平板计数法与纸片法检测食品微生物菌落总数的比较研究

目的找出平板倾注法与纸片法2种检测食品菌落总数方法之间的相关性,判断2种方法有无显著性差异。方法样品处理按GB 4789.2-2016《食品安全国家标准食品微生物学检验菌落总数测定》进行处理,平板倾注法取样品稀释液接种平皿倾注琼脂、纸片法取样品稀释液接种细菌计数纸片。用上述2种方法对市场上随机抽取30份饼干及糕点和2份质控样品进行菌落总数检测,最后做统计学分析(t-test)。结果倾注法与纸片法检测结果无显著差异(P0.05)且对不同菌落数区间(0～100CFU/g、100～1000CFU/g、1000～10000 CFU/g)都适用。2份质控样品评价结果为满意。结论纸片法可用于食品菌落总数的快速检测,缩短检测流程,提高工作效率。     

AOAC PetrifilmTM菌落总数测试片法与食品中菌落总数测定国标方法的比较研究

目的:确证AOAC 990.12PetrifilmTM菌落总数测试片计数食品中菌落总数的检测性能.方法:对AOAC990.12 PetrifilmTM菌落总数测试片法与国家标准GB4789.2菌落总数测定法进行比较实验.在20个政府机构和食品企业实验室,对生肉、熟肉、水产品、调味品、冰激凌、原奶、奶粉和豆制品等8大类845份食品样品进行了测定.结果:AOAC 990.12PetrifilmTM方法与国标GB4789.2法检测8类食品样品的菌落总数测定结果的P值均大于0.05,无显著性差异.结论:使用AOAC 990.12PetrifilmTM菌落总数测试片法检测食品中的菌落总数等效于食品微生物学检验菌落总数测定的国家标准方法.     

食品防腐剂对菌落总数检测影响的研究

研究几种常用食品防腐剂对风味饮料、果汁饮料菌落总数检测可能存在的影响。结果表明,食品防腐剂在使用限量范围内,样品菌落总数检测结果与对照样菌落总数检测结果没有显著性差异,因此可以认为,食品防腐剂不会对菌落总数检测产生影响。     

食品微生物检验菌落总数测定方法的效果分析

目的:分析研究食品微生物检验菌落总数测定方法的测定效果。方法:选取本疾控中心接收的220份食品样品,对其采取3种方法进行检测,包括平板菌落计数法、TCT培养基法以及菌落总数测定法,对其检验结果进行对比分析。结果:平板菌落计数法的不合格率为9.1%,菌落总数测定法的不合格率为8.2%,TCT培养基法的不合格率为10%,3种检测方法结果之间的差异不具有统计学意义(P0.05)。结论:食品微生物检验采取平板菌落计数法、TCT培养基法以及菌落总数测定法这3种方法均可以取得相对比较高的准确性,可以按照具体情况选择适宜的检验方法。     

用生理盐水作为含高盐食品细菌检验稀释液的商榷

GB4789·22-84中规定,对调味品包括酱油、酱类进行细菌检验时,检样处理应用灭菌蒸馏水稀释。在新出版的《食品卫生检验方法注解,衡生物部分》第二章,菌落总数测定中也规定“如果对含盐量较高的食品,如酱品等进行稀释,则宜采用蒸馏水。在国标颁布以前,我们对酱油、酱类进行细菌检验时,通常采用生理盐水作为稀释液稀释。为了弄清采用何种稀释液比较合理,我们从理论上进行了探讨。并采集了不同生产     

测试片法在食品菌落总数检测中的应用研究

目的 探究菌落总数测试片法检测食品中菌落总数的可行性.方法 用菌落总数测试片法和国家标准方法同时对制备的菌悬液、自然污染食品样品和人工污染食品样品的菌落总数进行检测,采用t-检验分析2种方法检测结果的差异,采用Pearson相关分析确定2种检测方法之间的相关性.结果 菌悬液和自然污染食品样品菌落总数测试片法的变异系数为...     

食品中菌落总数能力验证与质量控制分析

食品中菌落总数的检测是食品控制的常规检测指标,其检测结果关系到食品的质量是否在可控范围内,菌落总数检测方法的提升,检测环境的改善是影响其检测结果的直接因素。本文就食品中菌落总数检测能力验证质量控制的各种影响因素进行分析,提出确保实验室检测结果准确性的措施,为提升实验室检测技能,确保检测数据的准确性、可靠性奠定基础。     

基于测试片法与平板计数法对不同类型食品中菌落总数结果的比较分析

目的比较菌落测试片法与平板计数法在不同类型食品中菌落总数测定结果的差异。方法在市面上随机抽取生肉制品、鲜奶制品、豆制品、粮食制品、冷冻饮品、坚果籽实、即食果蔬制品共112批,同时按菌落测试片法和平板计数法进行菌落总数测定,并对计数结果进行统计学分析。结果菌落测试片法与平板计数法的测定结果对数值差值的平均值|d log|= 0.06(<0.5),配对t检验P=0.860(>0.05)。结论菌落测试片法与平板计数法对上述7种类型的食品菌落总数测定结果无显著性差异,菌落测试片法可用于上述食品的菌落总数测定。     

食品微生物检验中菌落总数测定的注意事项

近年来食品安全问题引起了社会各界的关注,食品微生物检验作为一种判定食物质量的重要手段,被广泛应用。菌落总数是食品微生物检验中的一项重要指标,可以用来反映食物的新鲜度以及污染程度。在进行菌落总数测定时,除了对实验环境有严格要求外,实验操作的流程、技术要点和注意事项等,也都是检验人员必须要熟练掌握的。本文分别从前期材料准备、稀释液制备、平板接种以及菌落数量统计等方面,就食品微生物检验中菌落总数测定的注意事项展开简要分析。     

食品中菌落总数测定的注意事项

本文通过分析总结影响食品中菌落总数检测结果的因素,交流探讨提高实验检验数据准确性和可靠性的措施。     

Influence of diluent and sample processing methods on the recovery of the biocontrol agent Pantoea agglomerans CPA-2 from different fruit surfaces

Determining the populations of biocontrol agents applied as a postharvest treatment on fruit surfaces is fundamental to the assessment of the microorganisms' ability to colonise and persist on fruit. To obtain maximum recovery, we must develop a methodology that involves both diluent and processing methods and that does not affect the viability of the microorganisms. The effect of diluent composition was evaluated using three diluents: phosphate buffer, peptone saline and buffered peptone saline. An additional study was performed to compare three processing methods (shaking plus sonication, stomaching and shaking plus centrifugation) on the recovery efficiency of Pantoea agglomerans strain CPA-2 from apples, oranges, nectarines and peaches treated with this biocontrol agent. Overall, slight differences occurred among diluents, although the phosphate buffer maintained the most ideal pH for CPA-2 growth (between 5.2 and 6.2). Stomaching, using the phosphate buffer as diluent, was the best procedure for recovering and enumerating the biocontrol agent; this fact suggested that no lethal effects from naturally occurring antimicrobial compounds present on the fruit skins and/or produced when the tissues were disrupted affected the recovery of the CPA-2 cells, regardless of fruit type. The growth pattern of CPA-2 on fruits maintained at 20°C and under cold conditions was similar to that obtained in previous studies, which confirms the excellent adaptation of this strain to conditions commonly used for fruit storage.     

Factors Influencing Recovery of Heat-injured Bacillus thuringiensis Spores. Statistical Approach

The influence of several factors on recovery of heat-treated Bacillus thuringiensis spores was examined including treatment conditions (time/temperature), dilution buffer (phosphate buffer, peptone water at 15 mg/L), recovery temperature and enumeration medium constituents (lysozyme, catalase, lactic acid hemicalcium salt, glucose, MgSO₄, sodium chloride). A fractional factorial design was used to determine the incidence and interactions of these factors. Specific significant factors (treatment conditions, dilution buffer, recovery temperature, glucose and NaCl addition) were derived from this analysis and then tested in a general linear regression model which assessed their influences. The maximal count was obtained when spores diluted in peptone buffer were incubated at 25°C in nutrient agar containing NaCl and glucose.     

Phosphate buffer increases recovery of Escherichia coli O157:H7 from frozen apple juice

It is common practice to dilute food products in 0.1% peptone before microbiological analysis. However, this diluent may not be appropriate for detection of injured organisms present in acidic foods. Shelf-stable unclarified apple juice (pH 3.6) was inoculated with approximately 1 x 10(7) CFU/ml of Escherichia coli O157:H7 and held at 23 +/- 2 degrees C (control) or frozen to -20 +/- 2 degrees C for 24 h to induce injury before sampling. Unfrozen or frozen and thawed juice was diluted 1:1 or 1:10 in 0.1% (wt/vol) peptone (pH 6.1) or 0.1 M phosphate buffer (pH 7.2). Juice samples were plated onto tryptic soy agar with 0.1% (wt/vol) sodium pyruvate (TSAP) to measure survival or onto sorbitol MacConkey agar (SMA) to indicate injury. Counts on TSAP or SMA were the same for control samples held in peptone or phosphate buffer for up to 45 min. However, populations of E. coli in frozen and thawed samples declined rapidly upon dilution in 0.1% peptone. Within 20 min, E. coli underwent a >1-log10 CFU/ml reduction in viability as measured on TSAP and a >2-log10 CFU/ml reduction to below the limit of detection (1.6 or 2.3 log10 CFU/ml) on SMA. In contrast, populations of E. coli in frozen and thawed samples diluted in phosphate buffer did not decrease significantly on TSAP and decreased by <0.6 log CFU/ml on SMA during a 45-min holding period. The acidity of apple juice appears to interfere with the recovery of freeze-thaw-injured E. coli O157:H7 during sampling. Using 0.1 M phosphate buffer (pH 7.2) as a diluent results in superior recovery of these organisms on both selective and nonselective plating media.     

Determination of fumonisins B1 and B2 in cornflakes by high performance liquid chromatography and immunoaffinity clean-up

The determination of fumonisins in cornflakes is a challenging matter as the actually available methods for the analysis of corn do not perform well when applied to this more complex matrix. After testing several factors that may affect the analytical performance, an accurate method for the determination of fumonisin B₁ (FB₁) and B₂ (FB₂) in cornflakes has been developed. The method uses immunoaffinity chromatography for clean-up and high performance liquid chromatography (HPLC) for quantification of the toxins. Samples were extracted twice with acetonitrile-methanol-water (25:25:50) and the combined extracts were diluted with phosphate buffered saline (PBS) and applied to a FumoniTest? immunoaffinity column. After washing with PBS, fumonisins were eluted from the column with methanol and reacted with o-phthaldialdehyde/2-mercaptoethanol to form fluorescent derivatives. Fumonisin derivatives were analysed by reversed phase HPLC with fluorometric detection using methanol-0.1 M phosphate buffer (77:23; pH adjusted at 3.35) as mobile phase. The average recoveries for FB₁ and FB₂     

选择性分离放线菌

进行了土样的预处理试验,探讨了平板培养基中抑制剂重酪酸钾的最适浓度．结果表明,选择性分离放线菌的比较适宜的方法为：采集的土样在２８℃或室温条件下风干１０～２０ｄ后,将土壤悬浮液（１０－１）于４０℃和ｐＨ７的条件下,加６％酵母膏和０．０５％ＳＤＳ（５ｍｍｏｌ／Ｌ磷酸缓冲液）,震荡２０ｍｉｎ,水稀释至１０－２;或土壤悬浮液（１０－１）于５０℃和ｐＨ７的条件下,加６％胨和０．０５％ＳＤＳ（５ｍｍｏｌ／Ｌ磷酸缓冲液）,震荡１０ｍｉｎ,水稀释至１０－２．然后用平板稀释法接菌在高氏合成１号琼脂＋重酪酸钾（质量浓度为２５０ｍｇ／Ｌ）的平板培养基上,培养７ｄ后挑菌分离     

Comparison of Homogenization by Blending or Stomaching on the Recovery of Listeria monocytogenes from Beef Tissues

Homogenization by blending or stomaching was compared for the recovery of Listeria monocytogenes from inoculated intact beef tissue. There were no differences in numbers of recovered bacteria (P>0.10) attributable to either homogenization time or method. Fewer viable bacteria (P<0.05) were recovered in phosphate buffer than either buffered peptone water or 2% trisodium citrate buffer. Tween 80 increased the numbers of bacteria recovered from fat tissue (P<0.05). Stomaching is an acceptable method for homogenizing samples for Listeria analysis.     

Effect of water activity on inactivation of Listeria monocytogenes and lactate dehydrogenase during high pressure processing

The aim of this study was to investigate the effect of water activity (a_w) on the inactivation of Listeria monocytogenes and lactate dehydrogenase (LDH) during high pressure processing (HPP). For microbial inactivation lyophilized cells of L. monocytogenes 19,115 were left dry or were suspended in 10 ml of 0.1% peptone water, 10 ml of glycerol, or mixtures of glycerol and peptone water. All samples of various a_ws were high pressure (HP) processed at ambient temperature at 600 MPa for 300 s. Following HPP, samples were serially diluted in 0.1% peptone and spread-plated on Tryptic Soy agar supplemented with Yeast Extract. For enzyme inactivation, 4.2 mg of lyophilized LDH was suspended in 2 ml of 100 mM phosphate buffer (pH 7.4), 2 ml of peptone water or glycerol, or in 2 ml mixtures of glycerol and peptone water. A lyophilized sample with no added liquid was also included. All enzyme samples were subjected to HPP as described above. After HPP, LDH was diluted to 0.28 μg/ml in 100 mM phosphate buffer (pH 7.4). LDH activity was assessed by measuring the change in concentration of β-NADH as a function of time. Dynamic light scattering analysis (DLS) was performed to examine the size distribution, polydispersity, and hydrodynamic radius of LDH before and after HPP. No significant difference in CFU/g was observed between lyophilized cells not subjected to HPP and lyophilized cells subjected to 600 MPa for 300 s (P < 0.05). However, lyophilized cells that were suspended in 100% to 60% peptone water showed a ~ 7.5-log₁₀ reduction when subjected to HPP. Survival of L. monocytogenes following HPP significantly increased (P < 0.05) when the peptone water concentration was decreased below 60% (a_w ~ 0.8). DLS results revealed that LDH suspended in buffer underwent aggregation following HPP (600 MPa, 300 s). Inactivation rate constants obtained using a first-order kinetic model indicated that untreated and HP processed lyophilized LDH had similar activities. When LDH was subject to HPP in solutions containing glycerol, enzyme activity decreased as the water content increased (r² = 0.95). Lyophilization completely protected L. monocytogenes and LDH from inactivation by high pressure. Furthermore, enzyme activity and cell survival increased as water activity was decreased. We postulate low a_w results in protein stabilization, which prevents protein denaturation and cell death during HPP.     

EFFECT OF SANITIZERS ON LISTERIA MONOCYTOGENES ATTACHED TO LATEX GLOVES

Contamination of ready-to-eat seafoods with Listeria monocytogenes is a major concern of the seafood industry. One means of control is the use of hand sanitizers. Five sanitizers (chlorine bleach, Zep-i-dine^TM, Zepamine A^TM, Zep^TM Instant Hand Sanitizer, and Ultra-Kleen^TM) were evaluated for effectiveness against L. monocytogenes attached to latex gloves in the presence of phosphate buffered saline or crab cooking water. Cooking water had been used to boil the crabs and was heavily laden with organic nutrients. Chlorine, Zepamine A^TM, and Ultra-Kleen^TM reduced numbers of attached L. monocytogenes to nondetectable levels in the presence of phosphate buffered saline; Zep-i-dine^TM and Zep^TM Instant Hand Sanitizer were less effective. In the presence of crab cooking water, only Ultra-Kleen^TM reduced cell numbers to nondetectable levels; the effectiveness of the remaining sanitizers was reduced. Extreme care must be taken when choosing hand sanitizers as their efficacy may be affected by organic residues on the gloves of food handlers .     

An immunoconcentration-PCR assay to detect Salmonella in the environment of poultry houses.

An immunoconcentration-PCR assay was developed for the rapid and specific detection of Salmonella. This assay was evaluated against a conventional bacteriological method for the detection of Salmonella from environmental swabs of poultry houses. The 120 samples investigated were pre-enriched in phosphate buffered peptone water and Salmonella was separated by an immunoconcentration process using an automated system (VIDAS bioMérieux, Marcy l'Etoile, France) prior to PCR. The specificity of the assay was high as no false-positives were found. The sensitivity of the assay was 70%. The correlation between the ICS-PCR assay and the bacteriological method was 84%.