• Food Science and Preservation
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• v.16 no.3
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• pp.333-341
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• 2009

The antioxidant properties of green tea leaves and powder extracts were determined using several tests including estimation of reducing power, DPPH(1,1-diphenyl-2- picrylhydrazyl) radical-scavenging activity, and FRAP(Ferric reducing/antioxidant power) assay. All tests indicated that extracts of green tea powder had higher antioxidant activities than extracts of green tea leaves, and the activities were concentration-dependent. However, each test yielded somewhat different results with respect to storage conditions. The reducing power of green tea leaves was highest at $1,000{\mu}g/mL$, storage at $4^{\circ}C$, and an Aw(water activity) value of 0.23. However, the reducing power of green tea powder, assayed at $1,000{\mu}g/mL$, was high under all storage conditions(with variations in temperature and Aw), and was about 1.5.2-fold greater than that of green tea leaves. Radical-scavenging activity, as assessed by the DPPH assay, increased in a dose-dependent manner over the range $15{\sim}125{\mu}g/mL$. At higher concentrations, activities were $80{\sim}90%$ of maximal were attained. The FRAP activity of green tea extract also increased with rising concentration. Particularly in the case of green tea leaves, antioxidant activity was most greatest with storage at $-20^{\circ}C$ and Aw values of 0.69 and 0.23 when assayed at a concentration of $1,000{\mu}g/mL$. These results indicate that the most important factor during storage of green tea is not the Aw value but rather temperature, and that use of refrigeration($4^{\circ}C$) is preferable to increase or maintain the antioxidant activities of biological components in green tea.

• Journal of the Korean Society of Food Science and Nutrition
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• v.17 no.4
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• pp.283-289
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• 1988

Lysine is known as a limiting amino acid in barley and easily inactivated by the browning reaction during processing or storage. The barley powders ground to 120 mesh in particle size were controlled at water activity of 0.44, 0.52, 0.65 and 0.75 by using saturated salt solutions and then stored at 35, 45 $55^{\circ}C$. Another portion of the sample of which the water activities were controlled as same above was stored at 35, 45, and $55^{\circ}C$ alternately with 7days interval. The reaction of available lysine loss in barley powders was found to be first order. The activation energies calculated from Arrhenius plot ranged $6.02{\sim}10.32Kcal/mole$, and $Q_10$ values were between 1.34 and 1.65. These kinetic parameters were used to predict the available lysine loss of barley powders under the fluctuating temperature storage The predicted shelf-life at various water activities tested was a little higher than the actual values.

• Journal of the Korean Society of Food Science and Nutrition
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• v.33 no.10
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• pp.1720-1725
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• 2004

Absorption characteristics of green tea powder were investigated. The monolayer moisture content determined by GAB equation was 0.024~0.052 g $H_2O$/g dry solid. The absorption enthalpy was calculated with different particle size and various water activities. It showed that the absorption energy was decreased with increasing water activity but no difference was found on particle size increasement. Among models applied for predicting equilibrium moisture content, Halsey model was the best fit model for green tea powders, showing the lowest prediction deviation of 2.1~4.0%. The prediction model equations for the water activity was established as function of relative humidity, time and temperature. The model equation will be helpful for future work on drying and storage of green tea powder.

• Journal of the Korean Society of Food Science and Nutrition
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• v.22 no.6
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• pp.785-791
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• 1993

Kinetic studies were performed to investigate free-fructose content change in rice during storage. The rice was stored at various water activities(0.44, 0.52, 0.65 and 0.75) and at fluctuating temperature($30/50^{\circ}C$) over period of 22 weeks. At early stage of storage free-furctose content increased by zero-order reaction, whereas at later stage, it decreased by first-order reaction. The reaction rates were positively related to water activity and/or temperature during storage. Activation energies calculated at range of aw 0.44~0.75 were found to be 10.76~19.56kcal/mole and 4.53~8.40kcal/mole, for the period of increase and decrease in the free-fructose contents, respectively. The shelf-life assessed at $25^{\circ}C$ was found to be 252(aw 0.44), 212 (aw 0.52), 193(aw 0.65) and 162(aw 0.75) days.

• Korean Journal of Food Science and Technology
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• v.22 no.4
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• pp.473-478
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• 1990

A computer-aided simulation technique was selected to predict the gain or loss of moisture in corn starch packaged with gas and moisture permeable materials under various conditions. Water activity and moisture content of corn starch was predicted by computer program at various conditions. A linear relationship was showed between water activity and equilibrium moisture content at the range of $A_w$ 0.332 to 0.90 and simulated values obtained by the proposed model was given to a dose approximation with the observed values.

• Journal of the Korean Applied Science and Technology
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• v.35 no.2
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• pp.560-567
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• 2018

In the cosmetics industry, many raw materials such as hyaluronic acid and glycerin have been developed and studied as moisturizing agents for long-lasting moisturizing effects. In this study, we investigated changes in moisture and transdermal water loss of skin by changing the surfactant, instead of the moisturizing agent. Particularly, surfactant types such as natural surfactant, lecithin surfactant, polyglyceryl ester surfactant, peg Surfactant and peg w/o surfactant showed changes in moisture and transdermal water loss according to the changes of their surfactants. The best results were obtained when using Lecithin surfactant.

• Korean Journal of Agricultural Science
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• v.22 no.2
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• pp.180-187
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• 1995

In order to distinguish the honey in the market whether it is real or not simply and conviniently, the changes of water activity was investigated due to the addition of starch syrup and sucrose solution to the honeys such as Korean, Acacia, Chestnut and Mixed. The regression equations were obtained to predict the water activity of the honeys. In general, the honey was below 21% in moisture, below 0.6% in ash, 420 to 710cP in the viscosity, 0.57 to 0.62 in the water activity and 77 to 80brix in sugar content. The water activity of the samples were higher as the quantity of starch syrup and sucrose solution added increased. Starch syrup was more influence than sucrose solution. The regression equations between water activity and starch syrup concentration of honeys were obtained and $R^2$ value were higher than 0.90.

• Journal of the Korean Society of Clothing and Textiles
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• v.32 no.6
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• pp.911-917
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• 2008

In this study, we reported the effect of porcine pancreas lipase treatment in the presence of a calcium chloride and Triton X-100 on moisture regain and wettability of PET fabrics. The moisture regain of PET fabrics in the presence of 0.5% surfactant showed a 1.5-fold decrease, compared to the absence of it. Triton X-100 acted as an inhibitor to porcine pancreas lipase hydrolytic activity. The moisture regain and wettability of porcine pancreas lipase treated PET fabrics improved when more than 10mM of calcium chloride was added to the treatment solution. Porcine pancreas lipase treatment caused voids and cracks on PET fabrics.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.27 no.1
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• pp.7-12
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• 1994

The kinetics of browning reaction of dried shrimp powder samples were investigated during storage. The temperature conditions of the ding process were $25^{\circ}C\;and\;45^{\circ}C$, and the samples were stored at water activity ($a_w$) of 0.33, 0.44, 0.52, 0.65 and temperatures of $35^{\circ}C,\;45^{\circ}C,\;55^{\circ}C$ and temperature fluctuations between $33^{\circ}C\;and\;55^{\circ}C$. When the shrimp was dried at $25^{\circ}C$ the activation energies obtained from the Arrhenius plot ranged from 13.57 to 14.33 kcal/mol. From these energies of activation, the $Q_{10}$ values at $25^{\circ}C$ showed 1.93 to 2.00. In the case of drying at $45^{\circ}C$ the activation energies were $13.12{\sim}13.61\;kcal/mol$ and $Q_{10}$ values were $1.89{\sim}1.93$, respectively. In addition, a storage study under square-wave fluctuating temperature conditions was carried out by varying the shrimp sample temperature between $35^{\circ}C\;and\;55^{\circ}C$ within 7 days regular fluctuation cycle. The data obtained from the fluctuating temperature storage study will be used in the prediction of shelf-lives. The shelf-lives assessed at $25^{\circ}C$ from the accelerated shelf-life tests ranged from 4 days at aw 0.65 to 139 days at aw 0.33.

• Journal of the Korean GEO-environmental Society
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• v.4 no.2
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• pp.39-46
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• 2003

An immobilization zone can be constructed by modifying soils in the vadose zone with surfactants, which can be used to promote retardation of organic contaminants in the subsurface. Column experiments were conducted to investigate the behavior of surfactants and organic contaminants in unsaturated and saturated conditions with different water contents (25%, 50%, 75%, 100%). Transport and sorption of surfactant (dialkylated disulfonated diphenyl oxide) in the columns containing aluminum oxide was similar under the conditions at different water contents. However, transport of a model organic compound (naphthalene) was retarded as the water content decreased by enhanced partitioning of the compound into the surfactants that were sorbed on the aluminum oxide. This suggests that the immobilization method could well be applied to vadose zone as well as to saturated zone.