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L R Beuchat

Publications and source records attributed to L R Beuchat.

At least 145 records · Page 8Linked to original sources
PubMed1987

Comparison of media and methods for detecting and enumerating Listeria monocytogenes in refrigerated cabbage.

Direct plating, selective enrichment, and cold enrichment followed by secondary selective enrichment procedures were compared for detecting and enumerating Listeria monocytogenes in chopped cabbage stored at 5 degrees C for up to 64 days. Addition of Fe3+ to solid media enhanced detection of the organism. Cold enrichment (5 degrees C) in nutrient broth and brain heart infusion broth followed by secondary enrichment (48 h, 30 degrees C) in Trypticase soy-yeast extract-antibiotic broth and thiocyanate-nalidixic acid broth and plating on selective agar media (Doyle and Schoeni selective enrichment agar [minus acriflavin hydrochloride, supplemented with 5 micrograms of Fe3+/ml] and McBride Listeria agar) resulted in the detection of highest populations.

Brassica↗
PubMed1986

Fermentation of aqueous plant seed extracts by lactic Acid bacteria.

The effects of lactic acid bacterial fermentation on chemical and physical changes in aqueous extracts of cowpea (Vigna unguiculata), peanut (Arachis hypogea), soybean (Glycine max), and sorghum (Sorghum vulgare) were studied. The bacteria investigated were Lactobacillus helveticus, L. delbrueckii, L. casei, L. bulgaricus, L. acidophilus, and Streptococcus thermophilus. Organisms were inoculated individually into all of the seed extracts; L. bulgaricus and S. thermophilus were also evaluated together as inocula for fermenting the legume extracts. During fermentation, bacterial population and changes in titratable acidity, pH, viscosity, and color were measured over a 72-h period at 37 degrees C. Maximum bacterial populations, titratable acidity, pH, and viscosity varied depending upon the type of extract and bacterial strain. The maximum population of each organism was influenced by fermentable carbohydrates, which, in turn, influenced acid production and change in pH. Change in viscosity was correlated with the amount of protein and titratable acidity of products. Color was affected by pasteurization treatment and fermentation as well as the source of extract. In the extracts inoculated simultaneously with L. bulgaricus and S. thermophilus, a synergistic effect resulted in increased bacterial populations, titratable acidity, and viscosity, and decreased pH in all the legume extracts when compared to the extracts fermented with either of these organisms individually. Fermented extracts offer potential as substitutes for cultured dairy products.

Journal Article↗
PubMed1986

Effect of temperature, sodium chloride, and pH on growth of Listeria monocytogenes in cabbage juice.

Human illness and death have resulted from the consumption of milk, cheese, and cole slaw contaminated with Listeria monocytogenes. Since the effects of temperature, NaCl, and pH on the growth of the organism in cabbage were unknown, a series of experiments was designed to investigate these factors. Two strains (LCDC 81-861 and Scott A, both serotype 4b) were examined. At 30 degrees C, the viable population of the LCDC 81-861 strain increased in sterile unclarified cabbage juice (CJ) containing 0 to 1.5% NaCl; a decrease in the population of both strains occurred in juice containing greater than or equal to 2% NaCl. At 5 degrees C, the population of the Scott A strain in CJ containing up to 5% NaCl was reduced by about 90% over a 70-day period; the LCDC 81-861 strain was more sensitive to refrigeration but remained viable in CJ containing less than or equal to 3.5% NaCl for 70 days. Growth in CJ at 30 degrees C resulted in a decrease in pH from 5.6 to 4.1 within 8 days. Death of L. monocytogenes occurred at 30 degrees C when the organism was inoculated into sterile CJ adjusted to pH less than or equal to 4.6 with lactic acid. No viable cells were detected after 3 days at pH less than or equal to 4.2. At 5 degrees C, the rate of death at pH less than or equal to 4.8 was slower than at 30 degrees C.(ABSTRACT TRUNCATED AT 250 WORDS)

Brassica↗
PubMed1986

Growth and thermal inactivation of Listeria monocytogenes in cabbage and cabbage juice.

Studies were done to determine the interacting effects of pH, NaCl, temperature, and time on growth, survival, and death of two strains of Listeria monocytogenes. Viable population of the organism steadily declined in heat-sterilized cabbage stored at 5 degrees C for 42 days. In contrast, the organism grew on raw cabbage during the first 25 days of a 64-day storage period at 5 degrees C. Growth was observed in heat-sterilized unclarified cabbage juice containing less than or equal to 5% NaCl and tryptic phosphate broth containing less than or equal to 10% NaCl. Rates of thermal inactivation increased as pH of clarified cabbage juice heating medium was decreased from 5.6 to 4.0. At 58 degrees C (pH 5.6), 4 X 10(6) cells/mL were reduced to undetectable levels within 10 min. Thermal inactivation rates in clarified cabbage juice (pH 5.6) were not significantly influenced by the presence of up to 2% NaCl; however, heat-stressed cells had increased sensitivity to NaCl in tryptic soy agar recovery medium. Cold enrichment of heat-stressed cells at 5 degrees C for 21 days enhanced resuscitation. Results indicate that L. monocytogenes can proliferate on refrigerated (5 degrees C) raw cabbage which, in turn, may represent a hazard to health of the consumer. Heat pasteurization treatments normally given to cabbage juice or sauerkraut would be expected to kill any L. monocytogenes cells which may be present.

Brassica↗
PubMed1986

Methods for detecting and enumerating Campylobacter jejuni and Campylobacter coli in poultry.

Methods, media, and biochemical tests for detecting, enumerating, isolating, and identifying Campylobacter jejuni and C. coli in foods are summarized with special consideration of poultry and poultry products. Information is drawn largely from the American Public Health Association Compendium of Methods for the Microbiological Examination of Foods and the US Food and Drug Administration Bacteriological Analytical Manual for Foods. Reference is also made to recently advanced techniques and procedures.

Animals↗
PubMed1986

Characteristics and application of immobilized papain in a continuous-flow reactor.

Papain was immobilized on an anion-exchange resin by physical adsorption followed by cross-linking with glutaraldehyde. The activity and rate of heat inactivation of the enzyme was determined at 37 to 95 degrees C. Activity increased with an increase in temperature up to 85 degrees C, then decreased slightly at 95 degrees C. Activation of the enzyme by cysteine in 2 mM EDTA increased proportionally with an increase in concentration from 0.004 to 0.12 M. Levels of dissolved oxygen in solutions of EDTA containing cysteine in a closed system and with nitrogen purging in the absence of cysteine in an open system were monitored at 51 degrees C. Both the presence of cysteine and purging with nitrogen were effective in depleting dissolved oxygen. The final oxygen level was essentially independent of cysteine concentrations of 0.01, 0.02, and 0.10 M, and was reached in 95, 85, and 55 min, respectively. However, final levels of oxygen were dependent upon the flow rate of nitrogen from 1 to 10 SLPM and were reached within 15 min. Immobilized papain in a continuous-flow stirred-tank (300 rpm) reactor with a 4-liter reaction volume accompanied by nitrogen purging of 4 SPLM was used to hydrolyze a 1.5% casein solution in the presence of 0.01 M cysteine in 2 mM EDTA at 51 degrees C. The reaction rate was 1 liter/h and activity was measured based on the content of trichloroacetic acid-soluble protein in the outflow. Papain activity was not observed to decrease during a 30-h reaction period.

Anion Exchange Resins↗
PubMed1985

Efficacy of media and methods for detecting and enumerating Campylobacter jejuni in refrigerated chicken meat.

A study was undertaken to compare several enrichment and direct isolation media for their suitability to detect and enumerate five strains of Campylobacter jejuni in refrigerated (5 degrees C) chicken meat. The influence of CO2 on survival at 5 degrees C was also investigated. Selective enrichment media evaluated included Preston broth (PB), selective semisolid brucella medium (SSBM), Campylobacter enrichment broth (CEB), VTP brucella-FBP broth (VTP), Rosef and Kapperud Campylobacter enrichment broth (RKCEB), and Doyle and Roman enrichment broth (DREB). Direct isolation agars included Campy brucella agar (CBAP), blood-free Campylobacter medium (BFCM) and modified Butzler agar (MBA). Comminuted chicken meat was inoculated with C. jejuni, sealed under atmospheric gas or CO2, and stored at 5 degrees C for up to 21 days. Viable population was determined by the most-probable-number technique (PB, SSBM, CEB, VTP, and RKCEB, followed by plating on CBAP, BFCM, and MBA), enrichment on DREB, followed by plating on CBAP, BFCM, and MBA, and direct isolation on CBAP, BFCM, and MBA. Without exception, direct plating of samples was superior to the most-probable-number technique for enumerating C. jejuni; MBA was inferior to CBAP and BFCM, and DREB performed at least as well as other enrichment media evaluated. Carbon dioxide afforded protection against death of three of the five strains of C. jejuni tested.

Animals↗
PubMed1984

Influence of temperature and water activity on growth and patulin production by Byssochlamys nivea in apple juice.

The influence of temperature and water activity (aw) on growth and patulin production by Byssochlamys nivea in apple syrups was determined over a 44-day incubation period. The minimum aw at which the mold was capable of growing was 0.915 and 0.886 at 21 and 30 degrees C, respectively. Growth at 37 degrees C was observed at 0.871 aw. Minimum aw values for patulin production were 0.978, 0.968, and 0.959 at 21, 30 and 37 degrees C, respectively.

Ascomycota↗
PubMed1984

Sensitivity of heat-stressed yeasts to essential oils of plants.

Eight strains of yeasts (Candida lipolytica, Debaryomyces hansenii, Hansenula anomala, Kloeckera apiculata, Lodderomyces elongisporus, Rhodotorula rubra, Saccharomyces cerevisiae, and Torulopsis glabrata) were examined for changes in sensitivity to eight essential oils of plants (allspice, cinnamon, clove, garlic, onion, oregano, savory, and thyme) after being sublethally heat stressed. With the exception of garlic oil for all test yeasts, onion oil for S. cerevisiae, and oregano oil for R. rubra, the essential oils at concentrations of up to 200 ppm in recovery media did not interfere with colony formation by unheated cells. However, some oils, at concentrations as low as 25 ppm in recovery media, reduced populations of sublethally heat-stressed cells compared to populations recovered in media containing no test oils. This demonstrates that the yeasts were either metabolically or structurally damaged as a result of being exposed to elevated temperatures and that essential oils prohibited repair of injury. The size (diameter) of colonies produced on oil-supplemented recovery agar by heat-stressed cells was reduced compared to that observed on unsupplemented agar. Pigment production by heated R. rubra was inhibited by oils of oregano, savory, and thyme, but enhanced by garlic and onion oils. The influence of essential oils on survival of yeasts in thermally processed foods and in the enumeration of stressed cells in these foods should not be minimized.

Condiments↗
PubMed1984

Injury and repair of yeasts and moulds.

Most information pertaining to injury and repair of micro-organisms has accumulated as a result of investigations on bacteria. Recently, however, increased attention has been focused on the effect of sublethal stress on the behaviour of yeasts and moulds and the available data indicate that a wide range of physiological and morphological types of these organisms are subject to injury upon exposure to adverse environmental conditions. Such cells require optimum recovery conditions if repair and eventual cell germination and/or division are to occur. Consequently, knowledge of the susceptibility of yeasts and moulds to sublethal injury enables researchers to select enumeration procedures which will adequately resuscitate cells and thereby give more accurate estimations of the mycological quality of foods.

Antioxidants↗
PubMed1982

Increased sensitivity of heat-stressed Saccharomyces cerevisiae cells to food-grade antioxidants.

Unheated and heat-stressed Saccharomyces cerevisiae cells were examined for their relative sensitivities to butylated hydroxyanisole (BHA), tertiary butylhydroquinone (TBHQ), and propyl gallate. Heated cells had significant (P less than or equal to 0.05) increases in sensitivity to 50 micrograms of BHA, 100 micrograms of TBHQ, and 1,000 micrograms of propyl gallate per ml as compared with unheated cells when surface plated on antioxidant-supplemented recovery agar. The rate of increase in size of colonies developed by heated cells was slower than that of unheated cells, and the presence of antioxidants in recovery agar enhanced this effect. Heat-stressed cells also had increased sensitivity to ethanol. Incubation temperatures of 15, 21, 30, and 37 degrees C for enumerating unheated cells had no significant effect on the numbers of colonies formed on unsupplemented recovery agar; however, incorporation of 100 micrograms of BHA, 200 micrograms of TBHQ, or 1,000 micrograms of propyl gallate per ml into agar resulted in significant decreases in the number of colonies formed by heated cells at various incubation temperatures. The detrimental effects of TBHQ and propyl gallate on repair of heat-injured cells are apparently expressed at a temperature higher than that observed for BHA. It is suggested that the adverse effects of antioxidants on repair of heat-injured S. cerevisiae cells may be associated with oxygen availability.

Antioxidants↗
PubMed1981

Combined effects of solutes and food preservatives on rates of inactivation of and colony formation by heated spores and vegetative cells of molds.

The combined and independent effects of sucrose, sodium chloride, potassium sorbate, and sodium benzoate on heat inactivation of conidia of Aspergillus flavus and Penicillium puberulum, ascospores of Byssochlamys nivea, and vegetative cells of Geotrichum candidum were studied. In addition, the effects of solutes and preservatives on colony formation by unheated and heated conidia of A. flavus were evaluated. Increased concentrations of sucrose were accompanied by increased tolerance to heat by A. flavus, B. nivea, and G. candidum. Low concentrations (3 and 6%) of sodium chloride protected A. flavus and G. candidum, whereas up to 12% sodium chloride protected B. nivea, but had little effect on the heat stability of P. puberulum. Potassium sorbate and sodium benzoate acted synergistically with heat to inactivate all four molds. At the same concentration, the two preservatives had varied degrees of effectiveness on molds and were influenced by the type of solute in the heating menstrua. Heated conidia of A. flavus had increased sensitivity to preservatives and reduced water activity, whether achieved by the presence of sucrose or sodium chloride, thus demonstrating heat-induced injury. At the same concentration, potassium sorbate was clearly more inhibitory than was sodium benzoate to colony formation by A. flavus, and the presence of sucrose and sodium chloride enhanced this inhibition.

Ascomycota↗
PubMed1980

Recovery of chill-stressed Vibrio parahaemolyticus from oysters with enrichment broths supplemented with magnesium and iron salts.

The effects of magnesium and iron salts on the recovery and growth of chill-stressed cells of Vibrio parahaemolyticus were studied. Supplementation of glucose salt Teepol (GST) broth with 20 to 100 mM of Mg2+ significantly (P less than or equal to 0.05) increased the number of cells recovered from oyster homogenate stored at 3 degrees C. Populations detected with supplemented GST were comparable to those obtained with Horie arabinose ethyl violet (HAE) broth, with or without Mg2+. Recovery of V. parahaemolyticus from homogenates stored at -18 degrees C was also improved when enrichment broths supplemented with Mg2+ were used. Ferric iron (added as FeCl3) at 240 microM in GST and 240 or 960 microM in HAE significantly enhanced the extent of recovery of chilled cells. Ferrous iron was generally less effective. Teepol did not influence the growth of nonchilled cells, but significantly reduced the viable population in suspensions of chilled cells when used at a level of 0.4% in GST. The relatively high pH (9.0) of HAE caused a significant reduction in the number of viable, chill-stressed cells of V. parahaemolyticus. The overall results indicated that HAE broth is superior to GST for recovering V. parahaemolyticus from refrigerated and frozen oyster homogenates.

Animals↗
PubMed1980

Comparison of anti-Vibrio activities of potassium sorbate, sodium benzoate, and glycerol and sucrose esters of fatty acids.

The effects of fatty acids and their glycerol and sucrose esters, potassium sorbate, and sodium benzoate on growth of Vibrio parahaemolyticus in laboratory media at pH 6.7 were evaluated. The minimum concentrations at which inhibition by esters of glycerol could be detected were lowest for monolaurin (5 microgram/ml) and monocaprin (40 microgram/ml); these concentrations were lower than those observed for inhibition by lauric and capric acids, respectively. Inhibitory action of sucrose caprylate was detected at 40 microgram/ml, whereas sucrose caprate was effective at 100 microgram/ml; sucrose esters of lauric, myristic, and palmitic acids were ineffective at 100 microgram/ml. Potassium sorbate and sodium benzoate inhibited growth at concentrations as low as 30 and 300 microgram/ml, respectively, and enhanced the rate of thermal inactivation of V. parahaemolyticus at slightly higher concentrations. Fatty acid esters of glycerol and sucrose offer potential as perservatives for slightly acid or alkaline low-fat foods which do not lend themselves to the full antimicrobial action of traditional food preservatives such as potassium sorbate and sodium benzoate.

Benzoates↗
PubMed1979

Protein quality of several multi-component, commercially prepared foods.

Eleven commercial food products that may be considered by consumers to be major sources of protein were evaluated. Most of these items contained significant amounts of carbohydrate in the form of cereal products or purified sugars. Seven of the products were at least equal to casein in protein efficiency ratio (PER). Canned spaghetti and meat balls, the TV dinner, canned chicken-and-vegetable baby food, and food bars had PER values between 91 and 73 per cent of that of casein, while PER values for ground beef and high-protein cereal were significantly higher than casein.

Animals↗
PubMed1978

Polygalacturonase, biomass and ascospore production by Byssochlamys fulva. II. Effects of sugars found in fruits.

Polygalacturonase, biomass, and ascospore production by four strains of Byssochlamys fulva cultured in laboratory media supplemented with glucose, sucrose, or fructose was studied over a 20-day incubation period at 30 degrees C. The production of polygalacturonase was variable, but most activity was detected between 4 and 8 days in 1% sugar media at an initial pH of 4 or 5. The rate of biomass production was retarded early in the incubation period in media initially at pH 3 or 4 as compared to pH 5, but the amount of growth was about the same in media containing the test sugars after 20 days. Large numbers of ascospores were produced between 8 and 10 days in media containing 5% sugar initially at pH 5 and 4. Production of ascospores was retarded at pH 3 in media containing 5% sugar as compared to media initially at pH 5 and 4.

Ascomycota↗