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991.
Garna H Mabon N Wathelet B Paquot M 《Journal of agricultural and food chemistry》2004,52(15):4652-4659
A new method for the determination of the main neutral sugars in pectin has been developed. The sample preparation involves a mild chemical attack followed by an enzymatic hydrolysis. The completeness and nondestructive character of the method are demonstrated by comparison of the results obtained with different acids such as H2SO4, HCl, and trifluoroacetic acid (TFA) at different concentrations (2, 1, or 0.2 M) at two temperatures (80 or 100 degrees C). The chemical hydrolysis of pectin neutral sugar chains with strong acid (1 or 2 M) and high temperature (100 degrees C) shows that the liberation of the pectin sugars is not realized at the same rate for each sugar. Different optimum conditions are thus obtained. However, the chemical pectin hydrolysis with 0.2 M TFA at 80 degrees C is characterized by the liberation of pectin neutral sugar side chains without any degradation within 72 h of hydrolysis. Under these conditions, the liberation of some pectin sugars, essentially galactose, glucose, and rhamnose, was not complete. An enzymatic hydrolysis is necessary to obtain a complete release of all the sugars. The combination of the two treatments, a chemical hydrolysis realized with diluted acid (0.2 M) for 72 h at low temperature (80 degrees C) on one hand and an enzymatic hydrolysis on the other hand, allow a total liberation of pectin sugars. The quantitative analysis of the carbohydrates is realized with accuracy, high selectivity, and sensitivity with high-performance anion-exchange chromatography with pulsed-amperometric detection. The sugars can be analyzed without any derivatization with a limit of quantification of 0.1 mM. 相似文献
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Sidney Bailey Geoffrey B. Collins F. Bernard Fishwick Harold V. Hart David F. Horler Keith A. Scudamore 《Pest management science》1982,13(4):373-378
Residue levels of organochlorine pesticides, organophosphorus pesticides, fumigants and bromide were determined in home-produced and imported wheat during the period October 1978 to April 1979. A total of 281 samples was analysed of which 133 contained low levels of carbon tetrachloride, 112 contained low levels of gamma-HCH and 26 contained low levels of malathion. One sample contained a residue of carbon tetrachloride, and another a residue of 1,2-dichloroethane, both of which were above the Codex Alimentarius guide-line levels. No other residue approached the proposed Codex Alimentarius maximum residue limits. 相似文献
1000.
Formulations of aldrin and dieldrin have been used for a number of years to treat exposed timber components used in the construction of freight containers. The extent to which these insecticides migrate to foodstuffs stored on or near treated plywood has been examined under laboratory conditions and is reported here. A limited survey of organochlorine insecticide residues in samples of foodstuffs, taken from commercial loads carried in freight containers, indicated that residue levels are unlikely to present a health hazard. 相似文献