Effect of irradiation and modified atmosphere packaging on the microbiological and sensory quality of pork stored at refrigeration temperatures

The effect of combining low-dose irradiation (1.75 kGy) with modified atmosphere packaging (MAP) on the microbiological and sensory quality of pork chops stored at refrigeration temperatures was studied. The microflora of irradiated MAP pork was almost exclusively composed of lactic acid bacteria, predominantly Lactobacillus spp. Modified atmospheres containing either 25 or 50% CO₂, balance N₂, resulted in the best microbial control in irradiated pork held at 4°C, compared to an unirradiated MAP control, and these atmospheres were subsequently used in sensory studies. The atmosphere containing 25% CO₂ 75% N₂ maintained the uncooked colour and odour of irradiated pork chops more effectively than 50% CO₂ 50% N₂. Therefore packaging in a modified atmosphere containing 25% CO₂, balance N₂, followed by irradiation to a dose of 1.75 kGy is recommended to improve the microbiological and sensory quality of pork chops.     

Elimination of Listeria monocytogenes in soft and red smear cheeses by irradiation with low energy electrons

Soft and red smear cheeses are frequently contaminated by Listeria monocytogenes , sometimes at relatively high concentration (< 10⁵ CFUg^-1). This bacterium is radiosensitive (D₁₀ value of approximately 0.45 kGy) but irradiation of the whole cheese by X-rays induced off-flavours when the dose exceeded 1.0 kGy. Irradiation could be effective in eliminating L. monocytogenes only from lightly contaminated cheeses (> 10²CFU g^-1).
L. monocytogenes appears only in the rind (where the pH is greater than 6.3) and never grows in the core of the cheese. Under these conditions, a specific irradiation of the rind after ripening, with a low-energy electron beam at relatively high doses (up to 3.0 kGy), allows the total elimination of L. monocytogenes in heavily contaminated samples (10⁵-10⁶ CFU g^-1) without noticeable modifications of the organoleptic properties of the cheese.     

Clostridium Perfringens Growth from Spore Inocula in Sous-Vide Processed Pork-Based Mexican Entrée

ABSTRACT:  The combined effect of Citricidal® wih irradiation on Clostridium perfringens growth from spores in a sous-vide processed marinated pork meat Mexican entrée was investigated. Citricidal was added at 200 or 800 ppm after mixing pork meat with tomatillo sauce and inoculated with 3 log₁₀ CFU/g of C. perfringens spores. Samples were irradiated at either 0 or 2 kGy, heated to an internal temperature of 71 °C, and stored at 4 °C for 28 d, 15 °C for 45 d, and 25 °C for 26 h. To simulate the conditions that may occur during transportation, distribution, storage, or handling in supermarkets or by consumers, the effect of static temperature abuse on C. perfringens growth was assessed by transferring samples stored at 4 to 25 °C for 13 and 15 h. Total C. perfringens populations were determined by plating diluted samples on tryptose-sulfite-cycloserine agar. Growth was not observed up to 45 d of storage at 15 °C in samples supplemented with 800 ppm of Citricidal. At 25 °C, no significant differences ( P > 0.05) on the lag phase duration due to antimicrobial treatments was observed. The temperature abuse of refrigerated products for up to 15 h did not lead to C. perfringens growth to high infective dose levels of 1 million cells required to cause food poisoning. The results suggest that 800 ppm Citricidal can have significant bacteriostatic activity against C. perfringens and may provide a degree of protection against this pathogen in sous-vide processed marinated pork meat Mexican entrée, under mild temperature abuse (≤ 15 °C) conditions.     

MICROBIOLOGICAL QUALITY OF THE DAIRY PRODUCT PEDHA AND ITS IMPROVEMENT USING GAMMA RADIATION

Eighteen pedha samples procured from A and B grade retail shops were examined for their overall microbiological quality and for the presence of foodborne pathogens viz. Staphylococcus aureus, Salmonella sp., Coliforms , Listeria monocytogenes, Yersinia enterocolitica and Bacillus cereus. The microbiological quality of pedha samples from B grade shops was very poor as compared to pedha from A grade shop as evidenced by the very high total bacterial counts (6 × 10⁷ cfu/g), high counts of S. aureus (as high as 7 × 10⁶ cfu/g) and presence of coliforms and Listeria and Yersinia sp. in 33% of the samples. All the samples from A grade shops were also positive for S. aureus though negative for coliforms , Yersinia, Salmonella, Listeria and B. cereus. Gamma irradiation of pedha at a dose of 3kGy at 0C reduced overall bacterial load by five log cycles and S. aureus and coliforms could be totally eliminated. However, 5 kGy dose was necessary to eliminate S. aureus if the initial number exceed 1 × 10⁵ cfu/g. Inoculated pack studies confirmed that 3 kGy dose was sufficient for the complete elimination of up to 1 × 10⁵ cfu/g of S. aureus. A dose of 3 kGy had minimal effect on the sensory quality of pedha and even pedha samples irradiated at 5 kGy dose were acceptable. Treatment with 3 kGy dose of gamma radiation totally eliminated S. aureus and coliforms in pedha, thereby ensuring their microbial safety.     

MICROBIOLOGICAL STATUS OF EGYPTIAN SALTED MEAT (BASTERMA) AND FRESH SAUSAGE

The microbiological quality of 125 samples of the most popular Egyptian meat products (75 Egyptian fresh sausage "EPS" and 50 basterma) was determined. The aerobic plate count (APC) and Lactobacillaceae count of basterma ranged from 1 × 10⁴ to 9 × 10⁶ CFU/g, respectively . Enterobacteriaceae, mold and yeast counts for basterma were similar (<1 × 10² CFU/g). Artificially contaminated slices of meat and garlic paste of basterma showed that the paste inhibited growth of Salmonella typhimurium. APC and Enterobacteriaceae counts of EFS ranged from 1.1 × 10⁴ to 1 × 10⁸ and from 1 × 10² to 1 × 10⁷ CFU/g, respectively. Nearly 26% and 29% of EFS were positive for Clostridium perfringens and coagulase-positive Staphylococcus aureus, respectively . Salmonella could not be detected in any examined samples. Bacteriologically, EFS might pose a potential health hazard, making it imperative to institute sanitary measures during its production and sale .; Accepted for Publication July 2, 1997     

HYGIENIZATION OF INDIAN CHICKEN MEAT BY IONIZING RADIATION

Both fresh and frozen chicken meat were evaluated for microbiological status by screening for total bacterial counts and for the presence of pathogens like Enterobacteria , Bacillus cereus, coagulase positive Staphylococci and Salmonella spp. Most of the samples exhibited heavy bacterial contamination (1.2 × 10⁵ - 2.6 × 10⁶/g), mainly with Staphylococcus spp. (1.5 × 10⁴ - 2.8 × 10⁵/g). All the chicken samples also showed the presence of Salmonellae (3 × 10¹ - 2.1 × 10²/g). Among the different serotypes observed in chickens . S. typhimurium was common in fresh as well as frozen chicken. Radicidation at 2 kGy at cryogenic conditions (−40°C) was efficient in eliminating the natural pathogenic contamination of the poultry . Salmonella spp. viz. S. seftenberg and S. typhimurium differed in radiation sensitivity, the D₁₀ values in phosphate buffer (pH 7.2) being 0.25 kGy and 0.12 kGy, respectively. Chicken homogenate (10%) offered approximately 2-fold protection to these cells. Chicken samples artificially inoculated with a heavy inoculum (10⁸ cells/g) of these 2 serotypes required higher gamma radiation doses of 4–5 kGy. The findings suggested that a dose of 2 kGy is adequate for normally contaminated chicken samples, but for the heavily contaminated chicken a dose of 4–5 kGy, depending upon the predominating Salmonella serotype present, is required .     

INACTIVATION OF BACTERIAL SPORES BY COMBINED ACTION OF HYDROSTATIC PRESSURE AND BACTERIOCINS IN ROAST BEEF

Foodborne bacterial spores are normally resistant to high hydrostatic pressure; however, at moderate pressure, they can be induced to germinate and outgrow. At this stage, they can be killed by bacteriocin-based biopreservatives (BP-containing pediocin and nisin at 3:7 ratio; BP_X, BP + 100 μg/mL lysozyme; BP_Y, BP_X+ 500 μg/mL Na-EDTA). Based on this principle, spores of the meat spoilage organism, Clostridium laramie (1–2 × 10² spores/bag) alone or a mixture of four clostridial spores (5 × 10³ spores/bag), Clostridium sporogenes, Clostridium perfringens, Clostridium tertium, and Clostridium laramie, were inoculated in roast beef in the presence of 5000 AU/g of bacteriocin-based biopreservatives. The roast beef samples were subjected to hydrostatic pressure (HP) at 345 MPa for 5 min at 60C and stored at 4 or 12C for 84 days or at 25C for 7 days. The HP treatment of roast beef samples inoculated with a mixture of clostridial spores could be stored for 42 days at 4C. The HP in combination with either BP_X or BP_Y extended the shelf-life of roast beef up to 7 days at 25C. The combined treatment of HP and BP controlled the growth of C. laramie spores and extended the shelf-life of roast beef for 84 days when stored at 4C.     

INFLUENCE OF MOISTURE CONTENT AND STORAGE TEMPERATURE ON THE PRODUCTION OF AFLATOXIN BY ASPERGILLUS FLAVUS EA-81 IN MAIZE AFTER EXPOSURE TO GAMMA RADIATION

The effect of gamma radiation on aflatoxin production by Aspergillus flavus EA-81 in maize with different initial moisture levels was determined over a 15-day period. The viability of A. flavus on maize decreased over time with increasing moisture contents and storage at 8C. After 45 days at 28C, levels of viable conidiospores of A. flavus increased from 4.5 × 10⁷ to about 3.0 × 10⁸ per gram of maize. Levels of aflatoxin B₁ produced by A. flavus were 10 μg kg^-1 in the maize stored at 8C after 45 days. Production of aflatoxin was highest at 40% moisture and 28C. Irradiation of 1.0 or 2.0 kGy greatly reduced the level of mold growth relative to unirradiated controls. A dose of 4.0 kGy eliminated all viable fungi. Aflatoxin B₁ production decreased with increased levels of irradiation and was negligible at 4.0 kGy. When maize was inoculated after irradiation and stored, the spore counts and aflatoxin levels were higher than in unirradiated and inoculated controls after 30 days. Apparently, the natural competitive microflora prevented growth and thus limited higher concentrations of aflatoxin in maize.     

INJURY AND SURVIVAL OF AEROMONAS HYDROPHILA 7965 AND YERSINIA ENTEROCOLITICA 9610 FROM HIGH HYDROSTATIC PRESSURE

Responses of Aeromonas hydrophila 7965 and Yersinia enterocolitica 9610 to high hydrostatic pressure were investigated in microbiological media and meat. Cultures were pressurized from 51 to 304 megaPascals (MPa) for 15 min in 200 mM sodium phosphate buffer (pH 7.0), tryptic soy broth and radiation-sterilized ground pork. Trends in pressure response were similar in all three pressure menstrua. A 7-log₁₀ CFU/g reduction of A. hydrophila in pork resulted from treatment of 253 MPa for 15 min. A 7-log₁₀ CFU/g reduction of Y. enterocolitica in pork resulted from treatment of 304 MPa for 15 min. Pressure-induced injury of both pathogens was detected in all pressure menstrua at most pressure levels. No growth of either pathogen occurred in irradiated pork after pressurization of 128–203 MPa for 15 min and storage at 4C for 14 days; however, an upshift to 30C of cold-stored A. hydrophila in pork resulted in growth after a lag time of approximately 10 h, and an upshift to 30C of cold-stored Y. enterocolitica in pork resulted in recovery of injured cells within 2 h, and growth after a lag time of 4–6 h. This suggests that temperature abuse (30C) of pressure-processed pork for greater than 6 h would allow growth and possibly repair of A. hydrophila and Y. enterocolitica which survive following pressure treatment. Although neither the processor nor the consumer would likely abuse the product to such an extent, the results suggest that A. hydrophila and Y. enterocolitica have the ability to repair or grow following pressure treatment in pork.     

EFFECT OF HIGH HYDROSTATIC PRESSURE, GAMMA-IRRADIATION AND COMBINATION TREATMENTS ON THE MICROBIOLOGICAL QUALITY OF LAMB MEAT DURING CHILLED STORAGE

The effect of gamma irradiation (1.0 kGy) and high hydrostatic pressure (200 MPa for 30 min), either alone or in combination on the shelf-life of lamb mince meat at 0–3C was studied. Untreated control samples initially had total microbial counts of 10⁵ CFU/g, 10² CFU/g of coliforms and 10⁴ CFU/g of Staphylococcus spp. Coliforms were eliminated by all the treatments . Staphylococcus spp. however, were reduced only by 1 log cycle when treated with irradiation alone and high pressure alone. These species were a mixture of mannitol-fermenting and mannitol-nonfermenting strains. In samples subjected to the combination treatment , Staphylococcus spp. appeared only after 3 weeks of storage and all were mannitol-nonfermenting. On the basis of microbiological and sensory quality, the shelf-life of the control sample was less than 1 week. All treated meat samples had a shelf-life of 3 weeks, but only combination treated samples were free from potentially pathogenic Staphylococcus spp .     

DECONTAMINATION OF SPICES BY IRRADIATION

The feasibility of inactivating microflora of foreign spices by means of gamma radiation, without causing significant organoleptic or chemical changes, was studied. Ground cinnamon, clove, coriander, nutmeg, white and black pepper were irradiated with doses of 7 and 10 kGy¹ of ⁶⁰Co.
Chemical analysis were performed so as to verify the Argentine Alimentary Codex specifications and the effect of radiation on those characteristics by which spices are appreciated, such as color and volatiles. No differences between control and irradiated samples could be found in any of these parameters.
Microbiological results showed that aerobic plate count was reduced by 2.5 to 4.0 log cycles with 7 kGy. At 10 kGy survivors could only be found in cinnamon (1.7 log cfu/g)².
Cinnamon and clove were sensorily evaluated. No differences due to irradiation were found.
So, it can be concluded that 10 kGy of gamma radiation suffice the purpose of this work. This good market condition was held at least during one year.     

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.     

INACTIVATION OF SHEWANELLA PUTREFACIENS BY GAMMA IRRADIATION OF RED MEAT AND POULTRY

The resistance of Shewanella putrefaciens ATCC 8071, 8072, and 8073 to gamma radiation was determined in the presence and absence of air on mechanically deboned chicken meat (MDCM). The presence or absence of air (oxygen) did not significantly influence resistance to gamma radiation at 5C, and it was very sensitive with a D₁₀ value of 0.11 ± 0.002 kilogray (kGy) on MDCM. A high percentage of cells surviving irradiation were shown by impedance measurements to have suffered injury. The bacteria were significantly more resistant to gamma radiation at temperatures below the freezing point. At a dose of 0.8 kGy lowering the temperature of irradiation by 10 degrees increased the survival of this food spoilage organism by a 1.66 log₁₀. The type of meat (hamburger, ground beef round, ground pork, and ground turkey breast) did not significantly alter resistance of S. putrefaciens to gamma radiation under identical conditions (D₁₀ value = 0.18 ± 0.01 kGy). The minimum radiation dose currently approved for poultry in the USA, 1.5 kGy, should eliminate S. putrefaciens from meats.     

Rapid dye reduction tests for the determination of microbiological quality of meat

Rapid dye reduction tests have been developed to determine the quality of meat. Three chemical indicators, resazurin and two tetrazolium compounds, were used to correlate the microbial numbers and reduction times in meat samples. Twenty-five surface samples from sheep carcasses were subjected to each reduction test. Total viable counts given were obtained at 37°C. Resazurin reduction time was 90–120 min when the bacterial counts ranged from 1.5×10⁶ to 7.7×10⁶/cm². Samples showing bacterial counts between 1.5×10⁶ and 6.0×10⁶/cm² reduced tetrazolium (NBT) in 360–390 min whereas samples containing bacterial counts of 2.1×10⁶/cm² took 420–450 min to reduce iodophenyl nitrophenyl tetrazolium (INT) dye. Regression equations relating the number of organisms per cm² and reduction time were applied to predict the microbiological quality of meat samples from reduction time data. Among the three dyes, resazurin gave the lowest reduction time.     

ENTEROTOXIN FORMATION IN FOODS BY CLOSTRIDIUM PERFRINGENS TYPE A

Growth, sporulation and enterotoxin formation in various foods inoculated with a Clostridium perfringens type A enterotoxin-producing strain were studied. Good vegetative growth, 10⁷–10⁸ cells/g, was obtained after 4 hr of anaerobic growth and remained almost the same throughout the 20–24 hr observation in most of the foods. A gradual increase in spore count to the level of 10⁴–10⁵/g was observed with an increase in the incubation time. Enterotoxin was detected in moist cooked chuck roast, ground beef and turkey as well as in moist cooked and dry roasted chicken at levels up to 0.125μg/g. The earliest time at which enterotoxin was detected was after 10 hr of anaerobic growth in moist cooked turkey at 37°C. Although growth and some sporulation occurred, enterotoxin was not detected in dry roasted beef or turkey with or without gravy, or in moist cooked pork or lamb. Poor growth and sporulation also were obtained with chicken broth, chicken gravy and beef gravy. In moist cooked turkey that had been temperature abused for 6 hr at 37°C, held cold for 15 hr and reheated to 37°C, toxin could be detected after only 5 hr of holding at 37°C. The ability of certain foods to support sporulation and enterotoxin formation indicates that such preformed enterotoxin may contribute to early onset of symptoms in some cases of C. perfringens food poisoning.     

EFFECTS OF VARIOUS FRESH MEAT STORAGE METHODS ON THE COLOR OF COOKED GROUND PORK

The effects of microbial growth in raw materials on cooked pork color were investigated. In two trials with sow meat held aerobically at 2C for 3 weeks, microbial load reached spoilage levels (10⁷ cfu/g), pH increased to 6.46, and samples cooked to 71C had red exudate, shown by absorption spectroscopy to contain myoglobin and cytochrome c. Samples cooked to 82C also received high panel ratings for red color, due to red, flocculent precipitate in the exudate, but undenatured myoglobin levels were low. In sow meat held frozen or vacuum-packaged at 2C, pH after 3 weeks was 6.03 and 6.18, and plate counts were 10⁴ and 10⁷, respectively, but exudates after cooking were much less red. In five trials with fresh pork legs, total plate counts also reached 10⁷ cfu/g by 3 weeks storage, and pH increased to 6.37, but cooked samples were not red. Higher myoglobin levels in sow meat probably accounted for the red color and level of undenatured myoglobin remaining after cooking of high pH, spoiled samples.     

POTENTIAL OF IRRADIATION TECHNOLOGY FOR IMPROVED SHELLFISH SANITATION

Ionizing radiation is shown capable of serving as an effective sanitizing treatment improving the sanitary quality of shellfish and providing an increased margin of safety for shellfish consumers. ⁶⁰Co irradiation of the hard-shelled clam , Mercenaria mercenaria, and the oyster , Crassostrea virginica, significantly reduced virus carriage numbers without unduly affecting shellfish survival rates or desirable organoleptic qualities. A D₁₀ value of 2 kGy was determined for depletion of hepatitis A virus in clams and oysters as measured by in situ hybridization fluorescent foci and cytopathology enumeration methods. A D₁₀ value of 2.4 kGy was determined for depletion of rotavirus SA11 in clams and oysters as measured by a plaque forming unit enumeration method. Study results showed ionizing radiation capable of providing an extra, highly effective safeguard of shellfish sanitary quality when combined with traditional depuration treatment. Data drawn from other studies is introduced which shows D₁₀ values as low as 1.0 kGy effectively eliminate Vibrio cholerae, and V. parahemolyticus, from shellfish.     

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.     

Effects of Low-dose Gamma Irradiation and Conventional Treatments on Shelf Life and Quality Characteristics of Diced Celery

ABSTRACT: The effects of 0.5 and 1.0 kGy gamma irradiation on microbial and sensory characteristics of diced celery were compared to conventional treatments such as acidification, blanching, and chlorination. Aerobic plate counts for the irradiated celery did not exceed 10⁷ CFU/g, in contrast, the acidified, blanched, chlorinated, and control samples surpassed aerobic microbial counts of 10⁸ CFU/g in 22, 19, 12, and 8 d, respectively. Importantly, the 1.0-kGy treatment eliminated inoculated Listeria monocytogenes and E. coli. While the acidified and blanched samples had significantly different sensory profiles compared to the other treatments, the irradiated samples maintained their color, texture, and aroma longer and were preferred in the sensory tests. The sensory shelf life of the 1.0-kGy-treated celery was 29 d compared to 22 d for the control, chlorinated, and 0.5 kGy, and 15 d for the acidified and blanched celery.     

Ionizing Radiation Effects on Starch as Shown by Staudinger Index and Differential Thermal Analysis

SUMMARY— Corn starch in the form of raw granules at commercial moisture was irradiated at two levels: 3 × 10⁵ and 6 × 10⁶ rad from a Co⁶⁰ source. The irradiated samples were completely dissolved in alkali, indicating there was no cross linking induced in the starch molecules by irradiation. Viscosity determinations of starch solution diluted with distilled water exhibited the ion charge effect generally observed in other macromolecules.
The Staudinger indices of unirradiated, irradiated at 3 × 10⁶ rad and 6 × 10⁶ rad were 42, 22 and 16 respectively, which were an indication of depolymerization of starch macromolecules with increasing irradiation. The differential thermal analysis of the three samples also showed the depolymerization of the polymer with irradiation.
It is suggested that these two simple techniques–the Staudinger index and D.T.A.–could be usefully employed to characterize small differences in starches.