Publication type: Article in scientific journal
Type of review: Peer review (publication)
Title: Real time monitoring of free radical processes during the roasting of coffee beans, using real electron paramagnetic resonance spectroscopy
Authors: Goodman, Bernard A.
Pascual, E. C.
Yeretzian, Chahan
DOI: 10.1016/j.foodchem.2010.07.072
Published in: Food Chemistry
Volume(Issue): 125
Issue: 1
Pages: 248
Pages to: 254
Issue Date: 1-Mar-2011
Publisher / Ed. Institution: Elsevier
Publisher / Ed. Institution: Amsterdam
ISSN: 0308-8146
Language: English
Subjects: Electron spin resonance; Radicals; Coffee; On-line
Subject (DDC): 663: Beverage technology
Abstract: Because of the roles of free radicals in the formation of Maillard reaction products and as markers of oxidation processes in foods, the dynamics of free radical generation during the roasting of coffee beans have been measured, and some exploratory investigations conducted on the extent to which these are influenced by the bean type, and the atmosphere (air vs. N2), in which the beans were roasted and cooled. The intensities of the free radical signals from individual Arabica and Robusta coffee beans were measured continuously in an EPR spectrometer, whilst beans underwent heating/cooling cycles in air or N2 atmospheres. Additional EPR measurements were performed on the products of coffee beans roasted in a laboratory, convectional hot air roaster. Two sets of experiments were performed: (i) single/half bean roasting in air or N2, and real time, in situ EPR analysis of the free radical content with a very high flow of roasting gas (convective roasting); (ii) batch roasting in air or N2, and EPR measurements of individual roasted beans in a rather low flow of gas. Large differences in intermediate and final free radical EPR signal intensities were observed between the specimens of Arabica and Robusta beans that were investigated, irrespective of the roasting atmosphere. During the heating phase of the roasting process, only minor differences were observed between beans of the same type roasted in air or nitrogen, but the presence of oxygen in the cooling cycle resulted in major increases of free radical levels compared to those observed in an inert atmosphere, although this O2-related effect was not observed in beans from the convectional hot air roaster. Large bean to bean variations were observed with a standard blend roasted in the convectional hot air roaster, but much smaller variations were observed with beans from a single batch. Three major conclusions can be drawn from this study: (i) when roasting with a very strong flow of hot gas, the atmosphere (air vs. N2) had a very limited impact (during the heating phase) on free radical formation, but a dramatic and fast increase during the cooling phase, irrespective of the type of coffee beans. (ii) It appears that the relative masses of coffee beans and air during the roasting process are critical for oxidation and hence the free radical content of the final product. Indeed, the dramatic increase in free radicals during air-cooling was only observed if roasting was performed with a very high flow of hot air. (iii) There are wide variations in the free radical dynamics of different types of coffee bean. Arabica beans showed stronger free radical formation during roasting and higher EPR intensities at the end of the roasting cycle, than did Robusta beans. Yet, as the sampling over different Arabicas and Robustas was limited here, a more systematic study is needed to ascertain this observation.
Fulltext version: Published version
License (according to publishing contract): Licence according to publishing contract
Departement: Life Sciences and Facility Management
Appears in Collections:Publikationen Life Sciences und Facility Management

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