Electron spin resonance (ESR) studies on the formation of roasting-induced antioxidative structures in coffee brews at different degrees of roast.
The antioxidative properties of coffee brew fractions were studied using electron spin resonance spectroscopy using 2,2,6,6-tetramethyl-1-piperidin-1-oxyl (TEMPO) and Fremy's salt (nitrosodisulfonate) as stabilized radicals. TEMPO was scavenged by antioxidants formed during roasting and not by chlorogenic acid, whereas Fremy's salt was scavenged by all antioxidants tested including chlorogenic acid. The stabilized radical TEMPO allowed the exclusive measurement of roasting-induced antioxidants. The roasting-induced antioxidant activity of coffee brews increased with increasing degree of roast, and most of these antioxidants were formed during the initial roasting stage. The majority of these roasting-induced antioxidants were present in the high molecular weight fractions, indicating that the formation of these antioxidants preferably occurs at specific high molecular weight structures, likely being arabinogalactan and/or protein moieties which might be part of the melanoidin complex. It was found that chlorogenic acids most probably do not lose their antioxidant activity and phenolic characteristics upon incorporation in coffee melanoidins. The parameter fast reacting antioxidants (FRA) was introduced as an alternative for the antioxidative potential. FRA levels showed that coffee fractions rich in roasting-induced antioxidants exposed their antioxidant activity relatively slowly, which must be a consequence of its complex structure. Finally, the melanoidin content and the roasting-induced antioxidant activity showed a positive and linear correlation for the coffee brew fractions, showing that roasting-induced antioxidants are present within melanoidins. This is the first time that the formation of roasting-induced antioxidants could be directly correlated with the extent of Maillard reaction and melanoidin formation in a complex product such as coffee.
Laboratory of Food Chemistry and Product Design and Quality Management Group, Department of Agrotechnology and Food Science, Wageningen University, P.O. Box 8129, 6700 EV Wageningen, The Netherlands.
E Koen
EK
Bekedam
Henk A
HA
Schols
Bettina
B
Cämmerer
Lothar W
LW
Kroh
Martinus A J S
MA
van Boekel
Gerrit
G
Smit
D000975:Antioxidants / Q000032:analysis* / Q000737:chemistry*; D003069:Coffee / Q000737:chemistry*; D003497:Cyclic N-Oxides; D004578:Electron Spin Resonance Spectroscopy; D006358:Hot Temperature; D008970:Molecular Weight; D011108:Polymers / Q000032:analysis*; D011801:Quinic Acid / Q000031:analogs & derivatives / Q000032:analysis; D013113:Spin Labels
D000975:Antioxidants; D003069:Coffee; D003497:Cyclic N-Oxides; D011108:Polymers; D013113:Spin Labels; C472707:caffeoylquinic acid; C011908:melanoidin polymers; D011801:Quinic Acid; C003959:TEMPO