Tea constituents (Camellia sinensis L.) as antioxidants in lipid systems

Edible fats, oils and fat-containing products undergo oxidation, both during production and storage. This process in food causes a sequence of unfavorable changes. From a nutritional and technological point of view, it is desirable to control oxidation processes by addition of inhibitory substances.

This review indicates the possible mechanism of antioxidant activity, antioxidant sections and potential antioxidant properties of tea polyphenols in different lipid systems and food products. Although research provides many promising examples, detailed studies are still needed to understand the benefits of tea polyphenols as food additives.

Introduction

Lipids make up one of the most essential components of food. They decide not only the taste, scent, colour or the texture of a food product, but they also give the feeling of satiety (Frankel, 1998a). In food technology, they are also a heating medium and different cooking techniques are possible (Dunford, 2001). First of all, fats are indispensable substances in human nutrition (Keller, 2000). Nutritional recommendations define that daily fat consumption in the diet should make up about 30% energy. Dietary lipids deliver 9 kcal (37.7 KJ)/g which is over twice more energy than proteins, or carbohydrates (Beare-Rogers, 1988). Moreover, fats are solvents for vitamins A, D, and E and they facilitate their assimilation from different products. The polyunsaturated fatty acids are a source of linoleic acid family (n−6) and α-linolenic acid family (n−3), which are not produced in the human body, but synthesized in plants, delivered to man in food. The polyunsaturated fatty acids take part in eicosanoid synthesis-biologically active substances such as prostaglandin, prostacycline, tromboxane (Dunford, 2001, Frankel, 1998b).

Edible fats, oils and products including fats undergo the processes of oxidation, both during production and storage. This process in food causes a sequence of unfavorable changes, mainly deterioration in the sensory properties of the product (rancidity, change of colour and texture), decrease in nutritional value, increase in the health risk and economic losses (Drozdowski, 1996, Frankel, 1998b, Gray, 1978, Małecka, 1997).

Lipid autoxidation is a free radical chain reaction, leading to an increase in reactive radicals and hydroxides, initiating further reactions (Frankel, 1985, Min and Boff, 2002). Three stages of autoxidation have been distinguished: initiation, propagation and termination (Frankel, 1998c, Gordon, 2001). Chemical reactions of oxidation require a low energy of activation, and their rate does not change considerably with lowering temperature of storage (Labuza, 1971, Hamilton, 1989). The chain reaction is catalyzed by presence of metals, light and temperature. Rate of triacylglycerol oxidation process depends on their degree of saturation and the position of fatty acids in the molecule (Szukalska, 1999, Yanishlieva-Maslarowa, 2001a). Polyunsaturated fatty acids are more sensitive to oxidation than saturated ones (Frankel, 1998c).

Oxidation reactions take place in living organisms as well as in food. For man, oxidation is a metabolic process delivering energy to living cells. Yet this process leads to a simultaneous rise of free radicals which can initiate different diseases, by means of damage to cell membrane function, modification of LDL lipoproteins, change in platelet function of and DNA mutations (Frankel, 1998a, Frankel, 1998b, Frankel, 1998c, Frankel, 1998d; Ziemlanski & Budzyńska-Topolowska, 1991).

Therefore, from a nutritional and technological point of view it is desirable to control oxidation processes by addition of inhibitory substances improving the quality of food products.