Forgotten fatty acids—Surface properties supply conclusive evidence for including carotenoic acids. (November 2018) - Zaidi, Asma
Graphical abstract: Highlights: Conjugated polyunsaturated alkali carotenoates behave like detergents as do alkali carboxylates. Conjugated polyunsaturated carotenoic acids react, as do saturated carboxylic acids, with diols and triols to form fats. Polyunsaturated alkali carotenoates are more amphiphilic than alkali carboxylates with the same number of C atoms. Conjugated polyunsaturated carotenoic acids are rationally related to fatty acids. Abstract: The term "fatty acids" is conceptually well defined with regard to fats, whose extent of saturation or unsaturation is precisely indicated in the content description of foodstuff. In contrast, the term "fatty acid" gives no hint of being associated with "soap" (Na and K salts of fatty acids). Fatty acids in edible fats or in cleaning soaps have one thing in common: they are colorless. The prevalence of colorless fats and unadulterated white soaps has ensured that fatty acids are not associated with color. However, colored conjugated polyunsaturated fatty acids do exist, occurring abundantly in nature or manufactured at large scale. We endeavor to extricate conjugated polyenoic acids from oblivion by presenting new data on surface tension and critical micelle concentration of Na-, K- and Cs-carotenoates, comparing these data with Na-, K- and Cs-carboxylates, revisiting previously synthesized glycol-, glycerol- and phospholipids with carotenoic acids. Based on the presented results (alkalicarotenoates have similar surface properties to alkalicarboxylates, carotenoic acids react like carboxylic acids to lipids), we argue for inclusion of conjugated carotenoic acids in fatty acid inventories and organic chemistry textbooks. Carotenoic acids and –salts have outstanding qualities by combining visibility and traceability with biological activity.