Microbial gums: introducing a novel functional component of edible coatings and packaging

In recent years, the accumulation of synthetic plastics has led to the development of a serious environmental problem. Nowadays, biodegradable films and coatings have been identified as a new approach to solve this problem by preparing renewable, abundant, low-cost materials. Gums are considered a large group of polysaccharides and polysaccharide derivatives that can easily form viscous solutions at low concentrations. Gums are mainly soluble in water and are composed of sugars like glucose, fructose, and mannose. These compounds are categorized into three groups: plant-origin gums, seaweed-based gums, and microbial gums. Microbial gums are listed as generally recognized as safe (GRAS) by the Food and Drug Administration and have a broad range of physicochemical properties suitable for various pharmacy, medicine, and food applications. In the food industry, they can be used as gelling, viscous, stabilizing, and thickening agents. Among the various materials that can potentially improve the properties of biodegradable packaging films, microbial gums such as gellan, xanthan, pullulan, bacterial cellulose, and curdlan have been the subject of numerous studies. These gums can be extruded into films and coatings with considerable barrier properties against the transport of moisture and oxygen. Microbial gums, due to their microbiological stability, adhesion, cohesion, wettability, solubility, transparency, and mechanical properties, can be used as edible films or coatings. Also, these gums can be applied in combination with bioactive compounds that induce the shelf-life extension of highly perishable products. This review focuses on the properties of films and coatings consisting of xanthan, curdlan, pullulan, gellan, and bacterial cellulose.