From the Kitchen to the Lab: Discovery and Application of Food Catalysts to Promote the Coupling of Quinone with Amines

Biocatalysts are used to catalyze specific reactions in various industries, and they often provide environmentally friendly and sustainable alternatives to chemical catalysts. Enzymes are well-known examples of biocatalysts; however, their cata-lytic activities are lost upon denaturation. We report the discovery of novel protein-based biocatalysts from processed foods, including skimmed milk, soy milk, cheese, and tofu (dried). Considering the reaction of the physiologically interest-ing pyrroloquinoline quinone (PQQ) dehydrogenase coenzyme with amino acids, it was found that the reaction with gly-cine to form imidazolopyrroquinoline (IPQ) did not proceed when PQQ was present at very low concentrations. In con-trast, in the presence of protein-based foods, this reaction was accelerated, and it even proceeded at significantly lower PQQ concentrations (i.e., 600-times lower). It was also deduced that milk can accelerate the reaction between PQQ and various amino acids, primary amines, and secondary amines. Investigations into the reaction rate revealed that food ca-talysis is a non-enzymatic reaction. Furthermore, nuclear magnetic resonance spectroscopy was used to demonstrate that the components of milk interacted with the amino substrates owing to the ability of amines to react with quinones on colloidal surfaces. Finally, the application of skimmed milk enhanced the PQQ detection limit during HPLC following IPQ derivatization. Such food catalysts therefore show promise in the fields of biocatalysis and food technology.