Comparative analysis of a modified ecolite method, the colicomplete method, and a most-probable-number method for detecting Escherichia coli in orange juice

The Ecolite High Volume Juice (HVJ) presence-absence method for a 10-ml juice sample was compared with the U.S. Food and Drug Administration Bacteriological Analytical Manual most-probable-number (MPN) method for analysis of artificially contaminated orange juices. Samples were added to Ecolite-HVJ medium and incubated at 35 degrees C for 24 to 48 h. Fluorescent blue results were positive for glucuronidase- and galactosidase-producing microorganisms, specifically indicative of about 94% of Escherichia coli strains. Four strains of E. coli were added to juices at concentrations of 0.21 to 6.8 CFU/ ml. Mixtures of enteric bacteria (Enterobacter plus Klebsiella, Citrobacter plus Proteus, or Hafnia plus Citrobacter plus Enterobacter) were added to simulate background flora. Three orange juice types were evaluated (n = 10) with and without the addition of the E. coli strains. Ecolite-HVJ produced 90 of 90 (10 of 10 samples of three juice types, each inoculated with three different E. coli strains) positive (blue-fluorescent) results with artificially contaminated E. coli that had MPN concentrations of <0.3 to 9.3 CFU/ml. Ten of 30 E. coli ATCC 11229 samples with MPN concentrations of <0.3 CFU/ml were identified as positive with Ecolite-HVJ. Isolated colonies recovered from positive Ecolite-HVJ samples were confirmed biochemically as E. coli. Thirty (10 samples each of three juice types) negative (not fluorescent) results were obtained for samples contaminated with only enteric bacteria and for uninoculated control samples. A juice manufacturer evaluated citrus juice production with both the Ecolite-HVJ and Colicomplete methods and recorded identical negative results for 95 20-ml samples and identical positive results for 5 20-ml samples artificially contaminated with E. coli. The Ecolite-HVJ method requires no preenrichment and subsequent transfer steps, which makes it a simple and easy method for use by juice producers.     

浓缩还原橙汁饮料中果汁含量快速检测方法探究

果汁含量是浓缩还原橙汁的主要质量指标,也是判定其是否掺假的重要依据。本研究发现:不同产地、不同果汁含量的浓缩还原橙汁饮料中,可溶性物质在325nm紫外波长处有特征吸收,并且与22种常用添加剂溶液的紫外吸收有明显区分;采用自主研制的快速检测设备,将橙汁中可溶性物质按分子量大小分离,325nm下连续检测,得到橙汁可溶性物质按分子量大小分布的紫外特征吸收峰,其峰面积与橙汁含量呈现正相关;以100%巴西浓缩还原橙汁为标准参照,用外标法计算果汁含量。该方法样品前处理简单,只需过滤、超声,即可经凝胶色谱柱分离、检测;色谱柱分离和325nm的检测波长,有效避免了22种常用添加剂对果汁含量检测的干扰;该方法精密度高(RSD6.0%)、线性关系好(R2=0.9988)、抗干扰性强,可用于果汁含量大(等)于10%的橙汁饮料中原果汁含量的快速、大批量检测。     

浓缩还原橙汁饮料中果汁含量快速检测方法探究

果汁含量是浓缩还原橙汁的主要质量指标,也是判定其是否掺假的重要依据。本研究发现:不同产地、不同果汁含量的浓缩还原橙汁饮料中,可溶性物质在325nm紫外波长处有特征吸收,并且与22种常用添加剂溶液的紫外吸收有明显区分;采用自主研制的快速检测设备,将橙汁中可溶性物质按分子量大小分离,325nm下连续检测,得到橙汁可溶性物质按分子量大小分布的紫外特征吸收峰,其峰面积与橙汁含量呈现正相关;以100%巴西浓缩还原橙汁为标准参照,用外标法计算果汁含量。该方法样品前处理简单,只需过滤、超声,即可经凝胶色谱柱分离、检测;色谱柱分离和325nm的检测波长,有效避免了22种常用添加剂对果汁含量检测的干扰;该方法精密度高(RSD<6.0%)、线性关系好(R2=0.9988)、抗干扰性强,可用于果汁含量大(等)于10%的橙汁饮料中原果汁含量的快速、大批量检测。      

郑州市部分食品中SO2残留结果的调查分析及快速检测法与国标法检测结果的比对

目的 调查郑州市部分食品中二氧化硫残留情况, 比对快速检测法与国标法检测二氧化硫的测定结果。方法 在郑州市随机选取大型的农贸市场及超市采集食用菌、坚果、干制蔬菜等6大类食品共计192份, 采用快检法与国标法对其中的二氧化硫进行检测, 并对2种方法的检测结果进行比对。结果 192份样品中, 国标法检出176份含有二氧化硫, 检出率为92%, 超标123份, 超标率为64%。而快检法只有部分高残留食品(枸杞、干制蔬菜及食用菌)的检测结果与国标法较为相近, 对调料及水果干检测结果不理想。结论 郑州市售部分调料、枸杞、干制蔬菜及食用菌中二氧化硫污染严重, 有关部门应加强日常监管工作。此外二氧化硫速测试剂盒并不是对所有的食品都有效, 在日常大量抽检工作的使用中应注意适用范围。     

利用缓冲能力检测橙汁饮料中橙汁含量的方法研究

根据橙汁是一种缓冲溶液,其含量不同则缓冲能力大小不同,即由橙汁调配的橙汁饮料的溶液pH随添加的柠檬酸量的变化幅度不同,设计实验得出橙汁饮料的缓冲系数与其中橙汁含量的关系式,根据该关系式可以推算出橙汁饮料中橙汁的含量。     

超高效液相色谱—串联质谱法快速同时检测茶叶中7种香料

基于超高效液相色谱—串联质谱(UHPLC-MS/MS),建立了同时检测茶叶中7种可能非法添加的香料(茴香烯、香豆素、胡椒酚甲醚、指甲花醌、甲基丁香酚、蒲勒酮和反式肉桂醛)的定性、定量方法。茶叶样品经过乙腈—水混合溶剂提取,涡旋振荡,适当稀释并加入无水硫酸钠、十八烷基键合硅胶(C18)和N-丙基乙二胺(PSA)进行净化,涡旋离心后,上清液过膜待测。以Kinetex C18色谱柱分离,在多反应检测扫描(MRM)模式下经MS/MS进行基质外标法定量检测。试验结果表明,7种目标物在0.8～1 600.0μg/L范围内呈良好线性,线性相关系数(R2)均大于0.999。方法的检出限为0.02～0.03mg/kg,定量限为0.05～0.10 mg/kg,平均回收率为82.5%～102.5%,日内、日间精密度分别小于16%和18%。该方法快速、可靠、灵敏度高,用于检测市面流通的100个茶叶样品,结果检出了反式茴香脑、香豆素和胡椒酚甲醚等物质,最大浓度值分别为65.0,2.0,72.2mg/kg。     

Combinations of High Intensity Light Pulses and Thermosonication for the inactivation of Escherichia coli in orange juice

The non-thermal technologies High Intensity Light Pulses (HILP) and Thermosonication (TS) were applied alone and in combination to study their effect on Escherichia coli inactivation in orange juice. Two different energy settings were chosen in the current study, ‘Low’ (L) and ‘High’ (H), being the combinations applied: HILP(L) (4.03 J/cm²), HILP(H) (5.1 J/cm²), TS(L) (2.8 min residence time at 40 °C) and TS(H) (5 min residence time at 50 °C). Both the individual technologies and their combinations (HILP&TS and TS&HILP) were studied. Results showed inactivation ranging from 1.10 (TS(H)) to 2.42 (HILP(H)) log cfu/ml for the hurdles when applied individually and from 2.5 (HILP(L)&TS(H)) to 3.93 (HILP(H)&TS(L)) log cfu/ml for the combined treatments. Similar reductions in E. coli populations were achieved in orange juice by all treatment combinations irrespective of the sequence in which they were applied.     

Nature of the inactivation of Escherichia coli suspended in an orange juice and milk beverage

The killing effect of pulsed electric fields (PEF) on Escherichia coli (ATCC 8739) suspended in an orange juice and milk beverage was studied. Bipolar square pulses with a pulse width of 2.5 μs were applied. Electric field strength and treatment times ranged from 15 to 40 kV/cm, and from 0 to 700 μs, respectively. A maximum of 3.83 log reductions was achieved at 15 kV/cm and 700 μs. The experimental data were fitted to Bigelow and Hülsheger models and Weibull distribution function. Results indicated that Weibull function best described the experimental data (lowest mean square error). As there were no significant differences in the values of the shape factor (n) at the electric field strength of 25–40 kV/cm, the number of parameters in the Weibull model were reduced, leading to a simplified model with a fit similar to that obtained with the full model.     

基于SiO2荧光纳米粒子快速检测果汁中 大肠杆菌的免疫传感器研究

目的设计一种基于SiO_2荧光纳米粒子快速检测果汁中大肠杆菌O157:H7的新型传感器。方法采用超分子组合法将荧光基团嵌入到SiO_2纳米颗粒中合成SiO_2荧光纳米粒子,然后将抗大肠杆菌O157:H7的单抗偶联到纳米粒子表面,最后通过抗原-抗体反应使纳米粒子与待检细菌结合,使用荧光显微镜观察并统计大肠杆菌O157:H7的个数。结果本方法与革兰氏染色法相比,对大肠杆菌O157:H7计数结果无统计学差异(P=0.930);该方法整个检测过程能够在15 min内完成,检测下限小于10 CFU/mL。结论该方法能增强检测果汁中大肠杆菌O157:H7的灵敏度,缩短检测时间,对其他病原体检测方法的改进具有重要的指导意义。     

萝卜甜橙复合果蔬汁的研制

以萝卜、甜橙为原料,采用正交设计及单因素实验,筛选出复合果蔬汁的最佳配方。结果表明:采用萝卜汁:甜橙汁=1:1.5,糖液浓度为8％,柠檬酸含量为0.003％,加入0.1％海藻酸钠和0.1％黄原胶做稳定剂,生产出风味爽口、营养全面的复合果蔬汁饮料。     

Quantification of Salmonella in food samples from India using the MINI-MSRV MPN and modified MINI-MSRV MPN methods

Salmonella is one of the most important food-borne pathogens. The MINI-MSRV MPN method was modified by replacing the isolation and confirmation of Salmonella on selective chromogenic agar with PCR/RT-PCR. This modification reduced the time for quantification by the MINI-MSRV MPN method by 24 h. Ninety-seven different food samples, comprising chicken, mutton, fish, and sprouts from different markets in Mumbai, India, were analyzed for quantification of Salmonella species by the MINI-MSRV MPN and modified MINI-MSRV MPN methods. Seventy-four percent of the chicken samples were found positive for Salmonella. However, Salmonella was found to be absent in fish, mutton, and sprouts samples. Salmonella load in the chicken sample was in the range of 1.30 to 120 MPN/g. This genotypic confirmation has advantage over variable phenotypic confirmation of pathogens.     

Multidimensional scaling as a method to correlate sensory and instrumental data of orange juice aromas

Changes of orange juice aromas due to storage time and temperature were studied through sensory detection of differences between samples, and by gas chromatographic analysis of 38 volatile constituents. Multidimensional scaling was applied to sensory and instrumental data prior to correlation analysis. Absolute concentrations of volatile constituents were not correlated with sensory data but higher correlations were observed with normalised analytical data. Thus, correlation coefficients were respectively 0.47 and 0.74 when considering (i) relative concentrations of all volatiles, by expressing the concentration of each constituent in a sample as a proportion of the maximum observed concentration of this constituent; and (ii) relative concentrations of only those constituents showing significant (95% level) changes due to storage length or temperature.     

气质联用结合多元分析法比较甜橙汁与宽皮柑橘汁的香气成分差异

比较宽皮柑橘汁和甜橙汁中香气物质的差异性,为宽皮柑橘制汁加工提供数据基础。榨取常见甜橙和宽皮柑橘各8个品种的果汁,通过顶空固相微萃取-气相色谱-质谱对柑橘汁样品中香气成分进行定性和定量,采用香气活度值(odor active value,OAV)计算特征香气,并利用主成分分析进行比较和区分。结果表明,16种柑橘汁中共检出77种香气成分,其中甜橙汁特有香气物质有14种,宽皮柑橘汁特有香气物质有7种。通过计算得到47种OAV> 1的特征香气成分,其中芳樟醇、正己醛、壬醛对两类柑橘汁的主体香气贡献极大。选取31种香气物质进行主成分分析,两类柑橘汁均可被明显区分开。研究表明两类柑橘汁中萜类化合物的种类和含量均最多,但甜橙汁中的酯类和醇类化合物的种类和含量远高于宽皮柑橘汁。     

Utilization of fluorogenic assay for rapid detection of Escherichia coli in acidic fruit juice

This study was undertaken to investigate interference by acids commonly found in fruit juice in Escherichia coli assays involving the use of 4-methylumbelliferyl-beta-D-glucuronide (MUG) as a fluorogenic substrate for enzyme reaction. Fluorescence intensity was negatively correlated (P < 0.001) with the volume of fresh citrus juice tested by the lauryl tryptose broth (LST)-MUG assay, and the permissible sample sizes were limited to 0.3 and 0.5 ml for fresh citrus juices with pHs of 3.3 and 3.9, respectively. In addition, false-negative results were visually observed under UV light when the E*Colite assay was used to test large volumes (5 to 10 ml per test) of fresh citrus juice or when the test broth used for the LST-MUG assay was supplemented with citric, malic, or tartaric acid at 2 to 4 g/liter. These results suggest that the size and pH of acidic samples should be controlled in MUG-based fluorogenic assays. The inhibitory effect on fluorescence was due to high acidity, which reduces fluorescence from 4-methylumbelliferone. Buffering improved the assays. When sodium bicarbonate was incorporated in the enrichment broth at 10 g/liter, the permissible sample sizes for fresh grapefruit juice (pH 3.1) increased from 0.3 to 1 ml for the LST-MUG (with 9.9 ml of broth) assay and from 3 to 10 ml for the E*Colite (with 99 ml of broth) assay.     

Effectiveness of High Intensity Light Pulses (HILP) treatments for the control of Escherichia coli and Listeria innocua in apple juice, orange juice and milk

High Intensity Light Pulses (HILP) represent an emerging processing technology which uses short (100-400 μs) light pulses (200-1100 nm) for product decontamination. In this study, model and real foods of differing transparencies (maximum recovery diluent (MRD), apple and orange juices and milk) were exposed to HILP in a batch system for 0, 2, 4 or 8 s at a frequency of 3 Hz. After treatment, inactivation of Escherichia coli or Listeria innocua was evaluated in pre-inoculated samples. Sensory and other quality attributes (colour, pH, Brix, titratable acidity, non-enzymatic browning, total phenols and antioxidant capacity (TEAC)) were assessed in apple juice. Microbial kill decreased with decreasing transparency of the medium. In apple juice (the most transparent beverage) E. coli decreased by 2.65 and 4.5 after exposure times of 2 or 4 s, respectively. No cell recovery was observed after 48 h storage at 4 °C. No significant differences were observed in quality parameters, excepting TEAC and flavour score, where 8 s exposure caused a significant decrease (p < 0.05). Based on these results, HILP with short exposure times could represent a potential alternative to thermal processing to eliminate undesirable microorganisms, while maintaining product quality, in transparent fruit juices.     

Combining ultraviolet light and mild temperatures for the inactivation of Escherichia coli in orange juice

It is difficult to guarantee the effectiveness of UV technology to reach 5 Log₁₀ cycles of inactivation of Escherichia coli in a large amount of fruit juices with high absorption coefficients and turbidities, such as orange juice. The aim of this work was to overcome this limitation by combining UV light and mild temperatures. UV treatments were carried out in an equipment with eight individual annular thin film flow-through reactors connected sequentially and submerged in a thermostatic water bath. A treatment of 13.55 J/mL reached 0.25 ± 0.04, 0.41 ± 0.13, 0.84 ± 0.32, 0.96 ± 0.12, 2.57 ± 0.05, 5.41 ± 0.23, and more than 6 Log₁₀ cycles of inactivation of E. coli STCC 4201 suspended in commercial sterilized orange juice at 25.0, 40.0, 50.0, 52.5, 55.0, 57.5, and 60.0 °C, respectively. The comparison of UV resistance at 25 °C with heat resistance at mild temperatures demonstrated a synergistic effect of both technologies applied simultaneously. The maximum synergistic lethal effect was reached at 55 °C (68.03%).     

An improved method for the recovery of Salmonella serovars from orange juice using universal preenrichment broth

The relative effectiveness of three methods for the recovery of Salmonella serovars from orange juice was determined. One method, a modified Bacteriological Analytical Manual (BAM) procedure consisted of preenrichment in lactose broth at 35 degrees C for 24 h, selective enrichment, and selective plating. Another method, a National Centers for Disease Control and Prevention (CDC 1) procedure, consisted of direct enrichment in tetrathionate broth at 35 degrees C for 24 and 48 h, followed by selective plating. The third method (also from CDC and designated CDC 2) consisted of preenrichment in Universal Preenrichment (UP) broth at 35 degrees C for 24 h, selective enrichment, and selective plating. In 10 experiments encompassing five different Salmonella serovars and 200 test portions per broth, the CDC 1 method recovered 141 Salmonella-positive test portions, the BAM method recovered 151, and the CDC 2 method recovered 171. In 2 of the 10 experiments, with two different Salmonella serovars, the BAM recovered significantly fewer (P < 0.05) Salmonella-positive test portions than did the CDC 2 method. On the basis of the above results, the second phase of this study focused on a comparison of the effectiveness of the BAM-recommended lactose broth and the CDC 2-recommended UP broth as preenrichment media for the recovery of Salmonella serovars from pasteurized and unpasteurized orange juice. Subsequent culture treatment of the two preenrichments was identical so that the effect of other variables (e.g., different selective enrichment media, various incubation temperatures, and different selective plating agars) on the relative performance of these two preenrichment media was excluded. In one of nine experiments, with pasteurized orange juice, lactose broth recovered significantly fewer (P < 0.05) Salmonella-positive test portions than did UP broth. For the combined results of the nine pasteurized orange juice experiments (180 test portions per broth), lactose broth recovered 99 Salmonella-positive test portions, and UP broth recovered 116. In three of seven experiments, with unpasteurized orange juice, lactose broth recovered significantly fewer (P < 0.05) Salmonella-positive test portions than did UP broth. For the combined results of the seven unpasteurized orange juice experiments (140 test portions per broth), lactose broth recovered 73 Salmonella-positive test portions, and UP broth recovered 117. For both pasteurized and unpasteurized orange juice, the total number of Salmonella-positive test portions recovered with UP broth was significantly greater than the number recovered with lactose broth. These results indicate that UP broth is a more effective enrichment broth for the recovery of Salmonella from orange juice than is lactose broth.     

流式细胞技术快速检测果汁中的霉菌、酵母菌

研究应用流式细胞技术（flow cytometry,FCM）快速检测果汁饮料中霉菌、酵母菌的方法。通过正交实验和方差分析,对样品前处理技术条件进行优化,去除了影响FCM检测的基质颗粒,使FCM检测限达到101cfu/mL数量级,检测时间从5d缩短到100min。从绘制的标准曲线可以看出,FCM与平板法线性相关,符合性好。FCM将以更加灵敏、准确、快速、操作简便的优点成为一种可替代平板法来检测果汁中霉菌、酵母菌的自动化仪器检测新技术。     

Evaluation of the MPN, Anderson-Baird-Parker, Petrifilm E. coli and Fluorocult ECD method for enumeration of Escherichia coli in foods of animal origin.

Commercially available beta-D-glucuronidase (GUR) based methods, Petrifilm E. coli (PEC) and Fluorocult ECD (FECD), and ISO standard MPN and Anderson-Baird-Parker (ABP) procedures were evaluated for routine enumeration of E. coli in naturally contaminated foods of animal origin. The methods concerned were classifiable in a sequence of best qualities for: production, MPN > ABP = PEC = FECD; costs, FECD > ABP = PEC > MPN; time per measurement, ABP = PEC = FECD > MPN; practical use, PEC > FECD > ABP > MPN; detection at low contamination, MPN > ABP = PEC > FECD. The ABP and PEC method appeared useful for routine counting of E. coli in raw meat, poultry and meat products, whereas the MPN procedure turned out to be more sensitive, however, impractical and considerably more expensive. The FECD method was inexpensive although suitable for the enumeration of E. coli at higher contamination level (> 50 cfu/g). The indole and MUG indicators both applied to demonstrate E. coli with the ABP or FECD method proved to be equal in specificity.     

Inactivation of Escherichia coli O157:H7 in orange juice using a combination of high pressure and mild heat

The effect of high pressure on the survival of a pressure-resistant strain of Escherichia coli O157:H7 (NCTC 12079) in orange juice was investigated over the pH range 3.4 to 5.0. The pH of commercial, sterile orange juice was adjusted to 3.4, 3.6, 3.9, 4.5, or 5.0. The juice was then inoculated with 10(8) CFU ml(-1) of E. coli O157:H7. The inoculated orange juice was subjected to pressure treatments of 400, 500, or 550 MPa at 20 degrees C or 30 degrees C to determine the conditions that would give a 6-log10 inactivation of E. coli O157:H7. A pressure treatment of 550 MPa for 5 min at 20 degrees C produced this level of kill at pH 3.4, 3.6, 3.9, and 4.5 but not at pH 5.0. Combining pressure treatment with mild heat (30 degrees C) did result in a 6-log10 inactivation at pH 5.0. Thus, the processing conditions (temperature and time) must be considered when pressure-treating orange juice to ensure microbiological safety.