低温低压等离子体处理对涤纶织物吸湿性能的影响

使用氩气／氧气混合气体对一涤纶织物进行了处理,通过测定处理后的织物吸湿性的差别,讨论了处理时间与处理压强对处理效果及抗老化效果的影响。结果证明,较长的处理时间与较大的处理压强对处理效果都有积极影响,但过大的处理压强会对处理的抗老化性能产生负面影响。     

Effect of growth temperature on yeast lipid composition and alcoholic fermentation at low temperature

The loss of viability of wine yeast strains due to low-temperature fermentations could be overcome by increasing their stress tolerance and adaptability. Changes in membrane lipid composition are one of the first responses to cold stress. The aim of this study was to analyze the various adaptation mechanisms to low temperatures by comparing the better adapted Saccharomyces species. The viability, vitality, fermentation capacity, and lipid composition of different Saccharomyces species (S. cerevisiae, S. bayanus, S. uvarum, and a hybrid S. cerevisiae/S. uvarum) with different fermentative origins (wine, beer, and baker’s strains together with a laboratory strain) were compared after culturing at low (13 °C) and optimal (25 °C) temperatures. In spite of specific responses of the different strains/species, the results showed that at low temperature, the medium-chain fatty acid and the triacylglyceride content increased, whereas the phosphatidic acid content and the phosphatidylcholine/phosphatidylethanolamine ratio decreased. Only the laboratory strain was not able to ferment the sugars, and after growing at both temperatures, its lipid composition was very different from that of the other strains. The hybrid strain showed the highest sugar consumption at 13 °C and the best vitality whatever the preculture temperature used. The rest of the species needed a preadaptation at low temperature involving a change in their lipid composition to improve their fermentation rate at 13 °C.     

The effect of temperature and low pH on survival of Shigella flexneri in broth

The survival characteristics of Shigella fiexneri strain 5348 were determined in brain heart infusion broth as a function of low pH (2 to 5) and temperature (4 to 37 degrees C). Stationary-phase cells were inoculated into sterile media to give initial populations of 6 to 7 log10 CFU/ml. Bacterial populations were determined periodically by aerobic plate counts. Survivor curves were fitted from plate count data using a two-phase linear model to derive lag times and slopes of the curves, from which D-values and times to a 4-D (99.99%) inactivation (T4D) were calculated. In general, survival increased as temperature decreased and as pH increased. Bacterial populations reached undetectable levels (<1.3 log10 CFU/ml) at 37, 28, 19, 12, and 4 degrees C in media adjusted to pH 4 after 5, 15, 23, 85, and 85 days, respectively, and in media adjusted to pH 3 after 1, 7, 9, 16, and 29 days, respectively. In media adjusted to pH 2, bacterial populations were stable for 2 to 12 h at temperatures of 19 degrees C or lower and reached undetectable levels after 1 to 3 days, while at 28 and 37 degrees C, the bacteria were undetectable after 8 and 2 h, respectively. In media adjusted to pH 5, bacterial levels decreased only 0.5 to 1.5 log10 CFU/ml after 75 days at 4 degrees C and decreased to undetectable levels after 135 days at 12 degrees C, while growth occurred at higher temperatures. These results indicate that S. flexneri is acid resistant and that acidic foods may serve as vehicles for infection.     

耐低温菌株的鉴定、低温生长特征及耐低温机理初步研究

该研究以分离自长白山常年积雪覆盖的苔原带土样的耐低温菌株7a-3为研究对象，采用形态观察、生理生化试验及分子生物学技术对其进行菌种鉴定，并对其生长特性及耐低温机制进行初步研究。结果表明，菌株7a-3被鉴定为莓实假单胞菌（Pseudomonas fragi），其生长温度范围为4～33 ℃，最适生长温度为30 ℃，表面活性剂不能促进该菌株在37 ℃条件下生长，但其自身低温发酵代谢物可促进该菌在37 ℃条件下生长。相对于30 ℃，4 ℃条件下，菌株7a-3细胞膜的脂肪酸种类由长链脂肪酸向短链脂肪酸转化，不饱和脂肪酸的相对含量增加，且单不饱和脂肪酸相对含量的变化较大，细胞膜较为粗糙，初步推测其耐低温能力与细胞膜不饱和脂肪酸含量增加导致细胞膜流动性增强相关。     

Influence of temperature variations on growth,injury survival and inactivation of Listeria monocytogenes in goat milk samples at laboratory scale

Transmission of the thermo‐tolerant pathogen Listeria monocytogenes via contaminated milk and its products, can lead to serious food‐borne illness. In this study, the effects of selected temperatures on survival, percentage injury and inactivation of L. monocytogenes in goat milk samples collected from two different farms were evaluated. Low temperature ranges (0, 5, 10 °C) had a bacteriostatic effect; while at temperatures of 25 and 45 °C, this pathogen grew luxuriantly. However, growth was comparatively slow at 15 °C throughout a 12‐h stress period. Furthermore, a high temperature range (50, 55, 60 and 65 °C) resulted in the elimination of this pathogen within 4 h of stress. Results of Scanning Electron Microscopy showed morphological changes in the cells upon induction of stress temperatures.     

High pressure–low temperature processing of beef: Effects on survival of internalized E. coli O157:H7 and quality characteristics

High pressure–low temperature (HPLT) processing was investigated to achieve Escherichia coli O157:H7 inactivation in non-intact, whole muscle beef while maintaining acceptable quality characteristics. Beef semitendinosus was internally inoculated with a four strain E. coli O157:H7 cocktail and frozen to − 35 °C, then subjected to 551 MPa for 4 min (HPLT). Compared to frozen, untreated control (F), HPLT reduced microbial population by 1.7 log colony forming units (CFU)/g on selective media and 1.4 log on non-selective media. High pressure without freezing (551 MPa/4 min/3 °C) increased pH and lightness while decreasing redness, cook yield, tenderness, and protein solubility. Aside from a 4% decrease in cook yield, HPLT, had no significant effects on quality parameters. It was demonstrated that HPLT treatment reduces internalized E. coli O157:H7 with minimal effect on quality factors, meaning it may have a potential role in reducing the risk associated with non-intact red meat.Industrial relevanceIn the current work, high pressure (551 MPa, 4 min) was applied to beef semitendinosus while it was at subfreezing temperatures (<− 30 °C). Most studies utilizing this high pressure–low temperature (HPLT) process employ subzero capable thermostatic high pressure equipment, which currently has no commercial equivalent. Successful HPLT runs were completed in this study using more conventional temperature control (1–3 °C) on pilot scale (20 L) high pressure processing equipment. The process yielded E. coli O157:H7 reductions of 1.4–1.7 log colony forming units (CFU)/g, which, while lower than conventional high pressure processing (HPP), may be sufficient to eliminate O157 populations typical of non-intact, whole muscle beef. Various quality factors, including color, purge losses and cooked tenderness, were unaffected by HPLT, while an equivalent HPP process at nonfreezing temperatures (551 MPa, 3 °C) induced color change (loss of redness), increased cook losses and decreased cooked tenderness compared to the control and HPLT beef. Producers of non-intact, whole muscle (blade tenderized or brine injected) meat, especially those that ship and sell frozen products, may look to HPLT processes to improve food safety.     

彭泽鲫夏季低温休眠保活技术研究

首先测定彭泽鲫的休眠温度和冻结温度,再运用生态冰温学原理,确定其生态冰温范围为0~7℃。通过单因素与正交试验,确定彭泽鲫夏季保活的最佳技术条件为:暂养24h,降温休眠,鱼水质量比11,NaCl添加0.3%,(13±1)℃下纯氧保活。在最佳条件下进行验证实验,得出彭泽鲫的保活时间为148h。该保活技术可以有效延长彭泽鲫的夏季保活时间,减少用水量,降低污染。     

低温染色对山羊绒纤维及纱线强伸性能的影响

采用低温染色工艺和常规染色工艺,将山羊绒条染成浅色(浅蓝灰)、中色(中绿)、深色(枣红)3种颜色,然后比较不同染色工艺和不同色泽的山羊绒纤维和纱线的强伸性能.结果表明,采用低温染色工艺的山羊绒纤维和纱线平均断裂强力增加了0.59 cN和12.16 cN,平均断裂伸长率增加了5.76％和1.16％,可以减轻对山羊绒纤维的损伤,提高纱线的强力,有利于后续工序的加工;同时降低染色温度,有利于企业降低生产成本.     

Influence of temperature on associative growth of Streptococcus thermophilus and Lactobacillus bulgaricus

Compatibility of Streptococcus thermophilus and Lactobacillus bulgaricus during associative growth as dependent on optimum growth temperature was determined. Optimum growth temperatures for 9 strains of S. thermophilus and 10 strains of L. bulgaricus ranged from 35 to 42 degrees C for S. thermophilus and 43 to 46 degrees C for L. bulgaricus. Streptococcus thermophilus and L. bulgaricus strains exhibiting similar to divergent optimum growth temperatures were combined (1:1 vol/vol) and incubated in milk at 37, 42, and 45 degrees C until pH 4.2 was reached. Initial and postincubation cell numbers were determined by plate count method. Streptococcus thermophilus strains reached greater cell numbers than L. bulgaricus at 37, 42, and 45 degrees C in 93.3% of the mixed culture trials. Average rod-coccus ratios obtained at 37, 42, and 45 degrees C were 1:2.2, 1:8, and 1:2.4, respectively. Optimum growth temperatures had no influence on growth of L. bulgaricus and S. thermophilus in mixed culture. Rather, temperature appeared to influence compatibility by determining the concentration or type of stimulatory factor(s) produced by L. bulgaricus. All strains of S. thermophilus exhibited an uncoupling of growth from acid production. Optimum temperature for acid production ranged from 2 to 8 degrees C above optimum growth temperature. These findings warrant consideration in the manufacture of yogurt and other fermented milk products.     

低温等离子体处理对芳纶界面性能的影响

为研究低温等离子体处理对芳纶界面性能的影响,制作了满足要求的试样并进行等离子体处理实验。采用扫描电子显微镜（SEM）、浸润性实验等方法对芳纶表面的刻蚀程度进行表征,并对低温等离子体处理前后的芳纶进行拉伸性能测试。结果表明：随着低温等离子体处理时间的延长、处理功率的增大,芳纶表面刻蚀度加剧;低温等离子体处理后芳纶的拉伸性能变化不大,但纤维的浸润性有了明显改善;纤维与树脂的结合强度也有近50%的提高。     

低温等离子体处理对兔毛纤维染色性能的影响

研究了用低温等离子体对兔毛纤维处理后兔毛纤维的染色性能。结果表明，处理后的兔毛纤维染色速率、平衡上染率都有所提高，可降低染色温度和染色时酸的用量，从而降低纤维所受到的损伤。     

氧气对干酪乳杆菌生长和活力的影响

以静置培养为对照,通过振荡培养制造有氧环境,对干酪乳杆菌的生长曲线、菌体活力进行分析。研究发现在有氧条件下菌体生长受到抑制,菌体密度小于静置发酵,在4℃保存时的活力迅速下降,另外,有氧生长菌体对热、胆汁等条件的耐受性较差,在50℃处理4h导致菌体迅速死亡,在含有胆汁的培养基中,菌体生长几乎停滞。通过透射电镜观察发现有氧条件下菌体细胞壁发生破裂,菌体细胞质成分溶出,导致菌体死亡。因此,氧气对干酪乳杆菌的生长具有抑制作用,造成细胞损伤,导致菌体活力降低。     

纸浆纤维低温等离子体改性对纸页强度的影响

研究了空气低温等离子体处理杉木CTMP、杨木CTMP和银星牌针叶木BKP对纸页物理强度的影响,并利用X-ray、XPS和SEM研究了处理前后杉木CTMP纤维结构与表面性质的变化。结果表明：低温等离子体处理后纤维结晶度略有下降,纸页湿抗张指数明显提高,抗张指数及零距抗张指数变化不大;等离子体处理对纤维表面有一定的氧化作用,可以部分脱除纤维表面的抽提物及木素。     

Influence of holding temperature on the growth and survival of Salmonella spp. and Staphylococcus aureus and the production of staphylococcal enterotoxin in egg products

In this study, growth and survival of Salmonella spp. and Staphylococcus aureus in steamed egg and scrambled egg held at 5, 18, 22, 37, 55 and 60 degrees C are investigated. The production of staphylococcal enterotoxin in steamed egg is also examined. Results reveal that Salmonella spp. and Staph. aureus in the egg products multiply best at 37 degrees C, followed closely by 22 and 18 degrees C. Neither pathogen showed growth in the egg products held at 5 degrees C. Initial inoculation dose, holding temperature and holding time affected the population of both organisms found in the egg products. Staphylococcal enterotoxin A (SEA) and B (SEB) are detected only in the egg products held at 37 or 22 degrees C. After holding at 37 degrees C for 36 h, scrambled egg inoculated with ca. 5.0 log cfu/g Staph. aureus contains the highest levels of SEA (> 64 ng/g) and SEB (> 64 ng/g). Although Salmonella spp. and Staph. aureus grow better in steamed eggs than in scrambled eggs, production of staphylococcal enterotoxin, in general, was higher in scrambled eggs than in steamed eggs. On the other hand, a repaid destruction of the test organisms in steamed eggs held at 60 degrees C was observed. Holding the steamed eggs at 60 degrees C, Salmonella spp. and Staph. aureus with an initial population of ca. 5.9 and 5.6 log cfu/g, respectively, reduced to a non-detectable level in 1 h.     

Effect of pH, NaCl content, and temperature on growth and survival of Arcobacter spp

Growth and survival of six human isolates of the pathogenic Arcobacter spp. in the presence of selected environmental factors were studied. Four strains of Arcobacter butzleri and two strains of Arcobacter cryaerophilus were exposed to pH levels of 3.5 to 8.0. Most strains grew between pH 5.5 and 8.0, with optimal growth of most A. butzleri and A. cryaerophilus strains at pH 6.0 to 7.0 and 7.0 to 7.5, respectively. The 24-h optimal growth range in the presence of NaCl was 0.5 to 1.0% for A. cryaerophilus. However, after 96 h, the optimum was between 0.5 and 2.0% NaCl. The optimum range for growth of A. butzleri strains was 0.09 to 0.5% NaCl after 96 h. The upper growth limits were 3.5 and 3.0% NaCl for A. butzleri and A. cryaerophilus, respectively. Survival at 25 degrees C in up to 5% NaCl was noted for A. butzleri 3556 and 3539 and A. cryaerophilus 3256. Decimal reduction times (D-values) at pH 7.3 in phosphate-buffered saline for three A. butzleri strains were 0.07 to 0.12 min at 60 degrees C, 0.38 to 0.76 min at 55 degrees C, and 5.12 to 5.81 min at 50 degrees C. At pH 5.5, decreased thermotolerance was observed, with D-values of 0.03 to 0.11 min at 60 degrees C, 0.30 to 0.42 min at 55 degrees C, and 1.97 to 4.42 min at 50 degrees C. Calculated z-values ranged from 5.20 to 6.28 degrees C. D-values of a three-strain mixture of A. butzleri in raw ground pork were 18.51 min at 50 degrees C and 2.18 min at 55 degrees C. Mild heat (50 degress C) followed by cold shock (4 or 8 degrees C exposure) had a synergistic lethal effect, reducing more cells than with an individual 50 degrees C treatment or with cold shock temperatures of 12 or 16 degrees C.     

Influence of temperature on growth of Legionella pneumophila biofilm determined by precise temperature gradient incubator

Bacterial growth is influenced by several different culture conditions. Temperature is one of an essential component which regulates bacterial growth and their morphology. The influence of temperature on the length of bacteria was investigated in broth and on agar in a temperature range from 30.0 degrees C to 47.0 degrees C in 0.5 degrees C steps using a newly developed temperature gradient incubator. The incubator is able to reach a set temperature within 2 h and maintain temperature as accurate as +/-0.1 degrees C of the set temperature. Three Legionella pneumophila serotype 1 strains were incubated for 48 h in BCYE-alpha agar at various temperatures ranging from 30.0 degrees C to 48.0 degrees C and length of bacteria grown at each temperature was microscopically measured. Ability of bacteria to multiply at a given temperature was also determined. L. pneumophila serotype 1 strains ATCC 33152, a clinical isolate Okinawa 02-001 were going to elongate to longer than 100 mum when cultured higher than at 39.5 degrees C and at 41.5 degrees C, respectively. Each strain was unable to multiply when cultured higher than at 44.2 degrees C (ATCC 33152) or at 44.0 degrees C (Okinawa 02-001). Those data would provide insights for establishing regulations in terms of maintaining hot water temperature in a facility where a circulating hot water supply-system is available and contamination with Legionella spp. is likely to happen.     

Influence of pH and temperature on growth of Bacillus cereus in vegetable substrates

Bacillus cereus is a food-borne pathogen which most often contaminates foods of plant origin. Spores of psychrotrophic strains have the ability to germinate and grow at refrigeration temperatures in different vegetable substrates, such as carrot broth, zucchini broth, and cooked carrot purée. In some circumstances, factors such as pH, heat treatment, and storage temperature play a fundamental role in controlling the growth of these psychrotrophic strains and in extending the shelf life of refrigerated, minimally processed vegetable-based products in relation to pathogenic spore-forming bacteria. The combination of mild acidification (pH 5.0) and refrigeration (相似文献