Biomedical subjects

L R Beuchat

Publications and source records attributed to L R Beuchat.

At least 91 records · Page 5Linked to original sources

PubMed1998

Combined effects of pH, nisin, and temperature on growth and survival of psychrotrophic Bacillus cereus.

Growth of vegetative cells and outgrowth of spores of enterotoxigenic psychrotrophic Bacillus cereus in refrigerated minimally processed food products is a public health concern. A study was undertaken to determine the combined effects of pH, nisin, and temperature on growth and survival of 20 strains of B. cereus. The minimum growth temperatures in tryptic soy broth (pH 7.3) and brain heart infusion broth (BHI broth, pH 7.4) were 5 degrees C for two strains and 8 degrees C for five other strains. Vegetative cells of four of eight strains grew at 8 degrees C in BHI broth (pH 6.01 and 6.57) containing 10 micrograms of nisin per ml. At 15 degrees C, all strains grew at pH 5.53 to 6.57; three strains tolerated nisin at 50 micrograms/ml (pH 6.57), whereas two other strains had a maximum tolerance of 10 micrograms of nisin per ml. Tolerance of vegetative cells of B. cereus to nisin increased as the pH of the broth was increased from 5.53 to 6.01 and again to pH 6.57. Outgrowth of spores (six of six strains tested) was inhibited by 5 and 50 micrograms of nisin per ml at 8 and 15 degrees C, respectively. At 15 degrees C, outgrowth of spores of two strains occurred at pH 6.52 in BHI broth containing 10 micrograms of nisin per ml. The effectiveness of nisin in controlling the growth of psychrotrophic strains of B. cereus capable of causing human illness was more pronounced at 8 degrees C than at 15 degrees C and as the pH was decreased from 6.57 to 5.53. Studies to determine the effectiveness of nisin in controlling growth of psychrotrophic B. cereus in nonpasteurized foods held at refrigeration temperatures are warranted.

Anti-Bacterial Agents↗

PubMed1998

Microbiological quality and the inability of proteolytic Clostridium botulinum to produce toxin in film-packaged fresh-cut cabbage and lettuce.

The production of toxin by a 10-strain mixture of proteolytic Clostridium botulinum in fresh produce packaged in polyethylene films having high (7,000 cc/m2/24 h; HOTR) and low (3,000 cc/m2/24 h; LOTR) relative oxygen permeability was determined. Shredded cabbage and lettuce inoculated with approximately 10(2) spores/g were placed in bags composed of the two films (1.4 kg/bag), and the bags were then vacuum sealed. Produce was stored at 4, 13, and 21 degrees C for up to 21 (cabbage) or 28 (lettuce) days and analyzed periodically. At each sampling time, the gas composition within the bags, pH of the produce, and microbial populations (total aerobic and anaerobic microorganisms, lactic acid bacteria, psychrotrophic bacteria, and yeasts and molds) were determined. In addition, the presence of botulinal toxin was determined using the standard U.S. Food and Drug Administration mouse bioassay protocol. Bags made of HOTR film prolonged sensory quality of cabbage and lettuce, especially at 13 and 4 degrees C. Packaging material had an effect on the growth of various groups of microorganisms; however, there was not a general trend. For example, lettuce packaged in HOTR bags had higher aerobic microbial populations than that packed in LOTR, but no significant difference (P < or = 0.05) was observed with cabbage. Growth of psychrotrophic bacteria was greater in vegetables packaged in HOTR film while growth of yeasts and molds was not affected by either packaging film. Most differences in microbial populations in produce packaged in LOTR and HOTR films were less than 1 log10 CFU/g. Botulinal toxin was not detected in cabbage or lettuce packaged in either film or stored under any test condition.

Animals↗

PubMed1997

Comparison of chemical treatments to kill Salmonella on alfalfa seeds destined for sprout production.

Outbreaks of salmonellosis in the US, Canada and Finland linked to alfalfa sprouts have been attributed to Salmonella stanley in 1995 and Salmonella newport in 1996. This study was undertaken to compare the efficacy of chemical treatments in killing a mixture of five Salmonella serovars inoculated onto alfalfa seeds. Solutions containing calcium hypochlorite or sodium hypochlorite at concentrations of 1800 and 2000 micrograms/ml active (available) chlorine respectively, as well as 6% hydrogen peroxide or 80% ethanol were effective in reducing Salmonella populations by more than 1000 fold. However, viable Salmonella cells were detected in seeds treated for 10 min in these solutions. The inaccessibility of Salmonella cells in crevices and between the cotyledon and testa of seeds to lethal concentrations of these chemicals are thought to be the reason for the lack of effectiveness.

Chlorine↗

PubMed1997

Effects of homogenization pressure and stabilizers on some physical characteristics of a beverage prepared from partially defatted, roasted peanuts.

A low-fat beverage with roasted peanut flavor was developed from peanuts. The potential milk substitute contained 11.8% total solids, 2.0% fat and 3.7% protein, and was whitish orange-yellow in color. The effects of stabilizing additives and homogenization pressure (13.8 x 10(6) Pa or 41.4 x 10(6) Pa) on selected physical characteristics were determined. Suspension stability was improved by addition of carrageenan [Benlacta CM61-B (CM), 0.02-0.04%] or a hydrogenated mono- and diglyceride [Emuldan HV52K (HV, 0.2-0.4%)]. Homogenizing at 41.4 x 10(6) Pa increased viscosity of all samples except that of the controls but did not improve the suspension stability (top:bottom solids) of the beverage. The most viscous formulations (17.5 +/- 0.95 cps) were those containing 0.04% CM. Treatments yielding the best combination, compared to cow's milk values, of high suspension stability (0.5 +/- 0.03, where 1.0 = maximum stability) and low viscosity (3.7 +/- 0.89 cps) were those containing 0.2% HV which were homogenized at 13.8 x 10(6) Pa.

Animals↗

PubMed1997

Effects of nisin and temperature on survival, growth, and enterotoxin production characteristics of psychrotrophic Bacillus cereus in beef gravy.

The presence of psychrotrophic enterotoxigenic Bacillus cereus in ready-to-serve meats and meat products that have not been subjected to sterilization treatment is a public health concern. A study was undertaken to determine the survival, growth, and diarrheal enterotoxin production characteristics of four strains of psychrotrophic B. cereus in brain heart infusion (BHI) broth and beef gravy as affected by temperature and supplementation with nisin. A portion of unheated vegetative cells from 24-h BHI broth cultures was sensitive to nisin as evidenced by an inability to form colonies on BHI agar containing 10 micrograms of nisin/ml. Heat-stressed cells exhibited increased sensitivity to nisin. At concentrations as low as 1 microgram/ml, nisin was lethal to B. cereus, the effect being more pronounced in BHI broth than in beef gravy. The inhibitory effect of nisin (1 microgram/ml) was greater on vegetative cells than on spores inoculated into beef gravy and was more pronounced at 8 degrees C than at 15 degrees C. Nisin, at a concentration of 5 or 50 micrograms/ml, inhibited growth in gravy inoculated with vegetative cells and stored at 8 or 15 degrees C, respectively, for 14 days. Growth of vegetative cells and spores of B. cereus after an initial period of inhibition is attributed to loss of activity of nisin. One of two test strains produced diarrheal enterotoxin in gravy stored at 8 or 15 degrees C within 9 or 3 days, respectively. Enterotoxin production was inhibited in gravy supplemented with 1 microgram of nisin/ml and stored at 8 degrees C for 14 days; 5 micrograms of nisin/ml was required for inhibition at 15 degrees C. Enterotoxin was not detected in gravy in which less than 5.85 log10 CFU of B. cereus/ml had grown. Results indicate that as little as 1 microgram of nisin/ml may be effective in inhibiting or retarding growth of and diarrheal enterotoxin production by vegetative cells and spores of psychrotrophic B. cereus in beef gravy at 8 degrees C, a temperature exceeding that recommended for storage or for most unpasteurized, ready-to-serve meat products.

Animals↗

PubMed1996

Comparison of dilution schemes for enumerating fungi in ground pepper: a collaborative study.

Ten lots of ground pepper were analyzed for fungal populations using 1:5 and 1:10 dilutions in sterile 0.1% peptone. Duplicate samples (0.1 ml) diluted 1:5 were surface plated on dichloran rose bengal chloramphenicol (DRBC) agar whereas quadruplicate samples (0.1 ml) diluted 1:10 were surface plated on DRBC agar. Nine collaborators from six countries participated in the study. Significantly (p < 0.05) higher fungal populations were detected in 7 of the 10 lots of pepper diluted using the 1:5 dilution scheme; the other three showed no significant difference. Using 1:5 and 1:10 dilution schemes, among-laboratory variability in mean fungal populations detected was not significant (p < 0.05) for 7 of 10 and 2 of 10 lots of peppers, respectively. Coefficients of variation for reproducibility (among-laboratory variation) were 2.8% and 6.2%, respectively, using 1:5 and 1:10 dilution schemes. Analysis of collapsed data from all ten lots of pepper revealed that significantly higher populations of fungi were detected using a 1:5 dilution scheme.

Colony Count, Microbial↗

PubMed1996

Evaluation of modified dichloran 18% glycerol (DG18) agar for enumerating fungi in wheat flour: a collaborative study.

Dichloran 18% glycerol agar base supplemented with 100 micrograms of chloramphenicol ml-1 (DG18 agar) was compared to DG18 agar supplemented with 100 micrograms of Triton X-301 ml-1 (DG18T) and DG18 agar supplemented with 1 microgram of iprodione [3-(3,5-dichlorophenyl)-N-(1-methyl-ethyl)-2,4-dioxo-1-imidazolidine- carboxamide] ml-1 (DG18I agar) for enumeration of fungi in ten brands of wheat flour. As the flours contained low fungal populations, all were inoculated with two to four strains of xerophilic fungi (Aspergillus candidus, A. penicillioides, Eurotium amstelodami, E. intermedium, E. repens, E. rubrum, E. tonophilum, E. umbrosum and Wallemia sebi), after which counts ranged from 3.87 to 6.37 log10 CFU g-1. Significantly higher populations (p < 0.05) were detected in four flours: three were on DG18T compared to DG18 and DG18I agar. A. candidus had been inoculated into all three flours. E. amstelodami, E. intermedium, E. repens or E. tonophilum had also been inoculated into at least one of the three flours showing significantly higher numbers of CFU on DG18T agar. Analysis of collapsed data from all samples showed that DG18T agar was significantly better than DG18 or DG18I agars at p < 0.10 but not at p < 0.05. Coefficients of variation for reproducibility (among-laboratory variation) were 8.4%, 7.5% and 8.6%, respectively, for DG18, DG18T and DG18I agars. DG18I agar restricted colony development most, especially for Eurotium species. Naturally occurring Penicillium species grew equally well on DG18 and DG18T agars, whereas W. sebi grew well on all three media. DG18T agar was judged to be superior to DG18 and DG18I agars for enumerating fungi in wheat flours.

Aminoimidazole Carboxamide↗

PubMed1996

Isolation of Escherichia coli O157:H7 from some Egyptian foods.

A survey was done in middle Egypt to determine if Escherichia coli O157:H7 was present in 175 samples of raw ground beef, chicken, lamb and unpasteurized milk. The pathogen was detected in 3 of 50 (6%) beef samples, 2 of 50 (4%) chicken samples, 1 of 25 (4%) lamb samples and 3 of 50 (6%) milk samples obtained from slaughterhouses, supermarkets and farmer's homes.

Animals↗

PubMed1996

Evaluation of media for enumerating heat-stressed, benzoate-resistant Zygosaccharomyces bailii.

A study was undertaken to determine the efficacy of yeast malt extract agar (YMA), acidified YMA (YMAA), acidified tryptone glucose yeast extract agar (TGYA) and Zygosaccharomyces bailii agar (ZBA) for enumerating two strains of Z. bailii (FRR 2227 and FRR 3680) grown and heated in blueberry syrup containing 0, 300 and 600 micrograms/ml sodium benzoate. Cells were heated at 50, 51 or 52 degrees C for 0, 15, 30 or 45 min before spread plating diluted samples on enumeration media and incubating at 30 degrees C for 5 days. Strain FRR 3680 exhibited higher heat resistance than did strain FRR 2227. Regardless of the sodium benzoate concentration in growth and heating media, or the temperature and time of heating, non-selective YMA supported recovery of the highest number of viable cells, followed by TGYA for strain FRR 2227 and TGYA or ZBA for strain FRR 3680. YMAA supported the lowest recovery of heat-stressed cells. The concentration of sodium benzoate in the growth medium did not have a significant effect on tolerance of strain FRR 3680 to heat; however, tolerance of strain FRR 2227 to heat decreased when cells were grown in blueberry syrup containing increased concentrations of sodium benzoate. Regardless of the sodium benzoate concentration in the growth medium, both strains exhibited increased sensitivity when heated in blueberry syrup containing increased concentrations of sodium benzoate. Overall, TGYA was judged best among selective media for enumerating Z. bailii because of its ability to support colony development by heat-stressed cells and because of the ease of counting and differentiating colonies.

Benzoates↗

PubMed1996

Cowpea flour: a potential ingredient in food products.

Cowpeas (Vigna unguiculata L. Walp) are an important grain legume in East and West African countries as well as in other developing countries. The U.S. is the only developed country producing large amounts of cowpeas. High protein (18 to 35%) and carbohydrate (50 to 65%) contents, together with an amino acid pattern complementary to that of cereal grains, make cowpeas potentially important to the human diet from a nutritional standpoint. Despite their potential as an inexpensive source of protein and energy, cowpeas are underutilized in the U.S. and other industrialized countries. A simple technology for preparing cowpea flour would stimulate increased consumption of this legume. This paper reviews the status of cowpea flour production technologies and uses of cowpea flour in various food products.

Africa, Eastern↗

PubMed1996

Inhibitory effects of sucrose monolaurate, alone and in combination with organic acids, on Listeria monocytogenes and Staphylococcus aureus.

The effects of sucrose esters of fatty acids, alone and in combination with ethylenediaminetetraacetic acid (EDTA), acetic acid, lactic acid and citric acid, on survival, growth and thermal inactivation of Listeria monocytogenes and Staphylococcus aureus were determined. The presence of sucrose monocaprate (400 micrograms ml-1) in tryptose phosphate broth (TPB) or tryptic soy broth (TSB) did not inhibit the growth of L. monocytogenes or Staph. aureus, respectively. However, significantly (P < or = 0.05) lower populations of L. monocytogenes were detected in TPB containing as little as 100 micrograms ml-1 sucrose monolaurate (SML) during the logarithmic growth phase compared to populations detected in TPB containing no SML. At 400 micrograms ml-1, SML was lethal to L. monocytogenes. Less marked inhibitory effects were observed with Staph. aureus. The addition of EDTA to broth containing SML had a synergistic effect on the inhibition of both organisms. The chelator alone had no effect at 100 micrograms ml-1 on either pathogen but was inhibitory at 200 micrograms ml-1. Inhibition of L. monocytogenes was more pronounced as the incubation temperature was decreased from 30 degrees C to 15 or 5 degrees C. The addition of 0.1% acetic or lactic acid to TPB minimized the inhibitory effect of 100 and 200 micrograms ml-1 SML during the first 32 h of incubation. Staphylococcus aureus behaved similarly, but not as dramatically, to L. monocytogenes when cultured in TSB supplemented with SML alone or SML and organic acids. A synergistic inhibitory effect of SML and EDTA on heat inactivation of L. monocytogenes was evident but the reverse phenomenon was observed with Staph. aureus. The effectiveness of SML in controlling the growth of L. monocytogenes and Staph. aureus in foods most likely to be contaminated with these pathogens should be further investigated.

Acetates↗

PubMed1996

Effectiveness of trisodium phosphate for killing Salmonella montevideo on tomatoes.

A study was undertaken to determine the effectiveness of trisodium phosphate (TSP) in wash water in the inactivation of Salmonella montevideo on the surface and in core tissue of unwashed, mature-green tomatoes. Complete inactivation on the tomato surface was achieved by dipping tomatoes in a 15% TSP solution for 15 s. Significant (P < 0.05) reductions were obtained by dipping tomatoes in a 1% solution for 15 s. Populations were significantly reduced in core tissue of tomatoes dipped in 4-15% TSP. However, even at 15%, only about 2 log10 reduction was achieved. Upon ripening, the hue and chroma of tomatoes, indices of colour and brightness, respectively, were unaffected by treatment of TSP. The use of TSP as sanitizing agent in wash water for mature-green tomatoes appears to have good potential.

Colony Count, Microbial↗

PubMed1996

Efficacy of chlorine and heat treatment in killing Salmonella stanley inoculated onto alfalfa seeds and growth and survival of the pathogen during sprouting and storage.

The efficacy of chlorine and hot water treatments in killing Salmonella stanley inoculated onto alfalfa seeds was determined. Treatment of seeds containing 10(2) to 10(3) CFU/g in 100-micrograms/ml active chlorine solution for 5 or 10 min caused a significant (P < or = 0.05) reduction in population, and treatment in 290-micrograms/ml chlorine solution resulted in a significant reduction compared with treatment in 100 micrograms of chlorine per ml. However, concentrations of chlorine of up to 1,010 micrograms/ml failed to result in further significant reductions. Treatment of seeds containing 10(1) to 10(2) CFU of S. stanley per g for 5 min in a solution containing 2,040 micrograms of chlorine per ml reduced the population to undetectable levels (< 1 CFU/g). Treatment of seeds in water for 5 or 10 min at 54 degrees C caused a significant reduction in the S. stanley population, and treatment at > or = 57 degrees C reduced populations to < or = 1 CFU/g. However, treatment at > or = 54 degrees C for 10 min caused a substantial reduction in viability of the seeds. Treatment at 57 or 60 degrees C for 5 min appears to be effective in killing S. stanley without substantially decreasing germinability of seeds. Storage of seeds for 8 to 9 weeks at 8 and 21 degrees C resulted in reductions in populations of S. stanley of about 1 log10 and 2 log10 CFU/g, respectively. The behavior of S. stanley on seeds during soaking germination, sprouting, and refrigerated storage of sprouts was determined. An initial population of 3.29 log10 CFU/g increased slightly during 6 h of soaking, by about 10(3) CFU/g during a 24-h germination period, and by an additional 10 CFU/g during a 72-h sprouting stage. A population of 10(7) CFU/g of mature alfalfa sprouts was detected throughout a subsequent 10-day storage period at 5 degrees C. These studies indicate that while populations of S. stanley can be greatly reduced, elimination of this organism from alfalfa seeds may not be reliably achieved with traditional disinfection procedures. If S. stanley is present on seeds at the initiation of the sprout production process, populations exceeding 10(7) CFU/g can develop and survive on mature sprouts exposed to handling practices used in commercial production and marketing.

Chlorine↗

PubMed1996

Survival of Escherichia coli O157:H7 in broth and processed salami as influenced by pH, water activity, and temperature and suitability of media for its recovery.

The survival of unheated and heat-stressed (52 degrees C, 30 min) cells of Escherichia coli O157:H7 inoculated into tryptic soy broth (TSB) adjusted to various pHs (6.0, 5.4, and 4.8) with lactic acid and various water activities (a(w)s) (0.99, 0.95, and 0.90) with NaCl and incubated at 5, 20, 30, and 37 degrees C was studied. The performance of tryptic soy agar (TSA), modified sorbitol MacConkey agar (MSMA), and modified eosin methylene blue agar in supporting colony development of incubated cells was determined. Unheated cells of E. coli O157:H7 grew to population densities of 10(8) to 10(9) CFU ml-1 in TSB (pHs 6.0 and 5.4) at an a(w) of 0.99. Regardless of the pH and a(w) of TSB, survival of E. coli O157:H7 was better at 5 degrees C than at 20 or 30 degrees C. At 30 degrees C, inactivation or inhibition of growth was enhanced by reduction of the a(w) and pH. A decrease in the a(w) (0.99 to 0.90) of TSB in which the cells were heated at 52 degrees C for 30 min resulted in a 1.5-log10 reduction in the number of E. coli O157:H7 cells recovered on TSA; pH did not significantly affect the viability of cells. Recovery was significantly reduced on MSMA when cells were heated in TSB with reduced pH or a(w) for an increased length of time. With the exception of TSB (a(w), 0.90) incubated at 37 degrees C, heat-stressed cells survived for 24 h in recovery broth. TSB (a(w), 0.99) at pH 6.0 or 5.4 supported growth of E. coli O157:H7 cells at 20 or 37 degrees C, but higher numbers of heated cells survived at 5 or 20 degrees C than at 37 degrees C. The ability of unheated and heat-stressed E. coli O157:H7 cells to survive or grow as affected by the a(w) of processed salami was investigated. Decreases of about 1 to 2 log10 CFU g-1 occurred soon after inoculation of salami (pHs 4.86 and 4.63 at a(w)s of 0.95 and 0.90, respectively). Regardless of the physiological condition of the cells before inoculation into processed salami at an a(w) of either 0.95 or 0.90, decreases in populations occurred during storage at 5 or 20 degrees C for 32 days. If present at < or = 100 CFU g-1, E. coli O157:H7 would unlikely survive storage at 5 degrees C for 32 days. However, contamination of salami with E. coli O157:H7 at 10(4) to 10(5) CFU g-1 after processing would pose a health risk to consumers for more than 32 days if storage were at 5 degrees C. Regardless of the treatment conditions, performance of the media tested for the recovery of E. coli O157:H7 cells followed the order TSA > modified eosin methylene blue agar > MSMA.

Culture Media↗

PubMed1995

Use of peanut and cowpea in wheat-based products containing composite flours.

Cowpeas and peanuts are legumes of major dietary and economic importance. They are favored worldwide because of their palatability, contribution to nutritional status, and low cost as a protein source compared to animal protein. Flours processed from cowpeas and peanuts have unique physico-chemical and sensory properties when used in composite flour mixtures. Appropriate blends of cowpea and peanut flours to replace wheat flour in Chinese-type noodles, muffins, and tortillas were determined using modelling and optimization procedures. For noodles, 15% peanut flour and 8% cowpea flour supplementation produced an acceptable product with high protein content (21%). For wheat flour replacement in muffins, up to 43% cowpea and up to 44% peanut flours may be used. However, when wheat flour replacement is 50% or greater, cassava flour should comprise 56 to 72% of the blend with a few exceptions. In tortillas, 24% cowpea and 46% peanut flours produced products similar in quality characteristics to those made from 100% wheat flour. The systematic approach used in these studies is more efficient than the traditional substitution method to optimize sensory qualities of wheat-based products containing composite flours.

Arachis↗

PubMed1995

Evaluation of diluents and media for enumerating Zygosaccharomyces rouxii in blueberry syrup.

Combinations of diluents and enumeration media were evaluated for their efficacy in enumerating Zygosaccharomyces rouxii in blueberry syrup (aw 0.818, 0.870 and 0.921). Diluents consisted of deionized water containing 0.1% peptone, 20%, 30%, 40% or 50% glucose, 50% glucose plus 0.05% Tween 80, and 12%, 18%, 26% or 35% glycerol, all calculated on a w/w basis. Enumeration media were dichloran rose bengal chloramphenicol (DRBC) agar, tryptone glucose yeast extract (TGY) agar, dichloran 18% glycerol (DG18) agar, plate count agar containing 52% sucrose (PCA52S) and malt extract yeast extract 50% glucose (MY50G) agar. Two test strains of Z. rouxii grown in blueberry syrup for 7 or 14 days responded similarly to diluent/enumeration medium combinations. The use of 0.1% peptone diluent or DRBC agar in combination with other enumeration media or diluents was inferior for recovering Z. rouxii. As the aw of the blueberry syrup decreased, the sensitivity of Z. rouxii to diluent containing decreased concentrations of glucose increased. The use of glycerol as a solute in diluent did not result in a similar trend, indicating that the protective effect of glycerol against osmotic stress to Z. rouxii cells is greater than that of glucose at high aw and that cells adapted to low aw in blueberry syrup are more sensitive to high aw in diluents. The addition of 0.05% Tween 80 to 50% glucose diluent did not influence performance. Overall, diluents containing 50% glucose (aw 0.898), 18% glycerol (aw 0.956) or 26% glycerol (0.934), in combination with TGY agar (aw 0.982), resulted in the highest recovery of Z. rouxii from blueberry syrup at aw 0.818 to 0.921.

Colony Count, Microbial↗

PubMed1995

Enrichment in Fraser broth supplemented with catalase or Oxyrase, combined with the microcolony immunoblot technique, for detecting heat-injured Listeria monocytogenes in foods.

The microcolony immunoblot technique using monoclonal antibodies to Listeria monocytogenes was evaluated for its suitability to detect heat-injured cells. Pasteurized milk and filtrates of homogenized raw ground beef slurry and cabbage were inoculated with L. monocytogenes Scott A, heated, diluted, inoculated into Fraser broth (FB) supplemented with 400 micrograms of catalase ml-1 or 0.01 unit of Oxyrase ml-1, and incubated at 30 degrees C for 6 h. Three inoculum populations (high, medium, and low) were used. The extent of injury was dependent on the heating menstruum. Forty percent of the cells were injured in beef slurry filtrate, whereas 79 and 94% were injured in milk and cabbage filtrate, respectively, when foods were heated at 52 degrees C for 20 min. Populations of viable cells were determined using the immunoblot technique and by surface plating on modified Oxford (mMOX) agar. Recovery of cells from heated foods was enhanced in FB supplemented with catalase or Oxyrase compared to recovery in control broth. Essentially all unheated (control) cells could be detected within about 30 h using enrichment and the immunoblot technique; 54 h were required to easily detect colonies on mMOX. In most cases, the number of cells detected in heated milk or filtrates of homogenized beef after enrichment in FB supplemented with catalase or Oxyrase was significantly higher than populations detected using unsupplemented FB; however, enrichment in FB supplemented with catalase or Oxyrase did not significantly increase cell populations in heated cabbage filtrate. Within each heat treatment and level of inoculum, cell populations detected on mMOX agar after incubating plates for 48 h or on immunoblots after 24 h were not significantly different. Results indicate that the immunoblot technique in conjunction with enrichment in FB containing either catalase or Oxyrase can be successfully used to detect healthy and heat-injured cells of L. monocytogenes in diverse types of foods within 34 h.

Animals↗

PubMed1995

Efficacy of a lactic acid/sodium benzoate wash solution in reducing bacterial contamination of raw chicken.

Raw chicken wings inoculated with Salmonella, Campylobacter jejuni, Listeria monocytogenes, Staphylococcus aureus, or Escherichia coli O157:H7 were washed in water (control) or a solution of a 0.5% lactic acid/0.05% sodium benzoate (LB) (pH 2.64) for 30 min. Viable cells of pathogenic bacteria and naturally occurring psychrotrophic bacteria on wings were enumerated after 0, 2, 4, 6, and 8 days of storage at 4 degrees C. Lower populations of pathogenic and psychrotrophic bacteria were detected on wings immediately after washing with LB compared to populations detected on control wings. LB solution was more effective in killing Salmonella, C. jejuni, and E. coli O157:H7 than L. monocytogenes, and S. aureus. During refrigerated storage, populations of Salmonella, C. jejuni, L. monocytogenes, and E. coli O157:H7 decreased significantly on LB-washed wings, as compared to populations of respective pathogens on control wings. The growth of psychrotrophic bacteria on LB-washed wings was significantly retarded as compared to growth on control wings during refrigerated storage. Washing chicken wings with a solution containing 0.5% lactic acid and 0.05% sodium benzoate can greatly reduce the populations of pathogenic and psychotrophic bacteria, thus enhancing safety and extending shelf life.

Animals↗