Schematic diagram on the preparation of polyethyleneimine-modified MOF-derived carbon (PEI@MDC) samples and the Congo red dye adsorption process.

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In last years,consumers pay more attention to natural and body-friendly pigments. There is a great tendency to promote and popularize natural dyes instead of synthetics. But instability of these natural pigments has many negative impacts on application. However,melanoidins,high molecular weight brown nitrogenous polymers formed at the end of the Maillard reaction,are increasingly studied by scholars ascribe to its enormous biological activity. They are normally formed during heat processing of foods. This brown-colored compounds may be a natural pigment due to its desirable dark brown and biological activity. what's more,its ability is superior to other natural pigments. On the other hand,this compounds' isolation and purification are the key step for further use and biological maintenance in various kinds of industries. However,the selection of methods is mainly dependent on their structure. It is necessary to seek out some effective modification or advanced technologies to update and even take place of the traditional methods, among which a large quantity of ways about extraction is time-consuming. Hence,this review summarizes extraction methods of melanoidins,exploring the recent literature regarding the feasibility of emerging extraction methods and as a new potential natural pigment.