• Login
• Admin

Papageorgiou, Christos (2024) Advancing the physical chemical understanding of coffee foam. PhD thesis, University of Nottingham.

Preview

PDF (Corrections) (Thesis - as examined) - Requires a PDF viewer such as GSview, Xpdf or Adobe Acrobat Reader Available under Licence Creative Commons Attribution. Download (28MB) | Preview

Abstract

Coffee foam is one of the important sensory characteristics of brewed coffee and defines the quality of a cup of coffee. However, there are no published mechanisms that describe the stability of the coffee foam system. The present PhD thesis aimed to advance the physical-chemical understanding of coffee foams in the pursuit of manufacturing high quality coffee beverages.

Firstly, the foam quality of 41 instant coffee was assessed and their performance was compared with a control instant coffee sample. It was found that 21 instant coffee samples were significantly (p<0.05) different from the control instant coffee in terms of foam quality. Foaming assessment experiments on coffee extracts from beans roasted to a range of degrees (0,2,4,6 minutes) showed that foam ability was significantly (p<0.05) increased only after 6 minutes of roasting. It was concluded that roasting degree plays a significant role in foam quality performance, and it was hypothesised that roasting generates foam-promoting compounds.

Chemical differences among the 21 instant coffee samples and control were established by employing targeted and untargeted metabolomic techniques via high resolution LC-MS-MS. The relative abundance of each chemical entity and foam quality performance parameters were correlated, in order to find which chemical compounds in coffee are associated with good foam quality. Six chemical compounds (Mannotetraose, Cyclo(Phe-Val), Cyclo(Pro-Val), Cyclo(Phe-Phe), Cyclo(Leu-Phe) , Cyclo(Phe-Phe)) were found to be strongly correlated with foam quality performance (Pearson’s R>0.87) and can be considered as good foam quality markers in the instant coffee process.

The role of 6 key foam compounds on foam quality was investigated by spiking each chemical compound at various amounts in a poor foaming coffee and assessing the foam quality. Cyclo(Pro-Val) was found to influence foam performance by increasing the bubble count per mm2. Therefore, Cyclo(Pro-Val) may reduce the coalescence rate during the aeration step or contribute to lowering the foam disproportionation rate. The dynamic surface tension of Cyclo(Pro-Val) over 30 minutes at 20˚C showed that it was similar to the surface tension of water at 20˚C. Hence, it was hypothesised that Cyclo(Pro-Val) might not be adsorbed on the air/beverage interface but interact with other molecules in coffee and influence foam quality through synergy.

Finally, comparison of the chemical profile of coffee brews across different degrees of roasting, showed that Cyclo(Pro-Val) along with the rest of the cyclopeptides are indeed generated during roasting, probably by the reported breakdown of proteins. Untargeted metabolomic analysis on the same coffee brews showed that the oligopeptide N-[(R)-3-[(L-Val-L-Pro-)Amino]-1,2-dioxopentyl]-D-Leu-L-Val-OH, which is associated with good foam quality performance, is generated during roasting and it might be the precursor compound for Cyclo(Pro-Val).

The utilization of key foam compounds as foam quality markers in the instant coffee process may assist in maintaining or improving the quality of the manufactured coffee products.

Item Type:	Thesis (University of Nottingham only) (PhD)
Supervisors:	Dew, Tristan Gould, Jo
Keywords:	coffee, foam, surface active, metabolomics, LCMS, foam ability, foam stability
Subjects:	T Technology > TP Chemical technology > TP 368 Food processing and manufacture
Faculties/Schools:	UK Campuses > Faculty of Science > School of Biosciences
Item ID:	78386
Depositing User:	Papageorgiou, Christos
Date Deposited:	11 Aug 2025 13:50
Last Modified:	11 Aug 2025 13:50
URI:	https://eprints.nottingham.ac.uk/id/eprint/78386

Actions (Archive Staff Only)

Edit View