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Singlet Oxygen Oxidation (singlet + oxygen_oxidation)

Distribution by Scientific Domains

Chemistry	60%

Selected Abstracts

Chemistry and Reaction of Singlet Oxygen in Foods

COMPREHENSIVE REVIEWS IN FOOD SCIENCE AND FOOD SAFETY, Issue 2 2002
D. B. Min
ABSTRACT Singlet oxygen is a highly reactive, electrophilic, and nonradical molecule. It is different from diradical triplet oxygen in its electron arrangement. Photosensitizers can form singlet oxygen from triplet oxygen in the presence of light. The reaction rate of singlet oxygen with foods is much greater than that of triplet oxygen due to the low activation energy. Singlet oxygen oxidation produces undesirable compounds in foods during processing and storage. However, carotenoids and tocopherols in foods can minimize singlet oxygen oxidation. The in-depth scientific knowledge on the formation, reactions, quenching mechanisms, and kinetics of singlet oxygen can greatly improve the quality of foods by minimizing the oxidation during processing and storage. The single oxygen oxidation of foods has contributed to the explanation of several important chemical reactions in the reversion flavor in soybean oil, sunlight flavor in milk products, and the rapid losses of vitamin D, riboflavin, and ascorbic acid in milk under light storage. [source]

Effects of singlet oxygen on membrane sterols in the yeast Saccharomyces cerevisiae

FEBS JOURNAL, Issue 6 2000
Till Böcking
Photodynamic treatment of the yeast Saccharomyces cerevisiae with the singlet oxygen sensitizer toluidine blue and visible light leads to rapid oxidation of ergosterol and accumulation of oxidized ergosterol derivatives in the plasma membrane. The predominant oxidation product accumulated was identified as 5,,6,-epoxy-(22E)-ergosta-8,22-dien-3,,7,-diol (8-DED). 9(11)-dehydroergosterol (DHE) was identified as a minor oxidation product. In heat inactivated cells ergosterol is photooxidized to ergosterol epidioxide (EEP) and DHE. Disrupted cell preparations of S. cerevisiae convert EEP to 8-DED, and this activity is abolished in a boiled control indicating the presence of a membrane associated enzyme with an EEP isomerase activity. Yeast selectively mobilizes ergosterol from the intracellular sterol ester pool to replenish the level of free ergosterol in the plasma membrane during singlet oxygen oxidation. The following reaction pathway is proposed: singlet oxygen-mediated oxidation of ergosterol leads to mainly the formation of EEP, which is enzymatically rearranged to 8-DED. Ergosterol 7-hydroperoxide, a known minor product of the reaction of singlet oxygen with ergosterol, is formed at a much lower rate and decomposes to give DHE. Changes of physical properties of the plasma membrane are induced by depletion of ergosterol and accumulation of polar derivatives. Subsequent permeation of photosensitizer through the plasma membrane into the cell leads to events including impairment of mitochondrial function and cell inactivation. [source]

Changes of Headspace Volatiles in Milk with Riboflavin Photosensitization

JOURNAL OF FOOD SCIENCE, Issue 7 2009
J.H. Lee
ABSTRACT:, Effects of fluorescent light, riboflavin, ascorbic acid, sodium azide, and butylated hydroxyanisole (BHA) on the volatiles in milk at 4 °C were determined using a combination of headspace-solid phase microextraction (HS-SPME), gas chromatography (GC), and mass spectrometry (MS). Pentanal, hexanal, heptanal, and dimethyl disulfide were formed only in the milk stored under light and increased significantly as the duration of light exposure increased from 0 to 8 h and the concentration of added riboflavin increased from 5 to 50 ppm (P,< 0.05). As fat content in milk increased, peak areas of pentanal, hexanal, and heptanal increased significantly (P,< 0.05) while those of dimethyl disulfide did not change significantly (P,> 0.05). Sodium azide prevented the formation of dimethyl disulfide in milk, implying that dimethyl disulfide can be formed through singlet oxygen oxidation (type II pathway). Addition of ascorbic acid and BHA reduced the formation of hexanal, heptanal, and dimethyl disulfide significantly (P,< 0.05). Generation mechanisms of pentanal seem to be different from those of hexanal and heptanal in milk. Both singlet oxygen oxidation (type II pathway) and free radicals (type I pathway) play important roles in the formation of light-induced volatiles in milk. [source]

Singlet Oxygen Oxidation Rates of ,-, ,-, and ,-Tocopherols

JOURNAL OF FOOD SCIENCE, Issue 8 2006
H.J. Kim
ABSTRACT:, The reaction rate constants of 5 × 10,4 M, 10 × 10,4 M, and 20 × 10,4 M ,-, ,-, and ,-tocopherols with singlet oxygen in methylene chloride containing 1 × 10,5 M chlorophyll under light at 25 °C for 60 min were studied. The oxidation of tocopherols determined by a spectrophotometric method showed that the losses of 20 × 10,4 M ,-, ,-, and ,-tocopherols after 60 min under light were 21%, 16%, and 9%, respectively. The degradation of ,-, ,-, and ,-tocopherols was undetectable in the absence of chlorophyll under light or in the presence of chlorophyll in dark. The losses of tocopherols under light were mainly due to singlet oxygen oxidation. The degradation rates of 20 × 10,4 M ,-, ,-, and ,-tocopherols were 6.6 ×10,6 M/min, 5.0 × 10,6 M/min, and 2.9 × 10,6 M/min, respectively. The reaction rates between ,-, ,-, or ,-tocopherol and singlet oxygen were 4.1 ×106/M s, 3.3 × 106/M s, and 1.4 × 106/M s, respectively. The singlet oxygen oxidation rate of ,-tocopherol was significantly lower than ,- or ,-tocopherol at ,= 0.05. As the electron density in the chromanol ring of tocopherol increased, the singlet oxygen oxidation was increased. [source]