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Simultaneous analysis of tea catechins, caffeine, gallic acid, theanine and ascorbic acid by micellar electrokinetic capillary chromatography 总被引:4,自引:0,他引:4
A micellar electrokinetic capillary chromatography (MEKC) method for the simultaneous analysis of five tea catechins, theanine, caffeine, gallic acid and ascorbic acid has been developed. The catechins are (-)-epicatechin, (+)-catechin, (-)-epigallocatechin, (-)-epicatechin gallate and (-)-epigallocatechin gallate. p-Nitrophenol serves as both reference and internal standard. All the components are separated within 13 min with a 57 cm uncoated fused-silica column. On-column detection was carried out at 200 nm. This method has been used to measure these compounds in fresh tea leaves and tea liquor. The limit of detection for all analytes ranged from 1 to 20 microg/ml. 相似文献
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Neglur R. Hosten E. Aucamp M. Liebenberg W. Grooff D. 《Journal of Thermal Analysis and Calorimetry》2018,132(1):373-384
Journal of Thermal Analysis and Calorimetry - This study investigated the solid-state physical stabilities of azithromycin dihydrate (AZM-DH), thermally prepared anhydrate and hemihydrate... 相似文献
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Chantelle Human Dalene de Beer Magdalena Muller Marieta van der Rijst Marique Aucamp Andreas Tredoux Andr de Villiers Elizabeth Joubert 《Molecules (Basel, Switzerland)》2021,26(17)
Green rooibos extract (GRE), shown to improve hyperglycemia and HDL/LDL blood cholesterol, has potential as a nutraceutical beverage ingredient. The main bioactive compound of the extract is aspalathin, a C-glucosyl dihydrochalcone. The study aimed to determine the effect of common iced tea ingredients (citric acid, ascorbic acid, and xylitol) on the stability of GRE, microencapsulated with inulin for production of a powdered beverage. The stability of the powder mixtures stored in semi-permeable (5 months) and impermeable (12 months) single-serve packaging at 30 °C and 40 °C/65% relative humidity was assessed. More pronounced clumping and darkening of the powders, in combination with higher first order reaction rate constants for dihydrochalcone degradation, indicated the negative effect of higher storage temperature and an increase in moisture content when stored in the semi-permeable packaging. These changes were further increased by the addition of crystalline ingredients, especially citric acid monohydrate. The sensory profile of the powders (reconstituted to beverage strength iced tea solutions) changed with storage from a predominant green-vegetal aroma to a fruity-sweet aroma, especially when stored at 40 °C/65% RH in the semi-permeable packaging. The change in the sensory profile of the powder mixtures could be attributed to a decrease in volatile compounds such as 2-hexenal, (Z)-2-heptenal, (E)-2-octenal, (E)-2-nonenal, (E,Z)-2,6-nonadienal and (E)-2-decenal associated with “green-like” aromas, rather than an increase in fruity and sweet aroma-impact compounds. Green rooibos extract powders would require storage at temperatures ≤ 30 °C and protection against moisture uptake to be chemically and physically shelf-stable and maintain their sensory profiles. 相似文献
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Donald C Aucamp 《European Journal of Operational Research》1982,9(1):61-63
This note gives a solution to a qualification of the standard EOQ problem in which freight costs are at least partially determined by the integer number of carloads required to fill the order. The model also applies to a broad class of problems in which there are multiple set-up costs. 相似文献
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A simple, verbal proof is offered that shows transportation algorithms automatically yield integral solutions when supplies and demands are integral. Thus, there is no need to avoid this aspect of the theory in introductory texts or in classroom presentations to non-mathematically sophisticated audiences. A fallout of the proof is the fact that tree solutions are basic and vice-versa. 相似文献
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In this study a new capillary electrophoresis (CE) method was developed to quantify the four major theaflavins occurring in black tea. Where aqueous based CE methods showed poor selectivity and considerable band broadening, non-aqueous CE achieved baseline separation of the theaflavins within 10 min. The effects of the organic solvent composition and background electrolyte concentration on the separation selectivity and electrophoretic mobilities were investigated. Our optimized separation solution consisted of acetonitrile-methanol-acetic acid (71:25:4, v/v) and 90 mM ammonium acetate. This method was used to analyze three black tea samples. 相似文献
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Donald C. Aucamp 《The Journal of the Operational Research Society》1989,40(12):1109-1119
A multiperiod linear programming model of the production planning problem is used to argue for a different costing, profit and resource-evaluation procedure in manufacturing. This procedure is based on the concept of ‘pseudo shadow prices’, and it avoids many of the pitfalls associated with the more traditional accounting methodologies. Conclusions are drawn which question the profit objectives used by many firms, as well as by those in academia. 相似文献