Nushin Niknia - PhD candidate of Food Science & Technology, Research Institute of Food Science & Technology,

Hydrogels are three-dimensional, hydrophilic, polymeric networks that are capable of absorbing large quantities of water without being dissolved. Their ability to absorb water arises from the hydrophilic functional groups attached to the polymeric backbone, while their resistance to dissolution is related to the cross-links among network chains. Due to high water content, hydrogels have similar physical properties as that of living tissue and, moreover, the ability of molecules of different size to diffuse into and out of their structural network makes them suitable candidate as delivery systems. According to the nature of the cross-link junctions, hydrogels can be categorized to chemical and physical ones. In physical hydrogels cross-linking is achieved by changing environmental condition i.e. pH, temperature, ionic strength and a variety of physicochemical interactions i.e. hydrophobic interactions, hydrogen bonding, charge interaction, and stereocomplexation. In contrast to physical cross-linking, the chemical type is achieved through the reaction of their functional groups (such as OH, COOH, and NH2) with cross-linkers. Building blocks of hydrogels can be of natural origin or synthetic. In this article we will review the methods used to make hydrogels from natural polymers for different delivery purposes in the food industry and the factors influencing the retaining properties and release rate of core material will be discussed.

Hydrogel, chemical gels, physical gels, drug release