Studies on the physicochemical properties and antioxidant activities of micron/nano-sized green tea
Date Issued
2009
Date
2009
Author(s)
Chen, Tzu-Hung
Abstract
Green tea contains abundant catechins, but the extraction yield of catechins is low due to its poor water-solubility. Large amounts of wastes including tea leaves and stems are produced during the commercial processing of green tea beverages. Recently, nanotechnology via media milling has been reported to improve some poorly water-soluble drugs into stable, biologically active nanoparticlulate dispersion and enable the use of whole raw materials. This thesis aims at preparing micron/nano-sized green tea by media milling and finding the appropriate media-milling conditions. Physicochemical properties, chemical components and antioxidant activities will be compared among micron/nano-sized green tea suspension, green tea extract and micron/nano-sized green tea waste. he appropriate milling condition was to use 0.3 mm Y.Z.T. (yttria-stabilized zirconia) beads and 3500 rpm to mill green tea powder suspension (0.38%, w/v) for 90 min. The particle size of micron/nano-sized green tea was 108 nm of number mean diameter (Dnm) and 7.83 μm of volume mean diameter (Dvm); the particle size of micron/nano-sized green tea waste was 114 nm of Dnm and 16.87 μm of Dvm. The green tea powder suspension and waste suspension were ground to micron/nanoscales. or physicochemical properties, the Hunter L, a, b color results showed that green tea extract was more bright and yellow-green than the media-milled products; the media-milled products had lower pH that might be caused by the release of acidic substances. Comparison of the chemical components (on one-gram basis of dry green tea powder) among the micron/nano-sized green tea suspension, green tea extract and micron/nano-sized green tea waste showed that micron/nano-sized green tea could release more catechins and L-theanine. Some components such as EGCG would be converted into EGC and gallic acid. Micron/nano-sized green tea released 111.43 mg of total phenollics that was significantly higher than those of the green tea extract (80.31 mg) and micron/nano-sized green tea waste (38.82 mg). Total dietary fiber of micron/nano-sized green tea was found to be 66.14 g/100 g of dry green tea powder that was higher than the sum of those from green tea extract and micron/nano-sized green tea waste (53.49 g/100 g green tea powder). These results showed that micron/nano-sized green tea could release higher amounts of effective components than green tea extract.omparison of antioxidant activities among micron/nano-sized green tea suspension, green tea extract and micron/nano-sized green tea waste on one-gram basis of dry green tea powder showed that micron/nano-sized green tea had higher antioxidant activity such as ORAC and LDL oxidation. The presence of abundant phenolic components might lead to a high antioxidant activity, while the correlations (R2) between ORAC and total phenolics as well as Tlag and total phenolics were above 0.88. In CAA assay, with or without PBS wash treatment did not affect the antioxidant activity of micron/nano-sized green tea significantly. It showed that the chemical components in micron/nano-sized green tea were easily uptake by cells or bound to the surface of cell membrane, or there might be some other smaller particles interacting with cells to present antioxidant activity.his study showed that media-milling process could release high amounts of effective components. The yields of total catechins, L-theanine, total phenolics and dietary fiber from micron/nano-sized green tea were higher than those from green tea extract and therefore, micron/nano-sized green tea was expected to be a new green tea product with rich source of antioxidant and dietary fiber. Media-milling process could help collect effective components from green tea powder, it is also possible develop a new method to collect catechins and other phenolic components.
Subjects
Micron/nano-sized green tea
media milling
particle size distribution
catechins
dietary fiber
antioxidant activity
Type
thesis
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