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At least 37 records · Page 2Linked to original sources

PubMed2002

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

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 degrees C) containing or not 20 mg l(-1) chlorine, for 90 s, then stored at 5 degrees C for up to 18 days or 15 degrees C for up to 7 days. The presence of 20 mg l(-1) chlorine in the treatment water did not significantly (alpha=0.05) affect populations of the pathogen, regardless of other test parameters. The population of L. monocytogenes on lettuce treated at 50 degrees C steadily increased throughout storage at 5 degrees C for up to 18 days. At day 10 and thereafter, populations were 1.7-2.3 log10 cfu g(-1) higher on lettuce treated at 50 degrees C after inoculation compared with untreated lettuce or lettuce treated at 20 degrees C, regardless of chlorine treatment. The population of L. monocytogenes increased rapidly on lettuce stored at 15 degrees C. At 2 and 4 days, significantly higher populations were detected on lettuce that had been treated at 50 degrees C, compared with respective samples that had been treated at 20 degrees 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 degrees 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.

Chlorine↗

PubMed2001

Decontamination of lettuce using acidic electrolyzed water.

The disinfectant effect of acidic electrolyzed water (AcEW), ozonated water, and sodium hypochlorite (NaOCl) solution on lettuce was examined. AcEW (pH 2.6; oxidation reduction potential, 1140 mV; 30 ppm of available chlorine) and NaOCl solution (150 ppm of available chlorine) reduced viable aerobes in lettuce by 2 log CFU/g within 10 min. For lettuce washed in alkaline electrolyzed water (AIEW) for 1 min and then disinfected in AcEW for 1 min, viable aerobes were reduced by 2 log CFU/g. On the other hand, ozonated water containing 5 ppm of ozone reduced viable aerobes in lettuce 1.5 log CFU/g within 10 min. It was discovered that AcEW showed a higher disinfectant effect than did ozonated water significantly at P < 0.05. It was confirmed by swabbing test that AcEW, ozonated water, and NaOCI solution removed aerobic bacteria, coliform bacteria, molds, and yeasts on the surface of lettuce. Therefore, residual microorganisms after the decontamination of lettuce were either in the inside of the cellular tissue, such as the stomata, or making biofilm on the surface of lettuce. Biofilms were observed by a scanning electron microscope on the surface of the lettuce treated with AcEW. Moreover, it was shown that the spores of bacteria on the surface were not removed by any treatment in this study. However, it was also observed that the surface structure of lettuce was not damaged by any treatment in this study. Thus, the use of AcEW for decontamination of fresh lettuce was suggested to be an effective means of controlling microorganisms.

Bacteria, Aerobic↗

PubMed2002

Sensorial and chemical quality of gamma-irradiated fresh-cut iceberg lettuce in modified atmosphere packages.

A study was conducted to investigate the effects of various doses of irradiation on the quality of fresh-cut iceberg lettuce and to determine a suitable maximum dose. Fresh-cut iceberg lettuce packaged in film bags was exposed to 0, 1, 2, 3, and 4 kGy of gamma radiation and stored at 3 degrees C for 14 days. CO2 levels were higher and O2 levels were lower in packages containing irradiated lettuce than in those containing nonirradiated lettuce for most of the storage period. Comparison with nonirradiated lettuce indicated that total ascorbic acid (ascorbic acid plus dehydroascorbic acid) content and firmness were not significantly influenced by irradiation at 1 or 2 kGy. The overall visual appearance was best for lettuce irradiated at 1 or 2 kGy. This improved quality may be related to the high CO2 and low O2 levels observed for the irradiated samples. Electrolyte leakage for lettuce increased with higher radiation doses and was correlated (R2 = 0.99) with a soggy appearance. The leakage for lettuce irradiated at > or = 2 kGy was significantly more extensive than that for nonirradiated lettuce. The irradiation of fresh-cut lettuce in modified atmosphere packages at doses of 1 kGy and perhaps 2 kGy for safety enhancement and quality improvement is feasible.

Ascorbic Acid↗

PubMed1989

Sulfite-treated lettuce challenges in sulfite-sensitive subjects with asthma.

This study was designed to determine whether lettuce treated with a commercially available sulfite-containing freshener prepared according to manufacturer's directions could provoke reactions in sulfite-sensitive subjects with asthma (SSAs). Five adult SSAs with stable asthma who had multiple prior reactions to double-blind, placebo-controlled, sulfite-capsule challenges were studied. Each patient ingested, in a double-blind, placebo-controlled fashion, four portions of lettuce (3 oz) pretreated with one of two commercially available, nearly identical vegetable fresheners. One freshener contained sodium bisulfite and was used on one portion of lettuce. The other freshener contained no sulfite and was used on three portions of lettuce. The fresheners were prepared and the lettuce was treated according to label instructions. After baseline spirometry, the SSAs consumed the lettuce samples with the same dressing of their choice, serial spirometry was performed, and a positive reaction was defined as a greater than 20% drop in FEV1 decreased 0% to 7%; mean, 3%. Two of the subjects experienced severe reactions to the sulfite-treated lettuce. One of these reactions was life threatening; the other reaction occurred despite placing only 30% of the usual sulfite dose on the lettuce. This study has demonstrated that sulfite-treated lettuce is capable of provoking bronchospasm in SSAs and suggests that such food is one cause of restaurant-provoked asthma in these individuals.

Adult↗

PubMed1996

Effect of CO2 levels on nutrient content of lettuce and radish.

Atmospheric carbon-dioxide enrichment is known to affect the yield of lettuce and radish grown in controlled environments, but little is known about CO2 enrichment effects on the chemical composition of lettuce and radish. These crops are useful model systems for a Controlled Ecological Life-Support System (CELSS), largely because of their relatively short production cycles. Lettuce (Lactuca sativa L.) cultivar 'Waldmann's Green' and radish (Raphanus sativus L.) cultivar 'Giant White Globe' were grown both in the field and in controlled environments, where hydroponic nutrient solution, light, and temperature were regulated, and where CO2 levels were controlled at 400, 1000, 5000, or 10,000 ppm. Plants were harvested at maturity, dried, and analyzed for proximate composition (protein, fat, ash, and carbohydrate), total nitrogen (N), nitrate N, free sugars, starch, total dietary fiber, and minerals. Total N, protein N, nonprotein N (NPN), and nitrate N generally increased for radish roots and lettuce leaves when grown under growth chamber conditions compared to field conditions. The nitrate-N level of lettuce leaves, as a percentage of total NPN, decreased with increasing levels of CO2 enrichment. The ash content of radish roots and of radish and lettuce leaves decreased with increasing levels of CO2 enrichment. The levels of certain minerals differed between field- and chamber-grown materials, including changes in the calcium (Ca) and phosphorus (P) contents of radish and lettuce leaves, resulting in reduced Ca/P ratio for chamber-grown materials. The free-sugar contents were similar between the field and chamber-grown lettuce leaves, but total dietary fiber content was much higher in the field-grown plant material. The starch content of growth-chamber lettuce increased with CO2 level.

Atmosphere↗

PubMedDate not supplied

Lettuce and carrot allergy: are they related?

Lettuce is commonly included in many elimination diets of subjects with either food allergy or atopic dermatitis since IgE-mediated allergic reactions have not been reported. We have observed a positive carrot skin test and/or RAST in two clinically lettuce sensitive, ragweed allergic subjects and positive lettuce skin test and/or RAST in two ragweed allergic patients with oral allergy syndrome to carrot. In this study lettuce allergy and the allergenic relationship between iceberg lettuce (Lactuca sativa L.), a member of the Asteraceae and carrot, a member of the Apiaceae, were investigated using sera from those four individuals. SDS-PAGE immunoblotting results indicated that iceberg lettuce can induce an IgE-mediated response. Fourteen allergens were detected between 13 and > 113 kD. RAST inhibition demonstrated that carrot does share common allergens with lettuce, although carrot allergens are more potent than those of lettuce. These findings may have some importance in patients with food-related symptoms, such as atopic dermatitis, because lettuce, when included in their diets, may aggravate the underlying disease.

Allergens↗

PubMed2001

Penetration of Escherichia coli O157:H7 into lettuce as influenced by modified atmosphere and temperature.

The effects of temperature and atmospheric oxygen concentration on the respiration rate of iceberg lettuce and Escherichia coli O157:H7 cells attachment to and penetration into damaged lettuce tissues were evaluated. Respiration rate of lettuce decreased as the temperature was reduced from 37 to 10 degrees C. Reducing the temperature further to 4 degrees C did not affect the respiration rate of lettuce. Respiration rate was also reduced by lowering the atmospheric oxygen concentration. Lettuce was submerged in E. coli O157:H7 inoculum at 4, 10, 22, or 37 degrees C under 21 or 2.7% oxygen. Attachment and penetration of E. coli O157:H7 were not related to the respiration rate. The greatest numbers of E. coli O157:H7 cells attached to damaged lettuce tissues at 22 degrees C at both oxygen concentrations. More cells were attached under 21% oxygen than under 2.7% oxygen at each temperature, but this difference was small. Penetration of E. coli O157:H7 into lettuce tissue was determined by immunostaining with a fluorescein isothiocyanate-labeled antibody. Under 21% oxygen, E. coli O157:H7 cells showed greatest penetration when lettuce was held at 4 degrees C, compared to 10, 22. or 37 degrees C, and were detected at an average of 101 microm below the surfaces of cut tissues. However, under 2.7% oxygen, there were no differences in degree of penetration among four incubation temperatures. The degree of E. coli O157:H7 penetration into lettuce tissue at 4 or 22 degrees C was greater under 21% oxygen than under 2.7% oxygen; however, no difference was observed at 37 degrees C. Conditions that promote pathogen penetration into tissue could decrease the effectiveness of decontamination treatments.

Bacterial Adhesion↗

PubMed2002

Inactivation of Escherichia coli O157:H7, Salmonella enterica serotype enteritidis, and Listeria monocytogenes on lettuce by hydrogen peroxide and lactic acid and by hydrogen peroxide with mild heat.

Iceberg lettuce is a major component in vegetable salad and has been associated with many outbreaks of foodborne illnesses. In this study, several combinations of lactic acid and hydrogen peroxide were tested to obtain effective antibacterial activity without adverse effects on sensory characteristics. A five-strain mixture of Escherichia coli O157:H7, Salmonella enterica serotype Enteritidis, and Listeria monocytogenes was inoculated separately onto fresh-cut lettuce leaves, which were later treated with 1.5% lactic acid plus 1.5% hydrogen peroxide (H2O2) at 40 degrees C for 15 min, 1.5% lactic acid plus 2% H2O2 at 22 degrees C for 5 min, and 2% H2O2 at 50 degrees C for 60 or 90 s. Control lettuce leaves were treated with deionized water under the same conditions. A 4-log reduction was obtained for lettuce treated with the combinations of lactic acid and H2O2 for E. coli O157:H7 and Salmonella Enteritidis, and a 3-log reduction was obtained for L. monocytogenes. However, the sensory characteristics of lettuce were compromised by these treatments. The treatment of lettuce leaves with 2% H2O2 at 50 degrees C was effective not only in reducing pathogenic bacteria but also in maintaining good sensory quality for up to 15 days. A < or = 4-log reduction of E. coli O157:H7 and Salmonella Enteritidis was achieved with the 2% H2O2 treatment, whereas a 3-log reduction of L. monocytogenes was obtained. There was no significant difference (P > 0.05) between pathogen population reductions obtained with 2% H2O2 with 60- and 90-s exposure times. Hydrogen peroxide residue was undetectable (the minimum level of sensitivity was 2 ppm) on lettuce surfaces after the treated lettuce was rinsed with cold water and centrifuged with a salad spinner. Hence, the treatment of lettuce with 2% H2O2 at 50 degrees C for 60 s is effective in initially reducing substantial populations of foodborne pathogens and maintaining high product quality.

Anti-Infective Agents, Local↗

PubMed2004

Influence of variations in methodology on populations of Listeria monocytogenes recovered from lettuce treated with sanitizers.

The elimination of Listeria monocytogenes inoculated onto a piece of cut iceberg lettuce (3.8 by 3.8 cm) by treatment with chlorinated water (200 micrograms/ml free chlorine) and a 0.5% (wt/vol) solution of FIT Professional Line Antibacterial Cleaner (FIT) was investigated. The efficacy of the two sanitizers was not influenced by the composition of the medium used to culture the L. monocytogenes used in the inocula, the number of strains in the inoculum, or the recovery medium used to enumerate the pathogen on lettuce after treatment. Drying inoculum on lettuce for 45 min at 37 degrees C caused more cells to die or not be retrieved compared with drying inoculum for 30 min at 25 degrees C. However, the percentage of cells in the inoculum recovered from lettuce treated with chlorine or FIT was not significantly different, regardless of the drying method. Stomaching, homogenizing, or stomaching followed by homogenizing lettuce treated with sanitizers resulted in recovery of similar numbers of L. monocytogenes, indicating that stomaching and homogenizing are equivalent in extracting cells; the sequential use of both processing methods did not substantially increase the efficiency of recovery. Washing lettuce with water or treating lettuce with 200 micrograms/ml chlorine or FIT resulted in decreases in populations of 0.60, 1.76, and 1.51 log CFU per lettuce piece, respectively, regardless of variations in test parameters. Reductions caused by sanitizers were significantly greater (alpha = 0.05) than that observed for water but not significantly different from each other. It is concluded that evaluation of sanitizers for their efficacy in killing L. monocytogenes on lettuce can be determined by spot inoculating 50 microliters of a five-strain mixture of cells from 24-h cultures suspended in 5% horse serum albumen, followed by drying the inoculum for 45 min at 37 degrees C, treatment by submerging in 50 ml of sanitizer for 5 min, stomaching samples in 50 ml of Dey-Engley neutralizing broth for 2 min, and enumerating survivors on modified Oxford medium.

Chlorine↗

PubMed2004

Survival and recovery of Escherichia coli O157:H7, Salmonella, and Listeria monocytogenes on lettuce and parsley as affected by method of inoculation, time between inoculation and analysis, and treatment with chlorinated water.

The effects of method for applying inoculum and of drying time after inoculation on survival and recovery of foodborne pathogens on iceberg lettuce and parsley were studied. Five-strain mixtures of Escherichia coli O157:H7, Salmonella, or Listeria monocytogenes were applied to lettuce and parsley by dip, spot, or spray inoculation methods. Inocula were dried for 2 h at 22 degrees C or for 2 h at 22 degrees C and then 22 h at 4 degrees C before being treated with water (control) or chlorine (200 microg/ml). Significantly higher populations (CFU per lettuce or parsley sample) of E. coli O157:H7 and Salmonella (alpha = 0.05) were recovered from dip-inoculated produce than from spot- or spray-inoculated produce. This difference was attributed to larger numbers of cells adhering to lettuce and parsley subjected to dip inoculation. Populations of E. coli O157:H7 and Salmonella recovered from lettuce inoculated by spot and spray methods were not significantly different, but populations recovered from spot-inoculated parsley were significantly higher than those recovered from spray-inoculated parsley, even though the number of cells applied was the same. Significantly different numbers of L. monocytogenes were recovered from inoculated lettuce (dip > spray > spot); populations recovered from dip-inoculated parsley were significantly higher than those recovered from spot- or spray-inoculated parsley, which were not significantly different from each other. Populations of pathogens recovered from lettuce and parsley after drying inoculum for 2 h at 22 degrees C were significantly higher than or equal to populations recovered after drying for 2 h at 22 degrees C and then for 22 h at 4 degrees C. Significant differences (water > chlorine) were observed in populations of all pathogens recovered from treated lettuce and parsley, regardless of inoculation method and drying time. It is recommended that spot inoculation with a drying time of 2 h at 22 degrees C followed by 22 h at 4 degrees C be used to determine the efficacy of chlorine and other sanitizers in killing foodborne pathogens on lettuce and parsley.

Bacterial Adhesion↗

PubMed2004

Health effect of vegetable-based diet: lettuce consumption improves cholesterol metabolism and antioxidant status in the rat.

BACKGROUND & AIMS: It is often assumed that fruits and vegetables contribute to protect against degenerative pathologies such as cardiovascular diseases. Besides epidemiological observations, scientific evidences for their mechanism of action are scarce. In the present study, we investigated the mean term and post-prandial effects of lettuce ingestion on lipid metabolism and antioxidant protection in the rat. RESULTS: Feeding rats a 20% lettuce diet for 3 weeks resulted in a decrease cholesterol LDL/HDL ratio and a marked decrease of liver cholesterol levels (-41%). Concurrently, fecal total steroid excretion increased (+44%) and apparent absorption of dietary cholesterol was significantly depressed (-37%) by the lettuce diet. Lettuce diet also displayed an improvement of vitamin E/TG ratio in plasma and limited lipid peroxidation in heart as evidenced by TBARS. In post-prandial experiment, lettuce intake significantly increased both ascorbic acid and alpha-tocopherol plasma levels which contribute to improve plasma antioxidant capacity within 2 h of consumption. Other lipid-soluble antioxidants (lutein and vitamin E) may also improve the plasma antioxidant capacity. CONCLUSION: Lettuce consumption increases the total cholesterol end-products excretion and improves antioxidant status due to the richness in antioxidants (vitamins C, E and carotenoids). In our model, lettuce clearly shows a beneficial effect on lipid metabolism and on tissue oxidation. Therefore regular consumption of lettuce should contribute to improve protection against cardiovascular diseases.

Animals↗

PubMed2006

Volatile metabolite production of spoilage micro-organisms on a mixed-lettuce agar during storage at 7 degrees C in air and low oxygen atmosphere.

This paper describes the volatile metabolite production of spoilage bacteria (Pantoea agglomerans and Rahnella aquatilis) and spoilage yeasts (Pichia fermentans and Cryptococcus laurentii), previously isolated from mixed lettuce, on a simulation medium of shredded mixed lettuce (mixed-lettuce agar) both under air conditions and modified atmosphere (MA)-conditions at 7 degrees C. These latter conditions simulated the equilibrium modified atmosphere packaging, which is used to extend the shelf-life of shredded mixed lettuce. Besides volatile metabolites, organic acid metabolites and consumption of sugars were measured. Microbiological growth on the mixed-lettuce agar resulted in metabolite production and consumption of sugars. Bacteria and yeasts produced a range of volatile organic compounds both under air conditions and MA-conditions: ethanol, ethyl acetate, 2-methyl-1-propanol, 2-methyl-1-butanol, 3-methyl-1-butanol, 2,3-butanedione, 3-methyl-1-pentanol, 1-butanol and 1-hexanol. Under MA-conditions, 2-methyl-1-butanol, 3-methyl-1-butanol and ethanol were the first compounds that were detected in the headspace as being produced by the inoculated micro-organisms. In the case of the yeast P. fermentans, production of these compounds was detected from a count of 5.0+/-0.1 log cfu/cm(2) with a fast increase when exceeding 6.0-6.5 log cfu/cm(2). Unlike P. fermentans, the yeast C. laurentii showed a slow metabolism under MA-conditions, compared to air conditions. In the case of the bacteria, production of 2-methyl-1-butanol and 3-methyl-1-butanol was detected starting from a count of 6.7+/-0.1 log cfu/cm(2) in the case of R. aquatilis and from a count of 7.1+/-0.4 log cfu/cm(2) in the case of P. agglomerans with a fast increase when exceeding 8 log cfu/cm(2). No production of ethanol by the bacteria under MA-conditions was detected in contradiction to air conditions. It could be concluded that, if these counts are reached on the cut surfaces of shredded mixed lettuce which are simulated by the mixed-lettuce agar, sensorial quality of shredded mixed lettuce could be influenced by the microbiological production of metabolites.

Bacteria↗

PubMed2002

Determination of anthraquinone in technical material, formulations, and lettuce by high performance liquid chromatography.

Foraging on lettuce seeds and seedlings by horned larks (Eremophila alpestris) causes millions of dollars in losses to the California lettuce crop annually. Anthraquinone (AQ; 9,10-anthracenedione) has been shown to deter pest birds from consuming the seeds and seedlings of several plant species and was evaluated as a repellent to horned larks when applied to lettuce seedlings. A set of analytical methods using simple liquid extraction followed by high-performance liquid chromatography analysis were developed for the quantitation of AQ as technical material, as an active ingredient in a commercial formulation, and as a residue in lettuce plants. The methods were easy, reliable, and repeatable. AQ recoveries from control formulation fortified to concentrations of either 24 or 600 mg g(-)(1) were 99 (+/-1.2%) and 98% (+/-1.2%), respectively, with a control formulation method limit of detection (MLOD) of 0.50 mg g(-)(1). Control lettuce tissues from three growth stages were AQ-fortified to concentrations of 0.50 and 500 microg g(-)(1). The resulting AQ recoveries for the two fortification levels were 99 (+/-8.5) and 89% (+/-1.5%) for 11 day old seedlings, 95 (+/-2.6%) and 86% (2.1%) for 16 day old plants, and 92 (+/-1.4%) and 93% (+/-1.1%) for adult head lettuce cover leaves, respectively. The MLODs for the same three lettuce tissues were 0.055, 0.058, and 0.077 microg g(-)(1), respectively. These methods were used to quantify AQ residues from field-grown, treated lettuce and associated fortified quality control samples.

Anthraquinones↗

PubMed2005

Accumulation and perchlorate exposure potential of lettuce produced in the Lower Colorado River region.

The Colorado River is contaminated with perchlorate concentrations of 1.5-8 microg/L, an anion linked to thyroid dysfunction. Over 90% of the lettuce (Lactuca sativa L.) consumed during the winter months in the United States is produced in the Lower Colorado River region. Studies were conducted in this region to survey the potential for lettuce perchlorate accumulation and estimate potential human exposure to perchlorate from lettuce. Total uptake of perchlorate in the above-ground plant of iceberg lettuce was approximately 5 g/ha. Exposure estimates ranged from 0.45 to 1.8 microg/day depending on lettuce types and trimming. For all lettuce types, hypothetical exposures were less than 4% of the reference dose recommended by the National Academy of Sciences. Results show the relative iodide uptake inhibition potential because of lettuce nitrate was 2 orders of magnitude greater than that associated with the corresponding trace levels of perchlorate. These data support the conclusion that potential perchlorate exposures from lettuce irrigated with Colorado River water are negligible relative to acute or long-term harmful amounts.

Arizona↗

PubMed2002

Effect of acute ingestion of fresh and stored lettuce (Lactuca sativa) on plasma total antioxidant capacity and antioxidant levels in human subjects.

The present study investigated whether storage under modified-atmosphere packaging (MAP) affected the antioxidant properties of fresh lettuce (Lactuca sativa). Eleven healthy volunteers (six men, five women) consumed 250 g fresh lettuce, and blood was sampled before (0 h) and 2, 3 and 6 h after consumption. The protocol was repeated 3 d later with the same lettuce stored at 5 degrees C under MAP conditions (O2-N2 (5:95, v/v)). Results showed that after ingestion of fresh lettuce, plasma total radical-trapping antioxidant potential (TRAP), measured as area under the curve, was significantly higher (1.3 (sem 0.3) mmol/l per 6 h; P<0.05) than the value obtained with MAP-stored lettuce (0.1 (sem 0.2) mmol/l per 6 h). Plasma TRAP, quercetin and p-coumaric acid were significantly different from baseline values (P<or=0.05) 2 and 3 h after fresh lettuce ingestion. Caffeic acid increased significantly at 3 h (P<0.05). Plasma beta-carotene levels increased significantly at 6 h (P<0.05). Vitamin C concentrations (mg/l) rose from 10.9 (sem 2.0) to 12.7 (sem 3.0) (P<0.001), 12.7 (sem 2.0) (P<0.01) and 12.9 (sem 3.0) (P<0.05) at 0, 2, 3 and 6 h respectively. No changes were observed after ingestion of MAP-stored lettuce for all the measured markers. Our present results showed that ingestion of MAP-stored lettuce does not modify plasma redox status in healthy subjects. Further research is needed to develop post-harvesting techniques able to preserve the bioactive molecule content of plant food.

Adult↗

PubMed1999

Survival of enterohemorrhagic Escherichia coli O157:H7 in bovine feces applied to lettuce and the effectiveness of chlorinated water as a disinfectant.

Bovine feces are a potential vehicle for transmitting enterohemorrhagic Escherichia coli O157:H7 to humans. A study was undertaken to determine survival characteristics of E. coli O157:H7 on iceberg lettuce using 0.1% peptone water and bovine feces as carriers for inocula. Four levels of inoculum, ranging from 10(0) to 10(5) CFU of E. coli O157:H7 per g of lettuce, were applied. Populations surviving on lettuce stored at 4 degrees C were monitored for up to 15 days. Regardless of the type of carrier, viable cells of E. coli O157:H7 were detected on lettuce after 15 days, even when the initial inoculum was 10(0) to 10(1) CFU/g. Spray treatments of lettuce with 200 ppm chlorine solution or deionized water were equally effective in killing or removing E. coli O157:H7 from lettuce. Holding lettuce for 5 min after spray treatment was not more effective in reducing populations than holding for 1 min before rinsing with water. Prevention of contamination of lettuce with bovine feces that may harbor E. coli O157:H7 as well as other infectious microorganisms is essential to minimizing the risk of illness. The development of sanitizers more efficacious than chlorine for the removal of pathogens from raw fruits and vegetable is needed.

Animals↗

PubMed2002

Consumer acceptance of fresh-cut iceberg lettuce treated with 2% hydrogen peroxide and mild heat.

An antibacterial treatment consisting of 2% hydrogen peroxide at 50 degrees C for 60 s was evaluated for its effects on the sensory quality of fresh-cut iceberg lettuce. Treated lettuce was packaged in polyethylene film by a protocol used in the fresh-cut produce industry and then stored along with untreated controls for 3, 10, and 15 days at 5 degrees C. Gas chromatographic analysis confirmed that the desired initial volume (approximately 6 liters) and oxygen gas content (approximately 10%) were maintained during storage. Consumers from the local community who were the primary shoppers for their households and who purchased and ate lettuce regularly evaluated the appearance, color, aroma, flavor, and texture of the lettuce and their overall liking of the lettuce. Forty consumers were recruited to evaluate processing replication 1 on 26 April, and another 40 were chosen to evaluate processing replication 2 on 3 May. Because replication differences were observed in instrumental color measurements and in mean sensory ratings, replications were not pooled for the two test dates. Lettuce purchased for processing replication 2 was considerably greener than that used in replication 1. Overall, the antibacterial treatment was more effective than the control treatment in maintaining sensory quality over 15 days of storage, provided that the lettuce was initially intensely green. Three-fourths of the participants indicated that they would be willing to buy precut packaged lettuce that had already been treated at the packinghouse or processing plant with an antibacterial solution, and of these participants, 62.5% indicated that they would be willing to pay 5 to 10 cents more per bag.

Anti-Infective Agents, Local↗

PubMed2006

Effect of ozonated water treatment on microbial control and on browning of iceberg lettuce (Lactuca sativa L.).

We examined the effect of ozonated water treatment on microbial control and quality of cut iceberg lettuce (Lactuca sativa L.). Fresh-cut lettuce was washed in ozonated water (3, 5, and 10 ppm) for 5 min at ambient temperature. The native bacterial population on the lettuce declined in response to a rise in ozone concentration. However, there was no further bacterial reduction (1.4 log CFU/g) above 5 ppm ozone. Although ozonated water treatment increased the phenylalanine ammonia lyase (PAL) activity of the lettuce stored at 10 degrees C compared with the water wash treatment after 1 day of storage, the concentration of ozone did not affect PAL activity. The a* value of the residue of the lettuce methanol extracts, which reflects the extent of browning, increased dramatically in lettuce treated with 10 ppm ozonated water compared with other treatments. Treatment with 3 or 5 ppm ozonated water resulted in more rapid changes in the a* value than after the water treatment. The combined treatment of hot water (50 degrees C, 2.5 min) followed by ozonated water (5 ppm, 2.5 min) had the same bactericidal effect as treatment with ozonated water (5 ppm, 5 min) or sodium hypochlorite (NaOCl, 200 ppm, 5 min), giving a reduction in bacteria numbers of 1.2 to 1.4 log CFU/g. The ascorbic acid content of the lettuce was not affected by these treatments. The combined treatment of hot water followed by ozonated water greatly inhibited PAL activity for up to 3 days of storage at 10 degrees C. Treatment with this combination greatly suppressed increases in the a* value, thus retarding the progress of browning compared with other treatments throughout the 6-day storage. NaOCl treatment also inhibited browning for up to 3 days of storage. Bacterial populations on the lettuce treated with sanitizers were initially reduced but then showed rapid growth compared with that of the water wash treatment, which did not reduce bacterial counts initially.

Consumer Product Safety↗