A new application of a commercial microtiter plate-based assay for assessing the antimicrobial activity of Maillard reaction products

A new application of a commercial microtiter plate-based assay was developed for the quantitative screening of antimicrobial compounds formed during the thermal treatment of foods. Such compounds called Maillard reaction products (MRP) are widely distributed in the diet of western countries. The reported method is fast, cheap and easy and facilitates the generation of a dose-response curve which allows calculating the antimicrobial activity of most substances at the same time as minimum inhibitory concentration (MIC) or as oxytetracyclin equivalent value (OTEV). The test is accurate and highly reproducible (inter- and intra-day variation of 2.3% and 1.8%, respectively). For the tested samples, the higher antimicrobial activity was found in coffee melanoidins (high molecular weight fraction of MRP) although non-covalently melanoidins-linked compounds showed antimicrobial activity too. In addition, melanoidins from more severely treated samples exerted higher inhibitory bacterial growing activity, such as CTn60 coffee (highest roasting degree) and dark beer.