Fatty acid dynamics of the adductor muscle of live cockles (Cerastoderma edule) during their shelf-life and its relevance for traceability of geographic origin

Cockles (Cerastoderma edule) are commercially important bivalves that support several fisheries in European waters. The fatty acid (FA) profile of the adductor muscle (AM) of freshly collected live cockles can be used to reliably confirm their geographic origin. This approach is paramount for traceability, expose fraud and ensure food safety. However, no study has ever addressed if the FA profile of the AM of live cockles remains stable during shelf-life, as significant shifts may blur FA signatures recorded at harvest. The present study investigated the FA dynamics of the AM of live cockles during their shelf-life (seven days post-harvest under a refrigerated environment). Fatty acid methyl esters were obtained after transesterification of lipid extracts and analyzed through gas chromatography–mass spectrometry (GC–MS). Results indicated that FA profiles remained stable until the third day post-harvest. After this period cockles started to exhibit contrasting FA profiles on their AM, namely a higher percentage of heptadecanoic acid (17:0). This FA is associated with the growth of pathogenic microorganisms responsible for food spoilage. In this way, the FA profile of the AM of live cockles can be used to reliably trace geographic origin up to three days post-harvest, as long as specimens are stored under refrigerated conditions during shelf-life.     

Determination of the shelf life of sardine (Sardina pilchardus) marinades in tomato sauce stored at 4 °C

In this study the shelf life of sardine marinades in tomato sauce was investigated. After the marination process, sardine fillets were packed into the glass jars with 2% acetic acid and 4% sodium chloride with tomato sauce and spices. The effect of pasteurization at 70 °C for 20 min on the shelf life of the sardine marinades was determinated. At the end of 6 months storage the differences between TBA, FA(free), FA(total) and pH value of pasteurized and non-pasteurizated marinades were not significantly (p > 0.05) different, while the difference between TVB-N, TMA-N, total plate count and lactic acid bacteria count of pasteurized and non-pasteurized marinades were significant (p < 0.05). Shelf life of pasteurized and non-pasteurized sardine marinades in tomato sauce was found to be 6 months at 4 °C.     

Influence of habituation to inorganic and organic acid conditions on the cytoplasmic membrane composition of Listeria monocytogenes

This study followed changes in the fatty acid (FA) composition of the membrane of Listeria monocytogenes habituated to organic acids known to induce resistance to acid and bile. Four human-pathogenic strains were separately grown in broth adjusted with HCl to pH 7.4 (baseline) or pH 6.0 (pH control) or broth at pH 6.0 containing 4.75 mM of L-lactic, levulinic or acetic acid. Membrane FAs were extracted from log phase cells and identified using GCMS. Habituation at pH 6.0 versus pH 7.4 decreased (P < 0.01) levels of four of five detected straight chain FAs, while levels of five of six branched chain FAs (BCFAs) increased leading to lowered FA ratios of anteiso:iso and C15:C17. Habituation in organic acids versus the pH control increased levels of most BCFAs and decreased levels of 15-carbon FAs leading to further reduction in the C15:C17 ratio. Those overall effects on membrane composition were largely mirrored in the individual strains known to develop variable resistance to acid and bile in response to habituation in the organic acids. Taken together, these observations suggest exposure of L. monocytogenes to organic acids induces resistance to acid and bile both through generalized changes in membrane composition plus other not-yet identified mechanisms.     

Combined effects of slightly acidic electrolyzed water and fumaric acid on the reduction of foodborne pathogens and shelf life extension of fresh pork

This study evaluated the efficacy of the individual treatments (slightly acidic electrolyzed water [SAcEW] or fumaric acid [FA]) and their combination to reduce Escherichia coli O157:H7, Listeria monocytogenes, Staphylococcus aureus, and Salmonella Typhimurium in fresh pork as well as to study the shelf life and sensory quality (color, odor, and texture) of pork during storage at 4 and 10 °C. The inoculated pork samples (10 g) were dipped for 3 min in each treatment (tap water [TW], SAcEW, strong acidic electrolyzed water [StAEW], 0.5% FA, or SAcEW + 0.5% FA) with or without mild heat (40 °C). Decontamination of fresh pork with SAcEW +0.5% FA at 40 °C for 3 min showed greater bactericidal effect compared to other treatments, which significantly (P < 0.05) reduced E. coli O157:H7, L. monocytogenes, S. aureus, and S. Typhimurium by 2.59, 2.69, 2.38, and 2.99 log CFU/g, respectively. This combined treatment significantly (P < 0.05) yielded in a longer lag time of naturally occurring bacteria (TBC) on pork stored at 4 °C. This combined treatment also prolonged the shelf life of pork up to 6 days and 4–5 days when stored at 4 °C and 10 °C, respectively, compared to those of the untreated pork. The results suggest that the combined treatment of SAcEW + 0.5% FA has potential as a novel method to enhance the microbial safety and quality of fresh pork.     

Inactivation of Escherichia coli O157:H7 during cooking of non-intact beef treated with tenderization/marination and flavoring ingredients

This study examined the effect of tenderizing/marinating and flavoring ingredients on thermal inactivation of Escherichia coli O157:H7 in a lean ground beef model system, simulating non-intact products. Ground beef (3% fat) was inoculated with E. coli O157:H7 (5 strains; 6–7 log CFU/g), followed by mixing with nothing (control) or solutions of water, a mixture of flavoring agents (FA), 0.23% calcium chloride (CC) + FA, CC + FA + 0.3% acetic acid (AA), 0.5% sodium chloride (NaCl) + 0.25% sodium tripolyphosphate (STP), NaCl + STP + FA, NaCl + STP + 1.8% potassium lactate (PL), NaCl + STP + PL + FA, NaCl + STP + PL + AA, and NaCl + STP + PL + AA + FA. Samples (30 g) were extruded into tubes, stored (4 °C) overnight, and cooked to 60 °C (rare) or 65 °C (medium-rare) in a water bath. Cooking weight losses, and fat and moisture contents, water activity, pH, and total bacterial and E. coli O157:H7 populations were determined after inoculation, after storage, and after heating. Reductions of the pathogen at 60 °C in acid (AA)-treated samples were higher than reductions obtained in samples not treated with acid. Surviving pathogen counts at 65 °C in NaCl and STP-treated samples with no acid were higher (P < 0.05) than those of samples of all other tested treatments; however, the counts decreased to 0.7–1.6 log CFU/g when AA was added. Overall, the results of the study indicate that tenderizing/flavoring ingredient formulations combined with 0.3% AA (i.e., CC + FA + AA, NaCl + STP + PL + AA, and NaCl + STP + PL + AA + FA) enhanced destruction of E. coli O157:H7 during cooking of a non-intact beef product.     

Frequency of contamination and antimicrobial resistance of thermotolerant Campylobacter isolated from some broiler farms and slaughterhouses in the region of Algiers

Campylobacteriosis in humans is caused by thermotolerant Campylobacter spp, following consumption of contaminated poultry, most commonly broiler.The aim of this study was to assess the frequency of contamination by thermotolerant Campylobacter and to characterize antimicrobial resistance of the strains isolated from broilers in some farms and slaughterhouses in the region of Algiers.One hundred droppings samples, 100 contents of ceaca and 100 neck skins were taken from six poultry farms and five slaughterhouses, than analyzed according to NF. ISO 10272-1/1995 norm and the OIE recommendations. Susceptibility to antibiotics was determined according to the guidelines of the CA-SFM/2010 by disc diffusion method.Thermotolerant Campylobacter strains were isolated from 85%, 98%, and 80% of droppings, caecal content and neck skin, respectively. All the strains (100%) were resistant to nalidixic acid and sensitive to gentamicin and to chloramphenicol. 83.7% of them were resistant to tetracycline and to ciprofloxacin, 75.3% to ampicillin, 46.8% to amoxicillin/clavulanic acid and 21.7% were resistant to erythromycin. All the isolates showed a multi-drug resistance. Nineteen different profiles were identified with “AM, AMC, NA, CIP, TE” combination as the most common profile identified for 27% (n = 74) of isolated strains. In addition, 15% of the strains were resistant to both erythromycin and ciprofloxacin, which are systematically used in treatment of human Campylobacter infections.Our results showed a high prevalence of thermotolerant Campylobacter with multidrug resistance profiles in poultry farms and slaughterhouses of Algiers. These results stress that the risk of human contamination throughout the food chain is very high, which may generate: i) a danger of food poisoning by ingestion of chicken meat and chicken meat products and, ii) a cross-resistance to antibiotics between human and avian strains.     

Tracing the food sources of isolated strains of Listeria monocytogenes through fatty acid profiles analysis

Listeria monocytogenes widely exists in different kinds of food. L. monocytogenes infection could induce to a highly fatality ratio up to 30–50%. The objection of this study is to provide a new way to trace the food sources of isolated strains of L. monocytogenes when a foodborne poisoning of L. monocytogenes breaking up. In this paper, the whole-cell fatty acid profiles for the 22 strains were detected by the microorganism identification system (MIS). Results showed that the major fatty acid components of L. monocytogenes were branched acids: anteiso C_15:0, anteiso C_17:0, iso C_15:0, iso C_17:0, iso C_16:0, iso C_14:0, saturated chain C_16:0 and C_14:0 and hydroxy acid C_8:0 3OH. Based on the fatty acid profiles, 22 L. monocytogenes strains were statistically clustered into three major subgroups, which were highly relative to their food sources. Strains in the same cluster were isolated from the same food source, while strains in different clusters were isolated from different food sources.     

Occurrence,antimicrobial resistance and biofilm formation of Salmonella isolates from a chicken slaughter plant in China

An investigation was undertaken to determine the occurrence, antibiotic resistance and biofilm formation of Salmonella spp. isolated from a chicken slaughter plant in Anhui, China. A total of 104 samples (52 from chicken carcasses and 52 from processing contact-surfaces) were collected from three processing points in a chicken slaughterhouse. The 23 isolates (22.1%, 23/104) were confirmed for Salmonella and belonged to six different serotypes, including S. Indiana (n = 9), S. Infantis (n = 4), S. Derby (n = 3), S. Heidelberg (n = 2), S. Agona (n = 2) and S. Typhimurium (n = 1), whereas two isolates (n = 2) were non-typable. Significant differences in occurrence were found between post-evisceration, post-chilling and post-grading processing points. A total of 20 (87%, 20/23) isolates were resistant to at least one antibiotic, of which 19 isolates (95%, 19/20) showed 13 multiple antibiotic resistance patterns against 11 different antibiotics. Resistance to ampicillin (78.3%, 18/23) was the most common. The multiple antibiotic resistance (MAR) index varied from 0.27 to 0.91. The Salmonella isolates from the chicken plant and from humans in the same area who were suffering Salmonella infections showed similar antimicrobial resistance patterns, namely resistance to ampicillin, trimethoprim/sulfamethoxazole, gentamicin, chloramphenicol and tretracycline, and abbreviated as “ATsGCT”. Meanwhile, Salmonella isolates exhibited variation in biofilm-forming behavior with regards to the incubation media and serotypes, a relatively high biofilm production was observed for S. Agona incubated in MTLB (meat thawing-loss broth) at 72 h. There was no significant correlation between antimicrobial resistance and biofilm formation of isolates. Our findings provide baseline information on the distribution of Salmonella serovars in this plant, and provide support to the need for improved farming practice and for more prudent use of antimicrobial agents.     

The Synthesis and Characterization of Methacrylic Acid Ester-maleic Anhydride Copolymer as a Lube Oil Pour Point Depressant

Abstract

The authors synthesized methacrylic acid ester (AE) monomers by direct esterification of methacrylic acid and fatty alcohols using paratoluenesulfonic acid as catalyst, hydroquinone as polymerization inhibitor, and toluene as solvent. Then, methacrylic acid ester-maleic anhydride (AM) copolymers were prepared by solution free radical copolymerization with benzoyl peroxide as initiator. The structures of the monomer and copolymer were confirmed by IR. Differential scanning calorimetry (DSC) was selected as the research method to investigate the wax formation process in the lube oils without and with adding AM. The results show that it possess the best solidification point depression (ΔSP) when the molar ratio of the reaction materials is 3:1 and the polydispersity is 1.81. It can execute a maximum depression of solidification point (SP) of the tested lube oils by 29, 21, and 20°C, respectively. The AM additive has little effect on the total amount of wax, but just shift the precipitation toward lower temperature.     

Antibacterial activity of lactic acid bacteria against spoilage and pathogenic bacteria isolated from the same meat small-scale facility: 1—Screening and characterization of the antibacterial compounds

A total of 87 lactic acid bacteria (LAB) (36 Lactobacillus sakei, 22 Enterococcus faecium, 16 Lactococcus garvieae, 11 Vagococcus carniphilus and 2 Enterococcus sp.) isolated from a small-scale facility producing traditional dry sausages were screened for antagonistic activity against other LAB and some spoilage and pathogenic microorganisms, also isolated from the same processing facility, except Listeria innocua (in lieu of Listeria monocytogenes) and Escherichia coli. The final goal was to investigate LAB antibacterial activity within the facility microbial ecosystem and to select interesting strains for the role of bio-preservatives.Twenty-one Ec. faecium, 6 Vc. carniphilus, 4 Lc. garvieae, 3 Lb. sakei and 2 Enterococcus sp. were shown to inhibit the growth of some indicator microorganisms in an agar well diffusion assay. Except 2 Lb. sakei and an Enterococcus sp., all these isolates exhibited antibacterial activity against L. innocua, but only 3 Ec. faecium, 5 Vc. carniphilus and 3 Lc. garvieae displayed also antagonistic activity against Staphylococcus aureus. The 5 Vc. carniphilus isolates were also found to be inhibitory for the Gram-negative bacterium Hafnia alvei.Isolates displaying antibacterial activity against L. innocua and/or Sc. aureus were investigated for the nature of antibacterial compounds synthesized against these indicator microorganisms. Bacteriocin-like production could be detected only on agar plated in overlay assays, and was unsuccessfully researched in cell-free culture supernatant fluids under conditions that eliminate acid and hydrogen peroxide inhibition. Results also showed that a Lb. sakei isolate displayed an additional inhibitory effect by H₂O₂ against L. innocua. These isolates will be investigated for their ability to repress the growth of undesirable bacteria in biofilms, i.e., the real mode of bacterial attachment.This is the first report on bacteriocin-like from Vc. carniphilus and on bacteriocin-like from Lc. garvieae active against both L. innocua and Sc. aureus species.     

Hydrogen peroxide oxidation of 2-cyanoethanol catalyzed by metal complexes

Oxidation of 2-cyanoethanol, a relatively inert primary alcohol, with several systems (both homogeneous and heterogenized) based on transition metal complexes was studied. The oxidation was performed under homogeneous conditions with 35% hydrogen peroxide upon catalysis by the chlorides FeCl₃ or OsCl₃. The best result was obtained upon the oxidation catalyzed by OsCl₃ at 70°C for 3 h in the absence of solvent: the total yield of the corresponding aldehyde and cyanoacetic acid reached 90%, and the turnover number was 1500. The systems [LMn^IV(O)₃Mn^IVL]_n(X)_m-oxalic acid (where L = 1,4,7-trimethyl-1,4,7-triazacyclononane) also catalyze oxidation of 2-cyanoethanol with yields of 50–70% either under homogeneous conditions (X = PF^? ₆, n = 1, and m = 2) or with the use of the catalyst in the heterogenized form (as insoluble heteropoly acid salt), where X = W₁₂SiO^4? ₄₀, n = 2, and m = 1.     

The influence of organic additives on the regioselectivity of oxygenation of alkanes with hydrogen peroxide in the presence of TS-1titanium silicalite

Hydrogen peroxide oxidizes n-hexane, n-heptane, and n-octane at 50°C in the presence titanium silicalite TS-1 as a catalyst, forming isomeric mixtures of ketones and alcohols. Admixtures of organic acids, alcohols, benzene, and ethylbenzene sharply change the ratio of position isomers. For example, the normalized ratio is C(4): C(3): C(2) = 0.44: 1.0: 0.47 for n-heptane oxidation in the absence of additives, but it becomes 0.52: 1.0: 1.00 in the presence of benzyl alcohol and the addition of ethylbenzene changes it to 0.16: 1.0: 0.94.     

丙烯酰胺/2-丙烯酰胺基-2-甲基丙磺酸共聚物的合成与评价

采用水溶液聚合法制备了丙烯酰胺(AM)/2-丙烯酰胺基-2-甲基丙磺酸(AMPS)二元共聚物。最佳合成条件为:总单体质量分数为20%,单体配比n(AM):n(AMPS)为6:4,初始反应温度19℃(反应4 h),后期恒温反应温度为40℃(反应2 h),引发剂用量为153.2 mg/L,pH=7～8,真空75℃烘干3～4 h。结果表明,共聚物在胶凝酸中的剪切粘度为71.290 mPa·s     

Genesis of biomarker hydrocarbons in the environment and their role in assessing an oil pollution source

Oil spills are classified according to chemical types that reflect qualitative and quantitative changes in petroleum composition during biodegradation in soil. Possible trends in composition of biomarker petroleum hydrocarbons in polluted soil, as determined by natural and climatic conditions and by activation of soil micro-flora, were revealed. It was shown that the use of selective bioremediation methods could lead to a noticeable redistribution of the relative amount of C₂₇:C₂₈:C₂₉ steranes in marine crude oils owing to more intense degradation of C₂₇ steranes (5α, 14β, 17β, 20R and 20S, as well as 5α, 14α, 17α, 20R and 20S) as compared with their higher C₂₉ homologues. The observed changes in the composition of steranes suggest another, namely, terrigenous origin of petroleum, and, thus, may lead to an erroneous conclusion concerning the genotype of crude oil as a pollution source. It was found that hopane hydrocarbons are highly stable under similar conditions. It was shown that the set of biomarker hydrocarbons might be useful as biological indicators in the assessment of a petroleum pollution source.     

Modeling of formation of petroleum biomarker hydrocarbons by thermolysis and thermocatalysis of bacterium biomass

Thermolysis and thermocatalysis of the insoluble part of chemoorganoheterotrophic aerobic bacteria Arthrobacter sp. RV and Pseudomonas aeruginosa RM have been performed. The thermolyzates and thermocatalyzates of these bacteria contain the hydrocarbon biomarkers n-alkanes, isoprenanes, steranes, and terpanes. Of n-alkanes, the C₉-C₃₅ hydrocarbons with unimodal distribution formed in the products of or C₉-C₃₉ n-alkanes with bimodal distribution are produced by thermolysis or thermocatalysis, respectively. n-Alkanes with odd number of carbon atoms in the molecule prevail over the even counterparts (n-C₉, n-C₁₁, n-C₁₅, and n-C₁₇) in the thermolysis products of both strains, whereas n-alkanes with even number of carbon atoms (n-C₁₆, n-C₁₈, and n-C₂₀) dominate in the thermocatalyzates. Isoprenanes of the C₁₃-C₂₀ composition are generated. It is noteworthy that regular C₁₇ isoprenane has been found for the first time among isoprenanes. The cyclic biomarker hydrocarbon steranes and terpanes are simultaneously generated, with the distribution of C₂₇-C₂₉ regular steranes resembles that in marine oils generated in argillaceous strata. At the same time, the adiantane to hopane ratio (H₂₉/H₃₀) is characteristic of the organic matter generated in carbonate strata.     

The formation of petroleum biomarker hydrocarbons from possible oxygen-containing precursors

Some possible oxygen-containing precursors of petroleum hydrocarbons were subjected to mild thermolysis. It has been first shown that n-alkylcyclohexanes and steranes are formed along with the expected hydrocarbons n-alkanes and isoprenanes, which result from the loss of a functional group, and there is good correlation between the molecular-mass distributions of n-alkanes and n-alkylcyclohexanes. It has been found experimentally that sterane fragments of oxygen-containing compounds are thermodynamically unstable, and this is confirmed by the formation of biological C₂₇–C₂₉ 5α,14α,17α,20S- and 20R-, and 5β,14α,17α,20R-(coprostane) steranes as a result of thermolysis.     

Microbiological quality and safety of minimally processed fruits in the marketplace of southern Portugal

The availability of fresh-cut fruit (FCF) in the marketplace has been increasing in Portugal, although reports of its microbial quality are not known. Due to the growing concerns of these commodities over their microbial safety, the objectives of this work were to study the microbiological quality and prevalence of Salmonella and Listeria monocytogenes on fresh-cut fruits sold in southern Portugal. A study to examine the changes in pH and microbial counts, before and after the expiration dates, was also made. A total of 160 samples was purchased in the local grocery stores between September 2011 and August 2014, before their sell-by date. These samples were assayed for aerobic mesophilic (AM) and psychrotrophic (AP) microorganisms, yeasts and molds (YM), lactic-acid bacteria (LAB), coliforms (TC), Escherichia coli and coagulase positive staphylococci as well as L. monocytogenes and Salmonella. The microbiological counts ranged from 3.0-9.2 lg cfu/g (AM); 2.2–10.7 lg cfu/g (AP); 2.3–10.4 lg cfu/g (YM); 1.9–9.0 lg cfu/g (LAB) and less than 1–9.1 lg cfu/g (TC). The melons and watermelon presented the highest levels of the microbial quality parameters studied. However, no E. coli, staphylococci, Salmonella and L. monocytogenes were detected in any of the samples. After the sell-by date, an increase of the AM, AP, LAB and YM values was observed in all fruits. Conversely, the differences found in TC counts before and after the best-before date had no statistical significance. A decrease in pH was observed in all fruits except pineapple whose pH slightly increased after 14 days of storage. The results highlight the importance of preventing contamination and cross contamination, selecting adequate decontamination technologies and maintaining a strict temperature control during processing, distribution and selling of FCF.     

聚乙二醇二丙烯酸酯交联共聚型酸液稠化剂的合成

 以丙烯酰胺(AM)和2-丙烯酰胺基-2-甲基丙烷磺酸(AMPS)为主要单体，以聚乙二醇二丙烯酸酯(PEGDA)为扩链剂，研制了一种注酸时稠化能力强、返排时黏度低的新型酸液稠化剂。通过正交试验，确定了合成AM-AMPS二元共聚物的最优条件为：AM/AMPS的摩尔比为7/3，单体的质量分数为20%，引发剂的加量为125mg/l，引发温度为15℃。在聚合过程中，加入占AM和AMPS单体质量分数7.5×10-6的PEGDA，增粘能力可提高近1倍。酸化过程中，由于PEGDA中的酯基断裂，稠化酸的黏度降低，有利于残酸返排。     

Influence of Pt nanoparticles modified by La and Ce oxides on catalytic dehydrocyclization of n-alkanes

Catalytic reforming accounts for a large share of the world’s gasoline production, it is the most important source of aromatics for the petrochemical industry. In addition, reforming of hydrocarbon on the dual-function catalysts has been found to form fundamentally different products in hydrogen diluents. Typical catalysts employed for this reforming process are Pt/Al₂O₃ and Pt-M/Al₂O₃, M being the promoter. These solids are characterized by both acid and metal functions which catalyze dehydrocyclization, dehydrogenation, isomerization and cracking processes. In this regard, information about cerium and lanthanum, as promoters, is hardly revealed. The present work aims to study the performance of Pt/Al₂O₃ catalysts modified by lanthanum or cerium during the conversion of cyclohexane, n-hexane and n-heptane. Catalytic activities of the prepared catalysts were tested using a micro catalytic pulse technique. Physicochemical characterization of the solid catalysts such as, surface area (S_BET), Fourier transform infrared (FTIR), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), hydrogen-temperature programed reduction (H₂-TPR), hydrogen-temperature-programed desorption (H₂-TPD), CO₂-TPD, NH₃-TPD, high resolution transmission electron microscopy (HRTEM) and X-ray diffraction (XRD) were depicted. Results indicated clearly that Pt/Al₂O₃ catalyst is selective toward dehydrogenation to benzene which could be explained as due to the decrease in the active acid sites and the comparative segregation of the alumina support especially at 3% load of CeO. The presence of La₂O₃ in the Pt/Al₂O₃ catalyst promotes aromatization of n-hexane and n-heptane, also the dehydrocyclization of n-hexane is more difficult than that of n-heptane. Thus, modification of the Pt/Al₂O₃ catalyst by La, resulted in a more active and selective reforming catalyst.     

Antimicrobial activity of malic acid against Listeria monocytogenes,Salmonella Enteritidis and Escherichia coli O157:H7 in apple,pear and melon juices

Minimal inhibitory (MIC) and minimal bactericidal (MBC) concentrations of malic acid against Listeria monocytogenes, Salmonella Enteritidis and Escherichia coli O157:H7 inoculated in apple, pear and melon juices stored at 5, 20 and 35 °C were evaluated. MICs and MBCs against L. monocytogenes, S. Enteritidis and E. coli O157:H7 were significantly affected by storage temperature, juice characteristics and type of microorganism. Malic acid was more effective at 35 and 20 °C than at 5 °C in all studied fruit juices. E. coli O157:H7 was more resistant to malic acid than S. Enteritidis and L. monocytogenes. Apple, pear and melon juices without malic acid were inhibitory to E. coli O157:H7, S. Enteritidis and L. monocytogenes at 5 °C, whereas, MBCs of 1.5% (v/v) of malic acid in apple and pear juices, and 2% (v/v) in melon juice at 5 °C were needed to reduce E. coli O157:H7, those concentrations being higher than those required to reduce S. Enteritidis and L. monocytogenes in those fruit juices. In addition, concentrations of 2%, 2.5% and 2.5% (v/v) of malic acid added to apple, pear and melon juices, respectively, were required to inactivate the three pathogens by more than 5 log cycles after 24 h of storage at 5 °C. Transmission electron microscopy showed that malic acid produced damage in the cell cytoplasm of pathogens without apparent changes in the cell membrane.