| Konjac mannan is a high molecular weight water-soluble non-ionic glucomannan extracted from the tubers of the Amorphophallus konjac plant. Konjac glucomannan(KGM) is a linear random copolymer of (-4)-linked B -D-mannose and P -D-glucose, containing mannose and glucose residues in a molar ratio of 1.6:1 or 3:2 with a low degree of acetyl groi ps (approximately 1 acetyl group per 19 residues at the C-6 position). The physicochemical propercies and applications are controlled by the presence of the acetyl units. When KGM is dissolved in water, it gives highly viscous solutions and so has potential use as a thickener, emulsifier, stabilizing agent and so on in food industry. In the past thirty years, i nany studies on the nutriology of KGM, the properties of its condensed solutions and its combined application with other polysaccharides were carried out. However, the detailed mechanism(s) of the interaction among the molecules and of its stabilizing effect for the above functions in application remain to be studied. KGM is considered as a water-soluble dietary fibre and i; hydrolyzed by Aerobacter mannanolyticus. Much research, mostly in Japan, has demonstratec the significant role of KGM in cholesterol and blood lipoid reduction.Tea drink is regarded as the 21st century healthy beverage and developed with combination of functional compounds in plants and tea extracts or pvvre tea extracts in Japan and America at the present time. But it is well known that the problem of 'cream down', or cooling precipitation, has not been fully settled until now, and the development of high-quality tea drink has been restrained by it. As a result, many kinds of chemical additives, antiseptics and antioxidants are introduced in the tea drink. The tea 'cream down' or precipitation seriously affects the sensory quality of the tea drink, especially when it is bottled with transparent container such as PET, BOPP and glass bottles. Therefore, it is an urgent task for companies or institutes to enhance the degree of clarification of tea drink, and to seek new measures to prevent tea 'cream down' or precipitation during its shelf life. So far, a series of methods including physical and chemical methods and bio-techniques have been adopted to clarify the tea 'cream down' or precipitation.The clarification effect of tannase is considered as the optimal choice. However, the price of the tannase enzyme is too expensive to be used extensively in tea drink. So, it is necessary to investigate alternative approaches.The objectives of the present study were: 1) to utilize KGM to solve the tea 'cream down' or cooling precipitation in tea drink at low temperatures; 2) to investigate the stabilizing mechanism of KGM additions for tea drink; 3) to develop a series of high-quality and marketable konjac-tea drinks; 4) to seek a new procedure for the rapid determination of the constituents of konjac-tea drink.Several experiments were carried out, which involved the processing of konjac-tea drink, rheological properties of diluted KGM and tea extracts with KGM additions, rapid determination of quality-related constituents of konjac-tea drink by using near-infrared spectroscopy, as well as stabilizing mechanism of konjac-tea drink.Part 1: Processing of konjac-tea drinkThe design of the experiments was a plan for the deliberate variation of variables to study their effect on certain specific results. The aim of this part was to determine the optimum ingrediems for konjac-tea drink and optimal additions of KGM.Materials: Materials were commercial black tea, oolong tea and konjac glucomannan.Experimental design and statistical analysis:1) Experimental design for konjac-tea drink without sugar-citric acidThe response-variable, overall preference, of the drink was assumed to be influenced by two independent variables (volume of tea extracts and volume of KGM), so the central composite design with 2 independent variables (5 levels of tea extracts and KGM sol-gel) was used to designate 13 treatments.2) Experimental design for ko... |
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