Factors controlling the growth of Clostridium botulinum types A and B in pasteurized, cured meats III. The effect of potassium sorbate

The growth of Clostridium botulinum types A and B spores, at 10¹ or 10³ per container, was studied in a pork slurry system containing nitrite (40 μg/g), sodium chloride (2.5, 3.5, 4.5% w/v) sodium isoascorbate (550 μg/g) at varying pH levels, with or without potassium sorbate (0.26% w/v), without heating and after two heat treatments (80°C for 7 min, and 80°C for 7 min + 70°C for 1 hr) followed by storage at 15, 17.5, 20 or 35°C for up to 6 months. At a given spore inoculum, potassium sorbate significantly decreased toxin production, as did increasing NaCl, decreasing pH or decreasing storage temperature. Heat treatment did not significantly affect spoilage or toxin production overall, but interacted significantly with some factors. The effect of sorbate was greater at 3.5% NaCl than at 2.5%, at pH values below 6.0, and at low storage temperature.     

Transaminases of Skeletal Muscle. 1. The Activity of Transaminases in Post-Mortem Bovine and Porcine Muscles

SUMMARY: The activity of glutamic-oxaloacetic transaminase (GOT) and glutamicpyruvic transaminase (GPT) of bovine and porcine muscle tissue and muscle press juice was determined. The total GPT activity of muscle tissue is about one tenth of the GOT activity. There are no remarkable differences in the activities of GOT and GPT between these slaughter animals and other species (rat, rabbit and man). The GOT activity of the longissimus dorsi muscle of pigs is significantly higher than that of the same bovine muscle. The mitochondrial (GOT_M) and sarcoplasmic isozymes (GOT_B) of GOT in skeletal muscles of cattle and pigs were determined after electrophoretic separation. The ratio GOT_M:GOT_S in skeletal muscle was found to be about 1:1. There is only a small decrease in GOT activty during storage of muscle tissue at 0 or +4°C for several weeks postmortem. The small activity of GOT_M in the muscle press juice does not substantially change during storage of muscle tissue under these conditions, indicating that there is no drastic change of the mitochondrial structure during aging of meat. Bacterial spoilage of meat, however, results in the release of GOT_M from the mitochondria.     

Cooked and brined shrimps packed in a modified atmosphere have a shelf-life of >7 months at 0 °C, but spoil in 4–6 days at 25 °C

Summary Spoilage and safety of cooked, brined and modified atmosphere packed shrimps were studied at 0, 5, 8, 15 and 25 °C. Shrimps from two sources, cold and warm waters, were brined in a sodium–chloride brine containing benzoic, citric and sorbic acids. Shelf-life was above 7 months at 0 °C but only 4–6 days at 25 °C. Apparent activation energy for the effect of temperature on shelf-life was > 100 kJ mol^-1. This pronounced effect of temperature was explained by changes in spoilage microflora at different storage temperatures. Simple and empirical mathematical models for rates of spoilage were developed for the prediction of shelf-life at different temperatures. To evaluate safety, products were challenged with Listeria monocytogenes and spores of Clostridium botulinum . Above 5 °C growth responses of L. monocytogenes followed the square root model with a T_min-value of +0.2 °C. Cl. botulinum produced toxin at the time of spoilage at 25 °C but only in shrimps with < 3% water-phase salt.     

DRY ICE IN VARIOUS SHIPPING BOXES FOR CHILLED POULTRY: EFFECT ON MICROBIOLOGICAL AND ORGANOLEPTIC QUALITY

SUMMARY– Comparisons were made of dry ice and weter ice in shipping boxes for chilled chickens. Three types of boxes were tested: wax-resin-coated corrugated fiberboard, expanded polystyrene foam, and wirebound wood-veneer. Microbial counts, CO₂ concentration, and off-odor development were determined. Microbial counts on poultry stored at 0.5°C for up to 9 days were not significantly different as a function of box type or coolant. Counts on poultry stored at 4.4°C were significantly greater at 9 days on poultry stored in fiberboard boxes with dry ice than on poultry with water ice in fiberboard boxes or polystyrene boxes with dry ice; at 3 and 6 days there were no significant differences. At 5.2°C, counts were significantly smaller in polystyrene boxes with dry ice than in either wirebound boxes with water ice or fiberboard boxes with dry ice. An off-odor not characteristic of spoilage odor could develop in CO₂ atmosphere storage earlier than spoilage odor in an air atmosphere if storage temperature was low (0.5°C). At higher temperature (5.2°C), spoilage odor in air occurred earlier than Co₂-related off-odor in Co₂ atmosphere.     

ANTIMICROBIAL PROPERTIES OF LAURICIDIN IN MECHANICALLY DEBONED CHICKEN, MINCED FISH AND CHICKEN SAUSAGE

Aerobic plate counts on Plate Count Agar at 25°C were used to determine the time required to reach a microbial spoilage level of 1.0 × 10⁷ C.F.U./g, for mechanically deboned chicken meat, minced fish and chicken sausage stored at 2°C. The storage times were 5, 8 and 9 days, respectively. Addition of citric acid (0.2%), ascorbic acid (0.2%) or lauricidin (250 ppm) alone extended the shelf-life by 0–2 days. The combination of lauricidin and citric acid or lauricidin and ascorbic acid extended the time required to reach a microbial spoilage level for mechanically deboned chicken meat by as much as 7 days, minced fish by as much 4 days and chicken sausage by 8 days.     

The relationship of bacterial numbers and types to diamine concentration in fresh and aerobically stored beef, pork and lamb

Bacterial numbers and putrescine and cadaverine concentrations were measured in intact beef, pork and lamb and minced beef at retail and during aerobic chill storage at 5°C. Putrescine concentrations increased consistently with 'total' aerobic viable count (TAVC) but cadaverine concentrations increased only when high numbers of presumptive Enterobacteriaceae were present. Significant changes in diamine concentration did not occur until the TAVC exceeded 4.2 × 10⁷/cm² or g when the meat was clearly spoiled. Changes prior to the onset of spoilage were not sufficient for their use as a predictive indicator of the acceptability of the meat.     

Development of a Predictive Model for Spoilage of Cooked Cured Meat Products and Its Validation Under Constant and Dynamic Temperature Storage Conditions

ABSTRACT:  In the present study, the spoilage flora of a sliced cooked cured meat product was studied to determine the specific spoilage organism (SSO). The physicochemical changes of the product during its storage in a temperature range of 0 to 12 °C were also studied. Among the primary models used to model the temperature effect on SSO growth, the modified Gompertz described better the experimental data than modified logistic and Baranyi. The derived growth kinetic parameters, such as maximum specific growth rate (μ_max) and lag phase duration (LPD), were modeled by using the square root and Arrhenius equation (secondary models). The latter described better the data of μ_max and LPD; therefore, this model was chosen for correlating temperature with kinetic parameters. The selection of the best model (primary or secondary) was based on some statistical indices (the root mean square error of residuals of the model, the coefficient of multiple determination, the F -test, the goodness of fit, the bias, and accuracy factor). The validation of the developed model was carried out under constant and dynamic temperature storage conditions. To validate its usefulness to similar products, another sliced cooked cured meat product stored under constant temperature conditions was also used. The log shelf life model was used for shelf life predictions based on the evident (visual defects) or the incipient spoilage (attainment of a certain spoilage level by SSO and/or chemical spoilage index). The possibility for shelf life predictions constitutes a valuable information source for the quality assurance systems of meat industries.     

Biochemical Properties of Natural Actomyosin Extracted from Normal and Pale, Soft, and Exudative Pork Loin After Frozen Storage

ABSTRACT: The studies of natural actomyosin (NAM) extracted from normal and pale, soft, and exudative (PSE) pork longissimus muscle stored at -20°C for up to 6 mo, revealed that the surface hydrophobicity (S₀-ANS) of NAM from PSE pork was significantly ( P < 0.05) higher than that from normal pork indicating greater conformational changes in proteins from PSE meat that resulted in the exposure of hydrophobic aromatic amino acid residues on the surface. Also, the S₀-ANS of NAM was a function of storage time. The equations were as follows: S₀-ANS = 16.9 × storage mo + 123 for normal and S₀-ANS = 17.5 × storage mo + 164 for PSE. NAM from frozen normal pork had lower α-helical content than comparable fresh pork. With extended frozen storage, viscosity of NAM from PSE meat was lower than that from normal pork. The sulfhydryl and disulfide contents were unchanged. Electrophoresis revealed an extra 95 to 100 kDa band from PSE meat NAM, possibly from α-actinin or myosin degradation. Water-binding capacity (WBC) of normal and PSE meat decreased with increasing storage time; however, there were only minor changes in thaw loss. The decrease of WBC of pork meat partially can be explained by the increase of S₀-ANS observed for the NAM. These results suggest that proteins from PSE pork are more susceptible to denaturation and degradation in fresh meat and following frozen storage.     

Production of Enterotoxin-B in Cured Meats

SUMMARY— A variety of laboratory cured hams were inoculated with 10³−10⁶ cells of S. aureus strain S-6 and incubated at 10, 22 and 30°C anaerobically for up to 16 weeks. Enterotoxin-B was detected by gel-diffusion in hams with original pH over 5.30, up to 9.2% NaCl (brine) and 0.54 ppm undissociated nitrous acid. There was better toxin production at 30° than at 22° or 10°C. Toxin was detected at 10°C after at least 2 weeks incubation and in most samples after 8 weeks when pH was greater than 5.6. Toxic hams had more than 4 × 10⁶ cells/g. Contaminants were always less than 10⁵/g. Tween 80 inhibited toxin production at 30° but not at 10°C. Toxic hams looked normal even after 2 months incubation at 10°C.     

Comparison of the Real-time Microrespirometer and Aerobic Plate Count Methods for Determination of Microbial Quality in Ground Beef

ABSTRACT Real-time microrespirometer measurements were compared with the aerobic plate count (APC) method to assess microbial quality of ground beef stored at 4°C and 7°C with and without previous freezing. The samples were monitored daily for CO2 evolution rate (CER) using a microrespirometer, APC, and were evaluated for color and odor changes by a sensory panel. The CER was highly correlated with the APC for all storage conditions ( r 2 = 0.787 to 0.952). The onset of meat spoilage was more closely associated with a specific CER value (>25 μL/h/g) than APC. The new method was found to be more accurate in predicting meat spoilage, especially for previously frozen samples.     

EARLY DETECTION OF CLOSTRIDIUM PERFRINGENS ENTEROTOXIN AND ITS RELATIONSHIP TO SENSORY QUALITY OF COOKED CHICKEN

Growth, sporulation, and enterotoxin formation by Clostridium perfringens NCTC 8239 were determined in chicken thigh meat incubated at 45°C for 1.5 h and 37°C for up to 12.5 h. With an inoculum of 10⁶ vegetative cells per g, the cell counts reached mean log ₁₀ 7.32/g after 6 h of incubation and remained in that range through 14 h. Heat-resistant spores (log₁₀ 2.48/g) were first detected at 4 h, and the number increased to log₁₀ 5.19/g at 14 h. Enterotoxin (0.19 μg/g) was first detected after 2 h of incubation (1.5 h at 45°C and 0.5 h at 37°C) in the absence of detectable sporulation, and the enterotoxin concentration increased to 0.76 μg/g after 14 h. Significant differences (p < 0.01) in the odor, color, and texture scores for inoculated versus uninoculated cooked chicken following 2 h incubation correlated with the production of enterotoxin and suggested that these parameters could be used as indices of chicken spoilage by C. perfringens.     

COMPARISON OF MARGIN OF SAFETY BETWEEN SENSORY SPOILAGE AND ONSET OF CLOSTRIDIUM BOTULINUM TOXIN DEVELOPMENT DURING STORAGE OF MODIFIED ATMOSPHERE (MA)-PACKAGED FRESH MARINE COD FILLETS WITH MA-PACKAGED AQUACULTURED FISH FILLETS

The margin of safety between shelf-life (onset of sensory spoilage) and potential time to toxin production by Clostridium botulinum type E in retail type packages of fresh marine cod fillets packaged in high barrier film under selected atmospheres [100% air, a modified atmosphere (MA) containing 75% CO₂:25% N₂, and vacuum] and stored under refrigeration (4C) and temperature-abuse conditions (8 and 16C) was investigated. Margin of safety data of MA-packaged marine cod fillets was also compared with MA-packaged aquacultured tilapia, catfish, and salmon fillets. Sensory spoilage preceded onset of toxin presence for the marine cod fillets packaged in any of the atmospheres and storage temperatures tested. At 4C, none of the marine cod fillets packaged in either atmosphere developed toxin, even 20 days after spoilage, as determined by sensory characteristics. During storage at refrigeration and mild (8C) temperature-abuse conditions, MA-packaged marine cod showed a greater margin of safety compared to aquacultured tilapia, catfish, and salmon packaged under the same atmospheres and conditions. Fat content appeared to potentially influence the margin of safety in MA-packaged aquacultured fresh fish fillets during storage.     

Storage characteristics of sous vide cooked roast beef

The technological, microbiological, and sensory storage characteristics of low temperature sous vide cooked roast beef were investigated. the effect of two heat treatments, 59°C (P₇₀¹⁰in core 8.4) and 62°C (P₇₀¹⁰ in core 15.9) on the stability of spiced roast beef made from Musculus semitendinosus with a high initial microbial load were compared as well as storage temperatures of 2 and 10°C. Although chilling baths with circulating water were used, recommended chilling rates for sous vide products could not be attained. Yield was significantly higher at 59°C and at a storage temperature of 2°C but decreased during storage. At 62°C the meat became significantly more tender than at 59°C as measured by shear force. No differences in microbiology were observed between heating regimes. At low storage temperature products were microbiologically stable over a 35-day period. At 10°C, however, a rise in psychrotrophic aerobic counts and occasional pack swelling was observed. In a commercial scale experiment conducted with sous vide cooked (62°C) beef with low initial counts, no increase in aerobic counts was observed at 2, 5 and 10°C while swelling occurred in 28% of the packages stored at 10°C and in none at 2 and 5°C. the swelling was due to different types of gas-producing clostridia. Warmed-over flavour (as TBARS) showed no development during storage in intact packages, while slicing and serving the roast beef under commercial conditions resulted in a marked increase to < 100 μmole kg⁻¹. In spiced roast beef only minor changes in off-odour and off-flavour of the product were observed during 23 days of storage at 2°C.     

Microbial growth and colour of minimally processed shiitake mushroom stored at different temperatures

The effect of storage temperature on the microbiological and sensory characteristics of minimally processed shiitake was investigated. Shiitake mushrooms were washed, sanitised, packed in polystyrene trays, overwrapped with plastic film and stored at 7, 10 or 15 °C. Microbial counts, polyphenoloxidase activity, external lightness ( L* ) and acceptance tests were conducted. Mesophilic, aerobic psychrotrophic bacteria, yeasts and moulds predominated during storage. Pseudomonas was detected after 10 days' storage showing an increase of, approximately, 7 log cycles at 15 °C. Mushroom rejection occurred when the microbial population was lower than 10⁶ CFU g⁻¹, suggesting that, other factors, such as browning, affect mushroom spoilage more than microbial activity. Mushrooms treated with citric or ascorbic acids maintained high L * value during 10 days. The shelf life of minimally processed shiitake mushrooms was 10 days at 7 °C, but less than 5 days at 10 °C, and approximately 3 days at 15 °C.     

HEAT PASTEURIZATION OF CRAB AND SHRIMP FROM THE PACIFIC COAST OF THE UNITED STATES: PUBLIC HEALTH ASPECTS

ABSTRACT— A study of the potential public health hazard presented by coagulase-positive staphy-lococci, salmonellae and Clostridium botulinum in the meat of Dungeness crab and Pacific Coast shrimp pasteurized in flexible plastic containers revealed potentially toxinogenic staphylococci on the commercial nonpasteurized product, in 15% of the shrimp and 9% of the crab samples. No salmonellae or Cl. botulinum were isolated from, respectively. 26 and 54 samples of shrimp or 74 samples of crab. Pasteurization for 1 min at 180°F destroyed large inocula (10⁷ and 10⁸ cells) of staphylococci and salmonellae introduced into packages of the products, but processing for 5 min at 180°F allowed some members of an inoculum containing 10³ spores of Cl. botulinum type E to survive. While storage at 40°F prevented the growth on crab and shrimp meat of all staphylococci and salmonellae tested, it permitted growth and toxin formation by Cl. botulinum type E after 30–40 days. No toxin could be detected in packages inoculated with type A and proteolytic B spores and held at 50°F or lower. A 0.1% dip of sodium benzoate, with or without fumaric acid, did not prevent growth and toxinogenesis by Cl. botulinum types A, proteolytic B or E. It was concluded that for complete safety a holding temperature of 36°F or lower at all times would be required, but that it could not be expected to be maintained in commercial channels.     

Effect of nisin and high temperature pasteurization on the shelf-life of whole milk

Two experiments were conducted to assess the effectiveness of nisin on the keeping quality of pasteurized whole milk. After pasteurization, milk samples were stored at 10°C and samples were analysed at intervals for total plate count (TPC), Lactobacillus count, calcium ion concentration, pH and total acidity (TA). In the first experiment nisin was added to milk samples in the range 0 to 50 IU ml^-1 prior to pasteurization at 72°C for 15 s. AH concentrations of nisin used were effective in controlling microbial growth. Milk containing 40 and 50 IU ml^-1 nisin had not spoiled after 41 days' storage compared to spoilage time of 14 days for the control milk. In the second experiment 40 IU ml^-1 of nisin was combined with three 'pasteurization' processes: 72°C for 15 s, 90°C for 15 s and 115°C for 2 s. The milk processed at 72°C for 15 s with nisin showed an increased keeping quality of about 7 days compared with the control and showed a significantly lower count for Lactobacillus. In contrast, nisin had a much greater effect on TPC counts in the milk pasteurized at 90°C for 15 s, and after 28 days' storage at 10°C the milk was still acceptable. Milks treated both with and without nisin at 115°C for 2 s were microbiologically acceptable after 28 days, with counts less than 10 ml^-1. However, the milk with nisin was superior in flavour, as no noticeable off-flavours were apparent after 32 days. All these results are consistent, as shown by the microbiological and chemical analyses. Addition of nisin to milk prior to pasteurization provides an opportunity to achieve extended shelf-life in regions with poor refrigeration.     

The yeast flora of stored ready-to-use carrots and their role in spoilage

Spoilage of ready-to-use grated raw carrots packaged in polymeric films and stored at 10°C was investigated for involvement of yeasts. Cryptococcus albidus was only isolated during the first 3 days of storage, increasing to levels of 10⁵–10⁶g^-1. Candida lambica was more commonly isolated after 3–7 days of storage, and reached 10⁷–10⁸g^-1 after 12 days. Candida sake was present throughout storage, increasing from 10⁵–10⁶ after 3 days to 10⁷–10⁸ after 12 days. In some samples, Candida parapsilosis and Candida tropicalis were also isolated at levels similars to C. sake . All the yeasts isolated at the end of storage were fermentative species and their metabolism was characterized with a Warburg apparatus. Neither the number of yeasts nor the composition of the yeast flora were related to the deterioration of the product. Although Candida lambica inoculated on grated carrots caused spoilage after 12 days at 10°C, the high O₂ permeable film was most effective in reducing exudate.     

Portable Electronic Nose for Detection of Spoiling Alaska Pink Salmon (Oncorhynchus gorbuscha)

ABSTRACT:  The ability of a portable hand-held electronic nose (EN) in detecting spoilage of whole Alaska pink salmon ( Oncorhynchus gorbuscha ) stored at 14 °C and in slush ice (1 °C) was investigated. Fish were sampled daily at 14 °C for up to 3 d, while fish stored in slush ice were sampled at various intervals up to 16 d. Sensory evaluations indicated that fish were rejected at day 3 when stored at 14 °C and at day 12 when stored in slush ice. Aerobic bacteria counts for fish skin at 14 °C ranged from 3.4 log₁₀ colony-forming units (CFU)/cm² (day 0) to 4.8 log₁₀ CFU/cm² (day 3) and for fish stored in slush ice ranged from 3.4 log₁₀ CFU/cm² (day 0) to 5.5 log₁₀ CFU/cm² (day 16). The correct classification rate using forward stepwise general discriminate analysis was 85% and 92% for EN analysis of belly cavity volatiles for fish held at 14 °C and in slush ice, respectively. A predictive model may be developed for spoilage of whole Alaska pink salmon by analyzing belly cavity odors using the EN.     

Reduction in microbial load on buffalo meat by hot water dip treatment

Buffalo meat cuts from shoulder and leg portions were subjected to hot water treatment (70 and 80 °C for 30 and 60 s). Meat cuts dipped in water at ambient temperature served as control. The surface samples were analysed for microbial load, visual score for colour and numerical values of colour parameters (a(?), b(?), L(?), W). Control samples of shoulder and leg meat had a mean total plate count (TPC) of 4.15 log CFU cm(-2) and 3.81 log CFU cm(-2) and enterobacteriaceae counts of 2.33 log CFU cm(-2) and 2.26 log CFU cm(-2), respectively. Treatment of meat cuts with hot water reduced the TPC significantly (p < 0.001)with a highest reduction of 1.60 log in leg meat and 1.80 log in shoulder meat at 80 °C. Hot water treatment of meat eliminated enterobacteriaceae. Although, there was discolouration of meat by hot water treatment, the colour regained during storage of meat at refrigerated temperature (4 ±1 °C). Hot water treatment of meat resulted in loss of redness (a(?)), increase in lightness (L(?)) and whiteness (W). After storage, a(?) increased and L(?) and W decreased. The results suggested that the dip treatment with hot water reduces the initial bacterial load substantially and improves the microbiological quality of buffalo meat without causing any permanent discolouration.     

The Effects of Residual Oxygen on the Storage Life of Retail-Ready Fresh Beef Steaks Masterpackaged Under a CO2 Atmosphere

ABSTRACT:  Retail-packed rump ( Gluteus medius , GM) and striploins ( Longissiumus dorsi, LD) steaks were masterpackaged under carbon dioxide (CO₂) and stored at 1 °C ± 1 °C for 14, 28, 35, and 42 d. A commercial oxygen (O₂) scavenger (ATCO HV1000®, Standa Industrie, Caen, France) was used in the masterpacks to achieve an O₂-free atmosphere. Similar packages without the O₂ scavengers were also prepared. At each storage time, 2 masterpacks of each treatment were opened and the retail trays were placed in a display case at 4 °C ± 2 °C for 1 and 48 h for microbiological and sensorial evaluations. The low growth rate of aerobic psychrotrophic flora on the stored beefsteaks demonstrated the bacteriostatic effect of CO₂ during storage. The maximum level of psychrotrophic aerobic bacteria reached during storage was approximately 10⁶ CFU/g. The steaks stored in masterpacks with scavengers bloomed to the desirable red color associated with freshly cut meat in the display case for all of the storage periods, except in the case of GM steaks, which showed a cycle of transient discoloration. GM and LD steaks were well accepted (65% and 82%, respectively) after 42 d under CO₂ at 1 °C ± 1 °C. The GM and LD steaks stored without the O₂ scavenger showed variable fractions of discoloration that significantly detracted from the appearance of the samples.