水産ねり製品の褐変について-7-Enterobacter cloacae UFF-107による褐変前駆物質の生成機構

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The brown discoloration by microorganisms in fish jelly products is very interesting as a reaction involved in the microbial deterioration of foods. In this paper, the mechanism of brown discoloration caused by the microorganism Enterobacter cloacae UFF-107 was studied, and the following results were obtained. 1. The browning precursor which was participating in the reaction with various amino acids or proteins to form the brown substance was confirmed to be formed from glucose or 2-ketogluconic acid by intact cells of E. cloacae UFF-107. 2. We tried to isolate the browning precursor from the fermented liquid containing glucose. This was not successful because the browning precursor was very unstable and decomposed very easily. So, we attempted to isolate it according to KATZNELSON et al., AIDA et al., or KONDO's method. By use of this method, Ca-2, 5-diketogluconate was isolated from the fermented liquid containing Ca-2-ketogluconate. The obtained substance was a pale yellow Casalt. The aqueous solution containing the Ca-salt and glycine formed a brown substance when it was heated for 1 minute at 100°C or incubated for 1 hour at 37°C. 3. We tried to detect the Ca-salt by descending paper chromatography using a solvent system of water saturated isobutylic acid. The RG value was 0.52. KATZNELSON et al. or HENDERSON et al. reported that the RG value for this compound was 0.54 or from 0.57 to 0.61. With p-anisidine hydrochloride as a developing agent, the Ca-salt appeared as a pale yellow spot. This Ca-salt reduces FEHLING's solution and ammoniacal silver nitrate in the cold. PINOFF's reaction, SELIWANOFF's reaction, and sodium nitroprusside reaction were all positive. The ferric chloride reaction and orcinol test was negative. These results agreed well with those reported by KATZNELSON et al. and AIDA et al. The preparation obtained from the fermented liquid of Gluconobacter melanogenus IAM-1836 showed a behavior similar to that of Ca-2, 5-diketogluconate. From these data, The browning precursor obtained was identified as 2, 5-diketogluconic acid. 4. Gluconobacter suboxydans IAM-1829, G. gluconicus IAM-1815, G. melanogenus IAM-1836, and G. melanogenus IAM-1822 were inoculated individually into broth media containing glucose, and were incubated for 2 days at 30°C. After incubation, various amino acids or proteins were then added to the culture media. Only the culture media fermented by G. melanogenus IAM-1836 or G. melanogenus IAM-1822 formed a brown substance when heated at 100°C for 7 minutes.

水産ねり製品の褐変について-7-Enterobacter cloacae UFF-107による褐変前駆物質の生成機構

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