Biomedical subjects

L R Beuchat

Publications and source records attributed to L R Beuchat.

At least 127 records · Page 7Linked to original sources

PubMed1991

Changes in chemical composition and sensory qualities of peanut milk fermented with lactic acid bacteria.

The effects of fermentation of aqueous extracts of peanuts (peanut milk) with Lactobacillus delbrueckii ssp. bulgaricus and Streptococcus salivarius ssp. thermophilus, separately and in combination, on selected chemical and sensory qualities were investigated. Changes in pH, titratable acidity and viable cell populations indicated that there was a synergistic interaction between L. delbrueckii ssp. bulgaricus and S. salivarius ssp. thermophilus during fermentation. Analysis of headspace volatiles revealed that hexanal, which is one of the compounds responsible for undesirable green/beany flavor in peanut milk, completely disappeared as a result of fermentation. S. salivarius ssp. thermophilus was more effective than L. delbrueckii ssp. bulgaricus in reducing the hexanal content. The acetaldehyde content of peanut milk increased during fermentation. Changes in concentrations of these volatile compounds were correlated with sensory evaluation scores which showed that a significant (P less than or equal to 0.05) decrease in green/beany flavor and a significant increase in creamy flavor occurred as a result of fermentation.

Acetaldehyde↗

PubMed1991

Behavior of Listeria monocytogenes inoculated into raw tomatoes and processed tomato products.

Rates of death and growth of Listeria monocytogenes inoculated onto raw whole and into chopped tomatoes stored at 10 and 21 degrees C were not influenced by prior treatment of tomatoes with chlorine or packaging under an atmosphere of 3% O2 and 97% N2. Growth of the pathogen occurred in whole tomatoes held at 21 degrees C but not at 10 degrees C, while death occurred in chopped tomatoes stored at these temperatures. Likewise, growth patterns of mesophilic aerobic microorganisms, psychrotrophic microorganisms, and yeasts and molds on whole and chopped tomatoes were essentially unaffected by chlorine and modified atmosphere packaging treatments. Populations of L. monocytogenes inoculated into commercially processed tomato juice and sauce and held at 5 degrees C remained constant for 14 days. A gradual decrease in the number of viable L. monocytogenes cells was observed in juice and sauce held at 21 degrees C. In contrast, the organism died rapidly when suspended in commercial tomato ketchup at 5 and 21 degrees C. Unlike low-acid raw salad vegetables such as lettuce, broccoli, asparagus, and cauliflower on which we have observed L. monocytogenes grow at refrigeration temperatures, tomatoes are not a good growth substrate for the organism. Nevertheless, L. monocytogens can remain viable on raw whole and chopped tomatoes and in commercial tomato juice and sauce for periods extending beyond their normal shelf-life expectancy.

Aerobiosis↗

PubMed1990

Toxin production by Alternaria alternata in tomatoes and apples stored under various conditions and quantitation of the toxins by high-performance liquid chromatography.

Alternaria alternata strain 8442-3 was inoculated into tomatoes (Lycopersicon esculentum Mill.) and Red Delicious cultivar apples (Malus domestica Borkh.). Half of the lots of each fruit were shrink-wrapped in high-density polyethylene film. Wrapped and unwrapped fruits were incubated under darkness at 4, 15 and 25 degrees C for up to 5 weeks. A high-performance liquid chromatography method was developed to quantitate tenuazonic acid (TeA), alternariol (AOH), alternariol methyl ether (AME), and altenuene (ALT). Shrink-wrapping retarded, but did not completely inhibit growth in tomatoes for 3-7 days. Concentrations of up to 120.6 mg of AOH and 63.7 mg of AME per 100 g of tissue were produced in unwrapped tomatoes stored at 15 degrees C for 4 weeks; 19.0 mg of ALT per 100 g of tomato tissue was produced after 3 weeks at 25 degrees C. AOH, AME and ALT were also produced in unwrapped tomatoes stored at 4 degrees C; however, no TeA was detected in decayed tomatoes, regardless of type of wrapping or storage temperature. Shrink-wrapping resulted in decreased production of AOH, AME, and ALT. Alternaria toxins were not detected in apples stored at 4 and 15 degrees C. The highest concentration of AOH produced (48.8 mg per 100 g of tissue) was in unwrapped apples stored at 25 degrees C for 2 weeks; 12.3 mg per 100 g of tissue of shrink-wrapped apples was detected after 5 weeks of storage at 25 degrees C, while ALT reached 5.7 mg per 100 g after 4 weeks. TeA was not detected in apples infected with A. alternata.

Alternaria↗

PubMed1990

Efficacy of direct plating media for recovering Listeria monocytogenes from foods.

Studies were done to evaluate 14 direct plating media for their suitability to recover Listeria monocytogenes strain Scott A from pasteurized whole milk, chocolate ice cream mix, Brie cheese and raw cabbage. Healthy cells were inoculated into foods to achieve viable populations of 10(2), 10(4), or 10(6) cells/ml(g). Bind's Acriflavine Agar, Trypaflavine Nalidixic Acid Serum Agar, Listeria Transport Enrichment Agar, Doyle and Schoeni Selective Enrichment Agar (DSSEA) and Modified DSSEA were not suitable for recovering L. monocytogenes from milk and Brie cheese and were therefore not evaluated as direct plating media for recovering the organism from ice cream mix and cabbage. McBride Listeria Agar (MLA), Gum Base Nalidixic Acid Tryptone Soya Agar (GBNTSA), Modified Despierres Agar (MDA) and Modified MLA (MMLA) performed best for recovering all inoculum populations from milk and ice cream mix. Enumeration of L. monocytogenes on several test media was complicated by the growth of large numbers of background microflora present in cabbage and Brie cheese, especially at the lowest test inoculum (10(2)/g). Generally, complete recovery of L. monocytogenes from Brie cheese and cabbage was attained on media when the inoculum population was greater than or equal to 10(4) cells/g. For Brie cheese, MLA, MDA, MMLA and Dominguez Rodriguez Isolation Agar were superior for recovering L. monocytogenes, while GBNTSA, DLEA, MDA and MMLA were best for recovering the organism from cabbage. Results of this experiment indicate that direct-plating procedures, without prior enrichment, can successfully be utilized for recovering L. monocytogenes from foods such as pasteurized milk and ice cream mix which contain low populations of background microflora. However, recovery of L. monocytogenes from foods such as raw cabbage and Brie cheese, which contain high populations of other microorganisms, was not satisfactory using the direct-plating procedures evaluated in this investigation.

Animals↗

PubMed1990

Influence of water activity and temperature on survival of and colony formation by heat-stressed Chrysosporium farinicola aleuriospores.

The ability of sublethally heat-stressed aleuriospores of Chrysosporium farinicola to form colonies on yeast extract-glucose agar (YGA) supplemented with sufficient glucose, sorbitol, glycerol, and NaCl to achieve reduced water activity (aw) in the range of 0.88 to 0.95 was determined. The effects of the aw of diluent and incubation temperature during recovery and colony formation were also investigated. Aleuriospores harvested from 14-day-old cultures grown at 25 degrees C were less resistant to heat inactivation compared with aleuriospores from 20-day-cultures. Increased populations of heat-stressed aleuriospores were recovered as the aw of YGA was decreased from 0.95 (glucose and glycerol) and 0.94 (sorbitol) to 0.89 and 0.88, respectively. In NaCl-supplemented YGA, populations recovered at an aw of 0.94 were greatly reduced compared with populations detected at an aw of 0.92; no colonies were formed on NaCl-supplemented YGA at an aw of 0.88. Tolerance to aw values above 0.88 to 0.89 as influenced by solute type was in the order of glucose greater than sorbitol greater than glycerol greater than NaCl. Incubation at 20 degrees generally resulted in an increase in recoverable aleuriospores compared with incubation at 25 degrees C or at 30 degrees C for 14 days followed by 20 degrees C for 10 days. The lethal effect of NaCl on heat-stressed aleuriospores was enhanced at 30 degrees C. The retention of viability of aleuriospores held in sucrose-peptone water diluent (aw, 0.936) for 20 min was essentially the same as that observed when aleuriospores were held in peptone water (aw, 0.997).(ABSTRACT TRUNCATED AT 250 WORDS)

Chrysosporium↗

PubMed1990

Pathogenicity of Listeria monocytogenes grown on crabmeat.

The pathogenicity of Listeria monocytogenes as influenced by growth on crabmeat at 5 and 10 degrees C was studied. Crabmeat was inoculated with L. monocytogenes V7 (ca. 10(4) CFU/g) and incubated for up to 14 days at 5 and 10 degrees C. At selected incubation times, L. monocytogenes was removed from crabmeat by washing with 0.1 M potassium phosphate buffer (pH 7.0), and populations were determined by surface plating on LiCl-phenylethanol-moxalactam agar. Buffered suspensions were then centrifuged, and the resulting pellets were suspended in phosphate buffer containing 10% glycerol and stored at -18 degrees C. Thawed, diluted suspensions of cells were tested for pathogenicity by intraperitoneal injection into immunocompromised and nonimmunocompromised mice. L. monocytogenes cells recovered from crabmeat and then recultured in tryptose phosphate broth (TPB), as well as cells which had not been passed through crabmeat but had been cultured in TPB, were likewise harvested, suspended in buffered 10% glycerol, frozen, thawed, diluted, and tested for pathogenicity by intraperitoneal injection. Growth on crabmeat at 5 and 10 degrees C did not have a significant effect on pathogenicity. The population of L. monocytogenes necessary to kill about 50% of the immunocompromised mice in each test set within 7 days was about 10(4) CFU, and this result was not significantly affected by storage temperature of the crabmeat or type of substrate, i.e., crabmeat or TPB, on which it had grown.

Animals↗

PubMed1990

Inhibitory effects of raw carrots on Listeria monocytogenes.

The survival and growth of two strains of Listeria monocytogenes on raw and cooked carrots stored at 5 and 15 degrees C and in carrot juice media at 30 degrees C were investigated. The influence of shredding, chlorine treatment, and packaging under an atmosphere containing 3% O2 and 97% N2 on the behavior of L. monocytogenes and naturally occurring microflora was determined. Populations of viable L. monocytogenes decreased upon contact with whole and shredded raw carrots but not cooked carrots. Viable populations also decreased in cell suspensions in which raw carrots were dipped. Small populations of L. monocytogenes detected on whole carrots immediately after dipping were essentially nondetectable after 7 days of storage at 5 or 15 degrees C. After a lag of 7 days at 5 degrees C, significant (P less than or equal to 0.05) increases in populations were detected on shredded carrots after 24 days of storage. Carrots stored at 5 or 15 degrees C spoiled before L. monocytogenes grew. Populations of mesophilic aerobes, psychrophiles, and yeasts and molds increased throughout storage at 5 and 15 degrees C. Cutting treatment (whole or shredded carrots), chlorine treatment, and modified-atmosphere packaging had no effect on the survival or growth of L. monocytogenes or naturally occurring microflora. The presence of raw carrot juice in tryptic phosphate broth at a concentration as low as 1% substantially reduced the maximum population of L. monocytogenes reached after 24 h at 30 degrees C. The anti-Listeria effect of carrots was essentially eliminated when the carrots were cooked.(ABSTRACT TRUNCATED AT 250 WORDS)

Beverages↗

PubMed1990

Colony formation by sublethally heat-injured Zygosaccharomyces rouxii as affected by solutes in the recovery medium and procedure for sterilizing medium.

Recovery and colony formation by healthy and sublethally heat-injured cells of Zygosaccharomyces rouxii as influenced by the procedure for sterilizing recovery media (YM agar [YMA], wort agar, cornmeal agar, and oatmeal agar) were investigated. Media were supplemented with various concentrations of glucose, sucrose, glycerol, or sorbitol and sterilized by autoclaving (110 degrees C, 15 min) and by repeated treatment with steam (100 degrees C). An increase in sensitivity was observed when heat-injured cells were plated on glucose-supplemented YMA at an aw of 0.880 compared with aws of 0.933 and 0.998. Colonies which developed from unheated and heated cells on YMA at aws of 0.998 and 0.933 generally exceeded 0.5 mm in diameter within 3.5 to 4 days of incubation at 25 degrees C, whereas colonies formed on YMA at an aw of 0.880 typically did not exceed 0.5 mm in diameter until after 5.5 to 6.5 days of incubation. The number of colonies exceeding 0.5 mm in diameter which were formed by heat-injured cells on YMA at an aw of 0.880 was 2 to 3 logs less than the total number of colonies detected, i.e., on YMA at an aw of 0.933 and using no limits of exclusion based on colony diameter. A substantial portion of cells which survived heat treatment were sublethally injured as evidenced by increased sensitivity to a suboptimum aw (0.880). In no instance was recovery of Z. rouxii significantly affected by medium sterilization procedure when glucose or sorbitol was used as the aw-suppressing solute.(ABSTRACT TRUNCATED AT 250 WORDS)

Carbohydrates↗

PubMed1990

Influence of solute, pH, and incubation temperature on recovery of heat-stressed Wallemia sebi conidia.

The influences of glucose, sorbitol, and NaCl in a basal enumeration medium at water activities (aw) from 0.82 to 0.97 on colony formation by sublethally heat-stressed Wallemia sebi conidia were determined. Over this aw range, glucose and sorbitol had similar effects on recovery, whereas at an aw of 0.82 to 0.92, NaCl had a detrimental effect. Colony diameters were generally largest on media containing sorbitol and smallest on media containing NaCl. Maximum colony size and viable population of heat-stressed conidia were observed on media at an aw of ca. 0.92. When the recovery incubation temperature was 20 degrees C, the number of uninjured conidia detected at an aw of 0.82 was reduced compared with the number detected at 25 degrees C, while at 30 degrees C, the number recovered at an aw of 0.97 was reduced. The effect on heat-stressed conidia was magnified. This suggests that W. sebi conidia may be more tolerant of aw values higher than the optimum 0.92 when the incubation temperature is decreased from the near optimum of 25 degrees C and less tolerant of aw values greater than 0.92 when the incubation temperature is higher than 25 degrees C. The sensitivity of heat-stressed conidia increased as the pH of the recovery medium was decreased from 6.55 to 3.71. W. sebi conidia dispersed in wheat flour at aw values of 0.43 and 0.71 and stored for up to 65 days at both 1 and 25 degrees C neither lost viability nor underwent sublethal desiccation or temperature injury.(ABSTRACT TRUNCATED AT 250 WORDS)

Culture Media↗

PubMed1989

Methods and media for the isolation and cultivation of Listeria monocytogenes from various foods.

Many methods and media currently exist for the detection and enumeration of Listeria monocytogenes. However, the suitability of any specific method or media is influenced by the purpose of the analysis and the type of food being analyzed. Food which are likely to contain high populations of contaminating microorganisms require highly selective media for enumeration. Moreover, media which contain indicator systems are also helpful in distinguishing L. monocytogenes colonies. In contrast, less selective media may be adequate for less contaminated foods.

Bacteriological Techniques↗

PubMed1989

Influence of modified-atmosphere storage on the growth of uninjured and heat-injured Aeromonas hydrophila.

The growth of uninjured and heat-injured Aeromonas hydrophila incubated at 5 degrees C (22 days) and 30 degrees C (31 h) under air, N2, and CO2 was investigated. At 30 degrees C, the growth patterns of cells on brain heart infusion agar incubated under air and N2 were similar, although slight differences in the lengths of the lag phases and the final populations were detected. The lag phases of cells incubated under air and N2 were substantially longer at 5 degrees C than at 30 degrees C. The population of uninjured A. hydrophila incubated at 5 degrees C under air and N2 remained constant, whereas the number of injured cells declined before the exponential growth phase. Growth at 5 degrees C was enhanced when uninjured and heat-injured A. hydrophila were incubated under N2. At 30 degrees C, cells incubated under CO2 exhibited noticeably longer lag phases and lower growth rates than did cells incubated under air and N2. The viable populations of uninjured and heat-injured cells incubated at 5 degrees C under CO2 declined steadily throughout incubation.

Aeromonas↗

PubMed1989

Evaluation of three newly developed direct plating media to enumerate Listeria monocytogenes in foods.

LiCl-phenylethanol-moxalactam Agar (LPMA), ARS Modified McBride Agar, and Modified Vogel Johnson Agar were compared with previously tested plating media in the enumeration of Listeria monocytogenes from pasteurized whole milk, chocolate ice cream mix, Brie cheese, and raw cabbage. LPMA was most suitable for analyzing Brie cheese and cabbage. Gum base-nalidixic acid-tryptone-soya medium (previously tested) was most suitable for analyzing milk and chocolate ice cream mix.

Agar↗

PubMed1989

Growth of Aeromonas hydrophila on fresh vegetables stored under a controlled atmosphere.

The effects of controlled-atmosphere storage (CAS) on the survival and growth of Aeromonas hydrophila on fresh asparagus, broccoli, and cauliflower were examined. Two lots of each vegetable were inoculated with A. hydrophila 1653 or K144. A third lot served as an uninoculated control. Following inoculation, vegetables were stored at 4 or 15 degrees C under a CAS system previously shown to extend the shelf life of each commodity or under ambient air. Populations of A. hydrophila were enumerated on the initial day of inoculation and at various intervals for 10 days (15 degrees C) or 21 days (4 degrees C) of storage. Direct plating of samples with selective media was used to enumerate A. hydrophila. The organism was detected on most lots of vegetables as they were received from a commercial produce supplier. Without exception, the CAS system lengthened the time vegetables were subjectively considered acceptable for consumption. However, CAS did not significantly affect populations of A. hydrophila which survived or grew on inoculated vegetables.

Aeromonas↗

PubMed1988

Evaluation of simplified and commercial systems for identification of foodborne yeasts.

Commercial identification kits (API 20C, API Yeast-Ident and API-Zym) were compared with a conventional but simplified identification method (SIM) for identifying seventy-two yeast isolates from fresh sweet corn. SIM failed to provide identification of two isolates. Of the twenty species identified, only eleven were included in the API 20C profile index. Three isolates were identified at the species level and three were identified at the genus level with 100% accuracy. The enzyme kit (Yeast-Ident) gave rather unreliable results, in that identification of only four isolates with 75 to 85% of appropriate reactions was made. The API 20C kit could be used to identify non-clinical yeasts, provided they were included in its database and a few additional tests (urease reaction, nitrate assimilation and glucose fermentation) were also performed.

Evaluation Studies as Topic↗

PubMed1988

Influence of organic acids on heat resistance characteristics of Talaromyces flavus ascospores.

Three strains of Talaromyces flavus were investigated for their tolerance to organic acids during and after exposure to elevated temperatures. Fumaric, sorbic and benzoic acids were clearly more lethal than acetic, malic, citric and tartaric acids, and lethality was enhanced as the pH of the heating medium was reduced from 5.0 to 2.5. The effects of sorbic and benzoic acids on viability of ascospores varied depending upon the strain and were influenced by other constituents in the heating medium. Ascospores of a T. flavus strain with greater heat tolerance were larger and less ellipsoid in shape than ascospores of a less heat-tolerant strain, as observed by scanning electron microscopy. While both strains are known to develop heat resistance with age, no external differences in shape, degree of ornamentation and size could be discerned between ascospores as influenced by age (11 and 51 day old) of cultures.

Antifungal Agents↗

PubMed1988

Evaluation of selective direct plating media for their suitability to recover uninjured, heat-injured, and freeze-injured Listeria monocytogenes from foods.

Six direct plating media were evaluated for their suitability to recover uninjured, heat-injured, and freeze-injured cells of four strains of Listeria monocytogenes from four foods. Cells were inoculated into foods to achieve ca. 10(2) to 10(3), 10(4) to 10(5), or 10(5) to 10(6) viable cells per ml or g (low, medium, and high populations, respectively). No appreciable differences in recovery of the four test strains within a treatment were observed. Generally, recovery on all test media was similar and not markedly affected by freeze treatment. Modified Despierres agar and modified McBride Listeria agar yielded poorer recovery of heat-injured cells than did McBride Listeria agar and gum base-nalidixic acid-tryptone soya agar. Overall, gum base-nalidixic acid-tryptone soya agar was best for recovering L. monocytogenes from pasteurized milk and chocolate ice cream mix. Enumeration was complicated by the growth of background microflora present in Brie cheese and cabbage, especially at the low inoculum. Dominguez Rodriguez isolation agar was superior for recovering L. monocytogenes from Brie cheese, whereas modified Despierres agar was best for recovering the organism from cabbage. Direct plating procedures can successfully be utilized for recovering healthy and injured L. monocytogenes from foods containing low populations of background microflora.

Animals↗

PubMed1988

Growth of and fumitremorgin production by Neosartorya fischeri as affected by temperature, light, and water activity.

The effects of temperature, light, and water activity (aw) on the growth and fumitremorgin production of a heat-resistant mold, Neosartorya fischeri, cultured on Czapek Yeast Autolysate agar (CYA) were studied for incubation periods of up to 74 days. Colonies were examined visually, and extracts of mycelia and CYA on which the mold was cultured were analyzed for mycotoxin content by high-performance liquid chromatography. Growth always resulted in the production of the tremorgenic mycotoxins verruculogen and fumitremorgins A and C. The optimum temperatures for the production of verruculogen and fumitremorgins A and C on CYA at pH 7.0 were 25, 30, and 37 degrees C, respectively. The production of fumitremorgin C by N. fischeri has not been previously reported. Fumitremorgin production was retarded at 15 degrees C, but an extension of the incubation period resulted in concentrations approaching those observed at 25 degrees C. Light clearly enhanced fumitremorgin production on CYA (pH 7.0, 25 degrees C), but not as dramatically as did the addition of glucose, fructose, or sucrose to CYA growth medium (pH 3.5, 25 degrees C). Growth and fumitremorgin production was greatest at aw of 0.980 on CYA supplemented with glucose or fructose and at aw of 0.990 on CYA supplemented with sucrose. Growth and fumitremorgin production were observed at aw as low as 0.925 on glucose-supplemented CYA but not at aw lower than 0.970 on CYA supplemented with sucrose. Verruculogen was produced in the highest amount on all test media, followed by fumitremorgin A and fumitremorgin C.

Ascomycota↗

PubMed1987

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

Four of five strains of Campylobacter jejuni survived in chicken meat stored at -18 degrees C for 12 months. Direct plating of samples was superior to the most probable number technique for enumerating C. jejuni. Enrichment culture using the Doyle & Roman enrichment method resulted in the highest rates of detection. Packaging under an atmosphere of CO2 did not substantially influence survival.

Animals↗