• Korean Journal of Food Science and Technology
• /
• v.11 no.2
• /
• pp.77-80
• /
• 1979

Effects of interfering substances on the determination of L-ascorbic acid (AsA) in green tea and it's extracts by 2,4-dinitrophenylhydrazine (DNP) method was studied. and the removal of these interfering substances was also investigated. Under the condition prescribed for DNP method, AsA content of green tea are effected by some sugar, reductones, dicarbonyl compounds, organic acids, amino acids and others. All interfering substances except amino acids were eliminated by the chloroform extraction after adding o-phenylendiamine to sample solution. and remaining amino acids were eliminated almost completely by the treatment with ion exchange resin$(Amberlite{\;}IR-120H^{+})$. After removing the interfering substances by the above mentioned procedure, total AsA in green tea was determined by DNP method. The values obtained by this method were in good agreement with those by thin layer chromatography (TLC) method. and the method was more rapid and simple than TLC method.

• Carbon letters
• /
• v.24
• /
• pp.1-9
• /
• 2017

We studied the basic properties and fabrication of reduced graphene oxide (rGO) prepared using eco-friendly reduction agents in the graphene solution process. Hydrazine is generally used to reduce graphene oxide (GO), which results in polluting emissions as well as fixed nitrogen functional groups on different defects in the graphene sheets. To replace hydrazine, we developed eco-friendly reduction agents with similar or better reducing properties, and selected of them for further analysis. In this study, GO layers were produced from graphite flakes using a modified Hummer's method, and rGO layers were reduced using hydrazine hydrate, L-ascorbic acid, and gluconic acid. We measured the particle sizes and the dispersion stabilities in the rGO dispersed solvents for the three agents and analyzed the structural, electrical, and optical properties of the rGO films. The results showed that the degree of reduction was in the order L-ascorbic acid ${\geq}$ hydrazine > glucose. GO reduced using L-ascorbic acid had a sheet resistance of $121k{\Omega}/sq$, while that reduced using gluconic acid showed worse electrical properties than the other two reduction agents. Therefore, L-ascorbic acid is the most suitable eco-friendly reduction agent that can be substituted for hydrazine.

• Korean journal of food and cookery science
• /
• v.18 no.5
• /
• pp.487-494
• /
• 2002

This study was conducted to investigate the thermal stability of water-soluble and fat-soluble vitamins dissolved in water and milk by various heat treatments. Vitamin samples were prepared by dissolving them in water and milk at various concentrations, and were heat treated for 30 min at 65$\^{C}$, 15 sec at 85$\^{C}$, 5 sec at 100$\^{C}$, 121$\^{C}$ at 15 min, the levels of residual vitamin were measured by using HPLC. Milk samples were fortified with vitamins before and after UHT treatment. As heating over 100$\^{C}$, riboflavin in water were destructed more than 92% but fortified in milk showed less than 20% destruction, suggesting that riboflavin was protected by milk components. Also retinol heated ever 100$\^{C}$ was more stable in milk than in water. L-Ascorbic acid and cholecalciferol(D$_3$) showed a similar destruction rate in water and in fortified milk. L-ascorbic acid was easily destructed by UHT treatment. Destruction of thiamin and tocopherol was increased in fortified milk. Among tour capsulated water-soluble vitamins, L-ascorbic acid was much more stable compared with powder form. Nicotinic acid and folic acid either in capsule or powder form showed a slight destruction by heat treatment. The results suggested that the fortification of unstable vitamins such as L-ascorbic acid, thiamin, tocopherol and cholecalciferol(D$_3$) should be made in milk after heat treatment.

• Korean journal of food and cookery science
• /
• v.13 no.4
• /
• pp.492-499
• /
• 1997

The effect of oxidants, gluten and gums on breadmaking quality of wheat-purple sweet potato(Ipomoea batatas) composite flour were studied. Alveograph tests of doughs showed that all additives increased the P, L and W values. Of these additives, L-Ascorbic acid, gluten, carboxy methyl cellulose have a significant effect on alveogram indexes. SEM showed that the dough added with additives changed some what in appearance when compared with the control. When oxidants was added, the doughs discontinuous gluten film were observed. No significant differences ,were evident in bread crumb color among the additives. And textural characteristics of bread crumb were influened by adding additives. Breads containing additives showed an increase in max weight, strength and hardness and a decrease in springness and cohesiveness. Average enthalpy values for all bread crumb after 7days increased with storage time. However, addition of additives decrease the rate of staling slightly more than that of the control. Addition of L-Ascorbic acid, L-Cystine, carboxy methyl cellulose and hydroxy propyl methyl cellulose increased the loaf volume significantly, and with except potassium bromate bread scores were acceptable.

• Journal of the Korean Chemical Society
• /
• v.38 no.11
• /
• pp.783-784
• /
• 1994

• Journal of the Korean Society of Food Science and Nutrition
• /
• v.12 no.1
• /
• pp.27-30
• /
• 1983

This study was carried out to measure the extracted L-ascorbic acid (AsA) amounts of Korean green tea under the different extracting conditions and the measurement followed the method of 2,4-dinitrophey lhydrazine (DNP) which were reformed by Tamula. The results are summarized as follows : 1. The better he quality of green tea was, the higher the rete of AsA extraction was and the green tea having a good quality was well extracted even in low temperature. 2. The rate of AsA extraction of green tea became higher in proportion to the temperature and in the case of $80^{\circ}C$ the extracted amounts reached to 85% in the first three minutes. 3. In relation between the boiling time of test water and the extracted AsA amounts, the extracted AsA amounts was increased in proportion to the boiling time of test water.

• Food Science and Biotechnology
• /
• v.17 no.3
• /
• pp.637-641
• /
• 2008

This study investigated the heat stability of L-ascorbic acid (AA) in acetic acid solution. To analyze the degradation of AA using high performance liquid chromatography (HPLC), AA was measured at a wavelength of 244 nm in acetic acid and 265 nm in distilled water. During the storage of AA in acetic acid or distilled water at $37^{\circ}C$, degradation of AA was slower in acetic acid than in distilled water. On examining various ratios of AA to acetic acid, the stability of AA at $100^{\circ}C$ for 30 min was the highest when the concentration of acetic acid was 10 times higher than the concentration of AA. After acetic acid was added into AA degraded by heating, the AA is stabilized by reheating. Ultimately, these results indicate that degraded AA is reduced by hydrogen ions dissociated from acetic acid, and the rate of reduction of degraded AA in acetic acid solution is improved with heat processing.

• Food Science and Preservation
• /
• v.13 no.4
• /
• pp.450-456
• /
• 2006

The favorable effect of ascorbic acid and cysteine on the improvement of rice bread quality was investigated by creating and comparing 6 experimental rice breads(RB-1 to RB-6). The RB-3 showed a relatively higher loaf volume, specific loaf volume and bread yield than the other breads. Crust and crumb color of breads were measured using a Hunter celery meter. The RB 5 and RB 6 showed the higher cut L-value than the other broads. As the proportion of the rice in the experimental breads increased, both the crust L-value and the crumb L-value showed higher values. According to the texture profile analysis, the hardness of the RB-1 to RB-3 were lower than those of the other breads. The springness of the experimental broads increased as the percentage of the rice in the breads increases. However, less proportions of rice to breads provided significantly lower level of the chewiness. The cohesiveness did not show any specific pattern by the proportion of rice to breads. The degree of retrogradation of the breads was accelerated when the breads contained more rice or when the breads had neither ascorbic acid nor cysteine. Therefore, RB 3, which contained ascorbic acid and cysteine and less rice, showed the highest retardation in the degree of retrogradation. In addition, the RB 3 showed the highest overall acceptance scores by sensory evaluation.

• Proceedings of the Korean Aquaculture Society Conference
• /
• 2003.10a
• /
• pp.19-19
• /
• 2003

This presentation reviewed the dietary vitamin C requirements in main marine finfish culture in Korea. In experiment I, an II-week feeding trial was conducted to study the effects of the different levels of dietary vitamin C on growth, tissue ascorbic acid concentrations and histopathological changes in parrot fish. Casein and gelatin based diets were formulated to contain 0, 60, 120, 240, 480 and 2000mg L-ascorbic acid (AA)kg diets on Ah equivalent basis in the form of L-ascorbyl-2-monophosphate (AMP), 60 and 240 mg AA/kg diet as L-ascorbic acid. Broken line analysis of weight gain indicated that the dietary vitamin C requirement of parrot fish is l18$\pm$12 mg AA/kg diet in the form of L-ascorbyl-2-monophosphate for maximum growth. In experiment II, a 12-week experiment was conducted to compare L-ascorbyl-2-monophosphate-Ca (AMP-Ca) with L-ascorbyl-2-monophosphate-Na/Ca (AMP-Na/Ca) for supplying the dietary vitamin C for juvenile Korean rockfish Sebastes schlegeli. Fish were fed one of 11 semi-purified diets containing equivalent of 0, 50, 100, 200, 400, and 800 mg ascorbic acid (AA)kg diet in the form of AMP-Ca or AMP-Na/Ca for 12 weeks. Broken line analysis of weight gain indicated that the dietary vitamin C requirement of Korean rockfish is 100 mg AA/kg diet in the form of AMP-Na/Ca, and 117 nag AA/kg diet in the form of AMP-Ca. In experiment III, a 12-week experiment was conducted to study the effects of different dietary levels of vitamin C, L-ascorbyl-2-polyphosphate (ASPP), on growth and tissue vitamin C concentrations in juvenile olive flounder. Fish were fed one of six semi-purified diets containing an equivalent of 0, 25, 50, 75, 150, or 1500 mg ascorbic acid (AA) kg 1 diet in the form of ASPP for 12 weeks. Based on broken line analyses for WG and PER, the optimum dietary levels of vitamin C were 91 and 93 mg AA/kg diet, respectively.

• Journal of Nutrition and Health
• /
• v.7 no.1
• /
• pp.37-43
• /
• 1974

The L-ascorbic acid, when various kinds of flavoring and spices were added to it's solution individually or in combination, was determined by the 2,4-Dinitrophenylhydrazine method. The remaining rate of it in the solution, to which such spices and flavoring as vinegar, sugar, salt, glutamic acid-Na, welshonion, garlic, sesame, rice jelly, soy, pimento, hotbean paste, pepper, ginger and cinnamon were added individually, was higher than in the solution of itself alone. In the case of pinenuts, sesame oil and, bean paste, however, the remained total ascorbic acid was of little quantity, The rate of it's autooxidation in the solution added with fennel, cinnamon, ginger, pepper, bean paste, pinenuts, curry in individual were found high, but relatively low in garlic, sesame oil, glutamicacid-Na, sugar, honey, salt, pickled shrimps, hot bean paste, and soy. When combined spices and flavoring were added, the content of ascorbic acid showed high values in all cases, indicating that particularly high in soy-bean sprout namul, chinese radish namul, and muchim, seasoned with the most frequently used flavoring, No. 7,8,9,10 while low values in the combination of mustard muchim.