Antimicrobial activity of essential oils on Salmonella enteritidis, Escherichia coli, and Listeria innocua in fruit juices

The antimicrobial properties of essential oils (EOs) and their derivatives have been known for years. However, the information published about the minimal effective concentration of EOs against microorganisms in fruit juices is scarce. In this study, both MIC and MBC of six EOs (lemongrass, cinnamon, geraniol, palmarosa, or benzaldehyde) against Salmonella Enteritidis, Escherichia coli, and Listeria innocua were determined by the agar and broth dilution methods, respectively. All of the six EOs inhibited the microbial (Salmonella Enteritidis, E. coli, and L. innocua) growth at a concentration from 1 microl/ ml (MIC). These studies led to choosing the three most effective EOs. Lemongrass, cinnamon, and geraniol were found to be most effective in inhibiting the growth of the microorganisms and thus were used for the MBC analysis. On this last point, significant differences (P < 0.05) among EOs, their concentrations, and culture media (apple, pear, and melon juices, or tryptone soy broth medium) were found after comparing the results on MBC for each microorganism. A concentration of 2 microl/ml from lemongrass, cinnamon, or geraniol was enough to inactivate Salmonella Enteritidis, E. coli, and L. innocua in apple and pear juices. However, in melon juice and tryptone soy broth medium, concentrations of 8 and 10 microl/ml from cinnamon, respectively, or 6 microl/ml from geraniol were necessary to eliminate the three microorganisms, whereas lemongrass required only 5 micro/ml to inactivate them. These results suggest that EOs represent a good alternative to eliminate microorganisms that can be a hazard for the consumer in unpasteurized fruit juices. The present study contributes to the knowledge of MBC of EOs against pathogenic bacteria on fruit juices.     

High-pressure resistance variation of Escherichia coli O157:H7 strains and Salmonella serovars in tryptic soy broth, distilled water, and fruit juice

The effect of high pressure on the log reduction of six strains of Escherichia coli O157:H7 and five serovars of Salmonella enterica was investigated in tryptic soy broth, sterile distilled water, and commercially sterile orange juice (for Salmonella) and apple cider (for E. coli). Samples were subjected to high-pressure processing treatment at 300 and 550 MPa for 2 min at 6 degrees C. Samples were plated onto tryptic soy agar directly after pressurization and after being held for 24 h at 4 degrees C. At 300 MPa, little effect was seen on E. coli O157:H7 strains, while Salmonella serovars varied in resistance, showing reductions between 0.26 and 3.95 log CFU/ml. At 550 MPa, E. coli O157:H7 strains exhibited a range of reductions (0.28 to 4.39 log CFU/ml), while most Salmonella populations decreased beyond the detection limit (> 5-log CFU/ml reduction). The most resistant strains tested were E. coli E009 and Salmonella Agona. Generally, bacterial populations in fruit juices showed larger decreases than did populations in tryptic soy broth and distilled water. E. coli O157:H7 cultures held for 24 h at 4 degrees C after treatment at 550 MPa showed a significant log decrease as compared with cultures directly after treatment (P < or = 0.05), while Salmonella serovars did not show this significant decrease (P > 0.05). All Salmonella serovars tested in orange juice treated at 550 MPa for 2 min at 6 degrees C and held for 24 h showed a > 5-log decrease, while E. coli O157:H7 strains require a higher pressure, higher temperature, longer pressurization, or a chemical additive to achieve a 5-log decrease.     

Proteolytic fungi isolated from decayed and damaged raw tomatoes and implications associated with changes in pericarp pH favorable for survival and growth of foodborne pathogens

Raw and minimally processed high-acid fruits and vegetables are considered to be at low or no risk for supporting growth of foodborne pathogens. The potential increase in the pH of tissues as a result of fungal growth, however, may enhance the potential for survival and growth. We examined 77 decayed and 138 damaged, raw, ripe tomatoes for the presence of yeasts and molds that produce proteolytic enzymes and other metabolites that can potentially increase the pH of pulp tissue. The pH of decayed and sound radial pericarp tissues (pulp) of decayed tomatoes ranged from 4.7 to 7.8 (mean = 6.2) and 4.3 to 5.8 (mean = 5.0), respectively, whereas the pH of damaged and sound pericarp of damaged tomatoes ranged from 4.2 to 7.8 (mean = 5.2) and 4.2 to 8.0 (mean = 4.9), respectively. The pH of sound pericarp of 8.5% of decayed tomatoes and 3.4% of damaged tomatoes, respectively, was > 5.41. In contrast, the pH of 70% of the decayed tissue and 18% of the damaged tissue was > 5.41. Fungal isolates (n = 371) recovered from decayed and damaged tomatoes on dichloran rose bengal chloramphenicol agar were examined for proteolytic activity on gelatin agar and standard methods caseinate agar. One hundred eight (29%) of the isolates exhibited proteolytic activity on one or both differential media; 96 (89%) were molds, and 12 (11%) were yeasts. The pH of both media increased at the edge of proteolytic fungal colonies. Growth of proteolytic isolates from decayed tomatoes on tomato juice agar (pH = 4.3) and on the surface of tomato juice (pH = 4.1) caused an increase in mean pH values at the colony/medium interface to 7.2 and 6.4, respectively. Results show that some fungi capable of infecting raw tomatoes, as well as the mycoflora incident on tomato surfaces, can increase the pH of pericarp and juice to levels favorable for growth of most foodborne pathogenic bacteria.     

腐败发酵蔬菜中产膜醭细菌的分离鉴定及其生长特性分析

以发酵蔬菜为研究对象,分离和鉴定其中形成腐败膜醭的主要微生物,并分析其生长特性。利用胰蛋白胨大豆琼脂培养基分离培养发酵蔬菜腐败膜醭中的微生物,挑取50株单克隆回接到发酵盐卤胰蛋白胨培养基中培养,将能够在培养液表面显著形成膜醭的菌株进行16S rDNA或18S rDNA分子生物学鉴定。结果表明这6株菌均为细菌,分别为枯草芽孢杆菌、弗氏柠檬酸杆菌、科氏葡萄球菌科氏亚种、普罗威登斯菌、克雷伯氏杆菌属和阴沟肠杆菌。利用5种发酵蔬菜模拟培养基培养上述6株细菌,发现不同菌株在不同培养基中产膜醭情况不同。枯草芽孢杆菌和科氏葡萄球菌科氏亚种除了能形成膜醭外,还能引起培养基pH值升高,并对氮源需求不高。克雷伯氏杆菌属和普罗威登斯菌仅在发酵盐卤胰蛋白胨培养基和发酵蔬菜汁胰蛋白胨培养基中形成膜醭。上述细菌可能是发酵蔬菜腐败膜醭形成的关键细菌和潜在威胁。     

In vitro antifungal activity of several antimicrobial compounds against Penicillium expansum

Fungicides used in the prevention and control of mold rots in stored apples are subjected to legal, social, and biological limitations. The aim of this study was to find an alternative to postharvest fungicides currently used in the prevention and control of blue mold rot caused by Penicillium expansum in apples. For this purpose, the antimicrobial activity and MIC of several substances against P. expansum were evaluated in vitro using different end point methods: agar diffusion assay, volatility method, and agar dilution and broth dilution MIC assays. Most of the substances tested are common food ingredients and have a recognized antimicrobial activity. Essential oils, such as thymol, eugenol, citral and cineole, vanillin, sodium hypochlorite, acetic acid, potassium sorbate, and hydrogen peroxide, were the substances evaluated. Thymol and citral were the essential oil components that showed the greatest inhibitory effects. The effectiveness of 5 and 10% hydrogen peroxide in growth inhibition of P. expansum in the agar diffusion assay was total, and its MIC as determined by the agar and broth dilution assays was less than 0.025%. These results indicate that the application of small quantities of hydrogen peroxide to the apple skin might be an alternative to fungicides in the elimination of P. expansum.     

Survival of Escherichia coli O157:H7 and Salmonella in apple cider and orange juice as affected by ozone and treatment temperature

Inactivation of Escherichia coli O157:H7 and Salmonella in apple cider and orange juice treated with ozone was evaluated. A five-strain mixture of E. coli O157:H7 or a five-serovar mixture of Salmonella was inoculated (7 log CFU/ml) into apple cider and orange juice. Ozone (0.9 g/h) was pumped into juices maintained at 4 degrees C, ambient temperature (approximately 20 degrees C), and 50 degrees C for up to 240 min, depending on organism, juice, and treatment temperature. Samples were withdrawn, diluted in 0.1% peptone water, and surface plated onto recovery media. Recovery of E. coli O157:H7 was compared on tryptic soy agar (TSA), sorbitol MacConkey agar, hemorrhagic coli agar, and modified eosin methylene blue agar; recovery of Salmonella was compared on TSA, bismuth sulfite agar, and xylose lysine tergitol 4 (XLT4) agar. After treatment at 50 degrees C, E. coli O157:H7 populations were undetectable (limit of 1.0 log CFU/ml; a minimum 6.0-log CFU/ml reduction) after 45 min in apple cider and 75 min in orange juice. At 50 degrees C, Salmonella was reduced by 4.8 log CFU/ml (apple cider) and was undetectable in orange juice after 15 min. E. coli O157:H7 at 4 degrees C was reduced by 4.8 log CFU/ml in apple cider and by 5.4 log CFU/ml in orange juice. Salmonella was reduced by 4.5 log CFU/ml (apple cider) and 4.2 log CFU/ml (orange juice) at 4 degrees C. Treatment at ambient temperature resulted in population reductions of less than 5.0 log CFU/ml. Recovery of E. coli O157:H7 and Salmonella on selective media was substantially lower than recovery on TSA, indicating development of sublethal injury. Ozone treatment of apple cider and orange juice at 4 degrees C or in combination with mild heating (50 degrees C) may provide an alternative to thermal pasteurization for reduction of E. coli O157:H7 and Salmonella in apple cider and orange juice.     

Attraction of a free-living nematode, Caenorhabditis elegans, to foodborne pathogenic bacteria and its potential as a vector of Salmonella poona for preharvest contamination of cantaloupe

Caenorhabditis elegans was studied to determine the potential role of free-living microbivorous nematodes as vectors for preharvest contamination of fruits and vegetables with foodborne pathogens. The propensity of C. elegans to be attracted to seven strains of Escherichia coli O157:H7, eight serotypes of Salmonella, six strains of Listeria monocytogenes, and cantaloupe juice was investigated. Twenty to 30 adult worms were placed on the surface of K agar midway between a 24-h bacterial colony and 10 microl of uninoculated tryptic soy broth (TSB) or cantaloupe juice positioned 1.5 cm apart. The numbers of nematodes that migrated to the colony, to the TSB, and to the cantaloupe juice within 5, 10, 15, and 20 min at 21 degrees C were determined, and then the plates were incubated at 37 degrees C for up to 7 days to determine the ability of C. elegans to survive and reproduce in bacterial colonies. The nematode was attracted to colonies of all test pathogens and survived and reproduced within colonies for up to 7 days. C. elegans was not attracted to cantaloupe juice. The potential of C. elegans to serve as a vector for the transport of Salmonella Poona to cantaloupe rinds was investigated. Adult worms that had been immersed in a suspension of Salmonella Poona were deposited 1 or 3 cm below the surface of soil on which a piece of cantaloupe rind was placed. The rind was analyzed for the presence of Salmonella Poona after 1, 3, 7, and 10 days at 21 degrees C. The presence of Salmonella Poona was evident more quickly on rinds positioned on soil beneath which C. elegans inoculated with Salmonella Poona was initially deposited than on rinds positioned on soil beneath which Salmonella Poona alone was deposited. The time required to detect Salmonella Poona on rinds was longer when the rind was placed 3 cm above the inoculum than when the rind was placed 1 cm above the inoculum. Free-living nematodes may play a role in the preharvest dispersal of incidental human pathogens in soil to the surfaces of raw fruits and vegetables in contact with soil during development and maturation, as evidenced by the behavior of C. elegans as a test model.     

Inactivation of Salmonella typhimurium and Escherichia coli O157:H7 in apple juice by a combination of nisin and cinnamon

Pasteurized apple juice with nisin (0, 25, 50, 100, and 200 ppm, wt/vol) and cinnamon (0 and 0.3%, wt/vol) was inoculated with Salmonella Typhimurium and Escherichia coli O157:H7 at 10(4) CFU/ml and stored at 5 and 20 degrees C. Counts on tryptic soy agar (TSA), selective medium (xylose Lysine desoxycholate agar for Salmonella Typhimurium, and MacConkey sorbitol agar for E. coli O157:H7), and thin agar layer (TAL) were determined at 1 h and 1, 3, 7, and 14 days. The TAL method (selective medium overlaid with TSA) was used for recovery of sublethally injured cells. The pathogens were gradually inactivated by the acidic pH of apple juice. Nisin and cinnamon greatly contributed to the inactivation. The killing effect was more marked at 20 degrees C, with counts in all treated samples being undetectable by direct plating in 3 days for Salmonella Typhimurium and 7 days for E. coli O157:H7. Thus, several factors influenced the decrease in counts: low pH, addition of nisin and cinnamon, and storage temperature. The TAL method was as effective as TSA in recovering injured cells of the pathogens. The combination of nisin and cinnamon accelerates death of Salmonella Typhimurium and E. coli O157:H7 in apple juice and so enhances the safety of the product.     

Salmonella isolation using RVS broth and MLCB agar

Experiments were carried out to determine sources of variation which might influence the reliability of Rappaport Vassiliadis (RV) broth and Mannitol lysine crystal violet brilliant green agar (MLCB). The amount of MgCl₂.6H₂O in the RV broth formula is critical and should be approximately 29 gl⁻¹ of the ready to use medium. When soya peptone is used instead of tryptone, the medium should be buffered when stored for longer periods of time before use. This buffered soya peptone medium is called RVS broth in order to prevent confusion with the ‘classical’ RV broth.MLCB agar proved in our hands to be an excellent medium for the isolation of H₂S positive Salmonella when used after enrichment in RVS broth. Care should be taken however that when ‘home-made’ the agar should contain sufficient Mg.     

苦瓜汁的抑菌活性及其热稳定性的研究

采用琼脂扩散法研究了苦瓜汁对大肠杆菌、金黄色葡萄球菌、枯草芽孢杆菌、沙门氏菌的抑菌活性。研究结果表明:苦瓜汁对四种菌均具有较好的抑菌活性,其中对大肠杆菌和沙门氏菌的抑菌活性明显强于对金黄色葡萄球菌和枯草芽孢杆菌的抑菌活性;在100℃以内,苦瓜汁具有良好的抑菌稳定性。     

Novel quantitative assays for estimating the antimicrobial activity of fresh garlic juice

Novel agar diffusion and broth dilution assays were developed for quantitatively estimating the antimicrobial activity of fresh garlic juice. Bacteria found to be inhibited by garlic juice in agar diffusion assay included two gram-positive and five gram-negative species. Leuconostoc mesenteroides was not inhibited. Escherichia coli B-103 (HB101, with pJH101, ampicillin resistant, 100 microg ml(-1)) was inhibited and chosen as the standard culture for quantitative assays. The agar diffusion assay was based on the slope ratio method, where the slope of dose response for garlic juice was divided by the slope of dose response for methylmethane thiosulfonate (MMTSO2). Juice from fresh garlic varied in activity between 1.76 and 2.31 microg of MMTSO2 per mg of garlic juice. The activity of juice decreased during 11 months of storage of garlic cloves at 5 degrees C from 2.31 to less than 0.1 microg of MMTSO2 per mg of juice. The broth dilution assay also used the E. coli B-103 culture, which permitted selective enumeration of this bacterium when 100 microg ml(-1) of ampicillin was incorporated into the enumerating agar. Selective enumeration was essential since the garlic juice was not sterile and, thus, contained natural flora. Growth of E. coli was unaffected by 0.1%, delayed by 0.25%, and completely inhibited at 0.5 and 2% garlic juice in broth during 24 h of incubation at 37 micro C. The minimum inhibition concentration of garlic juice by broth dilution assay was, thus, estimated to be 0.5%, which is equivalent to 3.46 microg of MMTSO2 per mg of garlic juice by the agar diffusion assay.     

Thermal injury and recovery of Salmonella enterica serovar enteritidis in ground chicken with temperature, pH, and sodium chloride as controlling factors

Cells of Salmonella enterica serovar Enteritidis were grown at 25 and 35 degrees C, heat injured (55, 60, and 62.5 degrees C), and recovered in tryptic soy broth (TSB) at various NaCl concentrations (2.0 and 3.5%) and pH levels (5.5 and 6.5). To assess the interactions of growth temperature, heating temperature, NaCl concentration and pH on the thermal injury and recovery of Salmonella Enteritidis in ground chicken, a randomized design with each experimental combination was used. When a logistic equation for nonlinear survival curves was used, D-values of cells of Salmonella Enteritidis grown at 25 degrees C were 7.60, 5.73, and 4.81 min at 55, 60, and 62.5 degrees C, respectively. For cells grown at 35 degrees C, the D-values were 12.38, 7.45, and 5.70 min at 55, 60, and 62.5 degrees C. The influence of tryptic soy agar and double modified lysine agar (DMLIA) on the recovery of heat-injured cells was determined. Recovery was significantly reduced on DMLIA at increased pH levels and NaCl concentrations. Higher numbers of cells were recovered in TSB with 2.0% NaCl than in TSB with 3.5% NaCl. It was observed that the rate of recovery of heat-injured cells was similar at each pH. Therefore, a pH range of 5.5 to 6.5 does not have a major inhibitory effect on the recovery of Salmonella Enteritidis.     

The post-harvest fruit rots of tomato (Lycopersicum esculentum) in Nigeria.

A survey of the post-harvest fruit rot diseases of tomato was conducted in five states of Nigeria. During severe infections, the diseases could cause 25% loss at harvest and 34% loss of the remaining product in transit, storage and market stalls; thus giving an overall loss of about 50% of the product. Two types of rots, soft and dry were recognised. The soft rot was found to account for about 85% and the dry rot about 15% of the overall loss. Erwinia carotovora, Rhizopus oryzae, R. stolonifer, Fusarium equiseti, F. nivale and F. oxysporum were established as the soft rot pathogens; while Aspergillus aculeatus, A. flavus, Cladosporium tenuissimum, Corynespora cassiicola, Curvularia lunata, Penicillium expansum P. multicolor and Rhizoctonia solani were established as the dry rot pathogens of tomato fruits in Nigeria.     

番茄制汁的工艺条件优化及货架期预测模型的建立

目的优化番茄制汁工艺条件,建立货架期预测模型。方法以红熟且无破损的番茄等外果为主要原料,经去蒂、清洗、热烫去皮、破碎榨汁制成新鲜的番茄汁,研究在不同温度(5、27、37℃)贮藏对产品品质的影响;利用Arrhenius方程为基础,建立相关联动力学模型;研究感官评价、pH、番茄花青素含量、色差在不同储藏时间变化进行番茄汁货架期预测研究。结果 0.03%的黄原胶、0.10%的羧甲基纤维素钠、0.05%的琼脂片组成的复合稳定剂稳定效果最好,口感饱满可口、细腻爽滑,番茄香气清新浓郁。采用模糊权重法对番茄汁货架期间的多项品质指标不同的加权系数进行综合评定。品质综合评价的加权关联度=感官评分sensory×0.25+pH×0.25+番茄红色×0.25+色差×0.25。结论该模型可以用于番茄汁货架期预测。     

Proteolytic yeasts isolated from raw,ripe tomatoes and metabiotic association of Geotrichum candidum with Salmonella

Metabiotic associations between food-borne fungi and bacteria capable of causing human diseases are a public health concern. A survey of decayed and damaged, uncooked, ripe tomatoes was done to determine the presence and prevalence of yeasts capable of increasing the pH pulp tissue, thus creating a more favorable environment for survival and growth of enteric pathogens. Sixty-two of the 371 (16.7%) fungi isolated from 215 decayed or damaged tomatoes; 12 of the 62 (19.4%) yeasts showed proteolytic activity on gelatin agar (GA) and/or standard methods caseinate (SMC) agar. The pH of tomato pericarp (pulp) tissue from which 9 of the 12 yeasts were isolated ranged from 4.3 to 7.5 (mean=5.3) compared to 4.2-5.1 (mean=4.8) for sound pulp tissue in the same tomatoes. The 12 proteolytic yeasts consisted of four strains of Cryptococcus albidus, two strains each of Debaryomyces hansenii and Trichosporon pullulans, and one strain each of Cryptococcus humicolus, Cryptococcus laurentii, Geotrichum candidum, and Sporidiobolus pararoseus. Survival and growth characteristics of a five-serotype mixture of Salmonella co-inoculated with G. candidum into sound (not chill injured) and chill-injured tomatoes were studied. Storage of sound tomatoes at 15 degrees C for 10 days resulted in an increase in population of 7.6 log(10) cfu of Salmonella/g of a 2-g sample of co-infected pulp tissue. Increases were less in tissue inoculated with Salmonella only, Salmonella on day 0 followed by G. candidum on day 3, or G. candidum on day 0 followed by Salmonella on day 3. Trends were similar in sound inoculated tomatoes stored at 25 degrees C. Growth of Salmonella was enhanced in chill-injured tomatoes compared to sound tomatoes; a population of 10 log(10) cfu/g of chill-injured pulp tissue was reached within 10 days at 25 degrees C. Results clearly show that growth of a proteolytic, alkalinizing yeast such as G. candidum in raw tomatoes enhances conditions for growth of Salmonella. The removal of tomatoes infected with proteolytic yeasts and other fungi from lots intended for minimally processed tomato products is an essential step in reducing the risk of human diseases caused by pathogenic bacteria favored by increased pH of decayed pulp tissue.     

Development of methods for the recovery of Escherichia coil O157:H7 and Salmonella from beef carcass sponge samples and bovine fecal and hide samples

Culture methods were developed for the concurrent recovery of Escherichia coli O157:H7 and Salmonella from bovine carcass, hide, and fecal samples. Several enrichment conditions were tested for the overall growth of pure cultures; tryptic soy broth for 2 h at 25 degrees C and then for 6 h at 42 degrees C was the protocol selected for use. Immunomagnetic separation (IMS) was incorporated for sensitivity and selectivity, along with a post-IMS enrichment for the recovery of Salmonella as recommended by the manufacturer. Selective agars for plating after IMS were chosen on the basis of ease of target colony identification. Sorbitol MacConkey agar supplemented with cefixime and potassium tellurite and Rainbow agar supplemented with novobiocin and potassium tellurite were chosen for the recovery of E. coli O157:H7. Brilliant green agar with sulfadiazine and Hektoen enteric agar supplemented with novobiocin were selected for the recovery of Salmonella. The resulting methods were evaluated along with standard or previously used methods for the recovery of E. coli O157:H7 and Salmonella from bovine hide and fecal samples and carcass sponge samples. The Meats Research Unit (MRU) methods performed at least as well as the established methods, except that a secondary enrichment in tetrathionate (TT) broth prior to IMS was required for the optimal recovery of Salmonella from feces. Thus, the MRU and MRU-TT methods are effective in the recovery of both E. coli O157:H7 and Salmonella from a single bovine carcass, hide, or fecal sample.     

Antibacterial activities of blueberry and muscadine phenolic extracts

Phenolics are one category of phyto-antimicrobials that refer to the antimicrobial substances extracted from plant sources. This study was undertaken to determine the influence of blueberry and muscadine phenolic extracts on the growths of 2 important foodborne bacterial pathogens, Salmonella Enteritidis and Listeria monocytogenes. Cells of S. Enteritidis (n = 4) or L. monocytogenes (n = 4) strains were inoculated (3 log CFU/mL) into tryptic soy broth (TSB) supplemented with 46.25 ppm of muscadine phenolics and 24 ppm of blueberry phenolics, respectively. The inoculated and un-inoculated broth with or without the supplemented phenolics were incubated at 37 °C for 24 h. Samples were drawn periodically, and cell populations of Salmonella and Listeria were determined on tryptic soy agar (TSA). It was observed that Salmonella was relatively more susceptible than Listeria to the phenolic extracts used in the study. The growth of Salmonella was significantly inhibited in all samples at all sampling points except for the sample that was supplemented with muscadine water extract and drawn at the 24-h sampling point. Blueberry phenolics were relatively more effective than muscadine phenolic extracts in inhibiting the growth of Salmonella. One tested strain of Listeria was more susceptible to ethanol than water phenolic extracts. The study revealed the potentials and limitations of using blueberry and muscadine phenolics to control the growths of selected Salmonella and Listeria strains.     

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.     

Destruction of Salmonella enteritidis inoculated in liquid whole egg by high hydrostatic pressure: comparative study in selective and non-selective media

The destruction of Salmonella enteritidis inoculated in liquid whole egg at approximately 10⁷−10⁸cfu ml^−lwas studied under combinations of pressure (350 and 450 MPa), temperature (50, 20, 2 and −15°C) and time (5, 10, 15 min and cycles of 5+5 and 5+5+5 min). One non-selective medium (tryptone soy agar) and two selective media (brilliant green agar and salmonella-shigella) were used to evaluate viability of S. enteritidis after pressurization. The inactivation rate increased with pressure and exposure time, being minimal at 350 MPa and −15°C for 5 min (over 1 log₁₀of reduction) and reaching total inactivation (8 log₁₀of reduction) in several treatments at 50°C. Treatments in cycles showed greater effectiveness than continuous treatments of the same total time. The effect of pressure was enhanced by elevated temperatures. The higher counts were obtained in the non-selective medium, indicating the presence of injured cells after pressure treatment. D -values obtained for two temperatures (2 and 20°C) and different times (0–60 min) under controlled pressure (400 MPa) showed that microbial inactivation followed a first-order kinetics with a decimal reduction time evaluated in tryptone soy agar medium of 9·5 min at 2°C and 8·8 min at 20°C.     

Carotenoids from tomatoes inhibit heterocyclic amine formation

Tomatoes are a rich source of antioxidants and they are commonly used for meat cooking in Mediterranean countries. The effects of tomato antioxidants on the formation of carcinogenic/mutagenic heterocyclic amines were investigated. A liquid model system containing as precursors creatinine, glucose and glycine in molar concentrations comparable to those present in bovine meat (chemical model system) was employed. A freeze-dried bovine meat juice (meat juice model system) was also used for some experiments. In both model systems, an inhibiting effect of tomato carotenoid fraction on the formation of imidazoquinolines (IQx, MeIQx and DiMeIQx) was observed. Using carotenoid extract at a concentration of 1000 ppm, inhibitions of 36% and 11% of IQx and MeIQx formation respectively in the chemical system and of 13% of MeIQx and of 5% of 4,8-DiMeIQx in the meat juice system was observed. The effect of the main tomato flavonoid, quercetin, was investigated using the meat juice system. Quercetin gave an inhibition of MeIQx formation between 9% and 57% with a maximum effect of 67% at 10 ppm.