pmrA影响酸胁迫鼠伤寒沙门氏菌生物膜的形成能力

为探究pmrA基因对酸胁迫鼠伤寒沙门氏菌生物膜形成能力的影响，以鼠伤寒沙门氏菌野生株(WT)和pmrA基因缺失株(ΔpmrA)为研究对象，对其诱导耐酸能力、菌株特性、生物膜形成能力以及影响生物膜形成的内在因素进行研究。结果:pH 5.4胁迫后ΔpmrA的诱导耐酸能力为WT的53.92%；生物膜培养至第4天，经酸胁迫(pH 5.4)后ΔpmrA的生物膜形成量仅为WT的54.68%；经酸胁迫后，ΔpmrA的泳动能力、疏水性分别为WT的35.20%，59.10%；ΔpmrA经酸胁迫后其生物膜代谢活性、胞外多糖和蛋白的生物合成量与未酸胁迫处理相比虽有一定程度升高，但仍显著低于酸胁迫后的WT(P < 0.05)，同时酸胁迫后pmrA基因缺失株生物膜的三维立体结构仍较为分散，且膜内活细胞数量显著低于WT。结论:pmrA基因与鼠伤寒沙门氏菌的耐酸能力及生物膜形成能力密切相关。     

牛肉低温贮藏环境中沙门氏菌诱导耐酸响应的存在程度及其产生机制

研究牛肉生产和销售过程中沙门氏菌诱导耐酸响应（acid tolerance response,ATR）的存在程度及其产生机制。探究微酸诱导、双组分基因敲除、低温长期贮藏对沙门氏菌耐酸能力的影响,同时借助λRed同源重组、实时聚合酶链式反应（real-time polymerase chain reaction,real-time PCR）及氨基酸添加实验探索菌株耐酸性产生的内在机理。结果表明,微酸诱导能够显著增强沙门氏菌的耐酸能力（P＜0.05）,并且ATR一旦形成,在牛肉低温贮藏（4 ℃）的过程中至少可以维持7 d,对食品安全有极大危害。牛肉培养基作为微酸的细菌生长介质,在低温下其本身并不能引发沙门氏菌产生ATR,说明低温处理可能是抑制沙门氏菌ATR的重要方法。real-time PCR和氨基酸添加实验表明,沙门氏菌的双组分系统PhoP/PhoQ和PmrA/PmrB均参与酸性环境的感知,并能通过调控精氨酸脱羧和赖氨酸脱羧系统提高菌株的耐酸性,这从氨基酸代谢角度解释了沙门氏菌诱导ATR的产生机制,同时也揭示了食品基质提升微生物耐酸性这一表观现象的内在机理。     

酸胁迫处理对鼠伤寒沙门氏菌抗酸性的影响

目的:以鼠伤寒沙门氏菌CGMCC 1.1190为试材,研究酸胁迫处理对其抗酸性的影响.方法:研究CGMCC 1.1190菌株经4种有机酸(柠檬酸、乳酸、醋酸和苹果酸)胁迫培养过程中其生长情况和形态的变化;对经4种有机酸胁迫培养至稳定期获得的耐酸性CGMCC 1.1190菌株在pH 2.5的强酸性基质中进行抗酸性分析;分...     

饲养方式对宰后苏尼特羊肉一磷酸腺苷激活的蛋白激酶活力及糖酵解的影响

本研究测定了放牧和圈养条件下苏尼特羊宰后羊肉一磷酸腺苷激活的蛋白激酶（AMP-activated protein kinase,AMPK）活力、AMPK基因（PRKAA1、PRKAA2、PRKAG3）mRNA相对表达量和糖酵解指标,分析了 AMPK活力与糖酵解指标之间的相关性,研究不同饲养方式对羊肉AMPK活力及糖酵解的影响。结果表明：放牧条 件下苏尼特羊背最长肌的剪切力、亮度值以及黄度值均显著大于圈养条件（P＜0.05）;两种饲养方式的胴体初pH值 （pH1）和静止排酸24 h后胴体最终pH值（pH24）差异不显著（P＞0.05）;圈养条件下苏尼特羊PRKAA1和PRKAG3基 因的相对表达量显著大于放牧条件（P＜0.05）,PRKAA2基因相对表达量显著小于放牧条件（P＜0.05）;AMPK活 力和己糖激酶活力均为圈养条件大于放牧条件,但差异不显著（P＞0.05）;圈养条件下乳酸含量显著大于放牧条件 （P＜0.05）。通过相关性分析可知：PRKAG3基因相对表达量与AMPK活力、己糖激酶活力以及乳酸含量均呈显 著正相关（P＜0.05）,与剪切力呈显著负相关（P＜0.05）;PRKAA1基因相对表达量仅与乳酸含量呈显著正相关 （P＜0.05）;PRKAA2基因相对表达量与AMPK活力以及糖酵解指标无显著相关性;AMPK活力和己糖激酶活力以 及乳酸含量均呈显著正相关（P＜0.05）。综上所述,PRKAA1和PRKAG3基因相对表达量高时,AMPK被激活,使 己糖激酶活力增加,加速组织内的糖酵解,增加肌肉乳酸含量,降低pH值,进而影响肉的品质。     

基于转录组学分析酸胁迫影响鼠伤寒沙门氏菌耐酸能力的机理

目的：探究酸胁迫和非酸胁迫条件下鼠伤寒沙门氏菌（Salmonella typhimurium）的转录组反应,分析差异基因（differentially expressed genes,DEGs）表达水平,阐明酸胁迫影响鼠伤寒沙门氏菌耐酸反应（acid tolerance response,ATR）的相关代谢通路。方法：对鼠伤寒沙门氏菌进行酸胁迫处理,利用转录组测序技术和生物信息学分析相关DEGs,并通过实时聚合酶链式反应（real-time polymerase chain reaction,real-time PCR）进行验证。结果：经酸胁迫后,共筛选到683 个DEGs,其中上调343 个,下调340 个。其中涉及细胞运动、氨基酸代谢、细胞膜组成等通路上调能够使鼠伤寒沙门氏菌快速适应酸环境;碳水化合物代谢相关通路上调能够为鼠伤寒沙门氏菌快速适应酸环境提供更多的能量,与此同时,嘧啶代谢等能量代谢通路下调能够使鼠伤寒沙门氏菌降低能量消耗以维持上述的必需代谢过程;细菌应激调控相关通路上调赋予鼠伤寒沙门氏菌交叉保护抗性;鞭毛、外膜蛋白、脂多糖等毒力相关基因表达上调增强了鼠伤寒沙门氏菌的毒力。real-time PCR验证结果与转录组测序分析表达趋势一致。结论：酸胁迫显著提高了鼠伤寒沙门氏菌的耐酸能力,其中与代谢和细胞过程相关的通路发挥主要作用,本研究结果为进一步了解该菌的酸胁迫反应及更好地控制其在食品中的污染提供了理论依据。     

不同种类的糖对中式香肠发酵的影响

葡萄糖、蔗糖、乳糖和麦芽糖对中式香肠发酵的影响进行了研究.结果表明,糖的添加有助于降低制品的pH值、增加乳酸量、减少亚硝酸盐残留量、促进良好风味的形成.37℃发酵36 h后,其pH值、乳酸量和亚硝酸盐残留量均与对照组有显著差异（P＜0.05）.发酵速率以葡萄糖组和蔗糖组较快,但这两者之间无显著差异（P＞0.05）.不同蔗糖添加量（1,2,4%）时,经36 h发酵,其PH值和乳酸量无明显差异（P＞0.05）.蔗糖用量为6%～8%时制品风味最佳.     

夏季运输和休息时间对肉鸡应激及肌肉品质的影响

189 只白羽肉鸡随机分配到9 个处理组,处理因素分别为运输时间（0.5、3、5 h）、休息时间（0、1、2 h）,工厂条件宰杀取样后,测定促肾上腺皮质激素（adrenocorticotropic hormone,ACTH）含量、皮质酮激素（corticosterone,CORT）含量、肌酸激酶（creatine kinase,CK）活性、亮度L*值、pH值、滴水损失、蒸煮损失、肌肉乳酸含量、糖原含量等指标,研究夏季不同运输和休息时间对肉鸡应激和肌肉品质的影响。结果表明：随着运输时间的延长,ACTH、CORT、CK含量及肌肉pH值呈上升趋势（P＜0.05）,L*值、滴水损失、蒸煮损失及肌肉乳酸和糖原含量都呈现下降趋势（P＜0.05）;随着休息时间的延长,ACTH、CORT、CK含量呈现下降趋势（P＜0.05）,休息时间对其他指标的影响则不显著（P＞0.05）;因子分析结果表明：运输时间对所测指标均影响极显著（P＜0.01）,休息时间对除ACTH、CORT外的所有指标影响均不显著（P＞0.05）,运输时间和休息时间的交互作用对CORT、1 h时L*值、滴水损失和蒸煮损失影响显著（P＜0.05）,对其余指标影响均不显著（P＞0.05）。提示,夏季运输会造成肉鸡应激,不利于宰后肌肉品质;合理的运输时间搭配适当的休息时间可以缓解肉鸡应激,提高肌肉品质。     

中国食醋中苯乳酸的检测、鉴定及其与醋酸的联合抑菌作用

从我国食醋中分离纯化并采用核磁共振（1H和13C）技术鉴定苯乳酸,建立苯乳酸的超高效液相色谱-三重四极杆串联质谱快速测定方法,分析我国72 种食醋中的苯乳酸含量。结果表明,72 种食醋中均可检出苯乳酸,谷物酿造食醋中苯乳酸含量显著高于果醋,平均质量浓度为227.89 mg/L,最高质量浓度为618.69 mg/L。工艺分析显示食醋中苯乳酸质量浓度与原料和发酵方式密切相关,以糯米为原料的食醋经固态发酵后,苯乳酸含量最高。采用时间杀菌曲线和扫描电镜法考察联合抑菌效应,结果表明食醋中苯乳酸与醋酸对食品中多种腐败菌和致病菌具有协同抑菌作用,苯乳酸和醋酸联用可以破坏金黄色葡萄球菌和鼠伤寒沙门氏菌的菌体形态,导致金黄色葡萄球菌内容物泄漏,鼠伤寒沙门氏菌菌体皱缩。本研究为解析食醋的健康功能提供了新的科学依据,为苯乳酸在食品生物防腐中的应用提供理论依据。     

加工处理对甘薯糖蛋白免疫调节和降胆固醇功能的影响

目的：以实验室提取的甘薯糖蛋白-1（sweet potato glycoprotein-1,SPG-1）为原料,研究不同加工处理对其蛋白免疫调节和降胆固醇功能的影响。方法：研究热处理、酸碱处理、紫外光照射、微波处理对甘薯糖蛋白SPG-1的免疫调节作用（包括巨噬细胞吞噬功能、细胞吞噬功能和血清溶血素含量）和降血清总胆固醇作用的影响。结果：热处理温度和pH值对甘薯糖蛋白SPG-1的免疫调节和降胆固醇作用的影响较大,热处理温度超过100 ℃、pH＜3.5或＞7.5时,糖蛋白处理组的吞噬指数（k）、酸性α-醋酸萘酯酶阳性率、半数溶血值（HC50）和血清胆固醇下降率（ΔTC）均显著性降低（P＜0.05或P＜0.01）;糖蛋白处理组的吞噬指数（k）和血清胆固醇下降率（ΔTC）在紫外光照射条件下与对照组相比差异不显著（P＞0.05）,而微波处理60 s以上时,与对照组相比有显著性或极显著性差异（P＜0.05或P＜0.01）。结论：甘薯糖蛋白SPG-1加工处理过程中应避免70 ℃以上的高温,选择合适的pH值范围（3.5～7.5）,避免较长时间（＞60 s）的微波处理。     

马克斯克鲁维酵母对发酵乳中糖代谢的影响

采用高效液相色谱等方法,对乳酸菌单独发酵和向其中添加马克斯克鲁维酵母这两种发酵乳中乳糖代谢主要产物及关键酶活力的变化情况进行对比分析,以确定添加酵母菌对乳糖无氧代谢产生乳酸途径的影响。结果表明：添加酵母菌后乳糖降解速率明显加快（P＜0.05）,贮藏期间马克斯克鲁维酵母可以对积累的半乳糖进行利用;发酵过程中,由于酵母菌的添加使β-半乳糖苷酶及乳酸脱氢酶活力有显著提高（P＜0.05）,糖酵解途径关键限速酶--己糖激酶和丙酮酸激酶活力增加（P＜0.05）;含有酵母菌的发酵乳pH值下降（滴定酸度上升）较乳酸菌单菌发酵快（P＜0.05）,这与添加酵母菌后发酵乳中乳酸含量显著增加（P＜0.05）有关;丙酮酸含量变化不显著（P＞0.05）。该研究揭示了马克斯克鲁维酵母的添加对乳糖酵解具有一定促进作用。     

Acetic, Lactic, and Hydrochloric Acid Effects on Staphylococcus aureus 196E Growth Based on a Predictive Model

Mathematical models were developed with a modified Gompertz function to predict Staphylococcus aureus 196E growth, where pH was altered with either acetic, lactic or hydrochloric acid. S. aureus 196E was inoculated into broth formulated with 0.5, 4.5 or 8.5% sodium chloride, adjusted to pH 5.0, 6.0 or 7.0, and incubated aerobically at 12, 20 or 28°C. Each model adequately predicted log growth, and some interactive relationships between independent variables upon population growth were significant (p<0.05). Predictions of growth showed that acetic was generally more inhibitory than lactic or hydrochloric acids.     

Inhibition of Spoilage Bacteria by Acidification of Soy Extended Ground Beef

Bacterial isolates from soy extended ground beef were used to test the effect of pH on their growth in trypticase soy broth (TSB), ground beef, and ground beef + 20% textured soy protein (TSP). Growth was measured in TSB acidified with hydrochloric, citric, lactic, or acetic acids at pH levels from 5.4–6.2. After incubation at 4°C for 7 days, acetic acid was determined to inhibit growth to the greatest extent with no growth at or below pH 5.8. Growth response was studied in meat blends at pH levels of 5.4, 5.7, 6.0, and 6.3. Growth was suppressed in ground beef initially at pH 5.4 and in ground beef + 20% TSP initially at pH 5.4 and 5.7. This resulted in an increased shelf life of 2 days in acidified blends.     

GROWTH RESPONSE OF A SALMONELLA TYPHIMURIUM POULTRY ISOLATE TO PROPIONIC ACID UNDER AEROBIC AND ANAEROBIC CONDITIONS

Organic acids have long been used as additives in poultry feed to reduce microbial populations, including Salmonella spp. Propionic acid addition to poultry feed has a potential role in reducing Salmonella spp. in the chicken intestine. In this study , in vitro growth response of S. typhimurium isolated from poultry to propionic acid under aerobic and anaerobic conditions was determined. When grown in tryptic soy broth (TSB) containing buffered propionic acid (BPA), the growth rate of S. typhimurium gradually decreased as the level of BPA increased and broth pH decreased. No growth was detected with BPA concentrations greater than 3% (volume/volume) of the broth. When the growth rates of S. typhimurium in aerobic and anaerobic TSB were compared at two pH levels (pH 5.0 and 7.0), the growth inhibition of S. typhimurium by propionic acid was markedly suppressed by anaerobiosis at both pHs, as indicated by significantly (p<0.05) higher half-inhibition constants (K°). Also, the growth rates of S. typhimurium in the presence of propionic acid were dramatically reduced by the decrease in pH from 7.0 to 5.0. The results of this study indicated that the growth inhibitory effect of propionic acid against S. typhimurium strains was enhanced by pH decrease and suppressed by anaerobiosis, suggesting that the growth response of S. typhimurium to propionic acid in the chicken intestine might be affected by the environmental conditions such as pH and anaerobiosis.     

Effect of acid shock with hydrochloric, citric, and lactic acids on the survival and growth of Salmonella typhi and Salmonella typhimurium in acidified media

The effect of acid shock with hydrochloric, citric, or lactic acid on the survival and growth of Salmonella Typhi and Salmonella Typhimurium in acidified broth was evaluated. Salmonella serovars were acid shocked (1 h at 35 degrees C) in Trypticase soy broth acidified with hydrochloric, citric, or lactic acid at pH 5.5. Unshocked cells were exposed to the same media that had been neutralized before use to pH 7.0. Shocked and unshocked cells were inoculated into broth acidified with hydrochloric acid (pH 3.0), citric acid (pH 3.0), or lactic acid (pH 3.8), and growth and survival ability were evaluated. The acid shock conferred protection to Salmonella against the lethal effects of low pH and organic acids. The adaptive response was not specific to the anion used for adaptation. The biggest difference in reduction of survival between shocked and unshocked strains (approximately 2 log CFU/ml) was observed when the microorganisms were shocked with lactic acid and then challenged with citric acid. Salmonella Typhi was more tolerant of citric acid than was Salmonella Typhimurium, but Salmonella Typhimurium had higher acid tolerance in response to acid shock than did Salmonella Typhi. The acid shock decreased the extension of the lag phase and enhanced the physiological state values of Salmonella Typhi and Salmonella Typhimurium when the pH of growth was 4.5. This increased ability to tolerate acidity may have an important impact on food safety, especially in the case of Salmonella Typhi, given the very low infectious dose of this pathogen.     

Lethal and Sublethal Action of Acetic Acid on Salmonella In Vitro and on Cut Surfaces of Apple Slices

ABSTRACT Antimicrobial action of acetic acid (AA) on Salmonella as affected by acid concentration, exposure time, culture age, and bacterial strains was investigated. Relative susceptibility of 6 Salmonella serovars to AA action was in the following order: S. bareilly > S. typhimurium > S. montevideo > S. poona > S. mbandaka > S. stanley. The stationary-phase cells of S. mbandaka were 100-fold more resistant to AA action than the log-phase cells. A mixture of Salmonella strains at a specified physiological stage should be used when testing the efficacy of the sanitizer treatment. Washing apple disks with NaOCl, H₂O₂, AA, or Na₃P0₄ greatly reduced the number of Salmonella and 30% to 40% of cells that survived were injured. Washing with a mixture of AA and H₂O₂ was the most effective in removing Salmonella from apple disks.     

Elucidation of the inhibitory factors of yogurt against Salmonella typhimurium.

The inhibitory nature of yogurt against contaminating microorganisms has been studied extensively. Nevertheless, the factors responsible for the death of Salmonella typhimurium in yogurt have not been elucidated. An understanding of these factors is important for the determination of yogurt's safety to consumer health. Yogurt fermented for 18 h at 42 C had a stable environment with the following conditions: pH 3.85, oxidation-reduction potential -80 mV, lactic acid concentration 158 mM, and acetic acid concentration 3.7 mM. Under these conditions, lactic acid was responsible for virtually all of yogurt's bactericidal activity against S. typhimurium at 37 C. Die-off rates were observed when these conditions were reproduced artificially in milk (artificial milk yogurt) and when lactic acid was added back to 18-h yogurt from which acids were removed by passage of the whey through a Dowex 1 (Cl-) anion exchange column (cationic yogurt). Factors that augmented lactic acid inhibition of S. typhimurium were low pH and low oxidation-reduction potential. The die-off rate of S. typhimurium was more rapid in yogurt whey (yogurt minus the casein fraction) than in whole yogurt, indicating that the casein fraction was partially able to protect Salmonella.     

Acid adaptation affects the viability of Salmonella typhimurium during the lactic fermentation of skim milk and product storage

In this study, Salmonella typhimurium was acid adapted at pH 5.5 for 4 h. The viability of the acid-adapted and non-adapted cells of S. typhimurium was investigated both during the lactic fermentation of skim milk with Streptococcus thermophilus or Lactobacillus bulgaricus, and during the storage of lactic fermented milk products at 5 degrees C. It was found that the viable population of S. typhimurium, regardless of acid adaptation, increased in skim milk during the initial 24 h of lactic fermentation and then declined. However, the viable population of acid-adapted S. typhimurium was significantly higher (P<.05) than that of non-adapted cell at the end of 48 h of fermentation. Acid-adapted cells of S. typhimurium were also found to have survived better than non-adapted cells in the S. thermophilus-prepared fermented milk and two commercial lactic fermented milk products. The viability of the acid-adapted and non-adapted S. typhimurium at 5 and 37 degrees C in cell-free fermented milks that had their pHs adjusted to 6.4 and skim milk (pH 6.4) was further investigated. Results revealed that acid adaptation, in addition to enhancing acid tolerance, reduced the susceptibility of S. typhimurium to refrigerated temperature and other detrimental factors which might be present in lactic fermented milk products. These responses all contribute to the enhanced survival of acid-adapted S. typhimurium in the lactic fermented milk products observed in the present study.     

The Acetic Acid Tolerance Response induces cross-protection to salt stress in Salmonella typhimurium

Salmonella typhimurium induces an Acid Tolerance Response (ATR) upon exposure to mildly acidic conditions in order to protect itself against severe acid shock. This response can also induce cross-protection to other stresses such as heat and salt. We investigated whether both the acetic acid induced and lactic acid induced ATR in S. typhimurium provided cross-protection to a salt stress at 20 degrees C. Acid-adapted cells were challenged with both a sodium chloride (NaCl) and potassium chloride (KCl) shock and their ability to survive ascertained. Acetic acid adaptation provided cells with protection against both NaCl and KCl stress. However, lactic acid adaptation did not protect against either osmotic stressor and rendered cells hypersensitive to NaCl. These results have implications for the food industry where hurdle technology means multiple sub-lethal stresses such as mild pH and low salt are commonly used in the preservation of products.     

胶束化和碱溶酸沉提取羽扇豆蛋白的物化特性

利用胶束化和碱溶酸沉2 种提取方法从羽扇豆中提取羽扇豆蛋白,并对2 种方法提取羽扇豆蛋白的物化特性进行研究。结果表明：羽扇豆蛋白分子质量主要集中在18～90 kDa之间,是由多种分子质量的蛋白组成。碱溶酸沉提取羽扇豆蛋白的氨基酸总含量（66.2%）显著（P＜0.05）高于胶束化提取羽扇豆蛋白的氨基酸总含量（27.8%）。2 种提取方法提取羽扇豆蛋白的等电点pI接近5.0。胶束化提取羽扇豆蛋白的持水性显著（P＜0.05）高于碱溶液酸沉法提取的羽扇豆蛋白,而持油性无显著差异（P＞0.05）。碱溶酸沉法提取羽扇豆蛋白的起泡性在pH 2.0～6.0之间显著减小,在pH 6.0时起泡性最低,其泡沫稳定性的变化趋势与其起泡性类似。而胶束化提取羽扇豆蛋白的起泡性受pH值的影响不显著（P＞0.05）。胶束化提取的羽扇豆蛋白在pH 4.0时乳化性最小,然后随pH值的升高蛋白乳化活性也随之增加,2 种提取方法所提羽扇豆蛋白在pH 10.0时乳化活性最高。碱溶酸沉法提取的羽扇豆蛋白在pH 4.0时溶解度最小,而随着pH 4.0～10.0的增加,蛋白溶解度迅速增加。而胶束化提取羽扇豆蛋白的溶解度随pH 2.0～10.0的升高也逐渐增大。该研究为羽扇豆蛋白在食品工业中的开发与应用提供一定理论支持。