Dissecting dietary alkylresorcinols: a compile of their distribution, biosynthesis, extraction and functional properties

Alkylresorcinols (ARs) are natural bioactive ingredients produced by: bacteria, fungi, sponges, and higher plants, possessing a lipophilic polyphenol structure with a myriad of biological properties. Focusing on the importance of ARs, several analogs can be extracted from different natural resources. Interestingly, the composition of ARs is usually reflective of their source, with structural differences to exist among ARs isolated from different natural sources. The identified compounds from marine are distinguished by sulfur atom and disulfide bond, while the alkyl chain of bacterial homologs are recognized for their saturated fatty acid chains. ARs occurrence in fungi is still poorly documented however most of the isolated fungal molecules are characterized by a sugar unit attached to their alkylated side chains. The biosynthetic pathway of ARs is postulated via a type III polyketide synthase in which the fatty-acyl chain is elongated and cyclized to generate ARs. The structure-activity relationship (SAR) has gained an increasing interest to mediate for ARs biological activities as discussed herein for the first time from their different resources. ARs extraction procedures showed much progress compared to classical methods compiling organic solvents with supercritical extraction appearing as a potential technique for producing highly purified food-grade of AR homologs. The current review also presents on the rapid qualitative and quantitative determination of ARs to increase accessibility for screening cereals as potential sources of these bioactives.