Showing papers by "Larry R. Beuchat published in 2002"

Evidence of association of salmonellae with tomato plants grown hydroponically in inoculated nutrient solution.

Abstract: The possibility of uptake of salmonellae by roots of hydroponically grown tomato plants was investigated. Within 1 day of exposure of plant roots to Hoagland nutrient solution containing 4.46 to 4.65 log10 CFU of salmonellae/ml, the sizes of the pathogen populations were 3.01 CFU/g of hypocotyls and cotyledons and 3.40 log10 CFU/g of stems for plants with intact root systems (control) and 2.55 log10 CFU/g of hypocotyls and cotyledons for plants from which portions of the roots had been removed. A population of ≥3.38 log10 CFU/g of hypocotyls-cotyledons, stems, and leaves of plants grown for 9 days was detected regardless of the root condition. Additional studies need to be done to unequivocally demonstrate that salmonellae can exist as endophytes in tomato plants grown under conditions that simulate commonly used agronomic practices.

Combined effects of chemical, heat and ultrasound treatments to kill Salmonella and Escherichia coli O157:H7 on alfalfa seeds

Abstract: AIMS To determine the effectiveness of combined treatments with chemicals, heat and ultrasound in killing or removing Salmonella and Escherichia coli O157:H7 on alfalfa seeds intended for sprout production. METHODS AND RESULTS Alfalfa seeds inoculated with Salmonella or E. coli O157:H7 were treated with ultrasound (38.5-40.5 kHz) in solutions containing 1% Ca(OH)(2), 1% Tween 80, 1% Ca(OH)(2) plus 1% Tween 80, 160 microg ml(-1) Tsunami 200 and 0.5% Fit at 23 and 55 degrees C for 2 and 5 min. Highest reductions were in chemical solutions at 55 degrees C, but seed viability was also reduced compared with treatment at 23 degrees C. Inactivation of Salmonella and E. coli O157:H7 was generally enhanced by simultaneous treatments with ultrasound, chemicals and heat. CONCLUSIONS Ultrasound treatment, in combination with chemicals and heat, had a modest enhancing effect on the effectiveness of chemicals in killing or removing pathogens on alfalfa seeds. Overall, treatment with 1% Ca(OH)(2) was most effective in killing Salmonella and E. coli O157:H7. SIGNIFICANCE AND IMPACT OF THE STUDY The use of 1% Ca(OH)(2) instead of 20,000 microg ml(-1) chlorine, which is currently recommended as a sanitizer for seeds intended for sprout production in the US, should be considered. Ultrasound treatment of alfalfa seeds containing Salmonella or E. coli O157:H7, in combination with chemical treatment, contributes to achieving greater reductions in populations of these pathogens, thereby reducing the risk of contamination and the presence of pathogens in sprouts produced from these seeds.

Combined effects of water activity, temperature and chemical treatments on the survival of Salmonella and Escherichia coli O157:H7 on alfalfa seeds.

Abstract: Aims: The objective of this study was to determine the combined effects of water activity (aw), chemical treatment and temperature on Salmonella and Escherichia coli O157:H7 inoculated onto alfalfa seeds. Methods and Results: Alfalfa seeds inoculated with Salmonella or E. coli O157:H7 and adjusted to various aw values were subjected to simultaneous and separate treatments with chemicals and heat. The rate of death of both pathogens was correlated with increased aw (0·15–0·60) and temperature (5–37°C) over a 52-week storage period. Higher seed aw enhanced the inactivation of pathogens on seeds heated at 50–70°C for up to 24 h. Treatment of seeds with water, 1% Ca(OH)2, 1% Tween 80, 1% Ca(OH)2 plus 1% Tween 80 or 40 mg l−1 Tsunami 200® at 23 or 55°C for 2 min significantly (α=0·05) reduced populations of Salmonella and E. coli O157:H7. Conclusions: Overall, at the combinations of temperature and concentrations of chemicals tested, 1% Ca(OH)2 was most effective in killing Salmonella and E. coli O157:H7 without reducing seed viability. Significance and Impact of the Study: None of the treatments evaluated in this study, whether applied separately or in combination, eliminated Salmonella or E. coli O157:H7 on alfalfa seeds without sacrificing the viability of the seeds. It remains essential that practices to prevent the contamination of alfalfa seeds be strictly followed in order to minimize the risk of Salmonella and E. coli O157:H7 infections associated with sprouts produced from these seeds.

Survival of Listeria monocytogenes in commercial food‐processing equipment cleaning solutions and subsequent sensitivity to sanitizers and heat

Abstract: Aims: To determine the ability of Listeria monocytogenes to survive exposure to commercial food-processing equipment cleaning solutions and subsequent treatment with sanitizers or heat. Methods and Results: Cells of five strains of L. monocytogenes were suspended in 1% solutions of eight commercial cleaners (pH 7·1–12·5) or in water (control) and incubated at 4°C for 30 min or 48 h before populations were determined by plating on tryptose phosphate agar. After exposure of cells to cleaning solutions for 30 min, populations of the most resistant strain of L. monocytogenes were reduced by ≤ 1·63 log10 cfu ml–1. In only three highly alkaline cleaning solutions (pH 11·6–12·4) were populations reduced significantly (P ≤ 0·05) compared with reductions in water. After 48 h, populations were significantly higher in one cleaning solution (pH 10·4) than in water, while populations in six of the other seven cleaning solutions were reduced by ≥ 4·72 log10 cfu ml–1. Cells exposed to cleaning solutions for 30 min became sensitive to 4·0 or 6·0 mg l–1 free chlorine and to 50 or 100 mg l–1 benzalkonium chloride and cetylpyridinium chloride, common components of quaternary ammonium sanitizers. Cells exposed to four of the five test cleaners had D56°C values less than or equal to those of the control cells. Conclusions:Listeria monocytogenes tolerates exposure to a high concentration of alkaline cleaning solutions but consequently becomes sensitized to sanitizers. Significance and Impact of the Study: The elimination of L. monocytogenes surviving exposure to alkaline cleaning solutions widely used for food-processing equipment is essential and the appropriate use of sanitizers for subsequent application to equipment is important in achieving this goal.

Mild heat treatment of lettuce enhances growth of Listeria monocytogenes during subsequent storage at 5°C or 15°C

Abstract: Y . L I , R . E . B R A C K E T T , J . C H E N A N D L . R . B E U C H A T . 2002. Aims: The objective of this study was to determine the influence of mild heat treatment, storage temperature and storage time on the survival and growth of Listeria monocytogenes inoculated onto cut iceberg lettuce leaves. Methods and Results: Before or after inoculation with L. monocytogenes, cut iceberg lettuce leaves were dipped in water (20 or 50∞C), containing or not 20 mg l ‐1 chlorine, for 90 s, then stored at 5∞C for up to 18 days or 15∞C for up to 7 days. The presence of 20 mg l ‐1 chlorine in the treatment water did not significantly (aa 0AE05) affect populations of the pathogen, regardless of other test parameters. The population of L. monocytogenes on lettuce treated at 50∞C steadily increased throughout storage at 5∞C for up to 18 days. At day 10 and thereafter, populations were 1AE7‐2AE3 log10 cfu g ‐1 higher on lettuce treated at 50∞C after inoculation compared with untreated lettuce or lettuce treated at 20∞C, regardless of chlorine treatment. The population of L. monocytogenes increased rapidly on lettuce stored at 15∞C. At 2 and 4 days, significantly higher populations were detected on lettuce that had been treated at 50∞C, compared with respective samples that had been treated at 20∞C, regardless of inoculation before or after treatment, or the presence of 20 mg l ‐1 chlorine in the treatment water. Conclusions: The results clearly demonstrated that mild heat treatment of cut lettuce leaves enhances the growth of L. monocytogenes during subsequent storage at 5 or 15∞C. Significance and Impact of the Study: Mild heat treatment of cut lettuce may result in a prolonged shelf life as a result of delaying the development of brown discoloration. However, heat treatment also facilitates the growth of L. monocytogenes during storage at refrigeration temperature, thereby increasing the potential risk of causing listeriosis.

Demand for food variety in an emerging market economy

Abstract: Using food intake survey data collected in Bulgaria in 1997, this study identified socioeconomic and demographic factors affecting demand for varied diet as measured by the count of food items and Entropy index. Consumer preference for food variety exhibited different patterns depending on the length of time allowed for consumption. Estimated correlation coefficients indicated that daily variety deviated from that measured weekly and monthly. Regression analysis showed that regional effects differed across the three periods of time, illustrating that the length of time allowed for consumption is an important element in measuring the demand for food variety.

Radio–frequency heating of alfalfa seed for reducing human pathogens

Abstract: The problem of bacterial contamination of vegetable seed sprouts produced for human consumption is reviewed briefly. The potential for controlling human bacterial pathogens on alfalfa seed used in the production of sprouts by dielectric heating was studied by experimental exposure of alfalfa seed artificially contaminated with Salmonella, Escherichia coli O157:H7, and Listeria monocytogenes to radio-frequency (RF) dielectric heating treatments at 39 MHz and different electric field intensities for varying times of exposure. Moisture content of alfalfa seed and final temperatures produced by the RF exposures were determined, and control and treated seed samples were analyzed in the laboratory for reduction of bacterial populations and effects on seed germination. Significant reductions in populations of all three pathogens were achieved without reductions in seed germination. However, exposures that provided substantial reductions in pathogen levels were not achieved without significant damage to seed germination. Treatments providing moderate reductions in bacterial pathogen populations also increased alfalfa seed germination through reductions in hard seed percentages, so the combined benefits need to be considered in evaluating dielectric heating treatments for practical use.

Inactivation of escherichia coli o157:h7 on inoculated alfalfa seeds with ozonated water under pressure

Abstract: Alfalfa seeds inoculated with Escherichia coli O157:H7 (∼10 5 CFU/g) were subjected to low hydrostatic pressure. Seeds immersed in ozonated water at 4C were held at 8 and 12-psi ozone pressure for 2, 4, 8, 16, 32, and 64 min. Alternatively, seeds were continuously sparged with ozone for up to 64 min and then held at 12 psi for 5 min. Controls consisted of sparging and pressurization with air. Thirty-two minute treatments of continuous ozone sparging followed by pressurization of seeds at 12 psi for 5 min were repeated with the addition of four surfactants (Tween 20, Tween 80, SPAN 20, and SPAN 80) in the treatment water. Enumeration of E. coli O157:H7 on treated, untreated, and control seeds was done on tryptic soy agar supplemented with 50 μg/mL of nalidixic acid. The reduction in population of E. coli O157:H7 on seeds treated with the 8 and 12 psi hydrostatic pressure in ozonated water ranged from 0.74 - 1.56 log 10 CFU/g and 0. 72 - 1.62 log 10 CFU/g, respectively. Control treatments carried out with air pressurization of seeds resulted in maximum population reductions of 1.55 log 10 and 1. 83 log 10 CFU/g for 8 and 12 psi, respectively. For seeds treated with continuous ozone sparging (2 - 64 min) followed by pressurization at 12 psi for 5 min, the highest reduction was 2. 03 log 10 CFU/g. Reductions were, however, not significantly different (P>0.05) from control treatment (with air) which reduced the populations by 0.57 - 2.19 log 10 CFU/g. The presence of surfactants during continuous sparging ofwater followed by pressurization at 12 psi was not beneficial. None of the treatments adversely affected the germination of the seeds. Des graines de luzerne inoculees avec Escherichia coli O157:H7 sont soumises a des pressions hydrostatiques faibles. Des graines immergees dans de l'eau ozonee a 4°C sont portees a des pressions en ozone de 8 et 12 psi pendant 2 a 64 mn. Alternativement, des graines sont continuellement traitees avec de l'ozone pendant plus de 64 mn et soumises a des pressions de 12 psi pendant 5 mn. L'effet de l'addition de surfactants dans l'eau de traitement est aussi evalue. L'application de l'ozone couplee avec les pressions evaluees et les surfactants n'augmentent pas l'inactivation de Escherichia coli O157:H7.

Survival and growth of Shigella flexneri, Salmonella enterica serovar enteritidis, and Vibrio cholerae O1 in reconstituted infant formula.

Abstract: Formula feeding is an alternative method to prevent mother-to-child infection with human immunodeficiency virus through breast-feeding in developing countries. Growth of bacterial pathogens in reconstituted infant formula has become a health hazard when contaminated water is used for rehydration. This study was conducted to assess bacterial safety risk of using contaminated water to reconstitute infant formula. Survival and growth characteristics were determined for three bacterial pathogens, Vibrio cholerae O1, Shigella flexneri, and Salmonella enterica serovar Enteritidis, inoculated into sterile tap water (3.2-3.4 log10 colony-forming units [CFU]/ml) and infant formula (1.5-1.7 and 3.2-3.4 log10 CFU/ml) and incubated at 4 degrees C or 30 degrees C for up to 24 hours. Vibrio cholerae O1 was the most sensitive of the three pathogens when inoculated into water, with no viable cells detected within 2 hours at 4 degrees C or 30 degrees C. The rate of inactivation in water was greater at 30 degrees C than at 4 degrees C. Vibrio cholerae O1, Shigella flexneri, and Salmonella enterica serovar Enteritidis grew rapidly in infant formula at 30 degrees C, reaching populations of 9.2, 8.7, and 9.2 log10 CFU/ml, respectively, at 24 hours. Populations of all three pathogens did not change significantly after incubating infant formula for 24 hours at 4 degrees C, but continuously decreased in water throughout incubation for 24 hours, regardless of temperature. Results suggest that unless refrigerated, reconstituted infant formula should be consumed soon after preparation to avoid increased risk of illness associated with increases in populations of pathogenic bacteria that may be introduced by contaminated water.

Customer profiles of retail food outlets in the emerging market economy of bulgaria

Abstract: The objective of this study was to identify profiles of consumers frequenting three types of food retail outlets- grocery stores, farmer markets, and street stalls- to purchase food in a transition economy in Bulgaria. This study estimated two-stage decision models to distinguish between the two decisions of choosing to shop at a particular outlet and how often to shop. Retail-outlet selection and shopping frequency were affected by different sets of sociodemographic characteristics. In particular, household income was a major factor influencing the selection of farmer markets and street stands, but had no effect on the selection of and shopping frequency at grocery stores.

Influence of composition of diluent on populations of yeasts and moulds recovered from raw fruits.

Abstract: Aims: The aims of this study were (i) to determine the retention of viability of mycoflora removed from raw fruits, and how this affected diluents used to prepare samples for enumeration of propagules, and (ii) to evaluate the performance of recovery media for supporting colony development. Methods and Results: Yeasts and moulds removed from seven types of raw fruit were held in seven diluents for 1 h before plating on dichloran rose bengal chloramphenicol (DRBC) agar and plate count agar supplemented with chloramphenicol (100 µg ml −1 ) (PCAC). Significant reductions (P=0·05) in populations of yeasts, moulds, and yeasts plus moulds occurred within the 1 h holding period, regardless of diluent composition. Overall, retention of viability was not influenced by diluent composition, and neither DRBC agar nor PCAC were superior in supporting colony development. Conclusions: The composition of diluents used to prepare food samples for mycological analysis has little affect on the number of yeasts and moulds recovered from seven types of naturally contaminated raw fruit. Both DRBC agar and PCAC are suitable as enumeration media. Significance and Impact of the Study: Diluents and media most often recommended for enumerating yeasts and moulds in foods are appropriate for raw fruits.