The effect of temperature abuse on Clostridium perfringens in cooked turkey stored under air and vacuum

The potential for growth of Clostridium perfringens in aerobic and anaerobic (vacuum) packaged cooked ground turkey was investigated. Samples of autoclaved ground turkey were inoculated with ∼3·0 log₁₀ cfu g^-1 of C. perfringens strain NCTC 8238 or NCTC 8239, packaged and stored at various temperatures. Vegetative growth and heat-resistant spores were enumerated by plating unheated and heated (75°C for 20 min) samples, respectively, on tryptose-sulfite-cycloserine agar. The type of atmosphere influenced the growth of C. perfringens at 15 and 28°C. Both strains grew to about 7 logs within 9 h anaerobically and by 24 h aerobically at 28°C. While aerobic growth was slow at 15°C, mean log₁₀ cfu g^-1 increased anaerobically by 4-4·5 logs by day 8 for both strains. Spores were not found at 4 and 15°C, but were detected as early as 24 h at 2°C under anaerobic conditions in both strains. C. perfringens population stabilized or slowly decreased at 4°C. Cyclic and static temperature abuse of refrigerated products for 5 h will not permit C. perfringens growth. However, temperature abuse of such products for relatively long periods may lead to high and dangerous numbers of organisms. Reheating such products to an internal temperature of 65°C before consumption would prevent food-poisoning since the vegetative cells were killed.     

The fate of Escherichia coli O157 : H7 in Myzithra,Anthotyros, and Manouri whey cheeses during storage at 2 and 12°C

Myzithra, Anthotyros and Manouri whey cheeses were inoculated the day after production withEscherichia coli O157 : H7 at concentrations of approx. 1·8×10⁶cfu g⁻¹, and stored at 2 and 12°C for 30 and 20 days, respectively. The pH of the whey cheeses decreased from an initial value of approx. 6·20 to 5·83 or 5·60 (Myzithra) 5·75 or 5·20 (Anthotyros) and 5·80 or 5·30 (Manouri) by the end of the corresponding storage periods at 2 and 12°C, respectively. Escherichia coli O157 : H7 populations in the whey cheeses at the end of the 12°C storage period, had grown with an increase of approx. 1·3 log₁₀cfu g⁻¹. E. coli O157 : H7 populations in whey cheeses at the end of the 2°C storage period did not grow and decreased, with an approx. 2·5 log₁₀cfu g⁻¹reduction. Results showed that E. coli O157 : H7 can grow at 12°C and survive at 2°C storage in Myzithra, Anthotyros and Manouri whey cheeses, and therefore post-manufacturing contamination with this pathogen must be avoided by employing hygienic control programmes such as HACCP.     

Production of Bacillus cereus emetic toxin (cereulide) in various foods

To determine the role of Bacillus cereus as a potential pathogen in food poisoning, the production of an emetic toxin (cereulide) by B. cereus was quantified in various food sources. The amount of emetic toxin in 13 of 14 food samples implicated in vomiting-type food poisoning cases ranged from 0.01 to 1.28 microg/g. A vomiting-type strain, B. cereus NC7401, was inoculated into various foods and incubated for 24 h at 20, 30, and 35 degrees C. In boiled rice, B. cereus rapidly increased to 10(7)-10(8) cfu/g and produced emetic toxin at both 30 and 35 degrees C. In farinaceous foods, the production of emetic toxin was as high as that in the food samples implicated in food poisoning. Low levels of emetic toxin were detectable in egg and meat and their products and a small quantity of toxin was detectable in liquid foods such as milk and soymilk when not aerated. Bacterial growth and toxin production was inhibited in foods cooked with vinegar, mayonnaise, and catsup, supposedly by the decreased pH of acetic acid. This is the first report that has quantified emetic toxin of B. cereus in various foods.     

The behaviour of log phase Escherichia coli at temperatures below the minimum for sustained growth

The behaviour of cold-adapted, log phase Escherichia coli broth cultures during incubation at 2°C or 6°C for upto 8 days, and during subsequent incubation at 12°C, was determined by measurement of absorbance values at 600 nm (A₆₀₀), enumeration of colony forming units (cfu) on plate count agar (PCA) and violet red bile agar (VRBA), and measurement of the length of cells viewed under phase contrast illumination. The A₆₀₀ values and the mean length of cells remained constant for cultures incubated at 2°C; however, numbers of cfu recovered on PCA declined by about 1 log cfu over 8 days, while the numbers of cfu recovered on VRBA declined by about 1 log cfu during the first day, and by about a further log cfu by day 8. For cultures incubated at 6°C, A₆₀₀ values increased about 0·6 log A₆₀₀ units during the first 4 days and declined by less than 0·1 log A₆₀₀ unit during the next 4 days. The numbers of cfu recovered on PCA increased by about 0·5 log cfu unit during the first day at 6°C and declined by about 1 log cfu during the subsequent 7 days. The numbers of cfu recovered on VRBA did not increase during the first day at 6°C, and at that and subsequent times were between 0·3 and 0·8 log cfu less than the log numbers recovered on PCA. The mean lengths of cells declined from 5 to less than 4 μ m during the first day at 6°C, but increased to 8 μ m between the fourth and eighth days, with the mean length of the longest 10% of cells increasing from 6 to 18 μ m. For cultures incubated at 12°C after incubation at 2°C or 6°C for 4 and 8 days, both A₆₀₀ values and enumeration of colonies on PCA indicated the initiation of growth after about 15 h. However, cultures that had been incubated at 2°C proceeded to sustained exponential growth, while cells in cultures that had been incubated at 6°C elongated during incubation at 12°C between 10 and 30 h. The division of elongated cells to cells of normal size resulted in numbers of cfu increasing at rates greater than the exponential growth rate at 12°C. The observations may have implications for the control of mesophilic pathogen proliferation in raw meats and other chilled foods.     

Inactivation ofEscherichia coliO157:H7 by combinations of GRAS chemicals and temperature

Reported outbreaks of foodborne illness involvingEscherichia coliO157:H7 have increased in the United States during the last decade, with a variety of food products being implicated as vehicles of infection. Studies were carried out to determine the efficacy of combinations of various GRAS chemicals and moderate temperatures to killE. coliO157:H7. A five-strain mixture ofE. coliO157:H7 of approximately 10⁸cfu ml⁻¹was inoculated into 0·1% peptone solutions containing 1·0 or 1·5% lactic acid plus 0·1% hydrogen peroxide, 0·1% sodium benzoate or 0·005% glycerol monolaurate. The solutions were incubated at 8°C for 0, 15 and 30 min; at 22°C for 0, 10 and 20 min; or at 40°C for 0, 10 and 15 min; populations ofE. coliO157:H7 were determined at each sampling time. At 40°C, the pathogen was inactivated to undetectable levels within 10 min of incubation in the presence of 1·0 or 1·5% lactic acid plus hydrogen peroxide, and within 15 min of incubation in the presence of 1·5% lactic acid plus sodium benzoate or glycerol monolaurate. At 22°C, complete inactivation ofE. coliO157:H7 was observed after 20 min of exposure to 1·5% lactic acid plus 0·1% hydrogen peroxide, whereas a reduction of 5 log₁₀cfu ml⁻¹was observed with a treatment of 1·5% lactic acid plus glycerol monolaurate. None of the treatments resulted in total inactivation of the pathogen at 8°C. The aforementioned treatments could potentially be used to inactivate or reduceE. coliO157:H7 populations on raw produce.     

Control of the bacteriological condition of calf brain. I. Impact of improving hygiene

Sixty calves of the Dutch Friesian (FH) breed were stunned mechanically. Without previously having been stunned, another 30 calves were stuck according to the Jewish rite. Upon opening of the skulls (1–2 h post mortem) brains of mechanically stunned calves were collected either conventionally (n = 30) or ‘hygienically’ (n = 30), i.e. using a fresh pair of surgical gloves during each removal to avoid cross contamination. For ritually slaughtered animals only the hygienic procedure was followed. Samples of 10 g were excised from undamaged hemispheres and in the mechanically stunned treatment group also from the site of impact of the captive bolt. After storage in polystyrene trays at 3 ± 1°C for 7 days sampling was repeated. Bacteriological examination included the assessment of aerobic colony counts at 30°C for 3 days (ACC-30) and 4°C for 14 days (ACC-4) and Enterobacteriaceae colony counts at 37°C for 20 h (ECC). In conventionally collected samples the ACC-30 and ACC-4 were 3.8 and 3.0 log₁₀ cfu g^?1 at day 1 and 6.2 and 6.4 log₁₀ cfu g^?1 at day 8. With hygienic collection these counts were reduced by approximately 1 log unit. Whilst by conventional practice the ECCs, at day 1 and 8 were 2.6 and 4.8 log₁₀ cfu g^?1 these counts were 1.8 and 2.6 log₁₀ cfu g^?1 for hygienic practice. In samples excised from the site of impact of the captive bolt the hygienic procedure had similar, though less marked effects. On day 1 brains from ritually slaughtered animals had a bacteriological contamination similar to that found in the hemispheres of mechanically stunned calves. However, whilst at day 8 their mean ECCs were 3.4 and 3.5 log₁₀ cfu g^?1 the percentages of plates ‘positive’ for Enterobacteriaceae were only 10% in the ritually vs. 53% in the mechanically stunned group. The Enterobacteriaceae in this case were composed of psychrotrophic non-pathogenic genera of environmental origin. Salmonella was not isolated from any sample.     

Survival of Campylobacter coli in porcine liver

Enteropathogenic Campylobacter jejuni, Campylobacter coli and Campylobacter lari are currently the most common causes of acute infectious diarrhoeal illness in the UK and in most developed countries. Many domestic animals, including pigs, act as natural reservoirs of these organisms and infection may occur through the ingestion of contaminated foodstuffs. Therefore, the safety of porcine liver produced in Northern Ireland was assessed in relation toCampylobacter spp. Storage trials showed that Campylobacter spp. were not able to proliferate in liver at 37°C, but could persist at 4°C and 15°C. Survival was better, however, during storage at 4°C than at 15°C.Campylobacter were rapidly killed in raw liver homogenates and distilled water at 37°C, but not at 4°C. An initial inoculum of 8 log₁₀cfu g⁻¹C. coli was undetectable in liver homogenates after 24h storage at 37°C. Campylobacter coli were sensitive to freezing on liver slices at −18°C and were reduced by 5 log₁₀cycles after 7 days storage. Cells survived better on chilled liver slices and in autoclaved liver homogenates than in raw liver homogenates at all temperatures, which indicates the presence of a heat-labile antagonistic agent in raw liver homogenates. Growth and survival of C. coli was not affected by Lactobacillus plantarum, as C. coli was able to reach 8·5 log₁₀cfu ml⁻¹in 7 days and maintain its viability in the presence of 8·0 log₁₀cfu ml⁻¹L. plantarum. Thus, storage of C. coli on porcine liver at 4°C selected for the survival of this pathogen compared to similar storage at 37°C.Such information may be useful in identifying conditions and treatments that could be integrated in HACCP strategies, or be used to design processes that prevent proliferation and/or destroy Campylobacter spp. that may be present in liver.     

Changes in appearance and natural microflora on iceberg lettuce treated in warm,chlorinated water and then stored at refrigeration temperature

The objective of this study was to determine the effect of warm, chlorinated water on the survival and subsequent growth of naturally occurring microorganisms and visual quality of fresh-cut iceberg lettuce. After dipping cut lettuce leaves in water containing 20 mg l⁻¹free chlorine for 90 s at 50°C, samples were stored at 5 or 15°C for up to 18 or 7 days, respectively. Populations of aerobic mesophiles, psychrotrophs, Enterobacteriaceae, lactic acid bacteria, and yeasts and molds were determined. The visual appearance and development of brown discoloration were monitored. Treatment of lettuce in warm (50°C) chlorinated water delayed browning of lettuce. Shelf life of lettuce stored at 5°C, as determined by subjective evaluation of color and general appearance, was about 5 days longer than that of lettuce stored at 15°C. Treatment in warm (50°) water, with or without 20 mg l⁻¹chlorine, and in chlorinated water at 20°C significantly (α= 0·05) reduced the initial population of mesophilic aerobic microflora by 1·73–1·96 log₁₀cfu g⁻¹. Populations increased, regardless of treatment, as storage time at 5°C and 15°C increased. The same trends were observed in populations of psychrotrophs and Enterobacteriaceae. Yeast populations increased slightly in lettuce stored at 5°C but were consistently about 3 logs lower than mesophilic aerobes. Populations of molds and lactic acid bacteria were less than 2 log₁₀cfu g⁻¹throughout storage at 5 or 15°C. Results suggest that heat (50°C) treatment may have delayed browning and reduced initial populations of some groups of micro-organisms naturally occurring on iceberg lettuce, but enhanced microbial growth during subsequent storage.     

Selection of starters for a traditional Turkish yayik butter made from yoghurt

Butter is produced from two different materials in Turkey, cream and yoghurt. The butter produced from fresh yoghurt or ‘tulum yoghurt’ (a strained yoghurt produced from cow, goat or sheep milk) is called ‘yayik butter’ and has been traditionally produced in Turkey for centuries. In this research, we attempted to isolate and identify the natural lactic acid bacteria (LAB) of yayik butter and to select the best LAB combination for butter production. Twenty samples of yayik butter were collected from Afyon, Antalya, Isparta and Konya regions in Turkey and determined to have a mean pH of 4·78±0·33, a mean titratable acidity (lactic acid) of 0·23±0·07% and a mean NaCl of 0·55±1·22%. The mean counts of LAB (log₁₀ cfu g⁻¹) were 2·66±0·84 and 1·72±0·82 on MRS agar at 30 and 42°C, 2·44±0·93 and 1·78±0·24 on M17 agar at 30 and 42°C, and 1·64±1·196 on Sodium Azide Leuconostoc agar at 21°C, respectively. Eighty-five different LAB isolates were obtained from 20 yayik butters and identified asStreptococcus salivarius ssp. thermophilus (21·2%), Streptococcus sp. (4·7%), Lactobacillus delbrueckii ssp. bulgaricus (20%), Lactobacillus casei ssp.casei (15·3%), Lactobacillus paracasei ssp. paracasei (2·3%),Enterococcus faecium (18·8%). Leuconostoc pseudomesenteroides (Leucono-stoc mesenteroides ssp. dextranicum) (7·1%), Leuconostoc gelidum (Leuconostoc mesenteroides ssp.mesenteroides ) (4·7%) and Weissella paramesenteroides (Leuconostoc paramesenteroides) (5·9%). Combinations of S. salivarius ssp. thermophilus S51, Lb. delbrueckii ssp.bulgaricus A42, Lb. casei ssp. casei K64, Lb. paracasei ssp. paracasei A27, andLeu. pseudomesenteroides E83 were used as starter bacteria for experimental butter production from cream. Six different groups of butters were produced using different combinations of these bacteria (B, C, D and E samples), commercial culture (F sample), and without culture (A sample). Sensory evaluations showed that the experimentally produced butter sample of group B was more acceptable than the other butters. In addition, the buttermilk of sample B had lowest fact content. LAB counts of experimental butters produced with combined cultures and commercial culture were similar (6·66±1·87–6·83±0·040 and 6·81±0·13 log₁₀ cfu g⁻¹ on MRS agar, respectively).     

Influence of Temperature on Germination and Growth of Spores of Emetic and Diarrheal Strains of Bacillus cereus in a Broth Medium and in Rice

Germination and growth of Bacillus cereus spores from emetic and diarrheal strains were measured in Trypticase soy broth (TSB) and in autoclaved rice/beef extract from 5°– 55°C. Growth for some strains occurred from 15°– 50°C, and little difference was noted between responses of diarrheal and emetic types or between media, except a higher maximum population was achieved in rice. Germination was more extensive in rice than in TSB at <15°C and was generally more extensive for diarrheal strains in either medium.     

Destruction of Salmonella enteritidis inoculated in liquid whole egg by high hydrostatic pressure: comparative study in selective and non-selective media

The destruction of Salmonella enteritidis inoculated in liquid whole egg at approximately 10⁷−10⁸cfu ml^−lwas studied under combinations of pressure (350 and 450 MPa), temperature (50, 20, 2 and −15°C) and time (5, 10, 15 min and cycles of 5+5 and 5+5+5 min). One non-selective medium (tryptone soy agar) and two selective media (brilliant green agar and salmonella-shigella) were used to evaluate viability of S. enteritidis after pressurization. The inactivation rate increased with pressure and exposure time, being minimal at 350 MPa and −15°C for 5 min (over 1 log₁₀of reduction) and reaching total inactivation (8 log₁₀of reduction) in several treatments at 50°C. Treatments in cycles showed greater effectiveness than continuous treatments of the same total time. The effect of pressure was enhanced by elevated temperatures. The higher counts were obtained in the non-selective medium, indicating the presence of injured cells after pressure treatment. D -values obtained for two temperatures (2 and 20°C) and different times (0–60 min) under controlled pressure (400 MPa) showed that microbial inactivation followed a first-order kinetics with a decimal reduction time evaluated in tryptone soy agar medium of 9·5 min at 2°C and 8·8 min at 20°C.     

Sensitivity of multidrug-resistant Salmonella typhimurium DT104 to organic acids and thermal inactivation in liquid egg products

A mixture of four Salmonella typhimurium DT104 strains and a mixture of four S. typhimurium non-DT104 strains were examined for their ability to grow in tryptic soy broth (TSB) acidified with acetic, lactic, citric, or malic acids at pH 5·4, 4·4, and 3·7. Significantly (P<0·05) higher numbers of S. typhimurium DT104 cells were detected at pH 4·4 and 4·0 in TSB acidified with acetic acid and at pH 4·4 and 3·7 in TSB acidified with lactic acid compared to non-DT104 cells. Acid-shocked and non-shocked (control) cells were plated on TSA (pH 7·3) acidified with lactic acid at pH 5·4, 4·4, and 4·0 and on TSA (pH 7·0±0·2) containing 0·5, 2·5, and 5% sodium chloride. Populations of acid-shockedS. typhimurium DT104 and non DT104 cells recovered on acidified or salt-supplemented TSA were significantly (P<0·05) lower than those of non-shocked cells. A significantly lower number of acid-shocked non-DT104 cells recovered on TSA at pH 5·4, compared to acid-shocked DT104 cells, suggests that DT104 cells may be more resistant to acid shock and subsequent exposure to acid pH. D values and z values of acid-shocked or non-shocked cells of DT104 and non-DT104 strains in liquid whole egg (WE), egg yolk (EY), egg white (EW), whole egg+10% salt (WES), and egg yolk+10% salt (EYS) were determined. Differences in thermal sensitivity of the two types of cells were few. Rates of thermal inactivation of S. typhimurium DT104 cells indicate that the USDA pasteurization process would eliminate >8 log₁₀cfu ml⁻¹of EW heated at 57°C and >11 log₁₀cfu ml⁻¹of WE, EY, WES, or EYS heated at 61°C. D values of acid-shocked DT104 and non-DT104 cells heated in liquid egg products were significantly (P<0·05) lower than those of respective non-shocked cells.     

Incorporation of bacteriocin in plastic retains activity and inhibits surface growth of bacteria on meat

The bacteriocin, nisin, was incorporated into a polyethylene based plastic film and retained activity against the indicator bacteria Lactobacillus helveticus and Brochothrix thermosphacta . Beef carcass surface tissue sections (BCT) topically inoculated with the psychrotrophic spoilage bacterium B. thermosphacta were vacuum-packaged both with and without wrapping with the nisin impregnated plastic and held at 4° C. An initial reduction of 2 log₁₀cycles of B. thermosphacta was observed with nisin-impregnated wrapped BCT within the first 2 days of storage. After 20 days of refrigerated storage, B. thermosphacta populations from nisin impregnated plastic wrapped samples were significantly less than (P<0·05) control vacuum-packaged samples; log₁₀5·8 vs 7·2 cfu cm⁻²respectively. Temperature abuse was simulated by shifting inoculated packs from 4° C (after 2 days) to 12° C. Again, by 20 days, the B. thermosphacta populations of treated samples wrapped with nisin impregnated plastic were significantly less than (P<0·05) control vacuum-packaged samples; log₁₀3·6 vs 6·3 cfu cm⁻²respectively. This work highlights the potential for incorporating antimicrobial peptides with a wider and different range of inhibitory activity directly into plastics of different properties for use in controlling food spoilage as well as preservation to enhance product microbial safety.     

Influence of Heating and Cooling Rates on Bacillus cereus Spore Survival and Growth in a Broth Medium and in Rice

Survival, spore germination, and growth of emetic and diarrheal type strains of Bacillus cereus were evaluated in broth and rice media during heating and cooling. Samples were heated to 80°C (20C°/hr or 40C°/hr) or 90°C (ca. 900C°/hr), prior to cooling to 10°C (5C°/hr or 10C°/hr). Following heating to 80°C, growth occurred during 5C°/hr cooling. After heating to 90°C, inactivation of three strains occurred during cooling from 90 to 80°C and again from 50 to 40°C. Great variability was observed among the responses of the four strains. Emetic strains exhibited greater survival than diarrheal strains. Rice reduced low temperature inactivation, and did not favor emetic strains. Significant two and three way interactions existed among media, strains, heating and cooling rates.     

A Study on the Growth Potential of Staphylococcus aureus In Boletus edulis, A Wild Edible Mushroom, Prompted by a Food Poisoning Outbreak

A dish of Boletus edulis, a wild edible mushroom, in vinegar caused staphylococcal food poisoning in 13 of 35 diners in a restaurant. Enterotoxicosis was confirmed by detection of toxins A and D in the dish. Staphylococcus aureus growth potential in B. edulis was studied by inoculating fresh and frozen and thawed bolete with S. aureus strains VTTE 530, 757, 793 and 805 and storing for 3 days at 15 and/or 21°C. Essentially no staphylococcal growth was observed in frozen and thawed mushrooms contaminated with strains 530, 793 or 805 and stored at 15 or 21°C. In fresh B. edulis the same strains showed slight growth at 21°C. Frozen and thawed bolete inoculated with strains 530 and 757 (isolated from mushroom soup, nonenterotoxigenic) supported staphylococcal growth in 2 days at 21°C from a level of 4.8±10⁴ and 5.4±10³ to 2.0±10⁶ and 7.0±10₇ cfu/g, respectively. Enterotoxin was not detected in these samples.     

Efficacy of media for promoting ascospore formation by Neosartorya fischeri,and the influence of age and culture temperature on heat resistance of ascospores

Gorodkowa agar (GA), Fowell's acetate agar (FAA), Kleyn's acetate agar (KAA), McClary's acetate agar (MAA), grape juice agar (GJA), apple juice agar (AJA) and vegetable juice agar (VJA) were evaluated for their efficacy to promote ascospore formation by three strains of Neosartorya fischeri. All three strains produced abundant mature ascospores when grown on FAA, GJA and AJA, but not on the other test media. Ascospores produced on GJA developed greater heat resistance with time when suspended in commercial apple juice (AJ), grape juice (GJ) and 0·1 M potassium phosphate buffer (PB) during heat treatment. From 10 to 13 days of incubation at 30°C, decimal reduction times at 80°C (D_80°C values) for ascospores increased from 27·0 to 66·7 min in AJ, 28·5 to 33·3 min in GJ and 18·2 to 50·0 min in PB. The rate of development of heat resistance was dependent upon the incubation temperature at which ascospores were produced. After treatment at 70°C for 60 min, survival percentages for 21-day-old ascospores were 0·32, 8·13, 54·95 and 53·70% of ascospores produced at 18, 21, 25 and 30°C, respectively. At 42 days, 0·23 and 38·02% of ascospores produced at 18 and 21°C, respectively survived 85°C for 30 min; this treatment did not inactivate 42-day-old ascospores produced at 25 and 30°C. During a 114-day test period, ascospores produced at all incubation temperatures became dormant to some extent and required heat activation to facilitate germination.     

Ecophysiology of Fusarium temperatum isolated from maize in Argentina

The effect of water activity (a_w = 0.95, 0.98 and 0.995), temperature (15, 25 and 30°C), incubation time (7, 14, 21 and 28 days), and their interactions on growth and moniliformin (MON), beauvericin (BEA), fusaproliferin (FUS) and fumonisin B₁ (FB₁) production by two strains of Fusarium temperatum isolated from Argentinean maize were determined in vitro on sterile layers of maize grains. The results showed that there was a wide range of conditions for growth and mycotoxins production by F. temperatum. Both strains were found to grow faster with increasing a_w and at 30°C. In relation to mycotoxin production, the two strains produced more FUS than the other mycotoxins regardless of a_w or temperature evaluated (maximum = 50 000 μg g^?1). For FUS, MON and BEA, the maximum levels were observed at 0.98 a_w and 30°C (50 000, 5000 and 2000 μg g^?1 respectively). The lowest levels for these three mycotoxins were detected at 15°C and 0.95 a_w (1700 and 100 μg g^?1 for FUS and MON respectively), and at 0.98 a_w (400 μg g^?1 for BEA). The maximum levels of FB₁ were produced at 15°C and 0.98 a_w (1000 μg g^?1). At all a_w and temperatures combinations evaluated there was an increase in toxin concentrations with time incubation. The maximum levels were detected at 21 days. Statistical analyses of a_w, temperature, incubation time, and the two- and three-way interactions between them showed significant effects on mycotoxins production by F. temperatum. For its versatility on growth and mycotoxin production, F. temperatum represents a toxicological risk for maize in the field and also during grain storage.     

Behavior of Shiga-toxin-producing Escherichia coli in ewe milk stored at different temperatures and during the manufacture and ripening of a raw milk sheep cheese (Zamorano style)

This study was conducted to assess the survival of 2 wild Shiga toxin-producing Escherichia coli strains (one serotype O157:H7 and one non-O157:H7) in ewe milk stored at different conditions and to examine the fate of the O157 strain during the manufacture and ripening of a Spanish sheep hard variety of raw milk cheese (Zamorano). The strains were selected among a population of 50 isolates, which we obtained from ewe milk, because of their high resistance to 0.3% lactic acid. Both strains were inoculated (approximately 2 log₁₀ cfu/mL) in raw and heat-treated (low-temperature holding, LTH; 63°C/30 min) ewe milk and stored for 5 d at 6, 8, and 10°C and also according to a simulation approach for assessing the effects of failures in the cold chain. The minimum growth temperature for the O157:H7 strain in LTH and raw ewe milk was 8°C. For the non-O157:H7 strain, the lowest temperature showing bacterial growth in LTH ewe milk was 6°C, but it did not grow at any of the tested conditions in raw milk. It appears that the O157 strain was more susceptible to cold stress but was likely a better competitor than the non-O157 strain against the milk autochthonous microbiota. For manufacture of Zamorano cheese, raw milk was inoculated with approximately 3 log₁₀ cfu/mL, and after 2 mo of ripening at 10 to 12°C, the cheeses showed the expected general characteristics for this variety. The O157:H7 strain increased 0.9 log₁₀ cfu/g after whey drainage and during ripening and storage decreased by 2.9 log₁₀ cfu/g. Nevertheless, its detectable level (estimated at 6.2 cfu/g) after 2 mo of ripening suggests that Zamorano cheese manufactured from raw ewe milk contaminated with E. coli O157:H7 could represent a public health concern.     

Variation in short chain fatty acid and ethanol concentration resulting from the natural fermentation of wheat and barley for inclusion in liquid diets for pigs

Fifty‐six samples of wheat and 44 samples of barley were taken, at harvest, from locations across the UK. Lactic acid bacteria (LAB) and yeasts were enumerated before the samples were ground. Following grinding, triplicate 30‐g samples of each cereal were mixed with sterile distilled water and incubated at 30, 35 or 40 °C. Samples were taken immediately after mixing and at 24‐h intervals for analysis of short‐chain fatty acids (SCFA) and ethanol by isocratic ion‐exclusion liquid chromatography. The number of LAB and yeasts present in samples ranged from 0 to 5.0 (mean 2.25 ± 1.31) and 3.30 to 6.25 (mean 4.96 ± 0.74) log₁₀ colony‐forming units (cfu) ml^?1 respectively. At 30 °C the mean concentrations (mmol l^?1) of SCFAs and ethanol were, lactic acid 59.6 ± 40.0 (range 0.14–134.9), acetic acid 23.2 ± 11.1 (range 2.9–51.4), butyric acid 17.2 ± 16.8 (range 0.0–62.2) and ethanol 15.0 ± 9.0 (range 4.6–53.7) respectively. After fermentation for 24 h only 9 of 300 fermentations produced more than 75 mmol l^?1 lactic acid, which has previously been demonstrated to prevent the growth of Salmonella in liquid pig feed. Fermenting at 35 or 40 °C had no effect on lactic acid concentration but significantly (p < 0.001) increased the concentrations of acetic and butyric acids and ethanol. These results indicate that natural fermentation cannot be relied upon to produce levels of SCFAs that will prevent the proliferation of enteropathogens. Copyright © 2004 Society of Chemical Industry     

Germination and Heat Resistance of Bacillus cereus Spores from Strains Associated with Diarrheal and Emetic Food-Borne Illnesses

Bacillus cereus has been implicated as the cause of both diarrheal and emetic forms of food-borne illness. Spores of eight strains of B. cereus, representing diairheal, emetic and atoxigenic origins, were examined for heat resistance and germination responses. No correlation was observed between heat resistance at 85° or 90°C and origin of the strain. Germination of spores in Trypticase soy broth at 30°C, measured by loss of heat resistance, was more extensive for diarrheal strains than for emetic strains. These data should be useful in evaluating potential hazards from B. cereus in foods.