title: High molecular weight melanoidins from coffee brew.
abstract: The composition of high molecular weight (HMw) coffee melanoidin populations, obtained after ethanol precipitation, was studied. The specific extinction coefficient (K(mix)) at 280, 325, 405 nm, sugar composition, phenolic group content, nitrogen content, amino acid composition, and non-protein nitrogen (NPN) content were investigated. Results show that most HMw coffee melanoidins are soluble at high ethanol concentrations. The amino acid composition of the HMw fractions was similar, while 17% (w/w) of the nitrogen was NPN, probably originating from degraded amino acids/proteins and now part of melanoidins. A strong correlation between the melanoidin content, the NPN, and protein content was found. It was concluded that proteins are incorporated into the melanoidins and that the degree of chemical modification, for example, by phenolic groups, determines the solubility of melanoidins in ethanol. Although the existence of covalent interaction between melanoidins and polysaccharides were not proven in this study, the findings suggest that especially arabinogalactan is likely involved in melanoidin formation. Finally, phenolic groups were present in the HMw fraction of coffee, and a correlation was found with the melanoidin concentration.
authors.affiliation: Laboratory of Food Chemistry, Wageningen University, P.O Box 8129, 6700 EV Wageningen, The Netherlands.
authors.forename: E Koen
authors.initials: EK
authors.lastname: Bekedam
authors.forename: Henk A
authors.initials: HA
authors.lastname: Schols
authors.forename: Martinus A J S
authors.initials: MA
authors.lastname: van Boekel
authors.forename: Gerrit
authors.initials: G
authors.lastname: Smit
mesh_terms: D000596:Amino Acids / Q000032:analysis; D002241:Carbohydrates / Q000032:analysis; D011232:Chemical Precipitation; D003069:Coffee / Q000737:chemistry*; D000431:Ethanol; D006358:Hot Temperature; D015416:Maillard Reaction; D008970:Molecular Weight; D010940:Plant Proteins / Q000032:analysis; D011108:Polymers / Q000032:analysis* / Q000737:chemistry; D012639:Seeds / Q000737:chemistry; D013053:Spectrophotometry
chemical_list: D000596:Amino Acids; D002241:Carbohydrates; D003069:Coffee; D010940:Plant Proteins; D011108:Polymers; C011908:melanoidin polymers; D000431:Ethanol