一种快速检测食醋产气变质菌培养方法的研究及应用

目的建立一种快速检测食醋产气变质菌的培养方法。方法在6种培养基筛选的基础上,选择适宜的培养基进行改良,对改良培养基的特异性、准确性和灵敏度进行考察后确定检测方法,应用本方法筛选针对食醋产气变质菌的热灭菌条件和常用防腐剂的抑菌浓度,并验证食醋产品的检测效果。结果采用改良MRS培养基(食醋产气变质菌检测培养基)仅能检出由产气变质菌引起的变质食醋样品,对12株食醋其他种类污染菌和致病菌的检测结果均为阴性;以塑料软瓶恒温培养法为对照,采用本法对未知产气变质情况的75个食醋样品进行检测,两种方法检测结果一致,而本法的检测速率是对照的3~5倍;检出限为1 CFU≤初始菌量(接种量)<10 CFU;样品菌量越大,检测时间越短,检测高污染菌量食醋样品只要1~2 d。方法应用结果表明,75~85℃维持5~15 min能有效杀灭食醋产气变质菌,常用防腐剂在最大使用限量内不能有效抑制食醋产气变质菌生长,验证食醋产品的检测效果与真实情况一致。结论食醋产气变质菌检测方法具有快速、特异、准确、灵敏的特点,为生产企业的食醋产气变质菌检测及综合防控提供了依据。

提高扇贝制品安全水分含量的初步研究

取活体栉孔扇贝(壳高55～65 mm),剖取贝柱或汽蒸开壳后取贝肉,制成3类不同水分活度(a_w)的试样,测定其制品水分含量和水分活度的关系以及贮藏试验中变质菌类型。结果表明,对于L-a_w型制品(o.60<a_w<0.70),传统制品干贝的安全水分含量为17.3％以下,添加糖、盐等调味品后制品安全水分含量提高到20.3％,使用山梨酸钾作防霉剂进一步提高到24.1％。对于M-a_w型制品(0.7O<a_w<0.90),采取真空包装,制品安全水分含量可提高到38％。对于H-a_w型制品(0.90<a_w<0.95),采取降低a_w和pH、热加工、真空包装、二次低温加热杀菌的联合措施,制品安全水分含量可达50％。因此,采用适当的科学方法,扇贝制品的安全水分含量是可以提高的。

Effect of Storage Temperature on the Quality of Glass Bottled Pasteurized Whole Milk

Shelf life of pasteurized milk is relatively short, mainly due to cold chain conditions. This study investigated the effects of different storage temperatures （8, 10 and 12 ℃） on acidity, microorganism index, physical and chemical indicators and sensory quality of pasteurized milk packaged in glass bottle to determine the main factor affecting the quality of pasteurized milk during shelf life under different tem- peratures. The results showed that within the first five days, the protein, fat, lactose and non-fat milk solids contents in the milk samples did not change under different storage temperatures; the acidity was almost unchanged at 8 and 10 ℃, and in- creased slightly at 12 ℃; the sensory quality of milk samples did not change at 8 and 10 ℃, and began to decline from the 4th d at 12 ℃; the aerobic plate count in the milk samples accorded with the requirement of national standard at 8 and 10℃, and exceeded the national standard on the 5th day at 12℃. No coliform bac- teria were detected in the milk samples within the storage time at 8 ℃. When the milk samples were stored at 10 ℃, the coliform group count exceeded the national standard on the 5th day. When the milk samples were stored at 12 ℃, coliform bacteria began to be found in the milk samples from the 2rd day, and the coliform group count exceeded the national standard from the 3rd day. It indicated that stor- age time had a great impact on the quality of glass bottled pasteurized milk. Low storage temperature and relatively short storage time were conducive to the reten- tion of high quality of pasteurized milk. Coliform group count was one of the impor- tant factors affecting the quality of glass bottled pasteurized milk during shelf life.

Screening and characterization of a high taxol producing fungus by protoplast mutagenesis

The preparation, regeneration and mutagenesis of the taxol-producing fungus UV40-19 protoplasts were discussed in the experiment. Totally 42 strains displayed hygromycin resistance. Six strains were found to be positive mutants when screened on plate containing 90μg/mL hygromycin. One hereditarily stable strain UN05-6 was obtained, which raised the taxol yield from （376.38 ± 8.41）μg/L to （493.12 ±11.36） μg/L. The optimal conditions for the preparation, regeneration and mutagenesis of the taxol producing fungus UV40-19 were as follows： 1 ）enzymolysis in a solution containing 3% lywallzyme, 4% snailase, 1% lysozyme and 3% cellulose at 30~C water bath, pH5.5 - 6.0 for 5h; 2） The prepared protoplasts were regenerated by using bilayer plate culturing method; 3）To mutagenize the fungus UV40-19, the protoplast suspension was treated with 0.8mg/mL NTG for 15min, followed by UV irradiation （30W, 30cm distance）for 40s under magnetic stirring. The purified products of the fungus UN05-6 fermented extracts have significant inhibitive effects on SMMC-7721 cell.

Simulation of the impacts of diagenesis or low-grade metamorphism on neutrophilic microaerobic Fe(II)-oxidizing biofilm

The microaerobic iron-oxidizing bacteria in circumneutral environment produce extracellular polymeric substances （EPS） with unique morphologic features, such as stalks or sheaths, which can be regarded as geobiological signatures. The Archean and early Palaeoproterozoic oceans were anoxic with high soluble Fe（Ⅱ） that were suggested to have been oxidized through the metabolism of Fe（II）-oxidizing bacteria. The precursor of the ultrafine hematite in banded iron formation （BIF）, e.g., ferrihy- drite, was suggested to be the mineral record of microbial Fe（Ⅱ）-oxidation at that time. However, both the biological materials and primary iron minerals were prone to being altered by diagenetic or low-grade metamorphic processes. This makes it diffi- cult to interpret the genesis of Precambrian BIFs. Here, we report experimental simulation on the effects of diagenesis or low-grade metamorphism on neutrophilic microaerobic Fe（Ⅱ）-oxidizing bacteria and their biomass. Stalks, sheaths, and iron oxide spheroidal aggregates are partially preserved after the 100 MPa/300℃ treatments, which indicates the mixed organic matters and iron oxides could survive the diagenetic or low-grade metamorphic processes. Some organic-mineral mixing structures carry information on microbial processes, though they appear similar to pseudomorphs of fossilized bacteria.

Cellular stress and redox activity proteins are involved in gastric carcinogenesis associated with Helicobacter pylori infection expressing high levels of thioredoxin-1

Heficobacterpylori infection is related to the development of gastric diseases. Our previous studies showed that high thioredoxin-1 （Trxl） expression in H. pylori can promote gastric carcinogenesis. To explore the underlying molecular mechanisms, we performed an isobaric tags for relative and absolute quantitation （iTRAQ）-based quantitative proteomic analysis of stomach tissues from Mongolian gerbil infected with H. pylori expressing high and low Trxl Differences in the profiles of the expressed proteins were analyzed by bioinformatics and verified using Western blot analysis. We found three candidate proteins, 14-3-3α/β, glutathione-S-transferase （GST）, and heat shock protein 70 （HSP70）, in high Trxl tissues compared with low Trxl tissues and concluded that cellular stress and redox activity- related proteins were involved in the pathogenesis of gastric cancer associated with H. pylori Trxl.