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Effects of catechins and green tea extract (GTE)on the photosensitized singlet oxygen oxidation of linoleic acid were studied. Epigallocatechin gallate (EGCG) showed the highest antioxidant activity, followed by gallocatechin gallate, epigallocatechin, and epicatechin in a decreasing order. α-Tocopherol showed strong antioxidative activity at the initial oxidation stage, but its antioxidative property rapidly decreased with illumination time. EGCG showed significantly stronger antioxidative activity than α-tocopherol at the later oxidation stage (p<0.05) due to the higher stability of EGCG. Unlike α-tocopherol, GTE possessed strong antioxidative activity even at the later oxidation stage. Overall, GTE was a better antioxidant than α-tocopherol for the protection of linoleic acid from singlet oxygen oxidation. Electron spin resonance (ESR) spectroscopy and visible-spectroscopic data showed unambiguous evidences that the protective activity of GTE against the photosensitized oxidation of linoleic acid was due to the singlet oxygen quenching mechanism.
Effects of green tea catechin (GTC, catechin content 61.4%) on the formations of hydroperoxide,malonaldehyde, and volatile compounds, and losses of retinol and tocopherol in milk during light illumination were studied. GTC showed surprisingly high protective activity of milk photooxidation, in a dose dependent manner. GTC at 25 ppm exerted 82.1 and 75.0% inhibitions of hydroperoxide and malonaldehyde formation during 30 h light illumination, respectively. GTC at 25 ppm exerted 88.7 and 94.3% inhibition of hexanal and heptanal formation in milk during 30 h light illumination, respectively. The 25 ppm GTC greatly suppressed the losses of retinol and α-tocopherol, showing 53.6 and 58.7% protections of their losses in milk after 12 h light illumination, respectively. The protective activity of GTC was at least 4 times higher than ascorbic acid. The inhibitory activities of GTC and ascorbic acid against the photooxidation of milk were in consistent with their singlet oxygen quenching abilities.
The comparative protective effects of gallic acid with well-known synthetic antioxidants (tert-butylhydroquinone, butylated hydroxylanisole, propylgallate) on the thermal oxidations of corn and soybean oils during heating for 8 h at 180oC were studied. The quantitative effects of gallic acid at three different concentrations on the time-course thermal oxidations in the two different vegetable oils were also studied for a prolonged heating of 6 days at 180oC. Gallic acid at 200 ppm exhibited higher protective activity than the synthetic antioxidants at the same concentration. Gallic acid also exhibited persistently strong protective activity, in a concentration dependent manner, on the changes in oxidation indices in corn and soybean oils throughout the prolonged heating period (6 days) at 180oC. The present results clearly suggested that gallic acid would be a potential natural substitute of synthetic antioxidants for the protection of vegetable oils during high temperature heating.
Inorganic arsenic contents in infant rice powders and infant rice snacks marketed in Korea determined by a highly sensitive gas chromatography-tandem mass spectrometry following derivatization with British Anti-Lewisite
Toxic inorganic arsenic (iAs) has been reported to be present in high quantity in rice and rice-based products. The inorganic arsenic contents in infant foods (n = 59) of ready-to-cook infant rice powders and infant rice snacks marketed in Korea were determined by a highly sensitive gas chromatography-tandem mass spectrometry (GC–MS/MS). The mean iAs contents in the infant rice powder and infant rice snacks were 65.6 and 54.0 μg/kg, respectively. The percentages of rice powders and rice snack containing iAs over the maximum level (100 μg/kg) set by EU for the infant foods were found to be 21, and 6%, respectively. This result clearly suggested that regulation regarding the maximum limit of iAs levels for the baby rice products is urgently needed to be set in Korea. This represents the first report on the iAs levels in ready-to-cook infant rice powder products and infant snacks marketed in Korea.
The impact of heat type, sample type, temperature and time on the heat-induced conversion of gingerols to shogaols in ginger were studied by an UHPLC–ESI–MS/ MS. Heat treatments greatly induced the conversion of gingerols to shogaols in ginger. As the temperature increased, the faster conversion of gingerols into shogaols were observed. However, the efficiency of the heat-induced conversion differed greatly with the heat types. Moist heat treatment induced significantly higher quantity of shogaols than dry heat treatment. The moist heat treatment at 120 C for 360 min induced the highest conversion, reaching to 2991 mg 6-shogaol per kg ginger. In addition, dry-heat induced conversion was affected by the sample type. The dry-heat treatment on dried powder induced significantly higher quantity of shogaols than that on sliced fresh ginger. This represents the first systematic comparative study on the heat and sample types on the heat-induced conversion of gingerols into shogaols in ginger.
Conjugated linoleic acid contents in hydrogenated vegetable oils were differentially determined using refractive indices when the iodine value could not be used. The refractive indices of soybean oil, cottonseed oil, and corn oil varied linearly with changes of linoleic acid contents of individual oils with determination coefficients of 0.91, 0.98, and 0.98, respectively. The refractive index can be used as a simple and fast method for control of the hydrogenation process of vegetable oils to obtain a desired conjugated linoleic acid content without fatty acid compositional analysis.
Soybean, cottonseed, and corn oils were hydrogenated to obtain triacyglycerols containing conjugated linoleic acids. The oxidative stability of soybean oil, cottonseed oil, and corn oil was less with CLA than without CLA during autoxidation. However, the autoxidative stability of oils increased as the CLA content increased. During photooxidation of oils, the oxidative stability of oils was higher with CLA than without CLA, and the stability of oils increased as the CLA content increased. The mechanisms of autoxidation and photooxidation of oils were probably due to the contents and anti- and prooxidant activities of individual conjugated linoleic acids in bulk oil, and minor compounds present in oils.