Antimicrobial activity of melanoidins against Escherichia coli is mediated by a membrane-damage mechanism.
Melanoidins are brown polymeric material formed during thermal processing of food and widely distributed in the Western diet. Three water-soluble fractions were isolated from both commercial coffee and biscuit by sequential ultrafiltration steps (3 and 10 kDa cutoff). Biscuits were enzymatically digested to solubilize the protein-linked melanoidin fraction. Antimicrobial activity of melanoidins was evaluated against a Gram-negative reference pathogenic bacterium (Escherichia coli). The high-molecular-weight fraction of water-soluble melanoidins (>10 kDa) exerted the highest antimicrobial activity. The mechanism of action was further investigated by cell integrity and outer- and inner-membrane permeabilization assays. At the minimum inhibitory concentration, melanoidins provoked irreversible cell membrane disruption, which was independent of the bacterial transmembrane potential. Results indicate that water-soluble melanoidins killed pathogenic bacteria strains ( E. coli) by causing irreversible changes in both the inner and outer membranes. Likely, it allows for interference with biosynthetic processes, such as the inhibition of nutrient transport and macromolecular precursors.
Rurián-Henares
Jose A
JA
Departamento de Nutrición y Bromatología, Facultad de Farmacia, Universidad de Granada, Granada, Spain.
Morales
Francisco J
FJ
D000890:Anti-Infective Agents / Q000494:pharmacology*; D002462:Cell Membrane / Q000187:drug effects; D002463:Cell Membrane Permeability / Q000187:drug effects; D003069:Coffee / Q000737:chemistry; D004926:Escherichia coli / Q000187:drug effects*; D011108:Polymers / Q000494:pharmacology*
D000890:Anti-Infective Agents; D003069:Coffee; D011108:Polymers; C011908:melanoidin polymers