Logarithmic Cycles Research Articles

Investigation and modeling on fatigue damage evolution of rock as a function of logarithmic cycle

AbstractThe fatigue damage behavior of granite under constant and variable amplitude loadings is studied. The experimental analysis reveals that there is a three‐stage law for the fatigue damage evolution as a function of absolute or relative cycle and the inverted‐S damage model proposed by the author, in this case, is capable of representing the damage behavior of rock. However, when the logarithmic cycle is considered, there are only two stages, i.e. steady and accelerated stages and the fatigue damage evolution greatly depends on the properties of rock and stress level. Accordingly, the fatigue damage evolution curves have been categorized into three types. Then, the effect of maximum stress, amplitude and fatigue initial damage on the damage evolution of rock is investigated. The analysis reveals that the damage evolution greatly depends on these influencing factors. The fatigue life decreases with the increase in the maximum stress, amplitude and fatigue initial damage due to the decrease in the proportion of the first stage to the whole fatigue process and the increase in the damage rate in the first stage. Meanwhile, a linear‐exponential formula is used to model the fatigue damage behavior of rock subjected to cyclic loading. This damage model is superior to the inverted‐S damage model in the convenience of establishment of critical instability point. The physical meanings of its constants have been illuminated and the applicability of this model to constant and variable amplitude cyclic loading explored. The fitting results for the test data show that this damage model can properly represent the fatigue damage behavior of rock. Copyright © 2010 John Wiley & Sons, Ltd.

Improvement of biomolecular methods for the identification and typing of Escherichia coli O157:H7 isolated from raw meat

The aim of the study was to evaluate the sensitivity of two m-PCR methods for the quantitative determination of E. coli O157:H7 in foodstuffs. Genomic serotyping was carried out on bacterial cultures, and the necessary time was optimized to increase the resolution of the method. Subsequently, artificial contamination trials using meat were conducted to assess method accuracy in foodstuffs and pursue the genetic typing of pathogens. Measurement thresholds were shown to range between 10(5) and 10(6) CFU/mL, but were reduced by four logarithmic cycles in 80% of samples. Relative to the meat contamination trials, serotypes were identified after 24 hours, corresponding to 10 CFU/mL inoculum, with higher rates seen when m-TSB was used for enrichment. Inoculated samples were found to contain three virulence factors (hlyA, eaeA, and stx1).

PREDICTIVE MODELS FOR THE SURVIVAL OFCAMPYLOBACTER JEJUNIINOCULATED IN CHICKEN MEAT

ABSTRACT Campylobacter jejuni is an emerging pathogen that is becoming more relevant due to the high percentage of isolations found in raw or undercooked poultry products. The objective of the present work was to analyze and to model mathematically the effect of storage temperature (+4 and −2C), potassium sorbate concentration (0, 500 and 1,000 ppm) and packaging in plastic films of different gas permeabilities (low and high gas permeability, polyethylene and EVA SARAN EVA) on the survival of C. jejuni inoculated into chicken meat. Different models (linear, Gompertz and Weibull equation) were applied to experimental data, obtaining the best fit with the Weibull model. Among analyzed factors, storage temperature (+4 and −2C) was the most effective factor to inhibit growth of C. jejuni in chicken meat that reduce microbial counts between 3 and 4 logarithmic cycles. However, at −2C, the inhibitory effect was more successful. Potassium sorbate and packaging in different permeability films did not show inhibitory effect on C. jejuni. PRACTICAL APPLICATIONS The results of this study suggest that potassium sorbate and packaging films did not show inhibitory effect on Campylobacter jejuni inoculated in chicken meat. Storage temperature (+4 and −2C) is the most important factor in controlling the growth of C. jejuni in chicken meat.

Resistance of Bacterial Biofilms Formed on Stainless Steel Surface to disinfecting Agent

The natural ability of microorganisms for adhesion and biofilm formation on various surfaces is one of the factors causing the inefficiency of a disinfection agent, despite its proven activity in vitro. The aim of the study was to determine the effectiveness of disinfecting substances on bacterial biofilms formed on stainless steel surface. A universally applied disinfecting agent was used in the tests. Bacterial strains: Listeria innocua, Pseudomonas putida, Micrococcus luteus, Staphylococcus hominis strains, were isolated from food contact surfaces, after a cleaning and disinfection process. The disinfecting agent was a commercially available acid specimen based on hydrogen peroxide and peroxyacetic acid, the substance that was designed for food industry usage. Model tests were carried out on biofilm formed on stainless steel (type 304, no 4 finish). Biofilms were recorded by electron scanning microscope. The disinfecting agent in usable concentration, 0.5% and during 10 minutes was ineffective for biofilms. The reduction of cells in biofilms was only 1-2 logarithmic cycles. The use of the agent in higher concentration--1% for 30 minutes caused reduction of cell number by around 5 logarithmic cycles only in the case of one microorganism, M. luteus. For other types: L. innocua, P. putida, S. hominis, the requirements placed on disinfecting agents were not fulfilled. The results of experiments proved that bacterial biofilms are resistant to the disinfectant applied in its operational parameters. Disinfecting effectiveness was achieved after twofold increase of the agent's concentration.

Manufacturing of Fermented dairy products by using Lactobacillus casei which had the ability to lower cholesterol

The study included manufacturing of fermented dairy products by using full cream milk of four kinds of mammalian: (Buffalos, Cows, Sheep's and Goats); with the use of Lactobacillus casei as a starter for the production of fermented dairy products which had the ability to lower cholesterol percentage in the above mentioned products by (71.4, 70, 74.8 and 67.7)% respectively. The viability of Lb. casei had not been affected significantly during storage shelf life of 21days " The product shelf life " , keeping their therapeutic properties unaltered with high viable number of bacteria at time of consumption. The viable counts of the bacteria after storage period for manufactured products were (1.06× 109, 8.1× 108, 7.5× 108and 8× 108) CFU/ml respectively. These numbers represent a decrease equal to one logarithmic cycle for each of manufactured products of Cows, Sheep's and Goats milk, and the decrease of bacteria's viability of manufactured products of Buffalos milk was less than one logarithmic cycle. Results of statistical analysis showed that there was highly significant differences (P<0.05) in the viable bacterial cells counts between manufactured products. By sensory comparison of the manufactured fermented products together, the results shows that the manufactured products from Buffalos milk was the best then the manufactured products of Cows milk then Sheep's milk then goats milk

Biocontrole de Listeria monocytogenes por Pediococcus acidilactici em couve minimamente processada

This study evaluated a biological control system for the inhibition of Listeria monocytogenes in minimally processed kale focusing on its freshness under refrigeration and extreme temperatures. The inhibitory potential of salt and cold tolerant lactic bacteria from natural microflora of kale, Lactobacillus delbrueckii ATCC 9649, Lactobacillus plantarum, and Lactobacillus casei CCT 1465 strains were evaluated against L. monocytogenes. Pediococcus acidilactici CCA3 isolated from kale exhibited a large inhibition zone of L. monocytogenes at 10 and 15 °C in MRS agar and was selected as a possible biological control bacterium. The population of L. monocytogenes inoculated in minimally processed kale increased 3.7 and 4.7 logarithmic cycles at 5 and 10 °C, respectively, after 20 days of storage and 4.6 logarithmic cycles at 15 °C after eight days. However, when 108 CFU.g-1 of P. acidilactici CCA3 was inoculated into processed product a reduction of L. monocytogenes of 2.3 logarithmic cycles under extreme temperature conditions (15 °C) occurred. P. acidilactici CCA3 did not alter the titratable acidity or the kale sensorial characteristics during the shelf life period. These results suggest the potential application of biopreservatives on minimally processed kale that need to be associated with refrigeration and sanitation to assure safety.

Effects of irradiation and storage on the physico‐chemical and sensory properties of hamburgers enriched with lycopene

SummaryIn order to increase their safety and shelf‐life, raw hamburgers containing 30, 45 and 60 g kg−1 dry tomato peel (DTP) as a source of lycopene were manufactured, vacuum‐packed and irradiated with 2 or 4 kGy. The effects of this treatment on microbial load, lycopene concentration, physico‐chemical and sensory properties were studied during 17 days of refrigerated storage. After irradiation with 4 kGy and 17 days of storage, microbial levels fell, four logarithmic cycles and the lycopene concentration fell to 15% of the initial value. Even with this decrease, hamburgers containing 6% DTP had a final lycopene concentration of 7.14 mg per 100 g of hamburger, an amount very close to the recommended daily intake for a healthy diet. DTP masks the brownish colour characteristic of irradiated meat, and 6% DTP gives to the hamburger similar redness (a* parameter), independently of the dose of radiation applied. Sensory characteristics were influenced by irradiation, but the higher lycopene concentration (6 g kg−1) masked these changes sufficiently to assure an acceptable colour and odour in the final product after the storage period.

Preservation of sliced ham through triclosan active film

AbstractActive packaging is an alternative to preserve perishable food. In this work, polyethylene antimicrobial active films containing different levels of triclosan (0, 2000 and 4000 mg kg−1) were developed by extrusion. The films' efficacies were evaluated against Escherichia coli, Staphylococcus aureus, Listeria innocua, Salmonella choleraesuis and Pseudomonas aeruginosa growth using agar diffusion test and by monitoring the inhibition of E. coli and S. aureus inoculated on sliced cooked ham. The mechanical characteristics of the films were also evaluated with Universal Test Machine (Instron). The incorporation of triclosan did not affect the mechanical properties of antimicrobial films compared to the control film. The average film thickness was 82.0 µm and the tensile strength and elongation to break were 30.3 N and 46.2%, respectively. Films containing triclosan showed an antimicrobial effect in vitro against E. coli and S. aureus, with formation of an inhibition halo for both. However, this result was not observed for L. innocua, S. choleraesuis and P. aeruginosa, although, a decrease in colony density occurred around the film for both incubation temperatures (7 ± 2°C and 35 ± 2°C). Sliced ham packed with the antimicrobial films showed a reduction of 1.5 logarithmic cycles in comparison to ham in contact with a control film after 12 days of storage at 7 ± 2°C, for E. coli and S. aureus. Antimicrobial films present potential for application as active packaging materials, as they showed effective against some pathogenic microorganisms that can be transmitted by foods. Copyright © 2009 John Wiley & Sons, Ltd.

Effect of Packaging Films Releasing Antimicrobial Agents on Stability of Food Products

The study was aimed to (<I>I</I>) test the effect of polyethylene (LDPE) films coated by commercially available polyvinylchloride (PVC) lacquer with addition of nisin preparation Nisaplin® (5% w/w) and/or natamycin preparation Delvocid<sup>TM</sup> (10% w/w) on the growth of target bacteria, yeasts and moulds on the surface of soft cheese Blaťácké zlato produced by company Madeta, a.s., Veselí nad Lužnicí, and (<I>ii</I>) prepare and study the antimicrobial films with incorporated lactic acid or sodium lactate, suitable for packaging of raw chicken meat. The cheese in contact with nisin/natamycin treated film was stored at temperature 4°C and 23°C for 23 days, while chicken meat packaged in lactic acid/sodium lactate releasing films was stored only at 4°C for 7 days. Released antimicrobial agents caused retardation of tested microorganism growth by more than 1 logarithmic cycle on the surface of cheese Blaťácké zlato and by more than 2 logarithmic cycles in raw chicken meat.

Isolated or associated experimental contamination of albumen and egg yolk for Salmonella Enteritidis and Escherichia coli: influence of temperature and storage time

The behavior of Salmonella enteritidis (SE) and Escherichia coli in albumen and yolk of chicken eggs submitted to two different temperatures, 8ºC and 30ºC, when separately inoculated or in the form of mixed cultures was studied. There was no difference in the behaviour of the tested agents even when inoculated together. Even under high temperature, E. coli did not multiply in the albumen, demonstrating the inhibition power for that microorganism, while SE increased its population up to three logarithmic cycles. In egg yolk, SE demonstrated psychrotrophic characteristics.

Mild Thermal Process Combined with Vanillin Plus Citral to Help Shorten the Inactivation Time for Listeria innocua in Orange Juice

The response of Listeria innocua (surrogate for Listeria monocytogenes) to combined treatments involving moderate temperatures (57 to 61 °C) and the addition of different levels of citral (0 to 75 ppm) was assessed to obtain a minimally processed orange juice. The presence of citral notoriously increased the bactericidal effect of mild heating treatment. This effect did not depend on the amount of added citral at all assayed temperatures. In a second stage, combinations of two natural antimicrobials (vanillin and citral) were assessed in order to find the most effective inactivation treatment in orange juice. Vanillin (900–1,100 ppm) and citral (25 ppm) combined with mild heating treatment (52 or 57 °C) were tested against L. innocua in orange juice. The addition of 900 ppm vanillin and 25 ppm citral halved or more the time required to achieve five logarithmic cycles of reduction at both temperatures with respect to thermal treatment without antimicrobial addition. The increase in the maximum growth rate calculated from the modified Gompertz model properly correlated with the increasing vanillin level for a given citral concentration. Complementary information was obtained from successfully fitting a Weibullian model to the nonlinear semilogarithmic survival curves: The addition of vanillin and citral significantly increased the bactericidal effect of mild thermal treatment, changing the distribution of inactivation times and obtaining narrower frequency shapes with lower variance and mode values. The combination of vanillin and citral with mild heating treatment resulted in an innovative alternative to minimize detrimental effects caused by thermal processing of fruit juices. In addition, a consumer panel evaluated them with an acceptable overall pleasantness.

Microbiological hazards involved in fresh‐cut lettuce processing

AbstractBACKGROUND: The increasing consumption of produce all over the world has resulted in increasing concern by the regulatory agencies with respect to the level of safety performed by the processors. The objective of the present study was to investigate the hazards involved in the various steps of fresh‐cut lettuce processing (reception/selection of raw material, washing, rinsing, sanitisation and final product) by means of microbiological analyses of microbial groups used as indicators of hygienic conditions and of pathogens.RESULTS: High microbial loads of mesophilic and psychrotrophic bacteria and Pseudomonas spp. were found in the ram reception (∼6 log colony‐forming units (CFU) g−1), which were reduced by a single logarithmic cycle for the last two microbial groups after the sanitisation step (P < 0.05), the latter being ineffective against the first microbial group (P > 0.05). Lower counts of yeasts and moulds, total coliforms (35 °C) and faecal coliforms (44 °C) were observed in the initial step (3.49–4.53 log CFU g−1, 0.65–1.55 log most probable number (MPN) g−1 and 0.50–0.90 log MPN g−1 respectively), these values increasing significantly after the sanitisation step for yeasts and moulds (∼5 log CFU g−1) but remaining unaltered for coliforms (P > 0.05). Salmonella spp. were not found in any of the experiments carried out, while the presence of Escherichia coli was observed in the final product.CONCLUSIONS: Practices compromising the hygienic quality of the final product during commercial storage were observed and corrective measures suggested. To the best of the authors' knowledge, these are the first data on microbiological safety in Brazilian fresh‐cut processing plants. Copyright © 2008 Society of Chemical Industry

Potentially probiotic açaí yogurt

The aim of this work was to evaluate the suitability of yogurt containing açaí pulp as a food carrier of probiotic cultures. Probiotic yogurts containing increasing amounts of açaí pulp (3, 5 and 7%) were processed and submitted to a physicochemical analysis and viable microbial count during refrigerated storage. In general, all the physicochemical parameters showed variations proportional to the amount of açaí pulp in the product formulation. Probiotic activity was verified throughout refrigerated storage for all the products, although there was a fall of one logarithmic cycle for both micro‐organisms during this period (107–108 CFU/mL).

Quality of mussels cultivated and commercialized in Ubatuba, SP, Brazil: monitoration Bacillus cereus and Staphylococcus aureus growth after post-harvest processing

Aiming at improving the quality of Perna perna mussels cultivated and commercialized Ubatuba, SP, Brazil, the growth and elimination of Staphylococcus aureus and Bacillus cereus artificially inoculated mussels were studied. The inoculation was carried out in natura and pre-cooked mussels for 30 min, and after that the mussels were kept for 10 hours at room temperature (25 ± 1 °C) and under refrigeration (7 ± 1 °C). Six thermal treatments were evaluated: three using steam (5, 10 and 15 minutes) and three boiling water (5, 10 and 15 minutes), order to find the best time/temperature binomial to provide pathogenic control. Yield and physical-chemical and sensory characteristics were evaluated. All thermal treatments were efficient to eliminate microorganisms 2 logarithmic cycles. However, the boiling water treatments presented better results than the steam treatments. The physical-chemical and sensory analyses did not show statistical differences among the thermal treatments studied. The best performances were reached the shortest times of heat exposure. Overall, the treatments boiling water presented better results than the steam treatments.

Viability of probiotic micro‐organisms (Lactobacillus casei Shirota and Bifidobacterium animalis subspp. lactis) in a milk‐based dessert with cranberry sauce

The objective of this study was to evaluate the survival of two probiotic micro‐organisms, Lactobacillus casei Shirota and Bifidobacterium animalis subspp. lactis, in a milk‐based dessert (2.7% fat) with cranberry sauce added. B. lactis had a final concentration of 1.99 × 106 cfu/g after 21 days of study, with a logarithmic decrease of 8.87%. On other hand, L. casei Shirota had a final concentration of 2.05 × 107 cfu/g at the end of the same period, a logarithmic decrease of 8.41%. Statistical analysis showed that significant differences existed between both micro‐organisms and over various storage times, the more viable micro‐organism being L. casei Shirota, which decreased less than one logarithmic cycle after 21 days.

Survival patterns of Dekkera bruxellensis in wines and inhibitory effect of sulphur dioxide

The wine spoilage yeast species Dekkera bruxellensis, after inoculation in red wines, displayed three survival patterns characterized by: i) initial lag phase followed by growth and sequential death; ii) initial death phase leading to reduced viable counts followed by growth and sequential death; and iii) death phase leading to complete loss of viability. These survival patterns were observed for the same strain in different dry red wine blends with 12% (v/v) ethanol and pH 3.50, in the absence of free sulphur dioxide. For the same wine blend, these patterns also varied with the tested strain. Under laboratory conditions the addition of 150 mg/l of potassium metabisulphite (PMB) to dry red wine with 12% (v/v) ethanol and pH 3.50 reduced initial cell counts by more than 6 logarithmic cycles, inducing full death within less than 24 h. Winery trials showed that D. bruxellensis blooms were only prevented in the presence of about 40 mg/l of free sulphur dioxide in dry red wine, with 13.8% (v/v) ethanol and pH 3.42, matured in oak barrels. These different amounts of PMB and sulphur dioxide corresponded to about 1 mg/l of molecular sulphur dioxide. Our results therefore demonstrate that the control of populations of D. bruxellensis growing in red wine can only be achieved under the presence of relatively high doses of molecular sulphur dioxide.

Ultra-high pressure homogenization treatment combined with lysozyme for controlling Lactobacillus brevis contamination in model system

Abstract It was studied the reduction of a population of Lactobacillus brevis in phosphate buffer by the combination of ultra-high pressure homogenization (UHPH) treatment and the use of lysozyme as antimicrobial. The minimum inhibitory concentration (MIC) of lysozyme against L. brevis was 50 mg.L − 1 . The observed inhibition was transitory and the growth curve showed that lysozyme addition was able to delay the L. brevis growth for 2 days. Lysozyme added at MIC concentration to a suspension of L. brevis caused a reduction of 1 logarithmic cycle after two hours of contact. The UHPH treatment against L. brevis resulted in a reduction of 7 log cycles at 200 MPa. Lysozyme was resistant to UHPH (200 MPa), without loss of muramidase activity or significant loss of antimicrobial power. A combined treatment was applied using 50 mg.L − 1 of lysozyme and pressure between 150 and 170 MPa; the combined effect showed a reduction of about 6 logarithmic cycles and the unaltered count of L. brevis after pressure treatment for a week, with the samples stored at room temperature (25 °C). Industrial relevance Ultra-high pressure homogenization is an alternative process for cold pasteurization that can be used to inactivate the common spoilage microorganisms of the juice and beer industry, for example, L. brevis . Combined treatment with lysozyme increases the pressure effect and, consequently, reduces the level of pressure required for treatment. The possibility of operating with lower pressures requires less robust equipment, which makes the utilization of lower-cost equipment possible.

Abrasion damage of a woven geotextile due to various gravelly flows

This study investigated some factors influencing the abrasion damage to a woven geotextile using a circular turbid flow chamber test system. Two uniformly graded aggregates composed of different minerals and angularities were used in the turbid flow test. Two important factors—particle concentration and flow velocity—were also investigated. It was found that the percentage of ultimate strength loss (PSR) due to abrasion damage was linearly related to these parameters and to the Los Angeles percentage weight loss, regardless of the particle size and angularity examined in this study. It was also found that the Rt method, which uses an average gradient (Rt = 18% per logarithmic cycle of test duration T) for the PSR-log T relationships obtained for T = 8 h, is potentially useful in predicting the values of PSR for relatively long test durations. The above findings are valid only for the limited test conditions investigated, and should be confirmed on the basis of comprehensive test results regarding the effect of size, hardness and shape of aggregate.

The antimicrobial effect of wine on Listeria innocua in a model stomach system

A model stomach, containing a food matrix and a synthetic gastric fluid, was used to study the bactericidal effect of ingested wine on Listeria innocua. Volumes of wine equivalent to the ingestion of one glass and half a bottle, led, over a period of less than 2 h, to a reduction of 3 and 4 logarithmic cycles of the initial population respectively. The influence of ethanol and organic acids, wine constituents with known antimicrobial properties, was investigated. Ethanol exhibited a higher bactericidal effect than the mixture of the main wine organic acids. When testing the organic acids separately, malic and lactic acids were found to have the strongest effect. The combination of ethanol with the organic acids acted synergistically but to a lesser extent than wine itself. The results suggest that the ingestion of wine during a meal may diminish the quantity of Listeria persisting further in the alimentary tract.

Heat Inactivation of Listeria monocytogenes and Salmonella enterica Serovar Typhi in a Typical Bologna Matrix during an Industrial Cooking-Cooling Cycle

The heat resistance of Salmonella enterica serovar Typhi PF-724 and Listeria monocytogenes 2812 was determined in a commercial bologna batter. The heat inactivation of the two bacterial species was also studied in a semiautomatic pilot smokehouse under cooking conditions that reproduced an industrial bologna process. S. enterica serovar Typhi PF-724 was less heat resistant than L. monocytogenes 2812. The D-values (times required to reduce the population by 1 logarithmic cycle) for S. enterica serovar Typhi PF-724 ranged from 10.11 to 0.04 min for temperatures of 50 to 70°C, while for L. monocytogenes 2812, the D-values were 2.5-, 4.9-, 3.8-, 3.3-, and 2-fold higher at 50, 55, 60, 65, and 70°C, respectively, than for S. enterica serovar Typhi PF-724. However, the z-value (temperature required to reduce log D by 1 logarithmic cycle) for S. enterica serovar Typhi PF-724 (5.72°C) was not significantly different from the z-value for L. monocytogenes 2812 (7.04°C), indicating that a given increase in temperature would have a similar effect on the decimal reduction time for both bacterial species in that meat emulsion. Our data on experimentally inoculated batter also showed that processing bologna at a cooking-cooling cycle commonly used in the industry resulted in a minimum 5-log reduction for both S. enterica serovar Typhi PF-724 and L. monocytogenes 2812.