Ultraviolet spectroscopic studies on the feathering of cream in instant coffee

Abstract

SummaryThe extent of cream feathering was observed in samples of six brands of instant coffee at 80 °C and classified on a scale of 0 (non-existent)–3 + (very severe). The hypothesis that it is caused by the amount of chlorogenic acid in the samples was tested. Ultraviolet spectra were recorded between 230 and 486 nm, and the amount of chlorogenic acid was measured from the absorbance at 340 nm. It was found that: (i) u.v. spectra of a given brand of coffee prepared at different concentrations could all be superimposed when concentration and dilution were taken into account, and the spectrum did not change between room temperature and 80 °C; (ii) for a given coffee a minimum amount of chlorogenic acid was needed to cause feathering, but that this amount differed by up to a factor of 10 depending upon the coffee; (iii) only two fundamental shapes of spectra were observed and coffees could be classified by a ratio, R, which lay between two ranges: 0·82 < R < 0·90 or 1·10 < R < 1·27; (iv) a knowledge of the chlorogenic acid content of a sample and the value of R appropriate to that coffee could be used to predict the occurrence of feathering.