A study of volatile carbonyl compounds of coffee

Mansour, Hafidh A. Razzak (1965) A study of volatile carbonyl compounds of coffee. MSc(R) thesis, University of Glasgow.

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The purpose of this work was to examine the carbonyl compounds in the volatile constituents of coffee, if possible to assess their contribution to coffee aroma. The work entailed mainly the collection of the carbonyl compounds and their subsequent separation, identification and quantitive estimation. The volatile constituents of coffee were stripped by nitrogen in a modified Shipton apparatus and the carbonyl compounds converted to their hydrazones. The carbonyl compounds were regenerated by a "flash-exchange" method which consisted essentially of heating a mixture of the hydrazones and ketoglutaric acid. The regenerated carbonyls were examined by gas chromatography using an argon ionisation detectors the bulk of the work was done using dinonylphthalate as liquid phase and carbowax 4500 for some confirmatory work. Both qualitative and quantitative determinations were made. Identification and quantitative estimation of the constituent carbonyl compounds was further supported by thin-layer chromatography, paper chromatography, and by visible, ultraviolet and infrared spectroscopy. A tasting panel was used to determine the effect of storage and also to test the significance of the volatile carbonyl compounds in relation to the flavour of coffee. The following carbonyl compounds were identified by gas chromatography and their quantities measured: acetaldehyde, propionaldehyde, acetone, iso-butyraldehyde, n-butyraldehyde, methylethylketone, diacetyl and iso-valeraldehyde;acetaldehyde and iso-valeraldehyde were present in approximately equal amounts forming the largest proportion of the total volatile carbonyl compounds. Formaldehyde, which was not detected by gas chromatography, was identified and estimated by a chromotropic acid colorimetric method. Evidence is offered that, contrary to one published method, formaldehyde is not regenerated from it's hydrozone. The quantitative determination of diacetyle using the argon-ionisation detector requires special consideration to avoid electron capture effects. Experiments with stored samples of instant coffee showed that: The quantity of volatile carbonyl compounds decrease with increasing time of storage. Tasting panel results suggest a relationship between this decrease and the palatability of the coffee. It suggested that the quantity of volatile carbonyl compounds expressed as the weight of dry hydrozones/100g coffee could be used as an index of the age and storage treatment of the coffee. The results also show that in the staling of instant coffee there is relative increase of acetaldehyde and an increase in the ratio of propionaldehyde to acetone. Results are given for the composition of the fats extracte6 from green and roasted coffee. The roasting of the extracted fat from the green beans gave no evidence for the production of volatile carbonyl compounds. Experience gained in this work has shown the necessity for standard methods of collection and analysis. Comparison of the results from different workers is almost impossible since the variations caused by different methods seems to be greater than would be expected from different materials.

Item Type: Thesis (MSc(R))
Qualification Level: Masters
Additional Information: Adviser: J Hawthorn
Keywords: Food science
Date of Award: 1965
Depositing User: Enlighten Team
Unique ID: glathesis:1965-72931
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 11 Jun 2019 11:06
Last Modified: 11 Jun 2019 11:06
URI: http://theses.gla.ac.uk/id/eprint/72931

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