Streptococcus macedonicus ACA-DC 198 produces the lantibiotic, macedocin, at temperature and pH conditions that prevail during cheese manufacture

Streptococcus macedonicus ACA-DC 198, a natural cheese isolate, produces the anticlostridial bacteriocin, macedocin. Bacteriocin activity was detected from the mid-exponential growth phase and remained constant during the stationary phase. A secondary model was setup to describe the influence of temperature (20-45 degrees C) and pH (5.1-6.9) on cell growth of and bacteriocin production by S. macedonicus ACA-DC 198 during in vitro laboratory fermentations. The optimum temperature for bacteriocin production (20-25 degrees C) was markedly lower than the optimum growth temperature (42.3 degrees C). In contrast, the specific macedocin production was maximal around pH 6.0, whereas growth was optimal at pH 6.4. Consequently, the maximum bacteriocin activity was reached between pH 6.0 and 6.5.     

Modelling growth and bacteriocin production by Lactobacillus curvatus LTH 1174 in response to temperature and pH values used for European sausage fermentation processes

Lactobacillus curvatus LTH 1174, a strain isolated from fermented sausage, produces the antilisterial bacteriocin curvacin A. Its biokinetics of cell growth and bacteriocin production as a function of temperature (20-38 degrees C) and pH (4.8-7.0) were investigated in vitro during laboratory fermentations using de Man, Rogosa and Sharpe (MRS) medium. A predictive, successfully validated model was set up to describe the influence of temperature and pH on the microbial behavior. Both cell growth and bacteriocin activity were influenced by changes in temperature and pH. The optimum temperature value for cell growth, 34.5 degrees C, did not correspond with the optimum temperature for curvacin A production (20-27 degrees C). Interestingly, the pH range for growth and curvacin A production was broad. Thus, Lb. curvatus LTH 1174 seems to be a promising bacteriocin-producing strain for use in European sausage fermentations that are performed at temperatures near 25 degrees C.     

Influence of pH and temperature on growth and bacteriocin production by Leuconostoc mesenteroides L124 and Lactobacillus curvatus L442

The aim of this study was to investigate the relationship between the microbial growth, the bacteriocin production and the effect of pH and temperature on the occurrence and the concentration of the maximum activity, to optimize the bacteriocin synthesis during the growth cycle. Two bacteriocins produced by lactic acid strains Leuconostoc mesenteroides L124 and Lactobacillus curvatus L442 were studied. A slight increase of the final biomass resulted in the improvement of the bacteriocin activity in the growth medium under controlled pH (5.0 and 5.5). Temperature and pH had a significant effect on the production of the two bacteriocins and was enhanced by the relatively low growth rates. The optimum production conditions of the bacteriocins did not coincide with those for growth. The optimum pH and temperature values for growth were 6.0-6.5 and 30?°C and for bacteriocin production were 5.5 and 25?°C.     

Temperature shows greater impact on bovine Longissimus dorsi muscle glycogen debranching enzyme activity than does salt concentration

The degradation of glycogen progresses by the co-operation of two enzymes: glycogen phosphorylase (phosphorylase) and glycogen debranching enzyme (GDE). We studied the effect of temperature (4–42 °C) and salt concentration (0–3% NaCl) on bovine M. longissimus dorsi GDE activity. GDE activity (n = 4) decreased significantly with decreasing temperature from about 40–4 °C. GDE exhibited 52% activity at 25 °C and 11% at 4 °C compared to its optimum activity measured at 39 °C. In rapidly chilled meat, the reduction in GDE activity may substantially delay the rate of glycolysis. However, residual GDE activity at 4 °C seems sufficient to enable the attainment of normal ultimate pH if the available time is long enough. An increase in salt concentration from 0% to 2% and to 3% induced a significant (P < 0.001) increase in the ultimate pH of ground bovine meat (n = 6), but showed no effect on GDE activity.     

Growth characteristics of motile Aeromonas spp. isolated from different environments

The growth of 80 strains of motile Aeromonas spp. derived from environments with temperatures above 25°C and below 15°C, respectively, were examined at five temperatures (5°C, 10°C, 25°C, 37°C and 44°C) and four salt levels (0.05%, 2%, 4% and 6% NaCl). Sixty-one strains were further examined at two pH levels (pH 7.3 and pH 5.3). All strains grew at 25°C and 10°C with the majority of the isolates proliferating from approx. 10² to approx. 10⁷ cfu/ml within 1 and 3 days, respectively. In contrast, there were significant differences in the proportion of isolates able to grow at 5°C and 37°C depending on the temperature of their source of isolation. The ecological background of the organisms thus influences their thermal growth range and their ability to proliferate at body temperature, a highly significant factor in infective disease. At 25°C and pH 7.3, all strains grew in 0.05% NaCl, 96% grew in 2% NaCl, 96% grew in 2% NaCl while few grew in broth containing 4% or 6% NaCl. Lowering the pH to 5.3 with lactic acid caused a marked increase in the lag phase at 25°C and prevented growth of a large number of isolates at suboptimal conditions. Thus, none of the isolates from warm environments and only 8% of the isolates from cold environments grew at this pH at 5°C. The observed differences in growth optima between strains from different environments are discussed in relation to food- or waterborne infection.     

Antibacterial activity of Lactobacillus plantarum UG1 isolated from dry sausage: characterization, production and bactericidal action of plantaricin UG1

Lactobacillus plantarum UG1 isolated from dry sausage produced an antimicrobial substance that inhibited other strains of the genera Lactobacillus and Lactococcus, and some foodborne pathogens including Listeria monocytogenes, Bacillus cereus, Clostridium perfringens and Clostridium sporogenes. This antibacterial substance was inactivated by proteolytic enzymes and showed a bactericidal mode of action. Consequently, it was characterized as a bacteriocin, and was designated plantaricin UG1. This bacteriocin was stable in the pH range 4.5 to 7.0, partially inactivated by amylolytic enzymes and relatively thermostable. It was not affected by organic or lipolytic enzymes. Production of plantaricin UG1 was pH-and temperature-dependant and maximum yields were obtained in MRS broth cultures maintained at initial pH 6.5, and incubated at 25 °C to 30 °C, in the exponential to the early stationary growth phase of the producer organism. Ultrafiltration studies indicated that plantaricin UG1 has a molecular weight between 3 and 10 KDa. Curing experiments with L. plantarum UG1 resulted in the appearance of variants that lost bacteriocin production ability but were still immune to the bacteriocin. Plantaricin UG1 production appeared to be chromosomal encoded. Sensitive and insensitive Gram-positive bacteria adsorbed plantaricin UG1 irrespective of their susceptibility to it. In contrast, Gram-negative bacteria did not adsorb plantaricin UG1. The bactericidal action of plantaricin UG1 did not depend on the physiological state of the indicator culture and did not cause cell lysis. The resistance of two indicator strains to plantaricin UG1 has been studied.     

A wild strain of Plodia interpunctella (Hübner) (Lepidoptera: Pyralidae) from farm-stored maize in South Carolina: Effect of temperature on mating, survival, and fecundity

The purpose of this study was to develop age-specific survivorship and fecundity schedules for adult Plodia interpunctella (Hübner) relevant to maize storages, with special reference to the southeastern states (USA). Laboratory cultures were established with moths collected from farm-stored maize in South Carolina and maintained on cracked maize at 30 °C and 60% r.h. Age-specific schedules of survivorship and fecundity, the length of the oviposition period, mating success, and mating frequency were determined at 20, 25, 30, and 35 °C and about 75% r.h. The maximum oviposition period was longest (18 d) at 20 and 25 °C, and shortest (8 d) at 35 °C. The optimum temperatures for reproduction (mating frequency and fecundity) were 25–30 °C, but mean life-span was longest (13.2 d) at 20 °C and declined linearly with increasing temperature. Mean total (lifetime) fecundity ranged from 16.9 eggs at 35 °C to 227.7 eggs at 25 °C.     

Fumigation with carbonyl sulfide: a model for the interaction of concentration, time and temperature

The new fumigant carbonyl sulfide offers an alternative to both methyl bromide and phosphine as a grain fumigant. Separate mathematical models for levels of kill, based on quantitative toxicological studies were developed for adults and eggs of the rice weevil Sitophilus oryzae (L.). These models suggest that fumigation exposure times for carbonyl sulfide will be a compromise between those of methyl bromide (typically 24 h) and phosphine (7–10 d) to achieve a very high kill of all developmental stages. S. oryzae eggs were more difficult to kill with carbonyl sulfide fumigation than the adults. At 30°C, a 25 g m⁻³ fumigation killed 99.9% of adults in less than 1 d, but took 4 d to kill the same percentage of eggs. Models were generated to describe the mortality of adults at 10, 15, 20, 25 and 30°C. From these models it is predicted that fumigation with carbonyl sulfide for 1–2 d at 30 g m⁻³ will kill 99.9% of adults. Furthermore the models illustrate that fumigations with concentrations below 10 g m⁻³ are unlikely to kill all adult S. oryzae. Significant variation was observed in the response of eggs to the fumigant over the temperature range of 10 to 30°C. Models were generated to describe the mortality of eggs at 10, 15, 20, 25 and 30°C. As the temperature was reduced below 25°C, the time taken to achieve an effective fumigation increased. Extrapolating from the models, a 25 g m⁻³ fumigation to control 99.9% of S. oryzae eggs will take 95 h (4 d) at 30°C, 77 h (3.2 d) at 25°C, 120 h (5 d) at 20°C, 174 h (7.5 d) at 15°C and about 290 h (11 d) at 10°C. The role of temperature in the time taken to kill eggs with carbonyl sulfide cannot be ignored. In order to achieve the desired level of kill of all developmental stages, the fumigation rates need to be set according to the most difficult life stage to kill, in this instance, the egg stage.     

Bacteriocin production by Lactobacillus pentosus B96 can be expressed as a function of temperature and NaCl concentration

Lactobacillus pentosus B96 is a bacteriocin-producing strain that was isolated from fermenting olive brines. The aim of the present work was the optimization of bacteriocin production, using response surface methodology (RS). A two-level screening Plackett–Burman design was used to select influencing factors. Then, a central composite design, with three repetitions in the centre, for pH, NaCl concentration, and temperature was carried out. Finally, an RS, which included the region of maximum accumulated bioactivity, was built as a function of NaCl concentration and temperature. Bioactivity accumulation was always observed during the exponential growth-phase, although no apparent correlation between maximum accumulated bioactivity and biomass formation was found. L. pentosus B96 is known to grow better at about 30 °C, neutral pH, and by the absence of NaCl; however, a suboptimal temperature (22 °C) and a moderate NaCl stress (0.65 mol l⁻¹) stimulated bacteriocin production. The research led to environmental conditions that maximized bacteriocin activity, which can be expressed as a polynomial function of temperature and NaCl concentration. The suboptimal growth conditions, which were found to produce the highest bacteriocin titres, resembled those prevailing during green table olive fermentation. This model can be used to improve “in situ” bacteriocin production thus contributing to the microbiological control of the process.     

Inactivation of polyphenol oxidases in cloudy apple juice exposed to supercritical carbon dioxide

The inactivation of polyphenol oxidase (PPO) in cloudy apple juice exposed to supercritical carbon dioxide (SCCO₂) treatment was investigated. Higher pressure, higher temperature, and longer treatment time caused more inactivation of PPO. The maximum reduction of PPO activity reached more than 60% at 30 MPa and 55 °C for 60 min. The experimental data followed first-order reaction kinetics; the kinetic rate constant k and the decimal reduction time D were closely related to the pressure and temperature of SCCO₂ treatment. Higher pressures or higher temperatures resulted in lower D values (higher k), the D value of PPO was minimized to 145 min treated by the combination of 30 MPa and 55 °C. Activation energy of 18.00 kJ /mol, was significantly reduced by SCCO₂ treatment at 30 MPa, as compared to activation energy of 72.0 kJ/mol for identical treatment at atmospheric pressure. Pressure and temperature sensitivity of kinetic parameters were studied. Z_P at 55 °C was 66.7 MPa and Z_T at 30 MPa was 108 °C.     

Effect of temperature and water activity on growth and ochratoxin A production by Australian Aspergillus carbonarius and A. niger isolates on a simulated grape juice medium

The effect of water activity (0.92, 0.95, 0.965 and 0.98) and temperature (15 °C, 25 °C, 30 °C and 35 °C) on growth rate and ochratoxin A (OA) production by five strains of Aspergillus carbonarius and two strains of A. niger isolated from Australian vineyards was characterised on a synthetic grape juice medium. Maximum growth for A. carbonarius occurred at ca 0.965 a_w and 30 °C, and for A. niger, at ca 0.98 a_w and 35 °C. The optimum temperature for OA production was 15 °C and little was produced above 25 °C. The optimum a_w for toxin production was 0.95–0.98 for A. carbonarius and 0.95 for A. niger. Toxin was produced in young colonies after and, typically, did not continue to accumulate the entire surface area of the plate was colonised. Rather, the amount decreased as colonies aged. Trends for growth and OA production were similar among Australian isolates and those from European grapes, as reported in the literature.     

Purification, partial characterisation and mode of action of enterococcin EFS2, an antilisterial bacteriocin produced by a strain of Enterococcus faecalis isolated from a cheese

Enterococcus faecalis strain EFS2, isolated from the surface of a traditional cheese, produced a bacteriocin active against Gram-positive bacteria including Listeria spp. and some Staphylococcus aureus strains. The bacteriocin, named enterococcin EFS2, has been purified to homogeneity by ammonium sulphate precipitation and reversed-phase high performance liquid chromatography (RP-HPLC). The molecular weight was determined by mass spectrometry to be 7149.6. The amino acid composition of enterococcin EFS2 revealed that it contained 67 amino acid residues and had a blocked amino-terminal end. Enterococcin EFS2 induced viability loss, efflux of K⁺ ions and ATP, and cell lysis. Kinetic study of bactericidal activity of enterococcin EFS2 on Listeria innocua strain LIN 11 indicated slower cell destruction than by nisin. At pH 7.0, the activity of enterococcin EFS2 was the highest at 35 °C and was lost at 15 °C. The bacteriocin was more active against L. innocua strain LIN11 in broth adjusted to pH 6.0, 7.0 and 8.0 than to pH 4.5 at 30 °C.     

Screening for anti-listerial bacteriocin-producing lactic acid bacteria from "Gueddid" a traditionally Tunisian fermented meat

Forty eight lactic acid bacteria strains isolated from “Gueddid”, a traditionally Tunisian fermented meat, were screened for bacteriocin production. Four strains named MMZ 04, 09, 13, and 17 showed antimicrobial activity and were identified as Enterococcus faecium by molecular methods based on the 16S-23S rDNA ISR, PCR-RFLP analysis of the 16S-23S rDNA ISR and species-specific primers. The four antimicrobial compounds were heat stable (121 °C for 15 min), active over a wide pH range (3–9) and the antimicrobial activity was lost after treatment with trypsin, -chymotrypsin and proteinase K but not by lysozyme and lipase. The mode of action of enterocin MMZ17 was identified as bactericidal. The MMZ17 bacteriocin was partially purified by ammonium sulphate precipitation and C₁₈ Sep-Pack chromatography. The apparent molecular size of enterocin MMZ17 as indicated by activity detection after SDS-PAGE was lower than 6.5 KDa. According to these assays, enterocin MMZ17 can be classified as a small, heat-stable Listeria-active peptide, presumably belonging to class IIa bacteriocins.     

Growth of Carnobacterium divergens M35 and production of Divergicin M35 in snow crab by-product, a natural-grade medium

This work aimed to study the factors influencing the growth of Carnobacterium divergens strain M35 and its ability to produce a new class IIa bacteriocin (divergicin M35) in various synthetic media and in medium supplemented with snow crab hepatopancreas (SCH), a natural-grade by-product of crustacean processing. C. divergens M35 growth and bacteriocin production in SCH-supplemented medium was evaluated at different temperatures in batch fermentations and under controlled pH. C. divergens M35 was shown to grow well in SCH medium at tested temperatures between 4 and 30 °C, except at 37 °C. Maximum divergicin M35 production was obtained after 10 h of growth in SCH medium at 25 and 30 °C with a total activity of 3.7 × 10⁴ AU mL⁻¹. Less growth was observed at 37 °C, for which a total bacteriocin activity of only 256 AU mL⁻¹ was obtained. The production of divergicin M35 was greatly influenced by the medium composition, especially by the type of added carbon source. The best production of divergicin M35 in SCH medium was observed at a controlled pH of 7.0. This study describes the optimal parameters for the growth of C. divergens M35 and production of divergicin M35 and demonstrates the effectiveness of the marine by-product as a medium supplement for this culture.     

Use of Byproducts of Food Industry for Production of Antimicrobial Activity by Bacillus sp. P11

Production of antimicrobial activity by Bacillus sp. P11 was tested on different byproducts of food industry, like fish meal, grape waste, an industrial fibrous soybean residue, soybean meal, and cheese whey. Bacillus sp. P11 produced the higher amount of antimicrobial activity on soybean meal, followed by fish meal and fibrous soybean residue. Soybean meal was the selected medium to determine the effect of three variables (temperature, initial pH, and substrate concentration) on bacteriocin activity by response surface methodology, using a 2³ factorial design. Statistical analysis showed good adequacy to the model (R ² of 0.8268). In the range studied, temperature and initial pH of the medium have a significant effect on bacteriocin production, and substrate concentration has no significant effect. Response surface data showed maximum bacteriocin production at initial pH between 7.0 and 8.5 and temperature between 39 and 42 °C. In the optimum conditions (initial pH 7.0 and 42 °C), production of bacteriocin activity by Bacillus sp. P11 was compared using a commercial medium (BHI broth) and soybean meal. Maximum activity achieved with the soybean meal-based medium was similar to that obtained with BHI, indicating that soybean meal may be a cost-effective substrate for production of antimicrobial activity by Bacillus sp. P11.     

Sorption isotherms of salted minced pork and of lean surface of dry-cured hams at the end of the resting period using KCl as substitute for NaCl

The effect of KCl on sorption isotherms was determined on salted minced meat (with 0%, 30% and 100% molar substitution of NaCl by KCl) at 5 °C and 25 °C and meat from a 3 mm thick slice from the surface of dry-cured hams (with 0% and 35% molar substitution of NaCl by KCl) held at 70–75%, 75–80% and 80–85% air relative humidity during the resting period.

The sorption isotherms were determined gravimetrically by exposing the meat samples to several atmospheres of known relative humidity controlled by different saturated salts according to the COST90 method. The sorption equipment consisted of a chamber containing 11 containers, covering the water activity (a_w) range from 0.112 to 0.946 at 25 °C. The hermetically closed sorption containers filled with KCl and minced meat samples were irradiated at 3 kGrey (gamma irradiation ⁶⁰Co). The water content at equilibrium was higher in minced meat with NaCl than in minced meat with KCl (100% molar substitution of NaCl by KCl) at 5 °C within the range of 0.4313 and 0.7565 a_w. However, when substitution was 30% in minced meat and 35% in hams the isotherms were similar to isotherm without substitution.     

Rheology of mozzarella cheese: Extrusion and rolling

A capillary rheometer was used to determine the processability and rheology of mozzarella cheese over the temperature range of 25–60 °C. End pressure corrections, which are corrections associated with the entry and exit of the mozzarella cheese in and out of the capillary die, were found to be significant. Surprisingly, wall slip was found to be insignificant up to shear stress values of 30 kPa. Capillary extrusion at low temperatures (<50 °C) resulted in extrudates that were distorted, while at higher temperatures (>50 °C), the extrudates were fairly smooth. Rolling experiments at 25 °C indicated that rolling can be used to shape mozzarella cheese (at a reduction ratio <2.1) without fracturing. Based on the extrusion and rolling experiments, mozzarella cheese can be described as a power law fluid with an index of about 0.24, while at higher temperatures (30 °C<T<60 °C), the power law index is about 0.4, indicating its increased flowability.     

Respiratory activity and phenolic compounds in pre-cut celery

The effect of temperature on respiratory activity and total phenol and flavonoid contents in pre-cut celery was assessed within the 24 h following this minimal processing. To this end, celery petioles were cut as strips, conditioned in crystal polyethylene terephthalate trays covered with PVC film and stored at 0, 10 and 20 °C. Samples were removed at 0, 2, 4, 6 and 24 h after processing to analyse respiratory activity and concentrations of total phenols and flavones. For the samples kept at 0 °C for 24 h, chlorogenic acid was also determined, along with total flavonoids and antioxidant power. At this temperature, the total phenol contents remained basically constant, though at 10 °C it increased considerably two hours after applying the cutting stress. At 20 °C the increase observed was less important. The flavones, identified by HPLC in pre-cut celery were apigenin and luteolin, whose concentrations also increased between two to six hours after processing. However, exposure for 24 h at 0 °C produced a considerable decrease in total flavonoids.     

Effect of temperature on reproductive parameters and the longevity of Acarus farris (Acari: Acaridae)

Reproductive parameters and the longevity of Acarus farris were examined at six constant temperatures, ranging from 7 to 29 °C, and a relative humidity of 90±5%. As temperature increased, the preoviposition period rapidly decreased to a minimum, above 25 °C. Fecundity was adversely affected by extreme temperatures while the oviposition period increased as temperature was reduced. The relationship between reproductive parameters and temperature was fitted using different polynomial and non-linear models. Male and female longevity increased as temperature decreased, except for the males at 7 °C, which showed significantly lower longevity than at 10 °C. Moreover, males showed significantly greater longevity than females. The effect of temperature on the capacity for increase of A. farris populations was also established. The non-linear Lactin model provided a reliable fit of the relationship between intrinsic rate of increase and temperature (R²>0.99). The optimum temperature for development was calculated to be 25 °C. At this temperature, the population doubling time was 2.8 days. The lower and upper thermal thresholds for A. farris populations were established at 6.4 and 29.9 °C, respectively.