The stability of soybean lecithin upon exposure to UV light, oxygen, and high temperature, and the effect of an antioxidant on the stability, were evaluated by the oxygen absorption method. The oxygen uptake of soybean lecithin was compared with oxygen content, POV and level of unsaturated fatty acid. Oxidation was greater at the surface of the soybean lecithin mass than at the center. Soybean lecithin was easily degraded at a high temperature in the presence of oxygen, and the degradation increased 1.8-2.0 times with an increase in temperature of 10°C. Antioxidant activities of 1, 000ppm α-tocopherol, catechin and melanoidin against the oxidation of soybean lecithin were 40-50%, but in a mixture of α-tocopherol and catechin showed antioxidant activity of 75%. The oxygen uptake was related to oxygen content, POV and content of unsaturated fatty acid under degradative conditions.
Some of the decomposition products of chlorophylls are known to cause photosensitivity in animals and photooxidation of foods. To evaluate the cell damage arising from prooxidant activities of chlorophyll-related compounds [chlorophylls (CHL) a and b, pheophytins (PHY) a and b, pyropheophytin (PYROPHY) a, pheophorbide (PHEO) a and pyropheophorbide (PYRO) a], we have studied the effect of each compound on hemolysis of erythrocytes under light irradiation. PYRO-a caused the strongest hemolysis, followed by PHEO-a. Pheophytins were stronger than chlorophylls and, especially, PHY-b caused higher hemolysis than PHY-a and PYROPHY-a. The 50% hemolysis doses of PYRO-a, PHEO-a, PHY-a and PHY-b with rabbit erythrocytes were 0.0005, 0.0012, 0.0156 and 0.0092μmol/ml, respectively. The hemolysis activities of chlorophylls were very weak, and a high dose (0.02μmol/ml) caused less than 20% hemolysis. The decomposition of chlorophyll-related compounds by erythrocytes was examined. PHY-b was decomposed most effectively; the residual amount (%) after a 5hr irradiation was 11%, and pheophorbide b was detected in the erythrocyte suspension. Similarly, PHEO-a and PYRO-a were detected after addition of PHY-a and PYROPHY-a to erythrocytes, respectively.
Pheophorbide a (PHEO-a) and pyropheophorbide a (PYRO-a), decomposition products of chlorophyll a, were found to be responsible for photosensitivity disease. The photosensitizing activity of PYRO-a was markedly higher than that of PHEO-a. Since PYRO-a was reported to exist in salted green vegetables, a green vegetable “TAKANA” was salted and fermented under various conditions to clarify the formation mechanism of both substances during fermentation, and the formation of PYRO-a (and PHEO-a) and the changes of microbial flora in salted Takana were pursued. For the first 7 days, production of PHEO-a and PYRO-a increased in quantity with the increase of the number of total microbial flora and genus Lactobacillus. Boiling of Takana and addition of sorbate reduced the quantities of PHEO-a, and PYRO-a. The supernatant of a homogenate of Takana salted for 7 days was filtered through a Millipore filter, and the residue (bacterial fraction) and the filtrate (bacteria-free fraction) were prepared. Production of PHEO-a and PYRO-a by addition of the residue to chlorophyll a was larger in quantity than that by the addition of the filtrate. In the case of addition of each fraction to PHEO-a, PYRO-a production was similarly seen. From those results it is assumed that PHEO-a was produced by bacterial enzyme(s) in addition to chlorophyllase, and the main cause of the formation of PYRO-a during storage and fermentation of salted Takana is the action of bacterial enzymes in the salted vegetable.
We tested the desmutagenic effect of hot water extracts of various oolong teas and some green teas. The desmutagenic effect was tested by a modification of the Ames method using Salmonella typhimurium TA 98 and TA 100 strains and a chromosome aberration test using Chinese hamster lung (CHL) cells. Three kinds of oolong teas and 2 kinds of green teas showed a desmutagenic effect against mutagenicity induced by benzo [a] pyrene. Taiwanese oolong tea also showed a desmutagenic effect on mutagenicity induced by extracts of gasoline vehicle exhaust gas and cooked salmon, 1, 6-dinitropyrene, Trp-P-2 (3-amino-1-methyl-5H-pyrido[4, 3-b] indole) and IQ (2-amino-3-methylimidazo [4, 5-f] quinoline). Oolong teas that were treated at 30°C for a month or were heated at 121°C for 20min showed the same desmutagenic effect. Moreover, this desmutagenic effect was also detected on activated Trp-P-2. These results indicated that the desmutagenic effect of oolong tea was not due to a metabolic inactivation of mutagens.
The antimicrobial effect of sodium chlorite on bacteria and yeasts was investigated in comparison with that of sodium hypochlorite, and the degradation of the two compounds in nutrient broth and YM broth was determined. Pseudomonas fluorescens and Bacillus subtilis were inoculated into nutrient broth followed by addition of NaClO2 or NaClO, and it was found that the minimum inhibitory concentration (MIC) of NaClO2 is lower than that of NaClO. On the other hand, when Candida lipolytica and Trichosporon cutaneum were inoculated to YM broth, the MIC of NaClO2 was higher than that of NaClO. When each microorganism was inoculated into sterile mackerel homogenates, the antimicrobial action of NaClO2 was stronger than that of NaClO. As a result of the determination of residual NaClO2 and NaClO in broths, it became clear that NaClO was degraded quickly, but NaClO2 was still present after 7 days. It seems that one of the reasons for the higher antimicrobial effect of NaClO2 than that of NaClO is its stability in the broths.
An analytical procedure for three cresol isomers (o-, p-, and m-isomers) contaminating beef was developed. Isolation of the compounds from the beef was efficiently carried out by steam distillation which was followed by liquid-liquid partition of the distillate with diethyl ether. The extracts were analyzed by gas chromatography (GC) in combination with capillary GC-mass spectrometry. The three isomers were all detected in a sample of ground beef and in hamburger containing that beef. The concentrations of o-, p- and m- cresol in the beef were 1.7, 7.9 and 17.9 ppm, respectively. Though the concentration of each cresol isomer in the hamburger was slightly less than that in the ground beef, the ratio of each isomer in the hamburger was the same as that in the beef. The cresol isomers were not detected in five other beef samples on the market. The detection limit of each isomer was 0.2 ppm.