A comprehensive review on marine by-products use for the recovery of value-added products

The research on valorizing marine by-products has gained momentum over the past few years due to the limited marine resources and the increasing demand for sustainable sources of functional, nutritional ingredients and biomaterials. Two mean valorization approaches are distinguished in the use of marine by-products: the massive production of fishmeal and fish oil for feed, primarily through the wet reduction process and the new trends of producing high-value bioactive compounds with developed technologies, such as protein hydrolysates, gelatin and collagen, chitin and chitosan, hydroxyapatite, astaxanthin, biofuels, and minerals. This review aims to provide a summary of the bioactive compounds derived from marine by-products, their properties and the various conventional and new technologies used for their valorization over the past two years. The review is organized into four sections that present the valorization of by-products according to four primary marine categories: fish, crustaceans, cephalopods, and bivalves.