Prediction of Listeria spp. growth as affected by various levels of chemicals, pH, temperature and storage time in a model broth

The effects of concentration of NaCl (0.5 to 12.5%), methyl paraben (0.0 to 0.2%), sodium propionate (0.3%), sodium benzoate (0.1%), potassium sorbate (0.3%), pH (>5.9) temperature (4 to 30°C), storage time (up to 58 d) and inoculum (>10⁵ to >10⁻² per ml) on the log₁₀ probability percentage of one cell of Listeria spp. to initiate growth in a broth system were evaluated in a factorial design study. At pH 5.96 and temperature ranging from 4 to 30°C the concentrations of sodium propionate, potassium sorbate, and sodium benzoate examined allowed growth of L. monocytogenes with lag phases at 4°C of 18, 27 and 21 days, respectively. For 0.1 and 0.2% methyl paraben growth of all Listeria spp. was initiated at 8°C and 30°C, respectively. At pH 6, concentration of 12% NaCl supported the growth of L. monocytogenes at 8 to 30°C, whereas 12.5% inhibited all Listeria species. Four regression equations were derived relating probability of growth initiation to temperature, concentrations of NaCl and preservatives storage time, and Listeria species specific effects. From these equations, the number of cells needed for growth initiation can be calculated. The impact of this type of quantitative study and its possible application on the development of microbial standards for foods is discussed.     

Behaviour of Listeria monocytogenes in raw sausages (merguez) in presence of a bacteriocin-producing lactococcal strain as a protective culture

The effectiveness of a bacteriocin produced by Lactococcus lactis subsp. lactis M in reducing population level and growth of Listeria monocytogenes ATCC 7644 in fermented merguez sausage was examined. Two different formulas (with or without added nitrites) were assayed and predetermined numbers of Listeria (ca 10⁶ cfu g⁻¹) were added to sausage mixture. The effect of in situ production of the bacteriocin by Lactococcus lactis M on Listeria monocytogenes ATCC 7644 during fermentation and storage of merguez sausages at room (ca 22 °C) or at refrigeration (ca 7 °C) temperature was tested. Results indicated that counts of Listeria monocytogenes were decreased during fermentation of merguez samples fermented with either the bacteriocin-producing Lactococcus lactis M (Bac⁺) or a nonbacteriocin-producing Lactococcus lactis J (Bac⁻). However, reduction in Listeria cfu's was greater in samples fermented with the Bac⁺ than in those fermented with the Bac⁻ starter. In merguez sausage made without nitrites addition, the Bac⁺ starter induced further decrease in Listeria counts by 1.5 log cycles compared with that induced by the Bac⁻ starter. While in merguez samples with added nitrites (0.4%), the effect of the bacteriocin produced in situ was less important than in those made without nitrites addition.     

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.     

Listeria innocua and aerobic mesophiles during chill storage of inoculated mechanically recovered poultry meat treated with high hydrostatic pressure

Mechanically recovered poultry meat (MRPM) was inoculated with Listeria innocua 910 CECT at a level of approximately 10⁸ CFU g⁻¹. Vacuum-packaged samples were treated by combinations of pressure (350, 400, 450 and 500 MPa), time (5, 10, 15 and 30 min) and temperature (2, 10 and 20°C) and later stored at 2°C for 2 months. Counts of L. innocua and aerobic mesophilic bacteria were determined 1, 4, 7, 15, 30 and 60 days after pressurisation. For mesophiles, in most treatments, pressurization at 2°C gave the significantly best results. High pressure caused a marked bactericidal effect on L. innocua: reductions higher than 7.5 log units were achieved in several cases. Some cells were just sublethally injured by pressure. Samples treated at 500 MPa for 30 min at 2°C had counts of only 2.3 log units after 60 days of chill storage. Noninoculated pressurised MRPM did not show Listeria growth throughout storage. These results suggest that high pressure processing can enhance the microbiological quality of MRPM.     

Identification of halothane genotypes by calcium accumulation and their meat quality using live pigs

The three halothane genotypes (NN, Nn, and nm) were identified by measuring the capacity for Ca²⁺ accumulation by sarcoplasmic reticulum in whole muscle homogenate preparations of M. longissimus dorsi with a Ca²⁺ specific electrode at 35°C. Significant differences (P < 0·001) in deterioration (%) of Ca²⁺ accumulation, 12% for NN, 35% for Nn, and 81% for nn pigs, were observed after ageing the whole muscle homogenate preparations for 24 h in ice.

Predictions of meat quality in live pigs (n = 34) based on the values for water-holding capacity, assessed as fluid (g/0·5 g wet wt LD), and pH (fluid) by using small biopsy LD samples (Cheah et al. 1993) were performed on all the halothane genotypes. The halothane genotype NN (n = 11) showed a fluid value of 0·37 ± 0·01 and a pH (fluid) value of 6·62 ± 0·03 as compared with 0·61 ± 0·02 and 5·84 ± 0·04, respectively, for the halothane genotype nn (n = 13). The Nn pigs (n = 10) showed fluid (0·49 ± 0·03) and pH (fluid) (6·19 ± 0·11) values between those values observed for the two homozygotes (NN and nn). Predictions of meat quality in live pigs from biopsy LD muscles were confirmed from assessments on post-mortem LD muscles based on pH₁ and fibre optic probe (FOP) measurements.

The extent of deterioration (%) in Ca²⁺ accumulation showed high correlations with fluid (r = −0·861) and pH (fluid) (r = −0·831) in the biopsy LD samples, and with pH₁ (r = 0·663), FOP (r = −0·812), and drip (%) loss (r = −0·777) in the post-mortem LD samples.     

Colour of normal and high pH beef heated to different temperatures as related to oxygenation

The effects of oxygenation and thermal treatment (internal temperature, T_i: 45, 60, 75°C) on the colour and some colour related physical and biochemical properties of beef longissimus dorsi (LD) muscle, both normal (pH_u5.6) and DFD (pH_u>6.6), were studied. The colour components (L^*, a^*, b^* values) for the raw and heated LD, both before and after oxygenation, were instrumentally and sensorily evaluated. The colour of raw and heated (60°C) DFD beef before and after oxygenation differed significantly from the normal meat and contained more native muscle pigment (TMP). pH also influenced the depth of the oxygenated layer, specific activity of cytochrome c oxidase (SACCO) and the amount of oxygen consumed. An increase in internal temperature was usually accompanied by a lower SACCO and a significant decrease of TMP, as well as a change of all colour parameters. Oxygenation of the raw and heated slices (except at 75°C) of both types of meat led to higher L^*, a^* and b^* values.     

Sorption of chloroanisole vapors by raisin packaging material

The behavior and concentration of 2,4,6-trichloroanisole (TCA) vapors migrating into low-density polyethylene film (PE) of 0.39 μm at various temperatures and desorption of TCA from PE were determined. After 12 h exposure, 1642 μg g⁻¹ TCA was sorbed at 30 °C compared with 675 μg g⁻¹ at 20 °C. For PE to reach equilibrium of 4200 μg g⁻¹ at 30 °C took 48 h, but 120 h at 20 °C. The transmission of TCA through PE occurred after 12 h at 30 °C (8.9 μg kg⁻¹ m⁻² h⁻¹) and after 36 h at 20 °C (5.0 μg kg⁻¹ m⁻² h⁻¹). Desorption of TCA from PE increased with temperature. At 80 °C, 99% TCA was desorbed in 1 h compared to 51% at 40 °C, 31% at 30 °C and 17% at 20 °C. The rate of sorption, desorption and transmission of TCA vapors by PE is highly temperature-dependent.     

Microbiological quality of ayib, a traditional Ethiopian cottage cheese

One-hundred samples of ayib, a traditional Ethiopian cottage cheese, were purchased from Awassa market and analysed for their aerobic mesophilic counts, psychrotropic counts, yeasts and molds, coliforms, spore-formers, enterococci, lactic acid bacteria, Listeria monocytogenes, staphylococci and Bacillus cereus. The majority of the samples showed counts of mesophilic aerobic bacteria, yeasts and enterococci of 10⁸, 10⁷ and 10⁷ cfu/g. About 55% of the samples were positive for coliforms and faecal coliforms. Listeria spp. were not detected in any of the samples. B. cereus and S. aureus were isolated at varying frequencies but at low numbers (10²–10³). The pH value of the samples varied between 3.3 and 4.6 with about 40% having pH lower than 3.7.     

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.     

Low Temperature Growth of Type E Clostridium botulinum Spores. 1. Effects of Sodium Chloride, Sodium Nitrite and pH

SUMMARY— The effects of pH and the addition of sodium chloride (NaCl) or sodium nitrite (NaNO₂) to trypticase-peptone-glucose (TPGI and trypticase-peptone-sucrose-yeast extract (TPSY) media upon spore outgrowth were investigated using seven Type E Clostridium botulinum strains. An inoculum of 1.0 × 10⁵ spores/ml was used and the pH was adjusted with hydrochloric acid to cover the range of 5.2 to 6.6. To define salt tolerance, NaCl was added to the media at intervals of 0.5% in the range of 2.0 to 5.0% and at 0.1% intervals in the 4.5 to 5.0% range. The effect of NaNO₂ was investigated with the addition of 100 and 200 ppm NaNO₂ to the media. Samples were incubated at 30, 15.6, 10, 7.2, 5.0 and 3.4°C. Outgrowth of all strains tested was inhibited at pH 5.2 at 15.6°C. Inhibition occurred at higher pH at lower temperatures. None of the strains showed outgrowth with 4.87% NaCl in the media at any of the incubation temperatures used. Addition of 100 and 200 ppm NaNO₂ to the media inhibited the outgrowth of the Minneapolis, 517, 26080 and A6247 strains but not the Kalamazoo and Seattle Forks strains.     

Physiological properties of Lactobacillus paracasei, L. danicus and L. curvatus strains isolated from Estonian semi-hard cheese

Growth and survival of Lactobacillus paracasei (six strains), L. danicus sp. nov. (four isolates, two strains) and L. curvatus (two strains) from semi-hard Estonian cheeses were comparatively studied in different environmental conditions of relevance for their growth in cheese and survival in gastric environment. Maximum specific growth rates for L. paracasei strains varied between 0.40 and 0.57 h⁻¹, and all strains were tolerant to low water activities, heating at 60 °C for 30 min and pH 3. The newly discovered genetically distinct species L. danicus was characterized by low maximum growth rates (0.26–0.38 h⁻¹) and low temperature optimum (<30 °C). It was acid and heat sensitive and inhibited at salt concentrations from 4% and water activities below 0.93. L. curvatus was characterized by the highest growth rates (0.65–0.70 h⁻¹), tolerance to high NaCl concentrations, but sensitivity to heating, bile salts and low pH. The study showed that genetically different LAB species isolated from cheese could be distinguished by simple cultivation experiments.     

Changes in histamine and microbiological analyses in fresh and frozen tuna muscle during temperature abuse

Temperature abuse of tuna (Thunnus alalunga) was carried out in order to assess the histamine buildup in fish-processing facilities where fish can be exposed to high temperatures for short periods of time. Histamine production was studied in tuna loins under different storage and abuse conditions. Tuna was stored at 0-2°C, 3-4°C, and 6-7°C, and abused for 2 h daily at 20°C and 30°C for 7-12 days. Loins abused at 30°C for 2 h daily contained potentially toxic histamine concentrations (67-382 mg kg^-1) when stored at a low refrigeration temperature (0-2°C), whereas when stored at 6-7°C, the loins contained highly toxic histamine concentrations (544.5-4156.6 mg kg^-1). Lower histamine concentrations (23-48 mg kg^-1 in loins stored at 0-2°C and 124.7-2435.8 mg kg^-1 in loins stored at 6-7°C) were observed in temperature-abused loins that were initially frozen. An increase over time was observed in most microbial counts tested. Bacteria isolated from the temperature-abused loins showed a varied ability of histamine production, with Morganella morganii, Klebsiella oxytoca, Staphylococcus hominis, and Enterococcus hirae being the most active histamine-producing bacteria.     

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.     

Impact of sorbitol on the thermostability and heat-induced gelation of bovine serum albumin

The influence of sorbitol (0–40 wt.%) on the thermal denaturation and gelation of bovine serum albumin (BSA, pH 7.0) in aqueous solution has been studied. The effect of sorbitol on heat denaturation of 0.5 wt.% BSA solutions was measured using ultrasensitive differential scanning calorimetry. The unfolding process was irreversible and was characterized by the thermal denaturation temperature (T_m). As the sorbitol concentration increased from 0 to 40 wt.%, T_m increased from 73.0 to 80.9 °C. The rise in T_m was attributed to the increased thermal stability of the globular state of BSA relative to its native state. The dynamic shear rheology of 4 wt.% BSA solutions containing 200 mM NaCl was monitored as they were heated from 30 to 90 °C at 1.5 °C min⁻¹, held at 90 °C for 120 min, and then cooled back to 30 °C at −1.5 °C min⁻¹. Sorbitol increased the protein gelation temperature (ΔT_gel +10 °C for 40 wt.% sorbitol), decreased the isothermal gelation rate at 90 °C, but increased the final shear modulus of the gels cooled to 30 °C. The impact of sorbitol on gel characteristics was attributed to its ability to increase protein thermal stability, increase the attractive force between proteins and decrease the protein–protein collision frequency.     

Modeling the effect of inoculum size and acid adaptation on growth/no growth interface of Escherichia coli O157:H7

The objective of this study was to model with logistic regression the growth/no growth interface of different initial inoculation levels (10¹, 10³ and 10⁵ CFU/ml; study 1), or nonadapted vs acid-adapted (study 2) Escherichia coli O157:H7 as influenced by pH, NaCl concentration and incubation temperature. Study 1 was conducted with a mixture of four E. coli O157:H7 strains grown (35 °C, 24 h) in tryptic soy broth (TSB). Study 2 was conducted with the same mixture of four E. coli O157:H7 strains grown (35 °C, 24 h) in glucose-free TSB with 1% added glucose (final pH 4.83), or in diluted lactic acid meat decontamination runoff fluids (washings; final pH 4.92), or nonadapted cultures prepared in glucose-free TSB (final pH 6.45), or in water washings (final pH 6.87). Parameters included incubation temperature (10–35 °C), pH (3.52–7.32), and NaCl concentration (0–10% w/v). Growth responses were evaluated for 60 days turbidimetrically (610 nm) every 5 days in 160 (study 1) and 360 (study 2) combinations in quadruplicate samples, with a microplate reader. The lower the initial inoculum the higher were the minimum pH and a_w values permitting growth. Differences in the pH and a_w growth limits among inoculum concentrations increased at 15 and 10 °C. Acid-adapted cultures were able to grow at lower pH than nonadapted cultures, while at temperatures below 25 °C, growth initiation of nonadapted cultures stopped at higher a_w compared to acid-adapted cultures for the whole pH range of 3.52 to 7.32. A comparison with available data indicated that our model for acid-adapted E. coli O157:H7 in different environments may provide representative growth probabilities covering both nonadapted and stress-adapted contaminants.     

Study of the effects of temperature, pH and NaCl on the peptidase activities of non-starter lactic acid bacteria (NSLAB) by quadratic response surface methodology

The individual and interactive effects of temperature, pH and NaCl on the aminopeptidase-types N and A and proline iminopeptidase activities of several strains of non-starter lactic acid bacteria (NSLAB) were studied by quadratic response surface methodology. The effects on enzyme activities depended on the interactions among the independent variables, species, strains within species and type of activity. With few exceptions, the aminopeptidases N and A and proline iminopeptidase activities of Lactobacillus casei ssp. pseudoplantarum and Lb. curvatus were strongly inhibited by the hostile cheese-like conditions, while the peptidases of Lb. casei ssp. casei and especially Lb. plantarum were tolerant or not affected by variations in pH and showed the least sensitivity to NaCl or even a requirement for NaCl for the optimal activity. Strains which maintained relatively high activity under cheese-like conditions were selected within the species. The proline iminopeptidase of Lb. casei ssp. casei 2107 as well as Lb. plantarum 2788 and 2789 greatly tolerated the interactions among the independent variables. At 10°C in the presence of 3.750% NaCl and independent of the pH, the PepN activity of Lb. plantarum 2788 and 2789 was at least 33% of the maximum determined at pH 7.5 and 35°C. Proline iminopeptidase activity was most sensitive to the individual and interactive variations in temperature, pH and NaCl. On the other hand, aminopeptidase-type A activity seemed to be least sensitive to cheese-like conditions.     

The effects of spray and blast-chilling on carcass shrinkage and pork muscle quality

Combinations of blast- and spray-chilling of pork carcasses were compared to spray-chilling at conventional chilling temperatures with regard to carcass shrinkage during chilling and pork muscle quality. In experiment 1, pork sides were spray-chilled at 1°C for the first 10 h (40 spray cycles of 60-s duration every 15 min) of cooling or blast-chilled at −20°C for 1, 2 or 3 h followed by spray-chilling for 9, 8 or 7 h duration, respectively. All pork sides were then chilled to 24 h post mortem at 1°C. Experiment 2 followed the same procedures as experiment 1, except that −40°C was used as the blast-chill temperature.

Carcass shrinkage was similar for all treatments in experiment 1 at 24 h ranging from 0·5–0·7 g 100 g⁻¹. Blast/spray-chilling increased the rate of chilling and reduced the rate of post-mortem pH decline in two muscles (longissimus thoracis, LT and semimembranosus, SM) compared to the combined conventional/spray-chill treatment. Carcasses that were blast-chilled for 3 h had LT muscles that were darker with a higher protein solubility, less drip loss, shorter lengths and higher shear values compared to those from carcasses in the conventional/spray-chill treatment. In experiment 2, carcasses blast-chilled for 3 h at −40°C recorded a weight gain at 24 h of 0·4 g 100 g⁻¹, compared to a weight loss in all other treatments (0·2–0·4 g 100 g⁻¹). Muscle colour was darker in both the LT and SM of carcasses blast-chilled for 3 h at −40°C compared to carcasses from the conventional/spray-chill treatment, but most other measurements of muscle quality showed an inconsistent response to chilling treatment.     

MICROBIOLOGICAL PROFILE OF MURCHA STARTERS AND PHYSICO-CHEMICAL CHARACTERISTICS OF POKO, A RICE BASED TRADITIONAL FERMENTED FOOD PRODUCT OF NEPAL

Poko is a traditional rice based fermented food of Nepal prepared using murcha as the starter. The microbiological evaluation of eleven murcha starters showed that the lactic acid bacteria and yeast were dominant at 5×10⁵ to 1.0×10⁹ cfu g^-1 range while fungi were present at 2×10⁵ to 1.0×10⁷ cfu g^-1. Coliforms (1×10² to 1.4×10⁵ cfu g^-1), E. coli (1×10³ cfu g^-1), and. S. aureus (1×10² g^-1) were present in some of the murcha starters. Bacillus cereus was absent in all the starters. The microbial succession during poko fermentation suggested that it was primarily a mixed fermentation of yeasts, molds and lactic acid bacteria. The quality poko product obtained after two days and three days of fermentation at 30°C had a pH, acidity, reducing sugar, total sugar, and alcohol in the range of 3.2-3.0, 1.1-1.3 (% LA), 14.4-15.6 (%), 14.6-18.2 (%) and 1-1.6 (%) respectively. These critical ranges of biochemicals in the poko, due to the fermentation process imparted desirable organoleptic characteristics to the product. Saccharomyces cerevisiae, Candida versatilis, Lactobacillus spp, Pediococcus spp and Rhizopus spp were the dominant microorganisms identified from the poko fermentation. The results suggest that the quality of poko depends upon the microbial flora of the traditional murcha starters.     

Optimisation of calcium-dependent protease and cathepsin D assays in ostrich muscle and the effect of chemical and physical dry-curing parameters

The best conditions for the assay of cathepsin D and Ca²⁺-dependent pro tease (CDP) activity in ostrich muscle was established in order to have a simple, rapid and reliable method for its determination. Measurements of A_280nm of TCA-soluble peptides and amino acid digests of casein and haemoglobin were used for measuring proteolytic activity in muscle extracts. The best conditions for the reliable determination of cathepsin D activity were found to be the incubation of an enzyme extract for 1 hr at 55 °C in a reaction mixture containing 0.9% (w/v) haemoglobin in 50 mM sodium formate buffer, pH 3.7. Characterization of the assay system for CDPs, obtained after phenyl-Sepharose chromatography, indicated that proteolytic degradation of casein by CDPs was linear with time up to 30 min at 30 °C and up to 0.1 units of activity. The effect of NaCl, KCl, nitrate, ascorbic acid, phosphate, glucose and sucrose on ostrich muscle CDP and cathepsin D activities has been studied. Salt (NaCl and KCl) acts as a strong inhibitor of proteolytic activity. Sodium and potassium nitrates (in the range 0–1000 mg l⁻¹) affected activity to varying degrees. CDP activity was enhanced by sodium nitrate concentrations below 700 mg l⁻¹ and unchanged by potassium nitrate. Cathepsin D activity was inhibited to some extent by sodium nitrate above 200 mg l⁻¹ and completely by potassium nitrate. Results showed that phosphate is an inhibitor of both activities. High concentrations of ascorbic acid (above 6 g l⁻¹) inhibited cathepsin D activity. Glucose (up to 2g l⁻¹) activated cathepsin D activity and inhibited CDP activity (up to 1 g l⁻¹). Sucrose activated enzyme activities at very low concentrations (1 × 10⁻³ M) and inhibited activities above 1 × 10⁻³ M.     

Survival of enterohaemorrhagic Escherichia coli O157:H7 strain in Turkish soudjouck during fermentation, drying and storage periods

Soudjouck (a kind of Turkish sausage) batter was inoculated with Escherichia coli O157:H7 at a level of 10⁵ colony-forming unit (CFUg) and kept overnight at 4°C. After stuffing the soudjouck batter into natural casing, fermentation was carried out at 24±2°C and 90–95% relative humidity (RH) for 3 days with subsequent drying at 22±2°C and 80–85% RH for 5 days. Then, half of soudjouck samples were vacuum-packed in polyethylene bags and the rest were kept open. All samples were stored at 4°C (55% RH) for 3 months. E. coli O157:H7 and lactic acid bacteria counts, moisture contents and pH values of the samples were determined during fermentation, drying and storage periods. Results showed that count of E. coli O157:H7 decreased by 3 log unit during fermentation and drying periods. It was observed that this pathogen survived longer in vacuum-packaged samples (more than 2 months) than non-vacuum samples (more than 1 month).