Use of Weibull frequency distribution model to describe the inactivation of Alicyclobacillus acidoterrestris by high pressure at different temperatures

The survival curves of Alicyclobacillus acidoterrestris by high hydrostatic pressure were obtained at two pressures (350 and 450 MPa) and three temperature levels (35, 45 and 50 °C) in BAM broth. Tailing (upward concavity) was observed in all survival curves. Weibull model was fitted to these data and goodness of fit of this model was investigated. Regression coefficients (R²), root mean square (RMSE) values and residual plot strongly suggested that Weibull model produced good fit to the data. A better fit was observed for the data at lower pressure (350 MPa). Shape factors of the Weibull model (n values) for 350 MPa at 35, 45 and 50 °C were significantly different from each other (P < 0.05). Two linear emprical equations were obtained for scale factors (b values) at the temperature values studied for 350 and 450 MPa. Such pressure–temperature inactivation models form the engineering basis for design, evaluation and optimization of high hydrostatic pressure processes as a new preservation technique.     

Combined treatment of high pressure and heat on killing spores of Alicyclobacillus acidoterrestris in apple juice concentrate

Alicyclobacillus acidoterrestris, a thermoacidophilic and spore-forming bacterium, has been isolated from spoiled acidic juices and is considered to be one of the important target microorganisms in quality control of acidic canned foods. Combined high pressure and heat treatment showed an effectiveness to control A. acidoterrestris spores. However, the effectiveness of the combined treatment may change upon the apple juice concentration. Therefore, the objective of this study was to evaluate different levels of apple juice concentrate for reduction of Alicyclobacillus spores by high pressure and heat. Spores of A. acidoterrestris were inoculated into three different concentrations of apple juice (17.5, 35, and 70 degrees Brix), and subjected to three high-pressure treatments (207, 414, and 621 MPa) at four different temperatures (22, 45, 71, and 90 degrees C). High-pressure treatment (207, 414, and 621 MPa) at 22degrees C did not reduce the level of spores regardless of the apple juice concentration (P > 0.05). In diluted apple juice (17.5 degrees Brix), the combined treatment of high pressure and heat resulted in spore reductions of about 2 log at 45 degrees C, and more than 5 log at higher temperatures (71 and 90 degrees C) in a high-pressure and temperature-dependent manner. For apple juice with a higher concentration (30 degrees Brix), high-pressure treatment showed no effect at 45 degrees C but resulted in about 2 and 4 log reduction at 71 and 90 degrees C, respectively. However, for apple juice concentrate (70 degrees Brix), treatment with heat or high pressure alone, or their combinations showed no inactivation against spores of A. acidoterrestris. It is likely that differences in the water availability explain the greater resistance of spores to high-pressure inactivation in the juice concentrates than in diluted juices. Our results demonstrate that the effect of high pressure combined with heat against spores of A. acidoterrestris was highly dependent on the apple juice concentration.     

The effect of intermittent shaking, headspace and temperature on the growth of Alicyclobacillus acidoterrestris in stored apple juice

The presence of Alicyclobacillus acidoterrestris in stored juices can be difficult to detect. In this study the effects of storage temperature, headspace and agitation of juice containers was investigated. The results indicate that the amount of headspace has a significant effect on growth of vegetative cells and spores of A. acidoterrestris at 35 °C. Intermittent shaking before sampling increased growth and therefore probable detection rates at 30 °C, Agitating containers and sampling from several areas within containers is therefore recommended for determining whether A. acidoterrestris is present or absent from stored juice, especially in large containers.     

Effects of microwave and ultrasonic wave treatment on inactivation of Alicyclobacillus

The objective of this study was to determine the effects of microwave (MW), ultrasonic wave (UW) and their combination treatments for the same length of time (10 or 30 min) on the inactivation of vegetative cells of three different strains of Alicyclobacillus, (Alicyclobacillus acidiphilus DSM 14558^T, Alicyclobacillus acidoterrestris DSM 3922^T and Alicyclobacillus cycloheptanicus DSM 4006^T) in a laboratory medium. The results showed that A. acidoterrestris DSM 3922^T seemed to be the most susceptible strain. It was also found that when MW or UW was employed separately, UW was more effective and the effectiveness of MW and UW was improved as the power and exposure time increased. By comparison, UW treatment followed by MW was significantly better than the treatment of MW followed by UW. Furthermore, combined MW and UW treatment had a markedly better effect than separate MW processing, but had a less effect than UW alone, except that the inactivation of A. cycloheptanicus DSM 4006^T was significantly increased (P < 0.05) by the 30‐min treatment of UW (400 W for 20 min) + MW (900 W for 10 min).     

The use of chlorine dioxide to control Alicyclobacillus acidoterrestris spores in aqueous suspension and on apples

Alicyclobacillus acidoterrestris, a thermoacidophilic, spore-forming bacterium, has been identified as a spoilage organism in commercial, pasteurized fruit juices. This study was undertaken to evaluate chlorine dioxide for reducing numbers of A. acidoterrestris spores on laboratory media and on apples. A. acidoterrestris spores in aqueous suspension and on apple surfaces of four different cultivars were treated with several concentrations of chlorine dioxide. Spores in aqueous suspension treated with 40 ppm for 5 min were reduced by more than 4 log. Treatment with 80 ppm for 1 min and 120 ppm for 30 s resulted in about 1.8 log and 4.8 log reductions of spore viability, respectively, and treatment at 80 and 120 ppm for 5 min reduced spore viability to undetectable levels (<0.7 log CFU/ml). When applied to the surfaces of four different apple cultivars ('Red Delicious', 'Golden Delicious', 'Gala', and 'Fuji'), 40 ppm free chlorine dioxide reduced A. acidoterrestris spore numbers by 1.5, 3.2, 4.5, >4.8 log after 1-, 2-, 3-, and 4-min treatments, respectively. Spore numbers were reduced by >4.8 log with 120 ppm free chlorine dioxide after only 1-min treatment. However, there was no significant difference between apple cultivars (P>0.05) on spore reduction. These results show the great effectiveness of chlorine dioxide in controlling A. acidoterrestris spores both in aqueous suspension and on apple surfaces. There was no synergistic effect on spore reduction when chlorine dioxide treatment of aqueous suspension was followed by heat.     

Germination and inactivation of Bacillus coagulans and Alicyclobacillus acidoterrestris spores by high hydrostatic pressure treatment in buffer and tomato sauce

Acidothermophilic bacteria like Alicyclobacillus acidoterrestris and Bacillus coagulans can cause spoilage of heat-processed acidic foods because they form spores with very high heat resistance and can grow at low pH. The objective of this work was to study the germination and inactivation of A. acidoterrestris and B. coagulans spores by high hydrostatic pressure (HP) treatment at temperatures up to 60 °C and both at low and neutral pH. In a first experiment, spores suspended in buffers at pH 4.0, 5.0 and 7.0 were processed for 10 min at different pressures (100-800 MPa) at 40 °C. None of these treatments caused any significant inactivation, except perhaps at 800 MPa in pH 4.0 buffer where close to 1 log inactivation of B. coagulans was observed. Spore germination up to about 2 log was observed for both bacteria but occurred mainly in a low pressure window (100-300 MPa) for A. acidoterrestris and only in a high pressure window (600-800 MPa) for B. coagulans. In addition, low pH suppressed germination in A. acidoterrestris, but stimulated it in B. coagulans. In a second series of experiments, spores were treated in tomato sauce of pH 4.2 and 5.0 at 100 - 800 MPa at 25, 40 and 60 °C for 10 min. At 40 °C, results for B. coagulans were similar as in buffer. For A. acidoterrestris, germination levels in tomato sauce were generally higher than in buffer, and showed little difference at low and high pressure. Remarkably, the pH dependence of A. acidoterrestris spore germination was reversed in tomato sauce, with more germination at the lowest pH. Furthermore, HP treatments in the pH 4.2 sauce caused between 1 and 1.5 log inactivation of A. acidoterrestris. Germination of spores in the high pressure window was strongly temperature dependent, whereas germination of A. acidoterrestris in the low pressure window showed little temperature dependence. When HP treatment was conducted at 60 °C, most of the germinated spores were also inactivated. For the pH 4.2 tomato sauce, this resulted in up to 3.5 and 2.0 log inactivation for A. acidoterrestris and B. coagulans respectively. We conclude that HP treatment can induce germination and inactivation of spores from thermoacidophilic bacteria in acidic foods, and may thus be useful to reduce spoilage of such foods caused by these bacteria.     

Efficacy of disinfectants in killing spores of Alicyclobacillus acidoterrestris and performance of media for supporting colony development by survivors

Alicyclobacillus has recently emerged as a spoilage microorganism of concern in a wide range of pasteurized fruit products. The focus of this study was to determine the efficacy of chemical disinfectants in killing Alicyclobacillus acidoterrestris spores. Direct plating media were evaluated for their suitability to support germination and outgrowth of spores surviving exposure to these disinfectants. Significant (P < or = 0.05) reductions of about 2.2, 0.4, and 0.1 logs in the number of viable A. acidoterrestris spores in a five-strain mixture were achieved when spores were suspended in 200 ppm chlorine, 500 ppm acidified sodium chlorite, or 0.2% H2O2 solutions, respectively, for 10 min at 23 degrees C. When treated with either 1,000 ppm chlorine or 4% H2O2, the number of spores was reduced by more than 5 logs. Treatment with 8% trisodium phosphate or 80 ppm Tsunami did not significantly reduce numbers of viable spores. Spores of individual strains of A. acidoterrestris varied little in resistance to the same chemical treatment. K agar (pH 3.7) was judged best for recovering chemically treated spores, compared to orange serum agar (pH 5.0) and potato dextrose agar (pH 3.5). Experiments were done to determine the effectiveness of chemical treatments in killing a mixed-strain inoculum of A. acidoterrestris spores on the surface of apples. Treatment with 500 ppm chlorine or 1,200 ppm acidified sodium chlorite for 1 min significantly (P < or = 0.05) reduced the number of viable spores, but reductions were less than 1 log. Hydrogen peroxide (2%) was ineffective in killing spores remaining on the apple skin after treatment.     

Determination of guaiacol produced by Alicyclobacillus acidoterrestris in apple juice by using HPLC and spectrophotometric methods, and mathematical modeling of guaiacol production

In this study, easy detection of Alicyclobacillus acidoterrestris was performed by determination of guaiacol in apple juice. Guaiacol produced by A. acidoterrestris was determined by using HPLC, UV-Vis spectrophotometer, and Minolta spectrophotometer. Statistical analysis showed that the methods used for measuring the guaiacol concentrations were not significantly different (p > 0.05). Guaiacol formation in apple juice spiked with different levels of A. acidoterrestris spores was also analyzed using Gompertz, Logistic, and Richards models. In all cases, a good agreement between experimental data and fitted values was obtained. Using the modified Gompertz model, the derived biological parameters were calculated. Guaiacol formation rates (μ) and final guaiacol concentrations (A) were very similar in all cases, regardless of the initial A. acidoterrestris spore counts. However, lag phase durations (λ) were found to be dependent on the initial bacterial counts, and increased from 28.4 to 37.6 h, when initial inoculation level decreased from ∼10³ to ∼10¹ cfu/mL.     

Lactic acid and trisodium phosphate treatment of lamb breast to reduce bacterial contamination

Lactic acid and trisodium phosphate (TSP) were evaluated for the ability to reduce Escherichia coli and aerobic plate counts (APCs) on lamb breasts that were inoculated with a lamb fecal paste. A 90-s water rinse was applied followed by either a 9-s (55 degrees C) 2% lactic acid spray, a 60-s (55 degrees C) 12% TSP dip, or a combined treatment of both lactic acid and TSP treatments. Lactic acid reduced E. coli and APCs by 1.6 log10/cm2, and TSP caused a 1.8-log10/cm2 reduction in E. coli and a 0.7-log10/cm2 reduction in APCs. Combined reductions by the lactic acid spray followed by the TSP dip were 1.8 and 1.5 log10/cm2 for E. coli and APCs, respectively. Lactic acid and trisodium phosphate, used alone or in combination, were effective in reducing numbers of E. coli and could be useful as pathogen intervention steps in lamb slaughter processing.     

Detection of guaiacol produced by Alicyclobacillus acidoterrestris in apple juice by sensory and chromatographic analyses, and comparison with spore and vegetative cell populations

Spoilage of fruit juice by Alicyclobacillus acidoterrestris is characterized by a distinct medicinal or antiseptic off odor attributed to guaiacol, a metabolic by product of the bacterium. Detection of low populations of A. acidoterrestris that would precede sensory detection of guaiacol would enable juice processors to select appropriate processing and storage conditions that would minimize or eliminate spoilage. The objective of this study was to determine the recognition threshold of guaiacol in apple juice by sensory analysis and the population of A. acidoterrestris and incubation time at 21 and 37 degrees C necessary for chemical detection of guaiacol. Commercially sterilized apple juice (pH 3.54 +/- 0.04, 11.3 +/- 0.3 degrees Brix) was inoculated with a five-strain mixture of A. acidoterrestris spores (2.98 log10 CFU/ml) and stored at 21 or 37 degrees C for up to 61 days. Using an experienced sensory panel and the forced-choice ascending concentration method of limits, the best estimate threshold (BET) for recognition of guaiacol added to uninoculated apple juice was 2.23 ppb. Numbers of A. acidoterrestris spores and cells in inoculated juice remained constant during the 61-day storage period; however, the panel detected (P < or = 0.01) guaiacol in juice stored at 37 degrees C within 8 days. At three of four sampling times ranging from 13 to 61 days at which the sensory panel detected (P < or = 0.001) guaiacol, concentrations of 8.1 to 11.4 ppb were detected by chromatographic analysis. The panel detected (P < or = 0.1 to P < or = 0.01) guaiacol in five samples stored at 21 to 37 degrees C for 8 to 61 days in which the compound was not detected by chromatographic analyses. It appears that guaiacol content in apple juice inoculated with A. acidoterrestris is not always correlated with numbers of cells, and the limit of sensitivity of chromatographic quantitation of the compound is higher than the BET.     

Use of commercial protease preparations to reduce protein and lipid content of maize starch

A method was developed to produce pure maize starch from maize flour using a protease processing step, and additional salt washing and sulphite steeping steps. A range of commercial protease enzymes were evaluated for this purpose. The laboratory scale procedure that was developed, using one protease in particular (Promod P25P, thermolysin), produced relatively pure starch (<0.45% protein). Using the same procedure, but applying to starches which had been produced in advance using traditional wet milling, starch protein contents could be reduced further by 25–50% with the lipid content reduced by up to 25%. The amount of starch damage was minimal using this approach (<1%). This procedure could be developed industrially for a ‘greener approach’ to starch extraction – although it may still be necessary to incorporate sulphite steeping stages to facilitate protein solubilisation and extraction.     

Use of antioxidants to reduce lipid oxidation and off-odor volatiles of irradiated pork homogenates and patties

Pork homogenates and patties treated with antioxidants (200 μM, final) were irradiated with an electron beam. Lipid oxidation of the pork homogenates and patties were determined at day 0 and 5 and volatile compounds were analyzed soon after irradiation. Ionizing radiation accelerated lipid oxidation and produced S-containing volatiles in pork homogenates and patties. Addition of an antioxidant (sesamol, gallate, Trolox, or α-tocopherol) and their combinations decreased, but carnosine did not affect the production of off-odor volatiles and lipid oxidation of pork homogenates and patties by irradiation. Antioxidant combinations showed distinct beneficial reduction in lipid oxidation of aerobically packaged irradiated pork patties. The effect of antioxidant combinations in reducing sulfur volatiles of irradiated pork patties was clearer under vacuum than aerobic conditions.     

微波膨化加工芒果脆片的研究

通过对预干燥后的芒果条、芒果片进行微波膨化,研究水分含量、物料形状、糊精、CaCl2对微渡膨化的影响,并对产品膨化率、酥脆度、色泽、外形平整性进行评价.结果表明:热风干燥温度以45℃为宜,片状物料比条状物料更适于微波膨化;芒果片微波膨化最适条件为,通过预干燥使膨化前芒果片水分质量分数降低至12%,再微波膨化22 s,得到产品其膨化率、酥脆度、色泽、外型都良好;糊精浓度在7%以下时,对脆片的酥脆性、色泽有一定的改善作用,CaCl2则没有改善芒果片品质的作用.     

Use of octanoic acid as a postlethality treatment to reduce Listeria monocytogenes on ready-to-eat meat and poultry products

The antilisterial efficacy and organoleptic impact of an octanoic acid (OA)-based treatment for ready-to-eat (RTE) meat and poultry products were investigated. Whole-muscle and comminuted RTE products were inoculated with a five-strain mixture of Listeria monocytogenes. The OA treatments were applied to the surface of RTE products by dispensing a specific volume of solution directly into the final package prior to vacuum sealing. Once sealed, the vacuum-packaged RTE products containing OA were immersed in water heated to 93.3 degrees C (200 degrees F) for 2 s to effect adequate film shrinkage. Extending the time at which the packaged, treated RTE products were exposed to water heated to 93.3 degrees C was also evaluated with a commercial cascading shrink tunnel fitted with a modified drip pan. Once treated, RTE products were examined for survivor populations of L. monocytogenes after 24 h of storage at 5 degrees C. Sensory evaluation was conducted with a 60-member trained panel on 11 uninoculated, treated RTE products. The OA treatment of RTE products reduced L. monocytogenes numbers to between 0.85 log CFU per sample (oil-browned turkey) and 2.89 log CFU per sample (cured ham) when compared with controls. The antilisterial activity of OA was improved by increasing the duration of the heat shrink exposure. Specifically, reductions of L. monocytogenes ranged from 1.46 log CFU per sample (oil-browned turkey) to 3.34 log CFU per sample (cured ham). Results from the sensory evaluation demonstrated that 10 of the 11 treated RTE products were not perceived as different (P < or = 0.05) from the untreated controls. Panelists detected reduced (P < or = 0.05) smoke flavor intensity with treated mesquite turkey, although the treated product was viewed as acceptable. Results demonstrate the effectiveness of OA as a postlethality treatment meeting U.S. Food Safety and Inspection Service regulatory guidelines for RTE meat and poultry products with minimal impact on sensory quality.     

Use of sodium caseinate/glycerol edible films to reduce lipid oxidation in sliced turkey meat

The objective of this study was to investigate the influence of sodium caseinate films containing glycerol [glycerol:protein ratio 0.32 (w/w)] on lipid oxidation in cooked turkey breast meat slices. Slices were wrapped in films of different thickness (22, 42, and 58 μm) and were stored at 4 °C for 1, 2, 3 and 4 days. Lipid oxidation was measured using TBARS and hexanal assays on each day of storage while an olfactory sensory analysis was carried out on all the samples after 4 days of storage. TBARS values and hexanal levels of unwrapped samples (~6.0 mg MDA/kg and ~8.0 mg hexanal/kg) were significantly (P ≤ 0.05) higher than those of the casein film wrapped samples (~3.0 mg MDA/kg and ~3.0 mg hexanal/kg). Sensory analysis also showed significant (P ≤ 0.05) differences between wrapped samples and unwrapped samples, the former being perceived as less rancid. Thus wrapping in caseinate films may help reduce lipid oxidation in cooked turkey meat.     

Application of a bacteriophage cocktail to reduce Salmonella Typhimurium U288 contamination on pig skin

Multidrug-resistant Salmonella Typhimurium U288 is a significant pathogen of pigs, accounting for over half of all outbreaks on UK pig production premises. The potential of this serovar, and other salmonellae, to enter the food chain during the slaughtering process requires that efforts be made to reduce the prevalence of these bacteria at both the pre- and post-harvest stages of production. A bacteriophage cocktail (PC1) capable of lysing various Salmonella enterica serovars was designed using the broad host-range phage Felix 01, and three phages isolated from sewage. PC1 applied to pig skin experimentally-contaminated with U288 achieved significant reductions (P < 0.05) in Salmonella counts when stored at 4 °C over 96 h. Reductions of > 1 log₁₀ unit were observed when the ratio of phage applied was in excess of the bacterial concentration. The treatment was found to be effective at a multiplicity of infection (MOI) of 10 or above, with no significant reductions taking place when the MOI was less than 10. Under these conditions U288 counts of log₁₀ 4.1-4.3 CFU were reduced to undetectable levels following the application of PC1 to pig skin (> 99% reduction). These data suggest phage cocktails could be employed post-slaughter as a means to reduce Salmonella contamination of pig carcasses.     

微波技术在马蹄糕生产中的应用研究

以马蹄淀粉糊为主要原料,比较了微波加热和传统加热方式对马蹄糕质量的影响,通过研究得到微波加热马蹄糕产品的最佳工艺.另外还研究了微波杀菌对马蹄糕贮藏效果的影响,从而为微波技术在像马蹄糕这类传统食品中的应用提供了依据.     

Use of ozone to reduce molds in a cheese ripening room

Cheese ripening rooms have an unusual environment, an environment that encourages mold growth. Ozone has been applied in various ways in the food industry. One useful advantage of ozone is that it inactivates molds. In this study, a cheese ripening room was ozonated, and the effectiveness of this treatment was evaluated both in air and on surfaces through sampling on a weekly basis over a 3-month period. The results obtained indicate that ozone treatment reduced the viable airborne mold load but did not affect viable mold on surfaces. Only by wiping the surfaces with a commercial sanitizer was it possible to decrease the viable mold load on surfaces. To improve overall hygiene in the ripening room, a combination of cleaning regimes is recommended. The mold genera occurring most frequently in the air of the cheese ripening room were Penicillium, Cladosporium, and Aspergillus, which accounted for 89.9% of the mold isolates. Penicillium and Aspergillus were identified to the species level, and data showed that P. brevicompactum and P. aurantiogriseum, as well as A. versicolor, were the species most frequently isolated.     

The effect of microwave treatment on the immunoreactivity of gliadin and wheat flour

Commercial gliadins and wheat flour were exposed to microwaves at power distribution of 70, 200, and 500 W for different time periods to achieve a level of applied energy doses up to 150 kJ. Ethanolic extracts (40 vol.% ethanol/water) of microwave treated samples were analyzed by ELISA with the use of either monoclonal antibodies against -gliadin or polyclonal anti-gliadin antibodies and by electrophoresis followed by immunoblotting. A significant increase in reactivity, almost 210% over the untreated control sample, was observed for gliadins exposed to the energy dose of 40 kJ. Gliadins treated with higher energy doses showed a drop in an immune response independent of monoclonal or polyclonal antibodies used in ELISA. Gliadin fractions extracted from wheat flour treated with microwaves demonstrated similar immunoreactivity changes vs applied energy, although the maximum of reactivity appeared at 30 kJ. The increase in immune response of microwave irradiated gliadins was also confirmed by immunoblotting assay with the use of sera of patients susceptible to wheat flour allergy. Reversed phase HPLC elution profiles of treated gliadins showed that the content of all gliadin fractions in microwave treated samples decreased with the increase of the dose of applied energy.