Investigation of taint characteristics relating to the quality and flavour of coffee
Onani, Martin Opiyo
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This thesis records the result of an attempt to substantiate an alleged complaint concerning the off-flavour in some batches of coffee as assessed by the trade liquorers of the Coffee Board of Kenya (CBK). The contribution potential of some of the volatile compounds derived from the fungicided used to control some pests and diseases was examined. These volatile substances are possibly produced during the biological breakdown of the fungicide and may be imparted to the coffee causing the taint. The methods of isolation of the volatile components of the fungicide and later the coffee samples were studied. The coffee samples were ground using a laboratory blender. The ground coffee samples were then extracted using 300ml of dichloromethane in a soxhlet apparatus for a period of eight hours. The excess solvent was evaporated in a rotary film evaporator and the concentrate stored at -20°C in the deep freezer. The conditions for the analysis of the extracts of the coffee samples were pre-determined. Analysis for the presence of the taint was done using the Sigma 3B gas chromatograph fitted with a fused silica capillary column, BPX5 (0.25), 25m X 0.32mm ID (SGE). The non-polar separatory phase was 5% phenyl equivalent modified siloxane. The carrier gas, hydrogen was used at a pressure of 6 pounds per square inch (PSI); the instrument was temperature programmed as follows: isothermal at 40°C for 1min, increased at a rate of 5°C/min to 190°C, and held for 5min. A Flame Ionization Detector (FID) was used. All the extracts were analysed using an on-column injection. Samples (0.025ml) were injected and chromatograms obtained. The retention times (Rt) from the chromatogram were compared to those of the standards run earlier and the results recorded. Analysis of the results supported the circumstantial evidence associated with the possible contribution of the fungicide prochloraz as responsible for the taint. The taint was observed in all the coffee samples from the areas where the fungicide was used. The fungicide Prochloraz is semi-systemic product and its degradation produces a number of metabolites including 2, 4, 6-trichlorophenol (TCP). Trichlorophenols are readily transformed to the corresponding trichloroanisole (TCA) in vivo. TCP has been shown in its own right to be a fungicide. This active ingredient could be the direct precursor of the TCA found in the tainted coffee samples. From this study there is a strong evidence that the fungicide Prochloraz produces the observed taint in the coffees studied. Continued usage of this fungicide should be dependant on the basis of further research, a check on application rates and taint appearance.