• Korean Journal of Materials Research
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• v.30 no.1
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• pp.38-43
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• 2020

Sand casting 3D printing uses a binder jetting method to produce a mold having complicated shape by spraying a binder on sand coated with activator. Appropriate heat treatment process in sand mold fabrication can increase the degree of polymerization to improve flexural strength. However, long heat treatment of over 24 hours decreases flexural strength and reliability due to chemical bond decomposition through thermal degradation. The main role of the activator is to control the reaction rate between the polymer chains. As a result, when the activator composition is increased from 0.15 wt% to 0.25 wt%, the flexural strength is increased by 218 N/㎠. However, excess activator (0.40 wt%) has been shown to decrease reliability without increasing flexural strength. The main role of the binder is to control the flexural strength of the specimen. As the binder composition is increased from 2.00 wt% to 4.00 wt%, the flexural strength increases to about 255 N/㎠, indicating the maximum flexural strength increase. Finally, the reliability of the flexural strength of the fabricated specimens is evaluated by a Weibull plot. Weibull modulus calculations are used to evaluate the flexural strength reliability of the specimens, and maximum reliability value of 11.7 is obtained at 0.20 wt% activator composition. Therefore, it is confirmed that this composition has maximum flexural strength reliability.

• Bulletin of the Korean Chemical Society
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• v.29 no.2
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• pp.413-416
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• 2008

A synthesis route to ordered mesoporous carbons with controllable nitrogen content has been developed for high-performance EDLC electrodes. Nitrogen-doped ordered mesoporous carbons (denoted as NMC) were prepared by carbonizing a mixture of two different carbon sources within the mesoporous silica designated by KIT-6. Furfuryl alcohol was used as a primary carbon precursor, and melamine as a nitrogen dopant. This synthesis procedure gave cubic Ia3d mesoporous carbons containing nitrogen as much as 13%. The carbon exhibited a narrow pore size distribution centered at 3-4 nm with large pore volume (0.6-1 cm3 g-1) and high specific BET surface area (700-1000 m2 g-1). Electrochemical behaviors of the NMC samples with various N-contents were investigated by a two-electrode measurement system at aqueous solutions. At low current density, the NMC exhibited markedly increasing capacitance due to the increase in the nitrogen content. This result could be attributed to the enhanced surface affinity between carbon electrode and electrolyte ions due to the hydrophilic nitrogen functional groups. At high current density conditions, the NMC samples exhibited decreasing specific capacitance against the increase in the nitrogen content. The loss of the capacitance with the N-content may be explained by high electric resistance which causes a significant IR drop at high current densities. The present results indicate that the optimal nitrogen content is required for achieving high power and high energy density simultaneously.

• Journal of the Korean Society of Food Science and Nutrition
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• v.41 no.1
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• pp.116-122
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• 2012

Volatile flavor compounds derived from four black garlic extracts purchased in a local market were analyzed for the purpose of quality assessment. A total of 68 compounds was detected in samples using solid phase microextraction (SPME)/GC/MSD, and they were mainly sulfur-containing compounds, including three unknown compounds (21), aldehydes (10), furans (7), alcohols (6), aromatic compounds (7), ketones (4), acids (4), nitrogen-containing compounds (3), esters (2), and miscellaneous compounds (4). 2,6-Dimethyl-4-heptanone having a fruity-sweet odor was the most abundant in all of the samples. Six sulfur-containing compounds including allyl sulfide, 4-methyl-1,2,4-thiazole, 1,3,5-trithiane, unknown I (RI 1564), unknown II (RI 1565), and unknown III (RI 1613) were detected in all of the samples and appeared to contribute to the garlic-like odor. Particularly, three aldehydes (3-methylbutanal, benzaldehyde, phenylacetaldehyde), four furans (furfural, 2-acetylfuran, 5-methyl-2-furfural, furfural alcohol), and others (2,6-dimethylpyrazine, acetic acid) formed through a Maillard reaction during garlic aging were detected in all of the samples, and they contributed to the characteristic burnt, sweet, and sour flavors of black garlic extracts.

• Korean Journal of Food Science and Technology
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• v.19 no.2
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• pp.157-163
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• 1987

Changes in the odor components of Sergia Lucens during fermentation were studied by simultaneous distillation and extraction method. Forty seven components were identified by GC and GC-MS. Major cooked odor components of raw material were alkyl pyrazines and thialdine. Alkyl pyrazines, furfuryl alcohol, isoamyl alcohol and sulfide compounds, such as dimethylsulfide and dimethyltrisulfide increased during the period of fermentation. On the other hand, thialdine content decreased as the period of fermentation was extended. Sensory evaluation of cooked Sergia Lucens odor was carried out by GC-sniff analysis. The odors of GC effluents at the sniffing port were sniffed in order to find out the key compound of cooked Sergia Lucens odor components. The results of the GC-sniff analysis indicated that 2,5-dimethylpyrazine, 2,6-dimethylpyrazine and 2,3-dimethylpyrazine had dried or roast shrimp-like odor and thialdin had dried small sardine-like odor. The result showed that pyrazines and thialdine could play an important role in the formation of cooked Sergia Lucens odor.

• Food Science and Preservation
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• v.30 no.3
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• pp.492-501
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• 2023

In this study, we wanted to understand the impact of different decaffeination processes on aroma compounds of coffee. Therefore, we analyzed differences in physical characteristics and volatile aroma compounds profiles of regular coffee (RC), Swiss water process decaffeinated coffee (SWDC), and supercritical CO₂ decaffeinated coffee (SCDC) after roasting the coffee beans. The electronic nose analysis identified RC and SCDC as different groups which indicates that these groups volatile aroma compound compositions were different. The principal component analysis of volatile compound patterns identified using an electronic nose indicated that there was a large difference in volatile compounds between RC, which was not decaffeinated, and both decaffeinated SWDC and SCDC. The major aroma compounds of RC, SWDC and SCDC were propan-2-one and hexan-2-one which are ketone, and hexanal and (E)-2-pentenal which are aldehyde and 3-methyl-1-butanol which is an alcohol. After roasting, the composition of major volatile compounds appearing in the beans was similar, but the relative odor intensity was different. We identified 28 volatile aroma compounds from RC, SWDC, and SCDC using headspace-solid phase microextraction-gas chromatography/mass spectrometry (HS-SPME-GC/MS), and analyzed 10 major compounds that were present in high abundance, including furfural, 2-furanmethanol, 2,5-dimethylpyrazine, and 2-ethyl-3-methylpyrazine.

• Korean Journal of Food Science and Technology
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• v.50 no.5
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• pp.464-473
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• 2018

The objective of the current study was to evaluate the effects of roasting methods on volatile flavor compounds of boricha using solvent-assisted flavor evaporation-gas chromatography (GC)-mass spectrometry and GC-olfactometry. The barley roasting methods tested were air roasting (AR), drum roasting (DR), and air/drum roasting (ADR). Twenty, twenty-one, and eighteen aroma-active compounds were detected in the products of AR, DR, and ADR, respectively. Guaiacol (smoky), 2-acetylpyrazine (almond-like), and furfuryl alcohol (burnt sugar-like) were detected as high intensity aroma-active compounds. Intensities of most aroma-active compounds produced by the DR method were higher. On the other hand, aroma intensities of phenols produced by the AR method, such as guaiacol and 2-methoxy-4-vinylphenol (curry-like), tended to be stronger. Aroma characteristics of phenols are not considered to be desirable for boricha. Although roasting time for DR was longer than that for AR, DR may be an effective barley roasting method for enhancing desirable aroma characteristics of boricha.

• Korean Journal of Food Science and Technology
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• v.50 no.2
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• pp.123-131
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• 2018

The objective of this study was to evaluate the effect of roasting degree of barley on aroma characteristics of boricha (barley tea) using solvent-assisted flavor evaporation-gas chromatography-mass spectrometry and gas chromatography-olfactometry. Fifteen volatile compounds including pyrazine, ethylpyrazine, butyrolactone, and guaiacol were considered important volatile compounds, which are generated by roasting barley, because concentrations of those volatiles were significantly increased (p<0.05) as roasting degree of barley was darker. Guaiacol (smoky), furfuryl alcohol (burnt sugar), and furfural (caramel) were detected as aroma-active compounds of boricha with high intensity. Aroma intensity of aroma-active compounds in boricha increased with increase in roasting degree of barley. However, one unknown compound with burnt smell was detected as off-flavor in dark roasted barley. Therefore, it is implied that medium roasting of barley is desirable during boricha manufacturing. Furthermore, boricha manufactured with steamed barley contained more abundant volatile flavor compounds, which may lead to better aroma quality of boricha.