EFFECT OF POLYPHOSPHATES AND NaCl ON AEROMONAS HYDROPHILA K144

Polyphosphates are multifunctional ingredients added to many foods, particularly meat products. In addition to their moisture-binding properties, polyphosphates have been reported to inhibit various bacteria. In the current study, four food-grade polyphosphates were evaluated for their effects on the growth of Aeromonas hydrophila K144 in both a model system and a food system. Since polyphosphates can interact with other food factors, effect of these compounds were studied at different NaCl levels and temperatures. The model system was BHI Broth modified by the addition of polyphosphates (sodium pyrophosphate, sodium tripolyphosphate, Hexaphos, or Sodaphos) and NaCl; incubation was aerobic at 5 or 28C. The food system was ground pork with NaCl and polyphosphate added and inoculated with A. hydrophila. Individually, the polyphosphates were relatively noninhibitory in both BHI broth and ground pork, but NaCl and temperature interacted with the polyphosphates in the model system to increase generation and lag times of A. hydrophila. In BHI broth, a combination of 2% of any of the polyphosphates tested and 3.5% NaCl inactivated the bacterium; this inactivation was temperature-dependent. By both a plating system and electron microscopy, the polyphosphate-NaCl combination was shown to injure the bacterium. In the ground pork, the polyphosphate-NaCl combination limited growth of the bacterium during refrigerated storage. These results suggest that polyphosphates could be useful to control the presence of A. hydrophila in certain foods .     

木芙蓉（Hibiscus mutabilis）叶提取物对大肠杆菌O1和金黄色葡萄球菌91053的体外抗菌效果研究

研究不同浓度木芙蓉(Hibiscus mutabilis)叶提取物对大肠杆菌(E.coliO1)和金黄色葡萄球菌(Staphylococcus aureus91053)的体外抗菌效果。利用二倍稀释法和涂布平板法,确定提取物对两种菌种的最低抑菌浓度(MIC)和最低杀菌浓度(MBC),并绘制杀菌曲线。结果为:提取物对大肠杆菌的MIC和MBC浓度均为0.25g/mL,8、4、2、1MIC浓度的木芙蓉叶提取物分别在第6、14、18h能完全杀灭细菌该菌;提取物对金黄色葡萄球菌的MIC和MBC浓度均为0.5g/mL,4、2、1MIC浓度的木芙蓉叶提取物对金黄色葡萄球菌的杀菌效果更佳,分别能在第6、10、14h完全杀灭该菌。木芙蓉叶提取物对大肠杆菌和金黄色葡萄球菌均具明显的杀菌效果。      

Antibacterial Activity of Carvacrol, Citral, and Geraniol against Salmonella typhimurium in Culture Medium and on Fish Cubes

Carvacrol, citral and geraniol showed potent antibacterial activity against Salmonella typhimurium and its rifampicin-resistant (Rif^R) strain as determined in txyptic soy broth and by zone of inhibition on agar-based medium. Carvacrol had the most potent bactericidal activity, with minimum inhibitory and bactericidal concentrations (MIC and MBC) of 250 μg/mL for both tester strains. When tested at 0.5, 1.5 and 3.0% in 1% Tween 20 for bactericidal activity against Rif^R-S. typhimurium inoculated on fish cubes, carvacrol at 3.0% completely killed the inoculated bacteria, while geraniol killed most of the bacteria, and citral killed the least. Carvacrol and geranial showed potent antibacterial activity at 1.5%. Bactericidal activity became more evident as storage of fish cubes at 4°C lengthened. The comparable inhibition of these strains of Salmonella and species of Gram-negative bacteria by carvacrol and geraniol support their application as potential antibacterial agents in food systems.     

Effect of Phosphates on Bacterial Growth in Refrigerated Uncooked Bratwurst

The effects of 0.5% sodium acid pyrophosphate (SAPP), sodium tripolyphosphate (STPP), tetrasodium pyrophosphate (TSPP) and sodium polyphosphate glassy (SPC) on aerobic mesophilic and psychrotrophic bacterial growth and on survival of inoculated Stuphylococcus aureus Z 88 were investigated in uncooked bratwurst stored at 5°C for 7 days. No significant microbial inhibition by phosphates was found, although SAPP addition resulted in consistently lower total aerobic plate counts. Phosphate-induced pH differences in the sausages had no effect on bacterial numbers. The possible role of meat enzymes in the hydrolysis of condensed phosphates to microbiologically inactive species is discussed.     

枯草芽孢杆菌抗菌脂肽对嗜水气单胞菌抑菌效果

为了研究Bacillus subtilis fmbJ 产生的抗菌脂肽对嗜水气单胞菌的抑菌效果,采用抑菌圈法测定抗菌脂肽对嗜水气单胞菌的最小抑菌质量浓度(MIC)和最小杀菌质量浓度(MBC),并从其对嗜水气单胞菌形态结构、膜通透性来探讨其抗菌作用。结果表明,嗜水气单胞菌对枯草芽孢杆菌抗菌脂肽具有较高的敏感性,最小抑菌质量浓度(MIC)为20μg/mL,最小杀菌质量浓度(MBC)为32μg/mL;该抗菌脂肽导致嗜水气单胞菌细胞膜通透性增加,使细胞内一些离子以及大分子的蛋白质和核酸泄漏到细胞外,从而引起细胞的死亡;显微结构影响的研究表明,该抗菌脂肽还可以造成嗜水气单胞菌细胞壁缺失、鞭毛散失、胞内物质模糊不清等现象,抑菌效果较明显,可用于嗜水气单胞菌感染引起的水生动物疾病预防和控制。     

Extension of the Shelf-Life of Fresh Ground Pork with Polyphosphates

The antimicrobial effects of 1.0% sodium acid pyrophosphate (SAPP) and sodium orthophosphate monobasic (ORTHO), alone or combined, were studied in fresh ground pork held at 2–4°C for 6 days. Addition of 1.0% SAPP to the meat inhibited psychrotrophic bacterial growth (P<0.01) and resulted in 50% longer meat shelf-life (equivalent to 2 days) in relation to control samples or to meat treated with 0.5% or 1.0% ORTHO. Addition of a 0.5% SAPP/0.5% ORTHO combination was less inhibitory to meat bacteria than 0.5% SAPP alone. Bacterial inhibition did not correlate with soluble orthophosphate content in ground pork.     

费菜黄酮对冷却猪肉腐败菌及品质的影响

通过二倍稀释法和牛津杯法确定了费菜黄酮对3种冷却猪肉腐败菌的最低抑菌浓度(minimum inhibitory concentration,MIC)、最低杀菌浓度(minimum bactericidal concentration,MBC)和抑菌活性,并研究了不同质量浓度费菜黄酮对猪肉的保鲜效果。结果表明,费菜黄酮对实验菌有不同程度的抑制作用,其中对于气单胞菌的抑制性最强,MIC和MBC分别为0.675、2.5 mg/mL,假单胞菌次之,MIC和MBC分别为1.25、5 mg/mL,乳酸菌抑制性最差,MIC和MBC分别为1.25、10 mg/mL。综合菌落总数和色差指标,选择2 mg/mL作为费菜黄酮对冷却猪肉保鲜的适宜质量浓度。在4℃贮藏条件下,黄酮处理组组织结构、pH值、持水力、挥发性盐基氮值和硫代巴比妥酸值各品质指标均优于对照组。     

Inhibition of Clostridium botulinum Growth from Spore Inocula in Media Containing Sodium Acid Pyrophosphate and Potassium Sorbate with or without added Sodium Chloride

The effects of sodium acid pyrophosphate (SAPP), sodium chloride (NaCl) and/or potassium sorbate (PS) on the growth from heat-activated spores of three individual strains or a mixture of ten strains of Clostridium botulinum in peptone-yeast extract-glucose broth at pH 5.55 or 5.85 were measured spectrophotometricalty at A_630nm. Growth ratios (GR = treatment/control) based on time to reach A₆₃₀= 0.35 or 0.04 were calculated and used to compare effects of additives on strains. SAPP, NaCl, PS, and pH exhibited independent significant main effects (p≦0.01) on delaying growth in most C. botulinum strains tested. Combinations of additives without NaCl consistently caused an increase in the GR and an increase in organism sensitivity to additives in the medium. Treatments containing SAPP (0.2 or 0.4%) and PS (0.13 or 0.26%) were more effective for delaying growth than other formulations tested.     

Evaluation of salt, polyphosphates and their blends at different levels on physicochemical properties of buffalo meat and patties

The effects of sodium pyrophosphate (SPP), sodium tripolyphosphate (STPP), sodium hexametaphosphate (SHMP), sodium acid pyrophosphate (SAPP) and their blends at different levels (0·3, 0·5 and 0·7%), along with 2% sodium chloride on certain quality parameters of buffalo meat and patties were evaluated. The SPP, STPP and phosphate blends significantly increased pH, water-holding capacity (WHC), emulsifying capacity (EC), extractability of salt soluble proteins (SSP), colour of ground meat, decreased cooking loss (CL), improved emulsion stability (ES) and enhanced yield, texture and moisture retention of cooked patties. Compared to these phosphates, SAPP and SHMP had significantly poorer effects on improving the quality of meat and patties. The order of effectiveness of phosphates was SPP > STPP > SHMP. In general, pH, WHC, SSP, ES, yield and moisture content of patties increased progressively with increasing level of phosphate while CL decreased. Among blends containing two polyphosphates, those of 90% SPP + 10% SHMP and 75% SPP + 25% STPP were relatively more effective. A phosphate blend consisting of 65% SPP, 17·5% STPP and 17·5% SAPP was equally effective as that of SPP in improving the functionality of hot and chilled meat and had the advantage of reducing the amount of sodium by 3%.     

丁香酚对金黄色葡萄球菌抗菌作用的探究

为了寻找代替化学防腐剂的绿色安全天然添加剂,研究了丁香酚对金黄色葡萄球菌的抑菌作用。以丁香酚为原材料,采用96孔板微量稀释法和琼脂平板稀释法确定最低抑菌浓度（MIC）和最低杀菌浓度（MBC）,通过菌落数直观地确定丁香酚对金黄色葡萄球菌的MIC值和MBC值;并以分光光度计法探究不同质量浓度丁香酚对金黄色葡萄球菌中苹果酸脱氢酶（MDH）和琥珀酸脱氢酶（SDH）酶活性的影响。结果表明,丁香酚对金黄色葡萄球菌的最低抑制浓度（MIC）为600 μg/mL,最低杀菌浓度（MBC）为700 μg/mL,其可将金黄色葡萄球菌菌体蛋白质质量浓度、苹果酸脱氢酶（MDH）酶活、琥珀酸脱氢酶（SDH）酶活分别降至0.033 mg/mL、8.28 U/mg、2.40 U/mL,原因可能是抑制了菌体三羧酸循环和电子链传递中相关关键酶的活性。     

壳寡糖及其溴络合物的抗菌活性研究

采用培养基稀释法测定壳寡糖及其溴络合物的最小抑菌浓度（MIC）和最小杀菌浓度（MBC）,研究壳寡糖及其溴络合物的抗菌活性。结果表明,壳寡糖对大肠杆菌的MIC和MBC均为6.5 g/L;对白色念珠菌的MIC为4.0 g/L,MBC为8.0 g/L;对枯草芽孢杆菌的MIC和MBC均为1.5 g/L。壳寡糖溴络合物对大肠杆菌的MIC为1.0 g/L,MBC为1.2 g/L;对白色念珠菌的MIC为1.5 g/L,MBC为2.0 g/L;对枯草芽孢杆菌的MIC为1.0 g/L,MBC为1.5 g/L。与壳寡糖相比,壳寡糖溴络合物对大肠杆菌、白色念珠菌和枯草芽孢杆菌的抑菌效果更好。     

Resistance of Listeria monocytogenes F2365 cells to synthetic gastric fluid is greater following growth on ready-to-eat deli turkey meat than in brain heart infusion broth

Ready-to-eat (RTE) deli meats have been categorized as high-risk foods for contraction of foodborne listeriosis. Several recent listeriosis outbreaks have been associated with the consumption of RTE deli turkey meat. In this study, we examined whether the growth of Listeria monocytogenes F2365 on commercially prepared RTE deli turkey meat causes listerial cells to become more resistant to inactivation by synthetic gastric fluid (SGF). Listerial cells grown on turkey meat to late logarithmic-early stationary phase were significantly more resistant to SGF at pH 7.0, 5.0, or 3.5 than listerial cells grown in brain heart infusion (BHI) broth. The pH was lower in the fluid in packages of turkey meat than in BHI broth (6.5 versus 7.5). However, listerial cells grown in BHI broth adjusted to a lower pH (6.0) did not exhibit enhanced resistance to SGF. The lesser resistance to SGF of listerial cells grown in BHI broth may be due, in part, to the presence of glucose (0.2%). This study indicates the environment presented by the growth of L. monocytogenes on deli turkey meat affects its ability to survive conditions it encounters in the gastrointestinal tract.     

SENSITIVITY OF LISTERIA MONOCYTOGENES TO SPICES AT TWO TEMPERATURES

Thirteen spices were screened for growth inhibition effect against Listeria monocytogenes at 24°C using a concentration gradient plate method. Cloves, and oregano were the two most inhibitory spices with MIC values ranging from 0.5 to 0.7% (W/V). Inhibition was also detected with sage and rosemary (MIC of 0.7 to 1.0%) as well as nutmeg (MIC of 1.1–1.4%). Black pepper, chili, cinnamon, garlic, mustard, paprika, parsley and red pepper at a concentration up to 3.0% did not inhibit the growth of the organisms. The effect of cloves, oregano and sage on the growth and survival of L. monocytogenes Scott A was further tested in tryptic soy broth at both 4 and 24°C. At a concentration of 0.5 or 1.0%, cloves were bactericidal and oregano was bacteriostatic to this organism at both incubation temperatures. Sage at these two concentrations was bactericidal at 4°C and bacteriostatic at 24°C. When tested in sterile meat slurry, a 1.0% level of either cloves or oregano had little effect on the growth of L. monocytogenes Scott A at 4 or 24°C.     

Inhibition of Listeria monocytogenes by food antimicrobials applied singly and in combination

Abstract: Combining food antimicrobials can enhance inhibition of Listeria monocytogenes in ready-to-eat (RTE) meats. A broth dilution assay was used to compare the inhibition of L. monocytogenes resulting from exposure to nisin, acidic calcium sulfate, ɛ-poly-L-lysine, and lauric arginate ester applied singly and in combination. Minimum inhibitory concentrations (MICs) were the lowest concentrations of single antimicrobials producing inhibition following 24 h incubation at 35 °C. Minimum bactericidal concentrations (MBCs) were the lowest concentrations that decreased populations by ≥3.0 log₁₀ CFU/mL. Combinations of nisin with acidic calcium sulfate, nisin with lauric arginate ester, and ɛ-poly-L-lysine with acidic calcium sulfate were prepared using a checkerboard assay to determine optimal inhibitory combinations (OICs). Fractional inhibitory concentrations (FICs) were calculated from OICs and were used to create FIC indices (FIC_Is) and isobolograms to classify combinations as synergistic (FIC_I < 1.00), additive/indifferent (FIC_I= 1.00), or antagonistic (FIC_I > 1.00). MIC values for nisin ranged from 3.13 to 6.25 μg/g with MBC values at 6.25 μg/g for all strains except for Natl. Animal Disease Center (NADC) 2045. MIC values for ɛ-poly-L-lysine ranged from 6.25 to 12.50 μg/g with MBCs from 12.50 to 25.00 μg/g. Lauric arginate ester at 12.50 μg/g was the MIC and MBC for all strains; 12.50 mL/L was the MIC and MBC for acidic calcium sulfate. Combining nisin with acidic calcium sulfate synergistically inhibited L. monocytogenes; nisin with lauric arginate ester produced additive-type inhibition, while ɛ-poly-L-lysine with acidic calcium sulfate produced antagonistic-type inhibition. Applying nisin along with acidic calcium sulfate should be further investigated for efficacy on RTE meat surfaces. Practical Application: This study demonstrates the potential for combinations of antimicrobials to result in greater pathogen inhibition as compared to the application of a single antimicrobial. The data presented in this study can aid the food industry in developing more efficient and effective application of antimicrobials. These findings should also prompt further studies validating the inhibitory effect of combinations of antimicrobials on ready-to-eat surfaces.     

葡萄籽和苹果原花青素对变形链球菌和金黄色葡萄球菌的抑制作用

研究苹果原花青素和葡萄籽原花青素对变形链球菌(Streptococcus mutans)和金黄色葡萄球菌(Staphylococcus aureus)的抑制作用,采用试管液体稀释法和琼脂稀释法抑菌实验测定其最低抑菌质量浓度(MIC)和质量最低杀菌质量浓度(MBC),并通过测定培养基pH值的变化,研究葡萄籽原花青素对变形链球菌产酸能力的影响。结果表明：苹果原花青素、葡萄籽原花青素对变形链球菌和金黄色葡萄球菌生长都有抑制作用;苹果原花青素对变形链球菌的MIC和MBC分别为1.25、4.00mg/mL,葡萄籽原花青素对变形链球菌的MIC和MBC分别为1.75、2.00mg/mL;苹果原花青素对金黄色葡萄球菌的MIC和MBC分别为4.00、9.00mg/mL,葡萄籽原花青素对金黄色葡萄球菌的MIC和MBC分别为2.00、6.50mg/mL。葡萄籽原花青素质量浓度大于1.00mg/mL对变形链球菌的产酸能力有显著抑制效果。     

中草药提取液对桃果实采后致腐真菌抑制效应

为探讨甘草、高良姜、黄柏、北豆根、艾叶、连翘等6种中草药提取液对桃果实采后致腐真菌毛霉和青霉的抑制效果,采用生长速率法与活体果实接种孢子悬液法,对不同中草药提取液的抑菌效果进行对比,筛选出抑菌效果良好的中草药种类,并进一步通过体积浓度梯度稀释法,对其最小抑菌浓度(MIC)和最小杀菌浓度(MBC)进行了探讨。结果表明:不同中草药提取液对桃果实采后致腐真菌毛霉和青霉均有不同程度的抑制作用,其中甘草和连翘提取液的抑菌效果较强,黄柏和高良姜提取液的抑菌效果一般,艾叶和北豆根提取液的抑菌效果较弱。甘草和连翘提取液对毛霉的MIC均为培养液体积分数的25%、MBC均为培养液体积分数的50%;甘草和连翘提取液对青霉的MIC均为培养液体积分数的12.5%、MBC均为占培养液体积分数的25%。     

Evaluation of a Rapid Impedimetric Procedure for the Quantitative Estimation of Coliforms

A selective coliform medium (CM), developed for the impedimetric detection of coliforms, produced better impedance signals than conventional media. The selectivity of CM was better than that of lauryl tryptose broth (LTB) and violet red bile agar (VRBA). The applicability of CM to the quantitative impedimetric detection of coliforms in meat was tested and compared with most probable number and VRBA plate counts. Approximately 90% of the typical VRBA colonies did not produce gas when tested in brilliant green bile broth (BGB). Therefore, the VRBA counts were corrected by the percentage of colonies which produced gas in BGB for each sample. A correlation coefficient of 0.90 was obtained between the impedimetric test and corrected VRBA plate counts using a combined total of 91 meat samples tested by two different laboratories.     

CHARACTERIZATION OF AEROMONAS SPECIES ISOLATED FROM FOOD

Characterization of ten Aeromonas spp. isolates from local foods and A. hydrophila ATCC 7965, revealed that all strains of A. hydrophila, A. sobria and one strain of A. caviae showed strong hemolytic activity. All of them were protease producers except one A. caviae strain. Some A. hydrophila and A. caviae strains fermented lactose, coagulated milk and reduced litmus. The majority of strains were resistant to at least 5 of 14 antibiotics tested. All the strains grew over the range of 5–42C except those of A. caviae which failed to grow at 42C. Frozen storage at -16C greatly decreased the viability of the tested strains. Radiation D₁₀values of strains ranged from 0.109–0.253 kGy in nutrient broth and increased when some strains were irradiated in ground meat at room temperature. Both strains of A. hydrophila ( ATCC andFI ), A. sobria FI and A. caviae FI grew normally in the presence of 1 and 3% salt. Only A. hydrophila FI tolerated 6.5% salt. These four strains were able to grow in the presence of 0.05–0.3% potassium sorbate at pH 7.0, while at pH 5.0 the presence of sorbate prevented their growth .     

Physiological adaptation of Escherichia coli after transfer onto refrigerated ground meat and other solid matrices: A molecular approach

Bacteria on meat are subjected to specific living conditions that differ drastically from typical laboratory procedures in synthetic media. This study was undertaken to determine the behavior of bacteria when transferred from a rich-liquid medium to solid matrices, as is the case during microbial process validation. Escherichia coli cultured in Brain-Heart Infusion (BHI) broth to different growth phases were inoculated in ground beef (GB) and stored at 5°C for 12 days or spread onto BHI agar and cooked meat medium (CMM), and incubated at 37°C for several hours. We monitored cell densities and the expression of σ factors and genes under their control over time. The initial growth phase of the inoculum influenced growth resumption after transfer onto BHI agar and CMM. Whatever the solid matrix, bacteria adapted to their new environment and did not perceive stress immediately after inoculation. During this period, the σ(E) and σ(H) regulons were not activated and rpoD mRNA levels adjusted quickly. The rpoS and gadA mRNA levels did not increase after inoculation on solid surfaces and displayed normal growth-dependent modifications. After transfer onto GB, dnaK and groEL gene expression was affected more by the low temperature than by the composition of a meat environment.     

Effect of Nisin on the Outgrowth of Clostridium botulinum Spores

Nisin, an antibiotic produced by certain strains of Streptococcus lactis, is effective in preventing the outgrowth of Clostridium botulinum spores. Type A C. botulinum spores were the most resistant to the inhibitory action of nisin requiring 1000-2000 I.U. of nisin/ml for a 50% inhibition of outgrowth on TPYG agar plates. Type E spores were more sensitive requiring only 50-100 I.U./ml for 50% inhibition of outgrowth on TPYG agar plates. Type B spores displayed an intermediate level of sensitivity requiring 500-1000 I.U. of nisin/ml for 50% inhibition of outgrowth on TPYG agar plates. Similar levels of nisin were necessary to prevent spore outgrowth in TPYG broth and BHI broth over a 7-day incubation period. With prolonged incubation periods of up to 65 days in TPYG broth, spore outgrowth was observed sporadically at higher nisin levels with the type A and B spores which may indicate some decomposition of nisin with storage. Nisin levels of 5000 I.U./ml for the type A spores and 2000 I.U./ml for the type B spores and the Minnesota E spores were insufficient to prevent spore outgrowth by C. botulinurn in cooked meat medium. For the Beluga E spores, a nisin level of 2000 I.U./ml was necessary to prevent spore outgrowth in cooked meat medium. The need for higher levels of nisin in cooked medium to prevent spore outgrowth may be due to the binding of the nisin by meat particles.