Valorization of animal by-products for gelatin extraction using conventional and green technologies: a comprehensive review

A large number of animal by-products including the bones, skins, tendons, scales, and feet are being generated around the world. These by-products are produced by meat processing facilities, slaughterhouses, and fish processing units. These are often put into landfills without any treatment, thus causing environmental pollution. However, these by-products can be used for the production of valuable compounds such as collagen and gelatin that can be used in different food products. Gelatin is the most widely used hydrocolloid in the world. By the year 2025, the market size of gelatin will exceed ~ $5 billion and is predicted to reach $6.7 billion in 2027. Therefore, gelatin recovery is beneficial both economically and environmentally. Commercially available gelatin is derived from porcine and bovine bones and skins. There are several other by-products from which gelatin can be extracted including by-products from chickens, ducks, fish, and camels. The increase in sustainable and green technologies that eliminate the usage of toxic solvents and less time for extraction has increased the demand for novel extraction processes in the food industries. The application of more recently developed techniques can be used for the extraction of gelatin to overcome several limitations of the traditional process. The present review discusses the application of conventional (hot water bath) and advanced technologies (ultrasound, microwave, or enzyme-assisted extraction) to extract the gelatin from different animal by-products. The physicochemical properties of gelatin depend on the source, extraction conditions, and pretreatment methods. These advanced techniques improve the functional properties, quality, and process efficiency of gelatin.