Jaecheol Kim

First-principles thermodynamic calculations and experimental investigation of Sr–Si–N–O system—synthesis of Sr2Si5N8:Eu phosphor

Thermodynamic stabilities of the phases of Sr–Si–N–O system were evaluated by simulating phase diagrams at various conditions based on first-principles density functional theory calculations. Synthesis conditions and stability of the compounds belonging to the system, in which oxidation and nitridation reactions are involved complicatedly, could be interpreted through this first systematic investigation on the two-gas system. Practical synthetic methods of nitrides, such as hydrogen-reduction and nitridation or carbothermal reduction and nitridation reactions, were studied with special attention. This study enabled us to calculate proper conditions for synthesis of the Sr2Si5N8 phase, which is drawing attention as a new phosphor material for light emitting diodes. The types of impurities appearing with deviation from the proper synthetic conditions were also investigated, which may provide information about optimizing synthesis conditions. Synthesis of Sr2Si5N8:Eu phosphor using SiO2, instead of conventionally used Si3N4, was predicted by first-principles calculations, and we succeeded in synthesizing Sr2Si5N8:Eu phosphor for the first time using all oxide raw materials under normal pressure on this basis. The results of this study are expected to provide useful guidelines for synthesis of nitrides and the established simulation method may effectively be applied to other multi-gas systems.

Quality Characteristics of Black Raspberry Wine Fermented with Different Yeasts

Four different yeasts (Fermivin (FM), Saf-instant yeast red (SI), Angest wine active dry yeast (AW) and Angest instant yeast high sugar (AI)) were used for the fermentation of black raspberry wine. The amount of reducing sugars in FM (2.7%) and AI (2.8%) were higher than those in SI (2.4%) and AW (2.5%). The amount of glucose (the major free sugar) was higher in AW (2.57 mg/mL) and AI (2.50 mg/mL) than FM (2.03 mg/mL) and SI (1.75 mg/mL). AW (11.95%) had the highest alcohol content, while SI (11.75%) had the lowest. The pH of FM (pH 3.73) was the lowest, and there were no significant differences in total acidity among the samples. The major organic acid in the wines was citric acid (6.71~8.18 mg/mL) and the amount of organic acids depended on the type of yeasts. The amount of malic acid was highest in SI (2.92 mg/mL), and lowest in AI (1.83 mg/mL). The Hunter color test showed that SI was highest in lightness, redness and yellowness, whereas AI was lowest. There were no differences in turbidity between the samples. There were no significant differences in total phenolic contents (TPC) and total anthocyanin contents (TAC). However, the TPC and TAC of black raspberry wines were higher than those in commercial red wines. The antioxidant activities of wines (determined by ABTS and FRAP) increased in the order of FM, AI, AW and SI. It could not be concluded which yeast is adequate for the fermentation of black raspberry wine because any of the tested yeasts showed the best in all the quality characteristics of the wines.

Physicochemical and Sensory Characteristics of Hot Water Extracts of Codonopsis lanceolata Root Skin and Flesh with Different Heat Treatments

In this study, the physicochemical and sensory characteristics of hot water extracts of Codonopsis lanceolata root skin (RS) and root flesh (RF) subjected to different heat treatments were analyzed to determine whether C. lanceolata RS can be used as a tea material. C. lanceolata RS and RF were roasted, hot-air dried (HDS and HDF, respectively), or steamed and hot-air dried (SHDS and SHDF, respectively). The heat-treated samples were extracted with hot water (90 o C) for 90 min. The hot water extracts of RS and RF had lower L-values and higher b-values than the other samples. The RS extracts had significantly higher polyphenol content and DPPH radical scavenging activities than RF samples. In the sensory evaluation, the color acceptability of the teas made from CS, HDS, and SHDS were found to be significantly different from those of the teas made from their respective flesh samples. The results suggest that the hot water extract of the C. lanceolata RS can be utilized as a tea material.

Chemical characteristics of potato chips fried in repeatedly used oils

The objective of the study was to evaluate chemical properties of potato chips fried in repeatedly used oils. Potato chips were deep-fat fried in refined coconut oil (PC: potato chips), refined soybean oil (PS), pure olive oil (PO), and vegetable shortening (PH) used up to 80 times repeatedly. Oils were extracted from PC (OC: extracted oil), PS (OS), PO (OO), and PH (OH) and analyzed for oxidative stability. The PH was higher in hexanal than the PS and PO (p < 0.05). Nonanal and 2-decenal were most detected in the PO (p < 0.05) and rarely in the PS. 2,4-Decadienal was least detected in the PC (p < 0.05). Fatty acid compositions of frying oils affected levels of nonanal, 2-decenal, and 2,4-decadienal in the potato chips during frying. Total polar compounds in the OC were lower than in the other extracted oils at the 80th repeated frying (p < 0.05). Peroxide value of the OC continuously increased during the repeated frying (p < 0.05), while those of the OO and OH little changed. Conjugated dienes, p-anisidine value, and total oxidation value of the OC were the lowest at all the repeated fryings (p < 0.05). Total polar compounds, peroxide value, and conjugated dienes of the oils extracted from potato chips did not exceed the rejection limits until 80 times repeated use of the oils. In this study, the PC might have less oxidative products, suggesting that the refined coconut oil was the most stable during the repeated frying.

Physicochemical characteristics and anti-oxidant activities of farm-cultivated and mountain-cultivated ginseng seeds

Physicochemical characteristics and anti-oxidant capacities of seeds from two farm-cultivated and one mountain-cultivated ginsengs (Panax ginseng Meyer) (MG) were determined. The seeds had 17.9–22.1% (dry basis) crude lipids, 11.5–15.2% crude proteins, and 1.4–1.7% ash. Oleic acid (77.9–78.5%) was the predominant fatty acid in the seed oils, followed by linoleic acid (16.6–17.4%). The highest Hunter b value, carotenoids, (β + γ)-tocotrienol, and δ-tocotrienol, and the lowest α-tocotrienol were observed in the seed oils from MG. Squalene was also the most abundant in the MG seed oils. β-Sitosterol was the major phytosterol in the seed oils with MG the highest. Defatted seed meal extracts from MG possessed the most total phenolics and flavonoids, and the highest DPPH and ABTS radical scavenging activities. These results suggest that MG seeds may be a novel source of functional foods.

Physicochemical and Sensory Characteristics of Beef-bone Broths Prepared under Atmospheric Pressure and Overpressure

This study was conducted to compare the physicochemical and sensory characteristics of beef-bone broths prepared under atmospheric pressure (BBAP) and overpressure (BBOP). Beef-bone was boiled in water (bone/water=1:2, w/w) for 1, 2, 4, 6, and 12 h under atmospheric pressure and overpressure (121oC, 1.25 atm). The BBOP broth samples were found to contain significantly higher amounts of solid, crude protein, crude ash, collagen, and chondroitin sulfate than the BBAP broth samples for a given boiling time (p<0.05). In addition, the Ca and Mg contents in the BBAP samples were higher than those in the BBOP samples, whereas the P, Na, and K contents were higher in BBOP than BBAP. The L value of BBAP was also significantly higher than that of BBOP (p<0.05). Further, as the boiling time increased, turbidity increased in the BBAP samples. In the quantitative descriptive analysis, the BBOP samples exhibited stronger brownness, transparency, meaty off-odor, meaty off-flavor, and sulfuric odor than the BBAP samples.