The Chemical Origin of Free Radicals in Coffee and Other Beverages

Abstract

Sugars or carbohydrates are identified as the source of free radicals in coffees, ersatz coffees, a number of other food flavouring and colouring agents formed by processes involving heating, and in beers and stouts. The radicals are not derived from phenolic constituents, in contrast to those in wine, and are unlikely to be due solely to the occurrence of Maillard reactions.

Stable Radical Content and Anti-Radical Activity of Roasted Arabica Coffee: From In-Tact Bean to Coffee Brew

“…Fig 1 shows the EPR spectra of the stable radical in whole coffee beans and in freshly-ground beans that were roasted for variable times ranging from 2–12 min. At maximum roasting (12 min), the spectrum was characterized by a g factor of ≈ 2.004 and a linewidth of 7 G, consistent with the radical species previously observed in roasted coffee [ 20 ] and instant coffee [ 12 , 26 ], in addition to several other beverages and foodstuffs including caramelized glucose [ 12 ]. Quantification of the radical intensity (determined by double-integration of the first derivative signal) showed a monotonic increase as a function of roasting time except for a local maximum after 6 min roasting, which was associated with the presence of a broad component underlying the more narrow signals present at short and long roasting times ( Fig 2 ).…”

“…It is well established that roasting of coffee beans produces stable radicals [ 17 – 21 ], which are associated with Maillard reaction products (MRPs) [ 2 ] rather than phenolic substituents [ 12 ]. Bekedam et al showed that the formation of non-phenolic roasting-induced AOs positively correlated with melanoidin content within coffee brew, but that these roasting-induced AOs are slow-reacting and have a limited contribution to the overall AO activity in comparison with phenolic constituents [ 2 ].…”

Influence of Environmental and Microclimate Factors on the Coffee Beans Quality (C. canephora): Correlation between Chemical Analysis and Stable Free Radicals

“…Quantitative assessment of stable free radicals was performed by double integration of the as-fitted first Lorentzian derivative and the results are shown in Table 2. We found that 1) the typical free radical signal from the ripe beans was detectable only in shade-grown coffee (Figure 2(a)); 2) free radicals from the unripe beans were observed in both cultivation groups although their level was about 260% higher in shade-grown coffee (Figure 2(b)); 3) as expected, the roasting process, carried out only for ripe beans (Figure 2(a)), resulted in an increased EPR signal for free radicals due to melanoidin formation through the Maillard and caramelization reactions [27] [36], with an approximately 40% higher level for shade-grown coffee (Figure 2(c)); 4) free radical intensities were consistently higher for the shade-grown coffee samples (Table 2). Our findings suggest that the higher humidity environment experienced by shade-grown coffee promoted an increase in formation of stable free radicals.…”

Hohenheim Consensus Talk: Coffee

“…Das Vorkommen stabiler freier Radikale im Kaffee ist seit vielen Jahren bekannt (O'Meara et al 1957, Troup et al 1989. Man geht davon aus, dass sie im Wesentlichen aus ¹verkohltenª Polysacchariden (Morrice et al 1993) oder Melanoidinen bestehen, die während der Maillardreaktion beim Kaffeeröstprozess entstanden sind (Djilas u. Milic 1994, Gonis et al 1995. Im üblichen Kaffee schwankt die Konzentration an freien Radikalen erheblich und scheint durch die Genetik und Herkunft der grünen Bohnen, sowie durch den Röstgrad bestimmt zu sein (Hernandez et al 1973, Santanilla et al 1981, Morrice et al 1993, Gonet 1994 (Kroyer et al 1989, Macku u. Shibamoto 1991, Nicoli et al 1997.…”