高压对米曲霉理化性质影响及诱变的研究

 在100~400 MPa压力、保压20 min的条件下处理酱油酿造菌种——米曲霉,研究高压对米曲霉存活率、形态特征、生理性质、蛋白酶、淀粉酶活性等的影响,并诱变筛选优良菌株。结果表明：高压对米曲霉的存活率、形态特征有明显的影响;压力对蛋白酶及淀粉酶活性的影响也有特异的规律,即在一定压力范围内（0.1~200 MPa）蛋白酶的活性随着压力的增加而减小,但随着压力的进一步升高（200~400 MPa）蛋白酶的活性又逐渐增强,在300 MPa时超过对照组,400 MPa时蛋白酶的活性达到最高值;淀粉酶在0.1~100 MPa时活性下降,在200 MPa时其平均的糊化和糖化活性最强、活力最高,当压力升高活性又开始降低,400 MPa时几乎又回到对照值。另外,高压处理后获得一株理想的变异菌株HP300a：生长速度快、孢子数量多、蛋白酶活力高,且不易被杂菌污染。其成曲的几项主要指标均优于对照株,酿出酱油的几项主要指标也明显优于对照株。为利用高压诱变筛选米曲霉优良菌种、提高酿造酱油产品的产量及质量提供了理论依据,并发现了高压处理米曲霉引起其蛋白酶及淀粉酶活性改变的特殊规律。     

牛奶中大肠菌群的耐压性研究

 在20 ℃及0.1~430 MPa压力范围内，不同的静水压力与不同的保压时间相结合，对接种了大肠菌群的牛奶做高压处理，研究大肠菌群的耐压性。结果表明：40 MPa压力难以杀死大肠菌群；100 MPa压力持续5 min，大肠菌群中70%以上的细菌死亡；直到430 MPa，大肠菌群中仍有少量耐压细菌存活。     

CH4水合物生长速率影响因素的分子动力学模拟

采用分子动力学模拟，研究了温度、压力和电解质溶液对CH4水合物生长速率的影响.通过分析势能、均方位移、氢键数量、径向分布函数和四体结构有序参数，表征了CH4水合物的生长动力学.模拟结果表明，降低温度和提高压力可以显著提高CH4水合物的生长速率.当压力恒为15MPa，温度高于290K时，势能升高，CH4水合物晶体发生分解；温度由290K降至260K时，势能降低，CH4水合物持续生长.当温度恒为275K，压力由3MPa增至50MPa时，CH4水合物生长速率提高12%.此外，电解质离子的存在抑制了水合物的生长，电解质溶液浓度由1.5wt%增加到3.5wt%时, CH4水合物生长速率降低25%.     

高压与加热协同处理对牛肌肉中蛋白酶活性的影响

在不同温度(20～60℃)和压力(0.1～600 MPa)下处理20 min,对牛肌肉中蛋白酶活性的影响进行了研究.结果显示:室温下,随着处理压力的增加,酶的活力显著下降,而压力达400 MPa及以上时,酶的活力则没有明显变化,同时在pH值为3和7.5时酶的活性几乎完全丧失.200 MPa以下的压力处理使肌肉中游离氨基...     

超高压处理对荔枝果肉中两种酶和可溶性蛋白的影响

 为了研究超高压处理对荔枝果肉中过氧化物酶（POD）、果胶甲基酯酶（PME）及可溶性蛋白含量的影响,将荔枝（“淮枝”品种）果肉在100~400 MPa压力、10 ℃温度条件下处理30 min,采用分光光度法测定果肉中POD、PME的活性,用天然凝胶电泳法以及活性染色法测定POD、PME同工酶的变化,用SDS凝胶电泳法测定果肉中可溶性蛋白含量。结果表明：100~200 MPa超高压处理使荔枝果肉中POD活性上升且出现新的同工酶,300~400 MPa超高压处理则使其活性降低且新出现的同工酶消失;100 MPa压力处理使荔枝果肉中PME活性上升且出现新的同工酶,200~400 MPa超高压处理则使其活性降低且新出现的同工酶消失;100 MPa超高压处理使荔枝果肉中可溶性蛋白含量有所增加,而在200~400 MPa压力处理下其含量持续下降。     

高压对小麦种子发芽和幼苗生长的影响初探

 以豫麦18号小麦种子为材料，初步探索了不同压力和时间对不同处理的小麦种子发芽的影响，并对95 MPa压力、不同时间处理下发芽种子幼苗的生长情况进行测定。结果表明：在50~95 MPa压力下，直接真空包装的小麦种子均丧失发芽能力；在不同压力和时间下处理直接加水包装的小麦种子，种子发芽受到显著抑制；将水浸6 h再加水包装的小麦种子在95 MPa压力下处理4 h，能抑制小麦种子的发芽势和发芽率，但抑制强度较弱，也表明水可以有效降低高压对小麦种子的损伤。在95 MPa压力下、不同时间处理的直接加水包装的小麦种子幼苗的平均苗高和幼苗鲜重均大于对照。     

超高压处理对海参自溶酶活性影响的研究

 海参的超高压处理与传统的处理方法相比有许多优越性,具有十分广阔的应用前景。研究了超高压处理过程中压力（0.1~550 MPa）、保压时间（0~30 min）、温度（24~62 ℃）及保压方式对海参自溶酶活性的影响。在室温、保压20 min的条件下,200 MPa左右较低压力下酶活性降低,相对残存活性为88.25%;250 MPa较高压力下自溶酶被激活,酶活性为106.77%;550 MPa高压下酶活性最低为29.81%。自溶酶活性随保压时间和温度的增加先上升后下降;保压方式对自溶酶活性的影响不大。同时利用误差反向传播神经网络（Back Propagation Neural Network,BP人工神经网络）,模拟了超高压钝酶效果,与实验结果比较,平均相对误差为0.9%,可以获得较好的预测结果。研究结果表明,在一定的压力、保压时间和温度下,酶被激活,其活性上升;而在一定的压力、保压时间和温度下,酶被钝化,活性降低。对优化海参超高压钝酶工艺具有一定的参考价值。     

超高压处理对多酚氧化酶活性的影响

 研究了超高压中温协同处理对砀山梨汁中多酚氧化酶活性的影响,实验压力为0.1~500 MPa,温度为20~60 ℃。此外,考察了不同pH值（3~7）和保压时间（2~34 min）超高压处理对酶活性的影响。实验结果分析表明：在处理温度为50 ℃、保压时间为10 min和梨汁pH值为5的条件下,200~300 MPa处理梨汁时多酚氧化酶被激活,活性表现最高;500 MPa时酶的活性下降到75.3%。协同温度为30 ℃处理梨汁时,酶的活性反而增大;30 ℃以后,酶活性随温度升高而迅速降低;有效协同高压处理的温度为40 ℃。随着保压时间的延长,梨汁中过氧化物酶的活性减小;18 min以前下降速度较快些,之后下降速度变缓。pH在5~6之间,酶的残留活性最大;pH值为6时,梨汁中多酚氧化酶最为耐压。     

高压氮气处理微型番茄种子对其生长特性的影响

 将微型番茄（Red Cherry）的种子分3组在以氮气为传压介质的高压装置中处理,分别在10 MPa、20 MPa、30 MPa 3种压力下保持4 h,与未经高压处理的对照组种子同时在相同的自然条件下播种培育。通过对随机选取的每组33株植株生长全过程的观察比较,初步研究了高压氮气处理番茄种子对其生长特性的影响。另外,还对各组果实的15种营养成份进行了检测对比。结果显示：在相同的自然条件下,加压组植株的发芽期、幼苗期和开花坐果期与对照组相比有缩短趋势;在同样的环境中,加压组植株遭受自然病害的死亡率较低;在生长后期,20 MPa和30 MPa加压组中出现异常高大的植株共3株。但是,各加压组与对照组相比,植株平均高度和平均基径没有显著性差异,平均单株果实产量和果实的营养成份也没有表现出明显变化。     

镧和铈对两种细菌生长的影响及胞内DNA的荧光光谱分析

为了研究镧,铈对细菌生长及核酸的影响,用光电比浊法测定了镧,铈和钙调蛋白抑制剂(氯丙嗪)存在时两种细菌的生长曲线,并用荧光光谱法研究了镧,铈对小牛胸腺DNA和细菌胞内DNA结构的影响。结果显示适当浓度(200 mg·L-1)稀土元素可以促进细菌的生长和繁殖,比对照提前进入对数期,扫描电镜观察也显示镧,铈可以促进枯草芽孢杆菌个体的生长,菌体体积比对照更大,但促进繁殖的作用会被氯丙嗪抑制,表明镧,铈促进细菌生长的机理可能与钙调蛋白的功能有关;荧光光谱分析显示镧,铈会使小牛胸腺DNA荧光增强,镧、铈浓度分别为5和10 mg·L-1时荧光增强作用最大;但镧使细菌胞内DNA荧光猝灭,铈使其荧光增强,结论认为镧,铈对核酸的影响远比想象的要复杂。     

Inactivation of Staphylococcus aureus and native microflora in human milk by high pressure processing

The storage of unpreserved food, including breast milk, is associated with the growth of microorganisms, including pathogenic bacteria. It is therefore necessary to use suitable processes to eliminate pathogenic microorganisms and reduce the total microbial count in order to ensure product safety for consumers. In the present study, samples of milk obtained from volunteers donating to the human milk bank were artificially contaminated with Staphylococcus aureus ATCC 6538. This bacteria was the model microorganism of choice, being relatively resistant to high pressure as well as posing the most serious risk to infant health. The results obtained show that high pressure processing can reduce the count of S. aureus by about 5?log units at 4°C and about 8?log units at 50°C, and totally eliminate Enterobacteriaceae after 5?min of treatment, and result in a total microbial count reduction after 10?min treatment at 500?MPa at 20°C and 50°C. This suggests the possibility of this technology being applied to ensure the adequate safety and quality of human breast milk in human milk banks.     

Evaluation of the importance of germinative cycles for destruction of bacillus cereus spores in miniature cheeses

Our objective was to determine the effect of high pressure on inactivation of spores of Bacillus cereus ATCC 9139 inoculated into cheese made of raw cow's milk. Inoculated miniature cheeses were manufactured under controlled bacteriological conditions, vacuum packed and kept at 8 °C for 15 days after pressure treatment. Cheeses were submitted to pressures of 300, 400 or 500 MPa at 30 °C, during 15 min. Some of them were treated with a germination cycle of 60 MPa at 30 °C for 210 min. Lethality was calculated comparing surviving sample counts to control ones. Adding the germinative cycle resulted in higher efficiency, and when applied with 500 MPa, lethality reached 2.0 log cfu/mL. We saw that with both cycles initial counts of spores diminish, but all of them were not inactivated. However, considering that in raw milk mesophilic spore counts are 2.6-2.9 log cfu/mL, this treatment may be useful.     

Effect of high pressure on heat and ethanol stabilities of milk

Abstract

The effect of high pressure (in range from 200 to 1000 MPa) and periods of exposure time (from 15 to 35min) on the changes of selected physico-chemical characteristics of skim milk, particularly considering its heat and ethanol stability, was studied.

Due to High pressure the conformation of milk proteins and the milk salt system were changing. Pressurization caused slightly change in the ethanol stability of milk. The influence of pressurization on heat stability was more evident. The heat stability of milk increased with an increase in pressure and exposure time.     

Effects of High Pressure Treatment on the Microbiological Quality,Texture and Colour of Vacuum Packed Pork Meat Products

The aim of the study was to define usefulness of high pressure treatment for inactivation of microorganisms and prolongation of shelf life of two types of cooked pork ham and raw smoked pork loin. The samples of ham and loin in the presentation of standard 200 g pieces were vacuum packed in polylayer polyethylene bags and exposed to high pressure treatment in the range of 300-600 MPa and time of exposure of 10-30 minutes. Results indicate that 300 MPa and 400 MPa pressure applied for 10 minutes was insufficient for prolongation of storage period of ham. Pressure of 500 MPa, applied for 10 minutes caused significant decrease of microbiological parameters studied such as: total bacterial count, psychrophylic bacteria, acidophylic bacteria and enterococci in investigated samples, stored in refrigarator conditions for 4 weeks. Pressure of 600 MPa applied for 10 minutes reduced the number of all investigated microorganisms by 10 5 -10 6 fold. Application of this pressure prolonged storage period of traditionally produced ham to 6-8 weeks. Physico-chemical characteristics of ham, measured 24 h after high pressure treatment and after 4, 6 and 8 weeks of storage, did not change when compared to the initial samples. High pressure treatment caused increase in the colour lightness parameters only in pork smoked loin.     

超临界CO2萃取黑色素条件的优化和筛选

以整穗黑糯玉米为原料,CO₂流量、萃取温度、萃取压力和萃取时间作为考察因素,采用正交试验优化黑糯玉米中黑色素的超临界CO₂萃取工艺。最终确定最佳工艺条件为:CO₂流量为120L/h,萃取压力为30MPa,萃取温度为50℃,萃取时间为90min。经过重复性实验验证,该工艺稳定可行,可作为黑糯玉米中黑色素的提取方法。     

High pressure applications in milk treatment for cheese-making and accelerated ripening

Abstract

Several studies have been carried out in order to evaluate the effect of high hydrostatic pressure on food components, its impact on microorganisms and enzymes, and the modifications it produces at the nutritional and sensory level. However, practical applications of high pressure treatment have received little attention. This paper examines our recent ongoing work toward the development of high pressure applications, such as the production of raw milk cheeses from high pressure-treated milk and the possibility of cheese ripening acceleration.     

同步荧光技术检测鲜牛乳中掺杂复原乳的可行性研究

近年来随着人们对乳制品需求的不断增加,将复原乳冒充或添加在鲜乳中出售的现象也日益严重,亟需简单、快速的检测方法监测掺假行为。利用同步荧光技术,分别对两种鲜牛乳(未经杀菌的生牛乳和低温处理的巴氏杀菌乳)掺杂复原乳的情况进行了定性判别和定量分析。以各类样本及全部样本的判别正确率作为定性判别模型的评价指标;以相关系数(r)、校正均方根误差(RMSEC)和预测均方根误差(RMSEP)作为定量分析模型的评价指标。通过分析牛乳的三维荧光图谱确定同步荧光扫描的固定波长差Δλ值为80 nm;在对图谱进行二阶求导后,偏最小二乘-判别分析法(PLS-DA)对生鲜牛乳、巴氏杀菌乳和复原乳的种类判别总正确率可达100%,并且在判断两种鲜乳中是否添加复原乳时,校正集样品的正确率均可达到100%,预测集样品的正确率分别为75%和81.25%,鲜牛乳和复原乳的种类判别模型,以及鲜乳与掺假乳的定性判别模型均取得了良好的效果;PLS回归对同步光谱值与复原乳含量建立线性关系时,两种鲜乳定量模型的r值分别为0.911 2和0.936 7,RMSEC分别为0.042 2和0.038 4,RMSEP分别为0.054 8和0.057 5,鲜乳中复原乳含量的定量分析模型的r值均可达到0.9以上,能对添加量较高的样品进行预测。因此,同步荧光技术可以较为准确、快速的检测鲜牛乳中是否掺杂复原乳。     

Electric strength of rocks at a pulsed voltage under high pressures at high temperatures

The electric strength of rocks (granite, limestone, and sandstone) for the first time has been measured under the simultaneous effect of the pressure up to 35 MPa and temperature up to 120°C in the system of rod-rod electrodes arranged on one sample surface and point-plane electrodes in the liquid medium of a drilling agent. With the simultaneous increase in pressure and temperature, the electric strength of rocks for point-plane electrodes continuously increases (especially rapidly in the pressure range of 10–24 MPa and temperature range of 35–85°C), while for rod-rod electrodes arranged on the same sample surface, the electric strength varies with a maximum at pressures of 5–12 MPa and temperatures 20–35°C.     

光纤光栅的压力传感特性研究

对聚合物封装的光纤光栅的压力敏感特性进行了实验研究,在10MPa的压力范围内,光纤光栅中心波长的相对变化与外界压力成良好的线性关系,由于聚合物基底的带动作用,两种不同聚合物封装的光纤光栅的压力灵敏度分别为-3.96×10^-5/MPa和-6.28×10^-5/MPa,提高为裸光栅的20倍和31.7倍。