Mun Yhung Jung

Riboflavin-sensitized photooxidation of ascorbic acid: kinetics and amino acid effects

Abstract The study on the effects of riboflavin contents and light intensity on the riboflavin-sensitized decomposition of ascorbic acid indicated that light and riboflavin accelerated the decomposition of ascorbic acid. The relative photosensitizing activity of riboflavin, methylene blue and protoporphyrin IX was 21:15:1 at 1–2 ppm. The rate constants for reaction of ascorbic acid with singlet oxygen at pH 7·5, 6·0 and 4·5 were 6·63 × 10 8 , 5·77 × 10 8 and 5·27 × 10 8 M −1 s −1 , respectively. Cysteine showed strong antioxidant activity on both riboflavin- and methylene blue-sensitized photooxidation of ascorbic acid and its antioxidant effect was concentration-dependent. Alanine and phenylalanine at 0·1% concentration showed antioxidant effects on the riboflavin-sensitized photooxidation of ascorbic acid but prooxidant effects on the methylene blue-sensitized photooxidation. Tyrosine (0·1%) exhibited strong prooxidant activity on both the riboflavin- and methylene blue-sensitized photooxidation of ascorbic acid. However, tryptophan (0·1%,) showed antioxidant or prooxidant activity on the photooxidation of ascorbic acid depending on the storage time.

Cytotoxic components from the dried rhizomes of Zingiber officinale Roscoe

Five compounds were isolated from the chloroform-soluble fraction of the methanolic extract of the dried rhizomes of Zingiber officinale (Zingiberaceae) through repeated column chromatography. Their chemical structures were elucidated as 4-, 6-, 8-, and 10-gingerols, and 6-shogaol using spectroscopic analysis. Among the five isolated compounds, 6-shogaol exhibited the most potent cytotoxicity against human A549, SK-OV-3, SK-MEL-2, and HCT15 tumor cells. 6-shogaol inhibited proliferation of the transgenic mouse ovarian cancer cell lines, C1 (genotype: p53-/-, c-myc, K-ras) and C2 (genotype: p53-/-, c-myc, Akt), with ED50 values of 0.58 μM (C1) and 10.7 μM (C2).

Free, esterified, and insoluble-bound phenolic acids in white and red Korean ginsengs (Panax ginseng C.A. Meyer)

Abstract Phenolic acids of dried white and red ginsengs were extracted and fractionated into free, esterified, and insoluble-bound forms. The contents of individual phenolic acids in different forms were quantified by gas–liquid chromatography. Identification of all phenolic acids was confirmed by gas chromatography–mass spectrometry and comparison of gas chromatographic retention times. Twelve different phenolic acids as free, esterified, and insoluble-bound forms were identified in Korean ginsengs. Total phenolic acids in white and red ginsengs were 27.2 and 26.8 mg/100 g, respectively. Seven free phenolic acids were identified and their total contents in white and red ginsengs were 4.70 and 4.14 mg/100 g, respectively. trans-Ferulic acid was the predominant free phenolic acid, representing 47.9 and 57.7% of total free phenolic acids in white and red ginsengs, respectively. Esterified phenolic acids represented 71.9 and 77.1% of total phenolic acids in white and red ginsengs, respectively. The most predominant esterified phenolic acids were cis-ferulic acid and trans-ferulic acid. Total insoluble-bound phenolic acid contents in white and red ginsengs were 2.93 and 1.99 mg/100 g, respectively. Ferulic acid (cis and trans isomers) was also the major insoluble-bound phenolic acids. This paper represents the first report of systematic identification and quantification of phenolic acids in different forms in white and red Korean ginsengs.

Pyrazine contents and oxidative stabilities of roasted soybean oils

Abstract Soybeans were roasted with constant stirring for 15 min at 130 °C, 150 °C and 170 °C, and oils were extracted from the roasted soybeans using an expeller. Color, conjugated diene, conjugated triene, peroxide values, tocopherols and fatty acid compositions in the oils were determined. Pyrazines in the oils were extracted by both simultaneous distillation-extraction and solvent extraction. Isolation and identification of pyrazines were carried out by gas chromatography and gas chromatography/mass spectrometry. Oxidative stabilities of the roasted soybean oils were studied during storage for 60 days at 65 °C. As roasting temperature increased, the oil became darker; the red and yellow colors increased. Conjugated diene and conjugated triene increased with increasing roasting temperature. Peroxide values of all the oils were 0 meq kg−1 oil. The contents of total tocopherols in the oils decreased markedly with increasing roasting temperatures. The total tocopherol contents in the oils from soybeans roasted at 130 °C, 150 °C and 170 °C were 70.0, 8.3 and 0.0 mg per 100 g oil, respectively. Fatty acid composition varied slightly with roasting temperatures. Nine alkyl pyrazines were identified: pyrazine, 2-methylpyrazine, 2,5-dimethylpyrazine, 2,6-dimethylpyrazine, 2,3-dimethylpyrazine, 2-ethyl-6-methylpyrazine, 2-ethyl-5-methylpyrazine, 2,3,5-trimethylpyrazine and tetramethylpyrazine. Total pyrazine contents greatly increased with increasing roasting temperature, showing 3.07, 9.46 and 19.7 mg total pyrazines per 100 g oils extracted from soybeans roasted at 130 °C, 150 °C and 170 °C, respectively. The oxidative stability tests showed that, as the roasting temperature increased, the oxidative stability of the oil increased greatly.

Purification of used frying oil by supercritical carbon dioxide extraction

Abstract Supercritical fluid extraction (SFE) was used for the purification of used frying oil at different temperatures (40 and 60°C) and pressures (150, 225 and 300 bar). The calculated solubilities of the oil ranged from 0.3×10 −3 to 7.4×10 −3 g oil/g CO 2 depending on the extraction conditions. The solubility and the selectivity of triglycerides (TG) were between those of the low molecular weight compounds (LMWC) and the polymers. The calculated relative separation efficiency ( R ) of low molecular weight compounds (LMWC) from TG was highest under the low pressure and high temperature extraction conditions, but the extraction rate was minimal under this condition. However, the separation efficiency ( R ) of polymers from TG was not greatly dependent on the pressure and temperature. Based on the relative separation efficiency result, two-stage supercritical carbon dioxide extraction was performed for the effective purification of TG from used frying oil. LMWC were removed under the low pressure extraction conditions (150 bar, 60°C) of the first stage extraction, and then TG were concentrated under the high pressure extraction conditions of the second stage extraction (300 bar, 60°C). The extracts obtained from the second to the fifth fraction of the second stage included less than 1% polymer, more than 92% TG, and less than 8% LMWC. The conjugated diene contents of these extracts ranged from 0.202 to 0.231%, showing a similar conjugated diene content to the fresh frying oil. The present data clearly showed that two-stage supercritical CO 2 extraction was an efficient method for the purification of TG from used frying oil.

Kinetic study of the quenching reaction of singlet oxygen by common synthetic antioxidants (tert-butylhydroxyanisol, tert-di-butylhydroxytoluene, and tert-butylhydroquinone) as compared with α-tocopherol.

Effects of synthetic phenolic antioxidants (BHA, BHT, and TBHQ) on the methylene blue (MB) sensitized photooxidation of linoleic acid as compared with that of alpha-tocopherol have been studied. Their antioxidative mechanism was studied by both ESR spectroscopy in a 2,2,6,6-tetramethylpiperidone (TMPD)-methylene blue (MB) system and spectroscopic analysis of rubrene oxidation induced by a chemical source of singlet oxygen. Total singlet oxygen quenching rate constants (k(ox-Q)+k(q)) were determined using a steady state kinetic equation. TBHQ showed the strongest protective activity against the MB sensitized photooxidation of linoleic acid, followed by BHA and BHT. TBHQ (1 x 10(-3) M) exhibited 86.5% and 71.4% inhibition of peroxide and conjugated diene formations, respectively, in linoleic acid photooxidation after 60-min light illumination. The protective activity of TBHQ against the photosensitized oxidation of linoleic acid was almost comparable to that of alpha-tocopherol. The data obtained from ESR and rubrene oxidation studies clearly showed the strong singlet oxygen quenching ability of TBHQ. The k(ox-Q)+k(q) of BHA, BHT, and TBHQ were determined to be 3.37 x 10(7), 4.26 x 10(6), and 1.67 x 10(8) M(-1) s(-1), respectively. The k(ox-Q)+k(q) of TBHQ was within the same order of magnitude of that of alpha-tocopherol, a known efficient singlet oxygen quencher. There was a high negative correlation (r(2) = -0.991) between log (k(ox-Q)+k(q)) and reported oxidation potentials for the synthetic antioxidants, indicating their charge-transfer mechanism for singlet oxygen quenching. This is the 1st report on the kinetic study on k(ox-Q)+k(q) of TBHQ in methanol as compared with other commonly used commercial synthetic antioxidants and alpha-tocopherol.

High resolution LC–ESI-TOF-mass spectrometry method for fast separation, identification, and quantification of 12 isoflavones in soybeans and soybean products

A high resolution LC-ESI-TOF-MS analytical method was established for the rapid isolation, identification, and quantification of 12 isoflavones in soybean and soybean products. Individual isoflavones were identified on the basis of the accurate mass data of their respective protonated mass ions, Na or K adduct ions, fragment ions, and isotope ion patterns. The protonated mass ions of isoflavones were extracted for their quantification in soybean products. Twelve different isoflavones in the soybean products were fully separated, identified and quantified within 12min separation time. The established LC-TOF/MS was an effective analytical method for the simultaneous characterization and quantification of isoflavones with exceptionally short analytical time, high selectivity, a high linearity (r(2)>0.992) in a wide range, low LOD and LOQ, high precision, inter-and intra-day repeatability, and no significant matrix effect. Furthermore, it requires simple sample preparation procedure (solvent extraction, dilution, and syringe filtration).

Bulk flow properties of model food powder at different water activity

Abstract Bulk flow properties of five kinds of model food powders composed of starchy powder (potato starch) and proteinaceous powder (wheat protein) were determined at different water activity by measuring loose bulk density, tapped bulk density, Hausner ratio, angel of repose and slide and shear stress of the model powders. Fitted equations relating these bulk properties to water activity were also developed. As the water activity of model food powders increased, all the tested properties of the model powders increased except loose bulk density and internal friction angle. As the protein content of model food powder increased, Hausner ratio, angle of slide, shear stress, and cohesion increased, but loose bulk density decreased. There were no significant differences in angle of frictions among the tested model powders. If a powder with high protein content is exposed to a high humidity environment, the powder may aggregate due to the low flowability. The correlation coefficients (R) for all the fitted eq...

Direct Spectroscopic Observation of Singlet Oxygen Quenching and Kinetic Studies of Physical and Chemical Singlet Oxygen Quenching Rate Constants of Synthetic Antioxidants (BHA, BHT, and TBHQ) in Methanol

Singlet oxygen quenching by synthetic antioxidants (BHA, BHT, and TBHQ) was directly observed by spectroscopic monitoring of luminescence at 1268 nm. The luminescence data showed unambiguous evidence of singlet oxygen quenching by synthetic phenolic antioxidants with the highest activity for TBHQ, followed by BHA and BHT. The protective activities of these synthetic antioxidants on alpha-terpinene oxidation with chemically-induced singlet oxygen under dark further confirmed their singlet oxygen quenching abilities. Total singlet oxygen quenching rate constants (k(r) + k(q)) of BHA, BHT, and TBHQ were determined in a system containing alpha-terpinene (as a singlet oxygen trap) and methylene blue (as a sensitizer) during light irradiation, and the values were 5.14 x 10(7), 3.41 x 10(6), and 1.99 x 10(8) M(-1)s(-1), respectively. After the k(r) value of alpha-terpinene was first determined, the k(r) values of the synthetic antioxidants were calculated by measuring their relative reaction rates with singlet oxygen to that of alpha-terpinene under the identical conditions. The k(r) values of the BHA, BHT, and TBHQ were 3.90 x 10(5), 1.23 x 10(5), and 2.93 x 10(6), M(-1)s(-1). The percent partition of chemical quenching over total singlet oxygen quenching (k(r) x 100)/(k(r) + k(q)) for BHA, BHT, and TBHQ were 0.76%, 3.61%, and 1.47%, respectively. The results showed that the synthetic antioxidants quench singlet oxygen almost exclusively through the mechanism of physical quenching. This represents the first report on the singlet oxygen quenching mechanism of these synthetic antioxidants. Practical Application: The synthetic antioxidants, especially TBHQ, have been found to have a strong singlet oxygen quenching ability. This article also clearly showed that singlet oxygen quenching by synthetic antioxidants was mainly by the physical quenching mechanism. The results suggested that these synthetic antioxidants, especially TBHQ, could be used practically for the protection of the food components such as edible oils and vitamins against singlet oxygen induced oxidations without significant losses of antioxidant activity during storage under light.

A Gas Chromatography‐Tandem Quadrupole Mass Spectrometric Analysis of Policosanols in Commercial Vegetable Oils

UNLABELLED Reportedly policosanols (PCs) have various beneficial functionalities on health. A gas chromatography-tandem mass spectrometry (GC-MS/MS) with a low limit of detection (LOD), and high specificity, recovery, and precision was successfully established for the PC analysis in vegetable oils. The LODs for the PCs were in the range of 0.002 to 0.016 μg/mL. The relative standard deviation (RSD) for the repeated analysis of PCs was less than 3.356%. The mean recoveries for spiked heptacosanol and octacosanol in vegetable oil were 102.3% and 106.3%, respectively. The total PC contents in the vegetable oils varied from 3.01 to 427.83 mg/kg oil. Perilla seed, grape seed, and rice bran oils were found to be highly rich sources of PCs, containing 427.83, 245.15, and 171.17 mg PCs/kg oil, respectively. Corn, sesame, and soybean oils contained only a negligible quantity of PCs. The PC composition in vegetable oils was greatly source dependent. In perilla seed oil, octacosanol was the single most predominant component, representing 55.93% of the total PC. In grape seed oil, however, hexacosanol is the most abundant PC, followed by octacosanol, tetracosanol, and triacontanol in a decreasing order. The major PCs in rice bran oil were triacontanol, octacosanol, hexacosanol, and tetracosanol, which constituted over 87.3% of the total PC. This represents the 1st report on the composition and contents of PC in most vegetable oils analyzed here. PRACTICAL APPLICATION The information might be used for the development of vegetable oil products with beneficial functionality.