Determination of the chemical composition of tea by chromatographic methods: a review

Despite the fact that mankind has been drinking tea for more than 5000 years, its chemical composition has been studied only in recent decades. These studies are primarily carried out using chromatographic methods. This review summarizes the latest information regarding the chemical composition of different tea grades by different chromatographic methods, which has not previously been reviewed in the same scope. Over the last 40 years, the qualitative and quantitative analyses of high volatile compounds were determined by GC and GC/MS. The main components responsible for aroma of green and black tea were revealed, and the low volatile compounds basically were determined by HPLC and LC/MS methods. Most studies focusing on the determination of catechins and caffeine in various teas (green, oolong, black and pu-erh) involved HPLC analysis. Knowledge of tea chemical composition helps in assessing its quality on the one hand, and helps to monitor and manage its growing, processing, and storage conditions on the other. In particular, this knowledge has enabled to establish the relationships between the chemical composition of tea and its properties by identifying the tea constituents which determine its aroma and taste. Therefore, assessment of tea quality does not only rely on subjective organoleptic evaluation, but also on objective physical and chemical methods, with extra determination of tea components most beneficial to human health. With this knowledge, the nutritional value of tea may be increased, and tea quality improved by providing via optimization of the growing, processing, and storage conditions.</p

Economic progress as cancer risk factor. II: Why is overall cancer risk higher in more developed countries?

Analysis of data on cancer incidence rates in different countries at different time periods revealed positive association between overall cancer risk and economic progress. Typical explanations of this phenomenon involve improved cancer diagnostics and elevated exposure to carcinogens in industrial countries. Here we provide evidence from human and experimental animal studies suggesting that some other factors associated with high economic development and Western life style may primarily increase the proportion of susceptible to cancer individuals in a population and thus contribute to elevated cancer risks in industrial countries. These factors include (but not limited to): (i) better medical and living conditions that “relax” environmental selection and increase share of individuals prone to chronic inflammation; (ii) several medicines and foods that are not carcinogenic themselves but affect the metabolism of established carcinogens; (iii) nutrition enriched with growth factors; (iv) delayed childbirth. The latter two factors may favor an increase in both cancer incidence rate and longevity in a population. This implies the presence of a trade-off between cancer and aging: factors that postpone aging may simultaneously enhance organism’s susceptibility to several cancers. Key words: cancer risk, individual susceptibility, economic progress, aging

Dialog System for Modeling Multidimensional Demographic Processes

A growing understanding of the importance of demographic processes in social and economic development places greater demands on the quality of demographic research and on the adequacy and convenience of tools used in the analysis of a population's characteristics. Multistate population models recently became popular in the study of many aspects of demographic transitions, such as migration, marriage, changes of health status, social status, occupation, etc.. Computer programs and software packages were developed to realize such models. However, most of these allow analysis of systems only when fertility, mortality, or transition coefficients do not depend on time. Some authors have overcome this drawback and have created the opportunity to analyze alternative evolutions of the system under various scenarios of natural and mechanical reproduction of the population. However, these programs are not always appropriate for use by the many demographers and health specialists who are not deeply involved in computer modeling. The software is often not flexible enough to enable choices of and changes in the variables that determine the scenarios, the representation of the results, and the control of modeling itself. The most important disadvantage of these packages is the inability to communicate interactively with the model. As experience shows, interactively working with computers essentially reduces the time spent on model design and debugging. It also creates additional opportunities for model analysis. Thus, there is a necessity to create a user-friendly system that allows a more effective analysis of demographic processes. In this paper an interactive system that uses the multistate demographic models is described. The system provides the opportunity to prepare scenarios, change coefficients of the model during the modeling procedure, and present intermediate results. The paper uses some results of research conducted at VNIISI and at IIASA: namely, the design of the man-machine modeling system and the modeling of multistate demographic processes

Season of birth influences life span of Mediterranean fruit flies, rats and mice

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