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Wpływ warunków parzenia na zawartość antyoksydantow w naparach różnych rodzajów herbat

Kurleto K., Kurowski G., Laskowska B., Malinowska M., Sikora E., Vogt O.

Wiadomości Chemiczne

2013

[Z] 67, 11-12

1129--1147

Tea has been consumed all over the World for over two thousand years and now it is the most popular caffeine-containing beverage. Its worldwide consumption is second only to water [1–3]. The tea is not only important because of its popularity but also due to its beneficial influence on human health [4]. The biological benefits of tea are due to their flavanol content [5–13]. Tea flavanols are a group of natural polyphenols (Fig. 2). Therapeutic effects of tea have been extensively examined in many in vitro and in vivo tests. It was confirmed that tea leaves ingredients have antibacterial, antifungial, antiviral properties, they also prevent cell mutations and they inhibit progress of heart diseases. Moreover, tea can stimulate neural system and regulate its functions [14–20]. All this activities are mostly due to antioxidant ability of tea polyphenols (Fig. 4). Tea production process can be run in different ways and this affects of the tea taste, aroma, colour and antioxidants content. According to fermentation degree, different tea kinds can be obtained (Fig. 1). During the manufacturing process of black and oolong teas, tea leaves are crushed to allow polyphenol oxidase to catalyze the oxidation and polymerization of catechins to polymers called theaflavins and thearubigins (Fig. 3) [21–23]. Green or white teas are obtained through shorter fermentation, so the catechin concentration remains higher. Tea is prepared by infusing tea leaves in hot water. Brewing process conditions like temperature, brewing time, pH, besides other factors has a significant influence on polyphenols content [24-32]. Many studies have determined total flavonoids content and antioxidant activity according to different tea type and brewing conditions, tea plantation type or fermentation process. The amount of total polyphenol was determined using the F-C method, catechins, caffeine and polyphenolic acids were analysed using High Performance Liquid Chromatography with reversed phase. Obtained results let compare how different production and brewing processes affect the tea quality [33–56].

Spektrofotometryczne i elektrochemiczne metody oznaczania aktywności antyoksydacyjnej

Małyszko J., Karbarz M.

Wiadomości Chemiczne

2009

[Z] 63, 1-2

17-38

In the last decades, free radicals have been discussed to play a key role in the pathology of several diseases, such as cancer, artheriosclerosis or inflammatory diseases [1, 2]. Numerous dietary antioxidants, e.g. vitamin C, phenolic and polyphenolic compounds as well as carotenoides are considered as effective agents in prevention of these diseases [4]. The chemical diversity of antioxidants occurring in food makes it difficult to separate individual antioxidant compounds from the animal or vegetable matrix and quantify them. Antioxidant activity is widely used as a parameter to characterize the redox status of different biological or dietary samples. Many analytical methods for determining of total antioxidant activity (TAA) have been proposed in the literature of the last decade. The present review deals with the methods involving electron-transfer reactions with chromogen compounds: the trolox equivalent antioxidant capacity (TEAC) [6-29], the DPPH assay [31-41], the ferric reducing antioxidant power (FRAP) assay [42-48], the cupric reducing antioxidant capacity (CUPRAC) assay [49-55], and the Folin-Ciocalteu (FC) method [56]. These assays enable to measure the activity of an antioxidant through the reduction of an oxidizing agent, which changes colour during the redox reaction. The degree of colour change corresponds to the concentration of antioxidant in the sample. The main purpose of this review is to describe and discuss the chemical fundamentals of these methods. The applications of voltammetry and other electroanalytical methods were also demonstrated [58-71]. In addition, properties and the use of reference compounds in the antioxidant activity assessment was considered [72-85]. The summary contains conclusions on the scope of application, the most important advantages and shortcomings of the methods described [50, 86-88].