The aroma of fermented fish sauce comprises three distinct notes, cheesy, meaty and ammoniacal. Analysis showed that the cheesy odour was produced by lower fatty acids and the ammoniacal odour by ammonia and amines. The meatyaroma was much more complicated and was not analysed, but it was shown that it could be produced by atmospheric oxidation of precursors that were still present in mature sauces. Individual fatty acids were determined in sauces at various stages of fermentation and an hypothesis explaining the origin of the acids is deduced from the results.
A plain black tea liquor was studied by HPLC. Flavonol glycosides were found to be present in the @actions used to determine the theajlavins and the thearubigins. It is shown that flavonol glycosides interfere with theaflavins and thearubigins determined spectrophotometrically resulting in overestimation of these flavour components.A Malawi black tea (clone SFS204) (4 g) was refluxed in distilled water (80 ml) for 30min. The extract was vacuum filtered through Whatman filter paper No 41, washed with 15 ml hot water, made up to 100 ml and cooled in a refrigerator for 10 min. This was analysed by HPLC using the equipment and procedure of Bailey et a1 (1990). Further extracts were made, using the procedure of Roberts and Smith (1961), and analysed by HPLC.The HPLC analysis of black tea, using a photodiode array detector (Bailey et a1 1990), has revealed the presence of quercetin-3-rhamnosylglucoside, quercetin-3-glucoside, another quercetin glycoside, kaempferol-3-rhamnosylglucoside and another kaempferol glycoside (Fig 2). The presence in black tea of such substances has been reported previously (Roberts et a1 1957; Cattell and Nursten 1976), but their influence on the colorimetric analysis of tea pigments, and their effect on quality, have been ignored. A colorimetric procedure for estimating the quality of plain black teas was developed by Roberts and Smith (1961) and modified by Ullah (1972), and remains the only method for the determination of thearubigins in tea. The extraction method is shown in Fig lA, and the equations are used in Fig 1B. The analysis involves the measurement of absorbance at 380 and 460 nm. The 380-nm values are used to determine the theaflavins and the thearubigins, which are considered to be the major contributors to plain black tea quality, being responsible for 'briskness' and 'body' respectively. The 460 nm values are used to determine the visual attributes known to tea tasters as 'brightness', 'total colour' and 'depth of 41 1 J Sci Food Agric 0022-5142/90/$03.50~ 1990 SCI. Printed in Great Britain
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