typical of hydrogels) during the drying process. In this method, the solvent originally present in the wet state is substituted with a gas. In the food industry, Polysaccharide-based Edible Gels (PEGs) have demonstrated utility in enhancing food characteristics and have applications in food packaging. PEGs can be employed to create edible coatings that either encapsulate food items or regulate the release of active compounds.
HYDROGELS
Hydrogels are polymers that swell upon contact with water, upholding a substantial quantity of water within their enormous structure. The swelling of hydrogels includes several steps. Firstly, the polar water-loving group within the matrix undergoes hydration by water exhibiting as bound water. In the next step, the water interacts with secondary-bound water which are hydrophobic. These two successive interactions with water assist in the overall swelling of hydrogel. The next step of swelling includes osmotic driving force exerted by the hydrogel network against the dilution faces resistant to chemical or physical crosslinks present. The resistance results in additional water absorption by the hydrogel. Food products from polysaccharide hydrogels are classified into soft gels, hard gels, and fluid gels. For example, gums like gellan at low concentrations are used to stabilize beverages or protein and often exhibit a pseudo-gel system. Pudding and drinkable jelly are a few examples of the upscale level of gelling hydrocolloids are soft gels. Jams and jellies with high solid contents are hard gels with robust gel networks formed by carrageenan, pectin, and gellan gum.
OLEOGELS
Oleogels mimic a solid-like structure, where the liquid phase is immobilized within the three-dimensional network. Oleogators such as sterols, waxes, ethyl cellulose, and fatty acids are edible structuring agents added additionally in the process to achieve a solid or semisolid network structure. Formation of oleo gels has approaches: Direct approaches involve rapid dispersion of melted oleo gelators in an oil medium, following a cooling step resulting in the self-supporting gel. Over the decades oleogels have gained huge attention, especially in regulations mandating in labelling of trans fat in food products.
The solid gel structure mimics solid fat in varied aspects. Research showed positive outcomes in structural, functional, and sensory attributes while incorporating oleogels in high-fat food formulations such as margarine, confectionery, bakery items, ice cream, and meat products. Oleogels as an alternative to saturated fats in processed and comminuted meat products such as sausages and frankfurters enhances the profile of meat products in terms of fatty acids, contributing to healthy dietary choices. Oleogels also act as carriers for bioactive substances which are water insoluble, facilitate oil binding, and stabilizers in emulsifier-free products. The versatility of oleogels makes them beneficial in enhancing multiple aspects of food formulation and product quality.
BIGELS
Bigels are biphasic systems consisting of phases with different polarities and exhibiting stable structures. Comparing oleogels and hydrogels, bigels have the advantage of both phases and demonstrate superior properties compared to either of the gel components. The primary application of bigels is currently in the pharmaceutical and cosmetic industries but has emerging applications in the food sector as well. Ongoing research on food-grade bigels reveals the possibility of tailoring their, rheology, mechanical properties, and thermal stability. This allows for the potential use of bigels in food products, especially as fat replacer. Bigels in terms of their properties make them promising for improving the nutritional profile of foods.
AEROGELS.
Aerogels are ultra-light porous three-dimensional materials with polymeric chains. It is observed that in wet state during drying it maintains nano-porous networks. The materials are nano-structured in nature with dry and open pores with over 90% porosity and a surface area of 100m2/g. Aerogels are produced through supercritical drying, removing the liquid in the gel leading to the highest pore volume and varied range of textures. Supercritical drying permits slower drying of the liquid than conventional evaporation which allows the integration of gas into a solid matric of gel.
Aerogels serve as coating materials with reduced density and weight with an increase in mechanical properties, substantial surface area, and high porosity. Aerogels can be effectively used in smart food packaging materials, assisting the controlled release of active substances into the food matrix. It also has antifungal and antibacterial functions, appropriate for drug delivery systems. Aerogels along with hemicellulose, marine polysaccharides, and cellulose, or effective moisture absorbers. Particularly in meat products to restrict water activity and water condensation thus inhibiting microbial growth. Pectin-based aerogels have potential applications in insulated food packaging. They restrict heat transfer maintaining the required temperature at constant values with minor variations. This property makes aerogels based on pectin significant for controlling the temperature of varied food products during transportation and storage.
XEROGELS
A low vacuum drying method using alcohol and water as solvents is employed in producing xerogels. Characteristics of xerogels depend on the physical properties of the solvent medium and the liquid-vapor interface. The formation of pores ranges from 1 to 10 nm which makes the gel denser and the porosity range is 15-50% when compared to that of aerogels. Tapioca-based xerogel produces 2D products, further coating with ethyl acetate and cellulose and treating with cold plasms along with oil and water activation to transform them into 3D shapes.
CRYOGELS
Lyophilization and freeze-thawing are two methods involved in the production of cryogels. The gel is frozen in the freeze-drying method, where the pressure is reduced, and the solvent frozen is removed by sublimation. However, freeze-drying can influence the initial pore structure of the gel, resulting in the formation of cracks. Further, this process leads to thicker pore walls. These gels have connected microporous networks which range to a few hundred micrometres in diameter and have good mechanical properties and low surface area.
CONCLUSION
The gels made from natural polymers sourced from food hydrocolloids, particularly polysaccharides, play a crucial role as essential and functional components in the development of traditional food items and innovative food trends. Stabilization, texture adjustment, emulsification, and suspension are some of the key attributes of gels from polysaccharides. The modification of the molecular structure while manufacturing or employing a blend of available natural gelling polymers to align with current food production processes is a strategic approach. This aims to enhance the value added to food products and further broaden the applications of gels in the food industry. PEGs (polyethylene glycols) play an important role in the development of smart materials, biodegradable, and safe coating materials. In terms of dietary fibre PEG’s contribute in modulating the population of gut microbes. This is achieved by controlling common bacteria and probiotics and reduction of development of pathogens. Furthermore, PEGs function as carriers of bioactive compounds, demonstrating a positive health impact, particularly in addressing issues related to obesity.
