基于GC/MS对1株芽孢杆菌FJAT-13831的鉴定

目的通过芽孢杆菌物质组学分析,快速地区分亲缘关系极近的芽胞杆菌种类。方法本文利用GC/MS检测了芽孢杆菌9个模式菌株和1个分离菌株FJAT-13831的胞外物质成分,并进行主成分和聚类分析。结果不同的芽孢杆菌种间胞外物质具有显著性差异,FJAT-13831的胞外物质成分与其相近种类差异很大,应是芽胞杆菌属的一个新种。结论该方法可从代谢水平上对芽孢杆菌亲缘关系相似的不同种进行区分,为芽孢杆菌的鉴定及新种判断提供一种新的技术手段。     

Fate of ochratoxin A during wheat milling and some Chinese breakfast processing

To estimate the dietary intake of ochratoxin A (OTA), information on the fate during wheat processing is needed. The wheat contaminated with OTA at both levels (93.22 and 248.93 μg/kg) was artificially inoculated by Aspergillus ochraceus. Concentrations of OTA were 1.43–1.66 times higher in bran than whole wheat and 1.27–1.50 times higher in shorts than bran. A concentration reduction of 43.29–55.16% for OTA in flour was observed, with the final concentrations of 41.80 and 138.33 μg/kg in flour respectively. Whereas, OTA was not transferred or decomposed during milling, as the total amount of OTA in all milling fractions didn't decreased. The further losses of OTA were various depending on different processes. The concentration of OTA increased by 11–16% when the flour was processed into Chinese steamed bread (CBS), with the OTA concentrations of 49.2 and 161.35 μg/kg in CBS. It revealed fermentation and steaming increased the OTA levels in CBS. The loss of OTA was small in the Chinese fried bread sticks (CFBS) (38.84 and 129.02 μg/kg), being of 6.73–9.63%. A higher reduction of 23.27–23.92% for OTA was detected in the noodles processing, with the final concentration of 32.98 and 108.24 μg/kg in noodles respectively. The result revealed that the temperature, pH values and strains involved the processes exerted different effects. High temperature (180 °C) and alkaline condition (pH > 7) facilitated to the removal of OTA, while fermentation (with dry yeast) increased the OTA levels in products.     

Partial purification and characterization of polyphenoloxidase from peppermint (Mentha piperita)

Polyphenoloxidase (PPO) of peppermint leaves ( Mentha piperita) was isolated by (NH₄)₂SO₄ precipitation and dialysis. Its pH and temperature optima were 7.0 and 30°C, respectively. On heat-inactivation, half of the activity was lost after 6.5 and 1.5 min of treatment at 70 and 80°C, respectively. Sucrose, (NH₄)₂SO₄, NaCl and KCl appeared to be protective agents of peppermint PPO against thermal denaturation. Km of this enzyme ranged from 6.25×10⁻³ M with catechol to 9.00×10⁻³ M with L-dopa. The I₅₀ values of inhibitors studied on PPO were determined by means of activity percentage (I) diagrams. Values were 1.4×10⁻⁴ M, 1.7×10⁻⁴ M, 9.7×10⁻⁵ M, 2.45×10⁻⁴ M, 2.16×10⁻¹ M, 1.83×10⁻⁵ M, 6.5×10⁻⁵ M, 1.4×10⁻² M, 7.5×10⁻⁵ M, for potassium cyanide, glutathione, ascorbic acid, thiourea, sodium azide, sodium metabisulfite, dithioerythritol, β-mercaptoethanol and sodium diethyl dithiocarbamate respectively. Therefore, sodium metabisulfite was the most effective inhibitor.