Effect of Polyphosphates in Combination with Nitrite-Sorbate or Sorbate on Clostridium botulinum Growth and Toxin Production in Chicken Frankfurter Emulsions

Sodium nitrite, sorbic acid, potassium sorbate and polyphosphates (sodium acid pyrophosphate, SAPP; sodium hexametaphosphate, SHMP; and sodium tripolyphosphate, STPP) were tested at similar preadjusted (before cooking) pH levels (in the range of pH 5.78 to 6.19 after cooking) to determine effective combinations capable of controlling Clostridium botulinum growth and toxin production in mechanically deboned chicken meat frankfurter emulsions incubated at 27°C. In combination with low levels of nitrite (40 ppm), potassium sorbate (0.26%, pH 6.06) was more effective than sorbic acid (0.20%, pH 6.03) in delaying toxin production (>27 d vs. 6 d) and in controlling growth. In formulations containing combinations of nitrite (40 ppm) and sorbic acid (0.20%) or nitrite (40 ppm) and potassium sorbate (0.26%), the addition of polyphosphates (0.4%) resulted in a greater delay of toxin production (8 to 25 d for nitrite-sorbic acid-SAPP vs. 28 d for nitrite-potassium sorbate-SAPP) at similar pH levels. Under these conditions, SAPP delayed production of detectable toxin longer (25 d) than did either SHMP (6 to 11 d) or STPP (4 to 14 d). The addition of polyphosphates to nitrite-free emulsions containing sorbic acid (0.20%) or potassium sorbate (0.26%) did not delay the development of botulinal toxin when the pH was essentially equivalent in the range of 5.78 to 6.07.

Proposed mechanism for sensitization by hypochlorite treatment of Clostridium botulinum spores

Hypochlorite-treated Clostridium botulinum 12885A spores, but not buffer-treated spores, could be germinated with lysozyme, indicating that their coats are made permeable to lysozyme by hypochlorite treatment so that the cortex is accessible. Hypochlorite-treated spores and spores extracted with 8 M urea-2-mercaptoethanol (pH 3.0) were sensitive to certain components of recovery media, but spores sensitized to lysozyme by other treatments were not. These data indicate that hypochlorite does more than increase coat permeability to lysozyme. Scanning electron microscopy revealed a more open-appearing surface of hypochlorite-treated spores, and sodium dodecyl sulfate-polyacrylamide gel electrophoresis indicated that a greater amount of protein was removed from hypochlorite-treated and other lysozyme-sensitized spores than from buffer-treated spores. The data suggest that spore coat proteins may be removed by hypochlorite treatment, and this may be responsible for the sensitivity of spores and for their observed ability to germinate in lysozyme.

Hypochlorite injury of Clostridium botulinum spores alters germination responses

Clostridium botulinum spores were sublethally damaged by exposure to 12 or 28 micrograms of available chlorine per ml for 2 min at 25 degrees C and pH 7.0. The damaging dose was 2.7 x 10(-6) to 3.1 x 10(-6) micrograms of available chlorine per spore. Damage was manifested by a consistent 1.6 to 2.4 log difference between the most probable number enumeration of spores (modified peptone colloid medium) and the colony count (modified peptone yeast extract glucose agar); this did not occur with control spores. Damaged spores could be enumerated by the colony count procedure. Germination responses were measured in several defined and nondefined media. Hypochlorite treatment altered the rate and extent of germination in some of the media. Calcium lactate (9 mM) permitted L-alanine (4.5 mM) germination of hypochlorite-treated spores in a medium containing 12 or 55 mM sodium bicarbonate, 0.8 mM sodium thiosulfate, and 100 mM Tris-hydrochloride (pH 7.0) buffer. Tryptose inhibited L-alanine germination of the spores. Treatments with hypochlorite and with hydrogen peroxide (7%, 25 degrees C, 2 min) caused similar enumeration and germination responses, indicating that the effect was due to a general oxidation phenomenon.

Differing L-alanine germination requirements of hypochlorite-treated Clostridium botulinum spores from two crops

Similar populations of hypochlorite-treated spores were enumerated from two crops of Clostridium botulinum 12885A produced by the same procedure; however, germination required different L-alanine concentrations. Lactate permitted the germination of spores from both crops with suboptimal L-alanine concentrations. The data suggest that the spores differ slightly in chemical or structural composition.

Proposed role of lactate in germination of hypochlorite-treated Clostridium botulinum spores

Clostridium botulinum 12885A spores treated with hypochlorite required added DL-calcium lactate for L-alanine germination. Lactate was the active component of calcium lactate. Equimolar concentrations of L-malate, but not of DL-propionate, could replace lactate, suggesting that the alpha-hydroxy acid structure is important. Neither lactate nor malate was an effective germinant for buffer-treated or hypochlorite-treated spores. If the L-alanine concentration was increased 100-fold (to 450 mM), the lactate germination requirement was overcome. The data suggest that the L-alanine germination sites were modified by hypochlorite so that a higher concentration of alanine was required for activity. Lactate appeared to be an activator of modified or non-hypochlorite-modified L-alanine germination sites.

Characterization of Germination of Desulfotomaculum nigrificans Spores 1

Germination of spores of Desulfotomaculum nigrificans was studied by measuring reduction in numbers of heat-resistant units. Complete (>99.9%) germination was observed with heat-activated spores suspended in a combination of 1% soytone, 0.1% ferric citrate, 0.1% sodium metabisulfite (Na₂S₂O₅), and distilled water. In this medium spores germinated most rapidly at pH 6.0 - 8.0 when incubated at 55°C after the spores were exposed to a 15 - 20 min heat-shock at 100°C. Twelve amino acids triggered germination either together or individually only in the presence of ferric citrate and Na₂S₂O₅. No one amino acid as a germinant was superior to the others evaluated. Of nine carbohydrates examined (at 1% levels), fructose, ribose, and arabinose initiated germination individually in distilled water. Ferrous ion initiated germination whereas the ferric ion did not. Cu⁺⁺ (10mM) initiated germation whereas Zn⁺⁺ (10mM) inhibited germination. Phosphate buffer (67mM) and EDTA (10mM) inhibited cation-initiated germination. Reducing agents such as Na₂S₂O₅ may provide ferrous ions needed for spore germination. Ferrous ions as germinants indicate a possible significant role for an iron source when enumerating D. nigrificans spores or when evaluating food spoilage caused by D. nigrificans .

Bacterial Spore Injury - An Update 1

Injury has long been recognized in bacterial spores, especially in evaluation of apparent survival after administration of treatments to control these resistant entities. Compared to vegetative cells, the complexity of the germination and outgrowth processes has retarded research activity on injury and resuscitation. Heat-injury has been observed and studied to the greatest extent, but irradiation and chemical treatments also damage spores from anaerobic or aerobic bacteria. Injury has been associated with germination or specific steps in outgrowth or both. Damage of enzymes, DNA, RNA, membranes or other systems may be implied by resuscitation studies. Injury has been manifested by increased sensitivity to selective or antimicrobial agents or by increased requirements for germination and growth. The need for extensive fundamental research on bacterial spore injury continues to exist, especially to aid in explaining unique spore resistance.

Antimicrobial Activity of Sorbate

During the last 30 years sorbate has been tested and used widely in the preservation of various food products throughout the world. Currently it has received increased attention as a potential replacer of nitrite for botulism control in processed meat products. Previous reports, however, had suggested sorbate as a selective agent for clostridia in laboratory media. Recent developments as well as the need for safe, practical and effective food preservatives in current and future food processing have generated intense interest in preservatives such as sorbate. This paper reviews the significant developments relating to use of sorbate as a food preservative - its antimicrobial effects, applications, advantages and limitations. A summary of the current status as well as unanswered questions relevant to the mechanism(s) through which the compound exerts its antimicrobial activity also is presented.

Heat resistance of Desulfotomaculum nigrificans spores in soy protein infant formula preparations

The heat resistance of Desulfotomaculum nigrificans spores was determined in soy protein infant formula preparations. Methods of sporulation were developed and evaluated. D. nigrificans spores of highest heat resistance were produced in a 40% infusion of spent mushroom compost. Fraction-negative D121 degrees C-values obtained in modified soy formula were 25.8 min for spores of ATCC 7946 produced at 55 degrees C and 54.4 min for an isolate designated RGI 1, which was sporulated at 66 degrees C. From the fraction-negative D-values, z-values were obtained of 6.7 degrees C for ATCC 7946 and 9.5 degrees C for RGI 1. Survivor-curve D121 degrees C-values were 5.6 min for ATCC 7946 and 2.7 min for RGI 1 sporulated at 55 degrees C and heated in modified soy formula. Corresponding D121 degrees C-values in Butterfield phosphate buffer (pH 7.2) were 3.3 min (ATCC 7946) and 1.1 min (RGI 1). The z-values generated from survivor-curve D-values were similar to those obtained by using fraction-negative procedures. In all instances the inactivation kinetics appeared to be linear. The isolate designated RGI 1, when sporulated at 66 degrees C and heated in a modified infant soy formula, exhibited an extraordinary heat resistance far in excess of previous reports.

Effect of Rising Temperatures on Growth and Survival of Clostridium perfringens Indigenous to Raw Beef 1

Growth and survival of Clostridium perfringens indigenous to raw beef were compared to that of a composite of eight strains of C. perfringens inoculated into raw ground beef round, beef-round strips, and beef-round cores. A constantly rising temperature rate of 6 C/h and a dynamic rising temperature rate, predetermined from long time-low temperature (LTLT) oven beef cookery processes, were used to evaluate growth and survival. Survivors of C. perfringens were observed in raw ground beef and autoclaved ground beef at temperatures between 59 and 63 C. Growth in raw ground beef was more rapid than in raw beef-round strips. Raw ground beef supported growth of the indigenous flora to a greater extent than did autoclaved ground beef inoculated with the composite. The populations in raw, domestic frozen beef rounds used in commercial cooking processes were low, ranging from < 70/g to 1000/g, and varied among lots.

Production of Phospholipase C by Nine Strains of Clostridium perfringens at 37 C and at a Constantly Rising Temperature 1

Nine strains of Clostridium perfringens were compared for phospholipase C production in autoclaved ground beef (AGB) at 37 C. Enzyme production is reported as units per colony forming unit (CFU). Phospholipase C concentrations were determined by the hemolysin indicator method and colonies were observed on Tryptose Sulfite Cycloserine agar. Enzyme production by each of the nine strains was significantly different. The increase and decrease of viable cells of C. perfringens in AGB exposed to temperatures rising constantly at a rate of 4.1 C/h was accompanied by the appearance and disappearance of phospholipase C. This demonstrated that C. perfringens can produce detectable levels of phospholipase C when grown during dynamic increasing temperatures.

Botulism Control by Nitrite and Sorbate in Cured Meats: A Review 1

Nitrite plays a major role in the botulinal safety of cured meat products. When used at appropriate levels, it retards Clostridium botulinum growth and delays production of its deadly neurotoxin. Even though the incidence of botulinal spores in meat is very low, factors such as the tonnage of cured meats consumed, the potential for mishandling such products, and the nature of the disease necessitate the use of nitrite or other equally effective compound(s) for extra safety. Residual nitrite and nitrosamine levels in cured meat products have been decreasing in recent years through control and research conducted by the meat industry and related institutions. Such levels are minimal compared to total nitrate and nitrite amounts ingested or formed in the human body. Sorbate, especially in combination with nitrite at concentrations adequate only for cured meat color and flavor development, is at least as effective as currently used nitrite levels in delaying C. botulinum growth and toxin production. The mechanism(s) through which nitrite and/or sorbate perform their actions upon C. botulinum remains to be found. A review of the pertinent research completed to date should be helpful in the search for the mechanism(s).

Food Protection for the 80's 1

New social, economic and political demands for conservation of energy, water and consumable products coupled with changes in lifestyle including more meals eaten away from home will require new approaches to food handling. These modifications may increase or uncover new hazards and potential opportunities for food borne illness. Microbial hazards will remain a major problem but will be only one of the many concerns of the consumer about food. Increases in awareness of newly identified pathogens, carcinogens, mutagens and the like will demand greater efforts but will also increase cost of foods. Acute sensitivity to escalating costs will in turn bring about more objective evaluations of benefit/risk ratios on all programs. Education of producers, handlers, processors and consumers will be required so that they may monitor and serve as protectors of the food system thus minimizing regulatory costs and placing responsibility at the point of action. This process will be successful only with appropriate educational and research support to evaluate and implement modified programs.

Sodium nitrite and sorbic acid effects on Clostridium botulinum spore germination and total microbial growth in chicken frankfurter emulsions during temperature abuse

Samples of (i) a control or of (ii) sodium nitrite-containing or (iii) sorbic acid-containing, mechanically deboned chicken meat frankfurter-type emulsions inoculated with Clostridium botulinum spores, or a combination of ii and iii, were temperature abuse at 27 degrees C. Spore germination and total microbial growth were followed and examined at specified times and until toxic samples were detected. The spores germinated within 3 days in both control and nitrite (20, 40 and 156 micrograms/g) treatments. Sorbic acid (0.2%) alone or in combination with nitrite (20, 40, and 156 micrograms/g) significantly (P less than 0.05) inhibited spore germinations. No significant germination was recorded until toxic samples were detected. A much longer incubation period was necessary for toxin to be formed in nitrite-sorbic acid combination treatments as contrasted with controls or nitrite and sorbic acid used individually. Total growth was not affected by the presence of nitrite, whereas sorbic acid appeared to depress it. Possible mechanisms explaining the effects of nitrite and sorbic acid on spore germination and growth are postulated.

Inactivation of Salmonellae in Autoclaved Ground Beef Exposed to Constantly Rising Temperatures 1

Inactivation of a composite of five serotypes of salmonellae was monitored in autoclaved ground beef exposed to constantly rising temperatures increased at rates similar to those used in beef cookery. Rising temperature rates of 6.0 C/h, 8.5 C/h and 12.5 C/h and constant temperatures of 55, 57, 61 and 63 C were examined. Survival of Salmonella typhimurium TM-1 was compared to survival of the composite. D and z values were compared for constant and rising temperature rates. The D₅₀ C for constant temperature data was 30.2 min, and the D₅₀ C for changing temperature data was 78.6 min (6.0 C/h), 82.4 min (8.5 C/h), and 49.8 min (12.5 C/h). Neither serotype nor heat treatment of ground beef had a major influence on apparent heat resistance of salmonellae. A comparison of these results to previous rising temperature work with Clostridium perfringens suggested that controlling C. perfringens will result in control of salmonellae. On the basis of these results, the July 18, 1978, USDA processing ruling appears adequate to control salmonellae in precooked beef roasts.

Growth of Clostridium perfringens in Three Different Beef Media and Fluid Thioglycollate Medium at Static and Constantly Rising Temperatures 1

Growth of an eight-strain composite of Clostridium perfringens was compared using rolled raw beef strips, raw and autoclaved ground beef and Fluid Thioglycollate medium. The inoculated media were exposed to either static or dynamic temperatures increasing at linear rates. The most rapid growth and shortest lag times were observed in autoclaved ground beef. Generation times in the beef media were directly related to oxidation-reduction potential. Fluid Thioglycollate medium supported the slowest growth even though it presented a favorable E_h.

Microbial Harboring Characteristics of Dishmachine-Filmed Glassware

Alkaline-earth type films, produced by detergent-water interactions, are frequently deposited on eating utensils during mechanical dishwashing. These films are aesthetically unacceptable but their public health significance and food spoilage potential have not been established. Sterile glass petri dishes were washed in an institutional-type dishmachine containing Bacillus subtilis spores in the washwater. A film-producing model system was developed to examine film formation in conjunction with spore deposition. The influence of three distinct detergent formulations on this association was also determined. Detergent formulations contained 6.75% phosphorus (P), as sodium tripolyphosphate (STP), 3.0% P as STP, a proprietary phosphate substitute, and the film-producing model formulation devoid of both STP and substitute water conditioning agents. Film deposition was quantified as μg Ca⁺⁺ per cm² by an acid rinse-atomic absorption spectrophotometric method. The quantity of B. subtilis spores recovered from washed petri dishes in the model system was related to film deposition. The relationship was dependent on the number of consecutive dishmachine cycles and the hardness of the water supply. Above a threshold value of 3 μg Ca⁺⁺ per cm², Ca⁺⁺ deposition and B. subtilis spore harborage were directly correlated. Both of these conditions were inhibited to varying degrees by the three detergent formulations. These data suggest that dishware filming may be cause for public health and food spoilage concerns.

Osmotically induced increase in thermal resistance of heat-sensitive, dipicolinic acid-less spores of Bacillus cereus Ht-8

Thermal resistance in heat-sensitive, dipicolinic acid (DPA)-less spores of Bacillus cereus Ht-8 heated in sucrose solutions increased at and above a concentration of 2 M sucrose. The decimal reduction times at 75 degrees C for spores heated in 0.0, 1.8, 2.2, and 2.6 M sucrose were 2.0, 2.8, 4.5, and 12 min, respectively. Maltose, fructose, and glucose increased heat resistance above that observed in water but did not elevate resistance to the level observed with sucrose at the same osmolality. Cation-induced loss of thermal resistance in chemically sensitized spores was reversed in the presence of sucrose. Spores germinated in brain heart infusion were resistant when heated in sucrose. In the presence of sucrose, spores exhibited an increase in optical density at 700 nm. Electron micrographs of the DPA-less spores suspended in 2.2 M sucrose revealed a shrinkage of outer coats and exosporium membranes. The results suggested that the osmotic property of sugars increased thermal resistance in DPA-less spores. The osmotic pressure exerted by sugars may be similar to the pressure that usually exists within the cortex of normal spores containing DPA and may cause the dehydration of the protoplast and the consequent thermal resistance. The role of dehydration and the nonessential nature of DPA for thermal resistance in spores were confirmed.

Dialysis technique for containment of microbial populations inoculated into food systems

A technique utilizing dialysis tubing was developed for the containment of microbial populations introduced into a food system. The entrapment of the inoculum was accomplished while reducing interference with interactions between the sample and the surrounding environment.

Heat-induced requirements for sucrose or magnesium for expression of heat resistance in Bacillus cereus forespores

The addition of 0.6 M sucrose of 0.016 M Mg2+ to the enumeration medium was required for early expression of heat resistance (10 min at 70 degrees C) in stage V Bacillus cereus forspores. The addition of Mg2+ to the sporulation medium did not remove this requirment for sucrose of Mg2+. The heat damage did not affect forespore germination or outgrowth, but injured cells in the absence of sucrose or Mg2+ were not capable of cell division. The heat-induced sublethal damage apparently affected the forspore component(s) that could be repaired or was capable of normal function in the presence of added Mg2+ or sucrose.

GLUCOSE INHIBITS GROWTH OF CLOSTRIDIUM PERFRINGENS IN FOOD PROTEINS1

A study of the effects of food components on Clostridium perfringens growth indicated that the addition of D-glucose to sodium caseinate or to isolated soy protein greatly extended the lag phase of growth. A final concentration of 10 g glucose per liter in a sodium caseinate medium containing NaCl, K2HPO4, Na2SO4, and sodium thioglycollate increased the lag time of C. perfringens strain S40 to 3.5 h compared to 2 h for the control with no glucose, Growth was determined by colony count or absorbance (650 nm) measurement, or both. Addition of Trypticase (2 g/1) or Fe++, Ca++, or Mg++ cations (1 mM) relieved the glucose inhibition. Similar inhibition by glucose was also observed when amino acids replaced sodium caseinate and the amount of cations was controlled by adding low levels or by adding EDTA. Other sugars tested did not give this inhibitory effect. The extent of the lag time varied with glucose concentration or with level of the cell inoculum. There was a direct linear relationship between the molecules of added glucose per cell and the lag time. The mechanism appears to involve competition by food proteins for cations that affect the glucose transport system (s). These data indicate a potential control or at least delay for initial growth of C. perfringens in certain fabricated protein foods.

INCIDENCE OF POTENTIALLY PATHOGENIC MICROORGANISMS IN FURTHER-PROCESSED TURKEY PRODUCTS1

Numbers of certain pathogenic microorganisms associated with turkey and turkey products were determined at three Minnesota turkey eviscerating and processing plants. The influence of processing and freezing was investigated. Using a predetermined sampling plan, skin and meat samples were obtained from 96 turkeys. Numbers of Clostridium perfringens, Staphylococcus aureus, salmonellae, and coliform organisms in each sample were determined. All types of organisms studied were found in 10 to 1000-fold higher levels in the skin than in meat samples. Clostridium perfringens and S. aureus organisms were recovered from samples obtained during each stage in the processing of the birds. Salmonellae were not found as frequently. Of 85 fresh skin and meat samples, 53 (62%) yielded C. perfringens and 46 (54%) yielded S. aureus. Salmonellae were recovered from 11 of 74 (15%) fresh samples and coliform organisms from 74 of 85 (85%) fresh samples, Frozen storage (31 days at −20 F) reduced recovery of the organisms to 56, 53, 9, and 67% respectively.