Impact of UV-B irradiation on chlorophyll degradation and chlorophyll-degrading enzyme activities in stored broccoli (Brassica oleracea L. Italica Group) florets

UV-B irradiation was applied to broccoli florets to investigate its effect on chlorophyll degradation and chlorophyll-degrading enzyme activities in stored broccoli. Broccoli florets were irradiated with UV-B doses at 4.4, 8.8, and 13.1 kJ m⁻² and then kept at 15 °C in darkness. We found that a UV-B dose of at least 8.8 kJ m⁻² efficiently delayed the decrease of the hue angle value and the contents of chlorophylls a and b. Chlorophyllide a and 13²-hydroxychlorohyll a gradually decreased with senescence. Pheophorbide a and pyropheophorbide a levels were significantly higher in broccoli without UV-B treatment. Chlorophyllase and chlorophyll-degrading peroxidase activities with UV-B treatment were suppressed, as well as the activity of Mg-dechelatase. Mg-dechelating substance activity was also suppressed with this treatment. We concluded that UV-B treatment effectively suppressed chlorophyll degradation in broccoli florets during storage, suggesting that the effect could be due to the suppression of chlorophyll-degrading enzyme activities.     

Archiving of food samples from restaurants and caterers--quantitative profiling of outbreaks of foodborne salmonellosis in Japan

The Ministry of Health, Labor and Welfare (former MHW) of Japan issued a Directive in 1997 advising restaurants and caterers to freeze portions of both raw food and cooked dishes for at least 2 weeks. This system has been useful for determining vehicle foods at outbreaks. Enumeration of bacteria in samples of stored food provide data about pathogen concentrations in the implicated food. Data on Salmonella concentrations in vehicle foods associated with salmonellosis outbreaks were collected in Japan between 1989 and 1998. The 39 outbreaks that occurred during this period were categorized by the settings where the outbreaks took place, and epidemiological data from each outbreak were summarized. Characteristics of outbreak groups were analyzed and compared. The effect of new food-storage system on determination of bacterial concentration was evaluated. Freezing and nonfreezing conditions prior to microbial examination were compared in the dose-response relationship. Data from outbreaks in which implicated foods had been kept frozen suggested apparent correlation between the Salmonella dose ingested and the disease rate. Combined with results of epidemiological investigation, quantitative data from the ingested pathogen could provide complete dose-response data sets.     

A facile method to produce rodlike β-Si3N4 seed crystallites for bimodal structure controlling

β-Si₃N₄ rodlike seed crystallites were successfully produced by single-step heat treatment of commercial α-Si₃N₄ powder at 1900°C for 20 h under an N₂ gas pressure of 980 kPa. The average diameter, length, and aspect ratio of the seed crystallites were 0.73 μm, 1.37 μm, and 1.86, respectively. The α- ⇀ β-Si₃N₄ phase transformation proceeded mainly at 1900°C, and this temperature was lower than the theoretical α-Si₃N₄ dissociation temperature (1933°C) under N₂ gas pressure of 980 kPa. The formation of metastable solid solution due to the dissolution of O impurity into the α-Si₃N₄ crystal lattice was suggested as the driving force for the present oxide additive-free α- ⇀ β-Si₃N₄ phase transformation. β-Si₃N₄ ceramics were fabricated by liquid phase sintering promoted by an additive system of 1 wt% MgO with 3 wt% Gd₂O₃. Starting α-Si₃N₄ powder with 10 vol% rodlike β-Si₃N₄ seed crystallites prepared in this study and an extended sintering time for up to 20 h at 1950°C resulted in the formation of bimodal microstructure composed of fine matrix grains and large elongated grains originated from the seed crystallites. The β-Si₃N₄ ceramics exhibited improved fracture toughness and thermal conductivity of 5.9 ± 0.8 MPa m^−1/2 and 109.3 ± 0.4 W m⁻¹ K⁻¹, respectively, retaining a high fracture strength of about 1 GPa.