Sensory Evaluation of Lamb After Growth of Yeasts at −5°C

Cryptococcus laurentii var laurentii was inoculated at various densities onto lamb loins, which were then frozen and stored at 5°C for 10 wk. During storage, yeast numbers increased by two log cycles. Loin samples that included yeast-bearing surfaces were prepared for evaluation by a trained taste panel. No foreign flavors associated with high yeast numbers could be discriminated by the panel.     

Suppression of postharvest blue mould of apple fruit by Cryptococcus laurentii and N6‐benzyladenine

BACKGROUND: Cryptococcus laurentii is a well‐known postharvest yeast antagonist. N⁶‐benzyladenine (6‐BA), a cytokinin plant hormone, has a role in retarding ripening and senescence of harvested produce. This study was conducted to evaluate the efficacy of C. laurentii and 6‐BA in reducing the blue mould disease of apple fruit. RESULTS: The combination of C. laurentii with 6‐BA (20 µg mL^?1) was more effective in suppressing the Penicillium expansum infection in apple fruit wounds than C. laurentii alone, although 6‐BA (20 µg mL^?1) alone neither affected the growth of C. laurentii nor reduced the incidence of the blue mould disease in vivo. Moreover, treatment of apple fruit with C. laurentii and 6‐BA (20 µg mL^?1) resulted in stimulation of superoxide dismutase activity but in inhibition of the increase in peroxidase activity. CONCLUSION: 6‐BA (20 µg mL^?1) could enhance the efficacy of C. laurentii in reducing the postharvest blue mould disease of apple fruit, which offered great potential in minimizing the postharvest decay of apple fruit in an integrated pest management strategy. Copyright © 2008 Society of Chemical Industry     

Utilisation of a yeast pectinase in olive oil extraction and red wine making processes

The possibility of using an endo-polygalacturonase produced by the yeast Cryptococcus albidus var albidus (yeast pectinase) in the mechanical olive oil extraction process and in the production of red wine was investigated. Compared with the control and olive pastes treated with a commercial enzyme preparation, an increase in oil yield was achieved by treatment with the yeast pectic preparation. Also, the finished oil quality (turbidity, oxidation induction time, chlorophyll, and the content of polyphenols and aromatic compounds) was generally better. Treatment of red musts with yeast pectinase resulted in an improved aromatic profile in the wines, even in the absence of an increase in colour intensity. Moreover, the use of the yeast pectinase did not cause any particular increase in the methanol content of the finished wines.     

Survival of three Mycobacterium avium subsp. hominissuis isolates in fish products after hot smoking and frying

Fish mycobacteriosis should be considered as one possible means of transmission of mycobacterial infections to humans. In our study, we examined the survival of three field Mycobacterium avium subsp. hominissuis (MAH) isolates in fish meat during thermal processing technologies using culture and quantitative real‐time PCR (qPCR) methods. Minced carp meat mixture was artificially contaminated with known amount of MAH cells and survival and absolute numbers of MAH was monitored after hot smoking and frying. The viability of MAH was significantly lower after the frying process, whereas in response to hot smoking viable MAH cells could still be cultured even after 10 min at 70 °C. Significant differences in thermal stability were also observed among the three different MAH isolates. The human isolate was the most resistant, whereas the environmental isolate was the least resistant, which is probably due to host adaptability. In this work we confirmed that MAH can survive temperatures of 70 °C and thus can pose a risk to consumers.     

CINNAMIC ACID AS THE BASIS OF A MEDIUM FOR THE DETECTION OF WILD YEASTS

Cinnamic acid (100 μg ml^?1) incorporated in a solid medium was found to inhibit the growth of brewing strains (Pof^?) of yeast while permitting the growth of Pof+ wild yeast contaminants. Typically, colonies of Saccharomyces cerevisiae var. diastaticus (Pof+) mixed with brewing yeast (S. cerevisiae NCYC 240) were visible after 5d incubation at 25°C. The incubation time required to detect a selection of brewery wild yeast isolates was found to vary from 3–12 d.     

Identification of Microbial Isolates from Vacuum-Packaged Ground Pork Irradiated at 1 kGy

Bacterial cultures from irradiated (1 kGy) and nonirradiated, vacuum-packaged ground pork held at 5°C were isolated and characterized over a 12-day storage period. The initial flora of the meat was composed mostly of Pseudomonas sp. and Enterobacter sp. Although the microflora of nonirradiated samples gradually shifted from Gram-negative to Gram-positive microorganisms, 76% of the isolates were characterized as Gram-negative at the onset of spoilage (9 days at 5°C). In contrast, the irradiated ground pork microflora was mainly Gram-positive (66%) shortly after irradiation and increased to 97% after 9 days at 5°C. A total of 720 isolates were identified to genus.     

Computer-Assisted Identification of Bacteria on Hot-Boned and Conventionally Processed Beef

Mesophilic and psychotrophic bacteria (706 isolates) obtained from hot-boned and conventionally processed beef at the time of fabrication and after 14-day vacuum storage at 2°C were analyzed by computer-assisted numerical taxonomy (108 attributes per isolate). There was no significant difference in terms of the number of phenons between hot-boned and conventionally processed beef both at the time of fabrication and after storage. Before storage, 24 mesophilic phenons and 11 psychrotrophic phenons were characterized. After storage in vacuum bags, there were 13 mesophilic phenons and 6 psychrotrophic phenons. The after storage flora consisted mainly of Streptococcus and Lactobacillus from both hot-boned and conventionally processed beef.     

The rheological properties of exudates from cured porcine muscle: effects of added non‐meat proteins

Meat exudates were collected from massaged cured porcine M semimembranosus using a model massaging unit. Exudates were used to observe changes in gelation properties due to the incorporation of commercially available non‐meat proteins. These included: soya isolate (90%), sodium (Na) caseinate (85%) and high gelling whey protein concentrates (WPCs, A‐35%, B‐75% and C‐β‐lactoglobulin (55%), as well as a regular 76% protein, WPC D. Compositional analysis ( n=6) showed that incorporation of non‐meat proteins significantly (P<0.05) increased the protein concentration of test exudates in all cases compared to controls. The viscoelastic properties of control and test meat exudate samples (n=6) were analysed using control stress rheology in oscillatory mode. All exudates were heated from 20 to 80°C at 1°C min⁻¹, and subsequently cooled after 30 min back down to 20°C at 1°C min ⁻¹. Addition of WPCs at a 1, 2 and 3% residual powder level and soya isolate at a 1% residual level, resulted in increased storage modulus G′ (Pa) values compared with controls. A 1% residual level of Na caseinate was detrimental to meat exudate gelation, resulting in lower final G′ (Pa) values than those observed for the control. © 1999 Society of Chemical Industry     

Control of postharvest<Emphasis Type="Italic"> Rhizopus</Emphasis> rot of peach by microwave treatment and yeast antagonist

The potential of using microwave power alone, or in combination with antagonistic yeast, for control of Rhizopus stolonifer on peach, and its effects on the postharvest quality of peach were investigated. In in vitro tests, the growth of R. stolonifer was completely inhibited by a 2,450 MHz microwave heating for 2 min or more. The population density of R. stolonifer in surface wounds of microwave treatment fruits was significantly lower than that in the control. In vivo studies of inoculation of peach fruit with R. stolonifer followed by microwave treatment, Cryptococcus laurentii or both of them, microwave power and C. laurentii, as stand-alone treatments, were capable of reducing the percentage of decayed fruit from 95% in control, untreated fruit to 42.1% and 75%, respectively. However, in fruit treated with a combination of microwave power and C. laurentii, the percentage of decayed fruits was only 23.7%. The experiments on reducing natural decay development of fruit gave similar results. The microwave treatment, C. laurentii, or both of them did not impair the quality parameters of the fruit. Thus, the combination of microwave and C. laurentii could be an alternative to chemicals for control of postharvest Rhizopus rot on peach fruits.     

Control of <Emphasis Type="Italic">Penicillium Expansum</Emphasis> and <Emphasis Type="Italic">Botrytis Cinerea</Emphasis> on Apple Fruit by Mixtures of Bacteria and Yeast

Antagonistic activity of the mixtures Rahnella aquatilis–Rhodotorula glutinis and R. aquatilis–Cryptococcus laurentii was assessed against Penicillium expansum (cause of blue rot) and Botrytis cinerea (cause of grey rot) on apple fruit at 4 °C and 95% relative humidity (RH). Under these cold-storage conditions, the mixture R. aquatilis–R. glutinis inhibited the development of B. cinerea and P. expansum in apples stored for 40 days and reduced the incidence of disease produced by these moulds to nearly zero. The other mixture, R. aquatilis–C. laurentii, was less effective; the incidences of the grey rot and the blue rot were about 25% and 15%, respectively. Population dynamics of the mixtures showed that the growth of R. aquatilis was strongly stimulated by the presence of the yeast R. glutinis, but in the case of the mixture R. aquatilis–C. laurentii, the same effect could not be observed. In this study, it was demonstrated that the combination of two microorganisms with different requirements and antagonistic abilities resulted in a successful mixture against the two pathogen molds, B. cinerea and P. expansum. In addition, it was also proved that it is possible to improve the biocontrol of these pathogens without increasing the inoculum size of the antagonist (alone or in mixtures), which was always 10⁶cell/ml, despite the high concentration of the pathogen (10⁶ conidia/ml) utilized.     

Fungi associated with post-harvest rot of sweet orange (Citrus sinensis) and aflatoxin B1 production by isolates of Aspergillus flavus on plain and supplemented orange juice

Samples of rotting sweet orange (Citrus sinensis) were obtained from the depots, sales counters and waste baskets. Fungi associated with rotting fruits were isolated and identified. Out of 12 species of fungi isolated, 8 are known to be producers of toxins. The 7 isolates of Aspergillus flavus obtained were screened for aflatoxin production in a nutrient solution, and 4 were found to be aflatoxigenic, producing primarily aflatoxin B₁. Aflatoxin B₁ production of the toxigenic isolates were further studied on plain juice and juice separately supplemented with 2.0% yeast extract and 2.0% sucrose. The highest yield of aflatoxin B₁ was produced on juice supplemented with yeast extract by the 4 toxigenic A. flavus isolates, followed by sucrose supplementation while the lowest amount of aflatoxin B₁ was detected on plain juice. Optimum temperature for aflatoxin B₁ production by A. flavus isolate (IBA-O1) was 25 °C to 30 °C, for an incubation period of 7–11 days on plain and supplemented juice media.     

Microbiological stability and diversity in raw pre-peeled potatoes packed in different atmospheres

Microbial growth on raw pre-peeled potatoes was analysed in relation to different process and storage parameters. Raw peeled potatoes with or without tumbling were packed in vacuum or modified atmosphere (MA) and stored at 4 °C and 15 °C for 7 and 5 days, respectively. Microbial growth was analysed throughout the storage period and growth was observed for mesophilic and psychrotrophic bacteria, lactic acid bacteria, Pseudomonas spp., and coliform bacteria. Growth at 4 °C was significantly lower compared to 15 °C. The number of bacteria was after seven days significantly higher on tumbled potatoes stored at 4 °C than on the untumbled potatoes. The bacterial counts generally exceeded 10⁶ CFU/g on tumbled potatoes after 7 days at 4 °C and 5 days at 15 °C, respectively. The CO₂ content increased during the storage period. A total of 243 isolates were grouped according to ITS-PCR profiles. Of these 47% had similar band profiles and thereby constituted the dominating flora at the end of shelf life. The dominating flora, identified on the basis of sequencing and microbial analysis of a subset of isolates, belonged to Enterobacteriaceae and consisted mainly of Enterobacter spp. and Kluyvera spp.     

Identification of yeasts from black olives in rapid system microtitre plates

A total of 125 yeasts were isolated from Greek-style black olives produced in different factories. Identification was based on 65 morphological and physiological characteristics. The majority of the tests were conducted in microtitration plates. The predominant species proved to be mainlyTorulaspora delbruekii,Debaryomyces hanseniiandCryptococcus laurentii. The speciesCryptococcus albidus,Dekkera bruxellensis,Sporobolomyces roseus,Bullera variabilis,Pichia farinosa,Pichia membranaefaciens, andZygosaccharomyces bailiiwere identified sporadically. A selection of the characteristics may aid to the simplified identification of the species and is easily applicable in the wells of microtitration plates.     

Microbial background flora in small-scale cheese production facilities does not inhibit growth and surface attachment of Listeria monocytogenes

The background microbiota of 5 Norwegian small-scale cheese production sites was examined and the effect of the isolated strains on the growth and survival of Listeria monocytogenes was investigated. Samples were taken from the air, food contact surfaces (storage surfaces, cheese molds, and brine) and noncontact surfaces (floor, drains, and doors) and all isolates were identified by sequencing and morphology (mold). A total of 1,314 isolates were identified and found to belong to 55 bacterial genera, 1 species of yeast, and 6 species of mold. Lactococcus spp. (all of which were Lactococcus lactis), Staphylococcus spp., Microbacterium spp., and Psychrobacter sp. were isolated from all 5 sites and Rhodococcus spp. and Chryseobacterium spp. from 4 sites. Thirty-two genera were only found in 1 out of 5 facilities each. Great variations were observed in the microbial background flora both between the 5 producers, and also within the various production sites. The greatest diversity of bacteria was found in drains and on rubber seals of doors. The flora on cheese storage shelves and in salt brines was less varied. A total of 62 bacterial isolates and 1 yeast isolate were tested for antilisterial activity in an overlay assay and a spot-on-lawn assay, but none showed significant inhibitory effects. Listeria monocytogenes was also co-cultured on ceramic tiles with bacteria dominating in the cheese production plants: Lactococcus lactis, Pseudomonas putida, Staphylococcus equorum, Rhodococcus spp., or Psychrobacter spp. None of the tested isolates altered the survival of L. monocytogenes on ceramic tiles. The conclusion of the study was that no common background flora exists in cheese production environments. None of the tested isolates inhibited the growth of L. monocytogenes. Hence, this study does not support the hypothesis that the natural background flora in cheese production environments inhibits the growth or survival of L. monocytogenes.     

Prevalence and Characterization of Salmonella Isolated from Chicken Meat in Turkey

This study was conducted in a Turkish province to investigate the presence of Salmonella spp. in 150 chicken meat samples using 2 phenotyping techniques: classic culture technique (CCT) and immunomagnetic separation (IMS). For the confirmation of the isolates at molecular levels, invA gene was detected in these isolates. The presence of invA, class 1 (Cls1) integrons, and integrase (Int1) genes was demonstrated by PCR assay; and the resistance of the isolated Salmonella spp. strains to antibiotics was determined by disk diffusion test. All the cultural and PCR results were evaluated together; Salmonella spp. were detected in a total of 64 (42.66%) chicken meat samples. Contamination rate was higher in carcasses (53.33%, n = 75) than in meat pieces (32%, n = 75). When results of standard culture were compared with IMS technique, IMS (n = 54) showed a clear superiority over the CCT (n = 38). A very high resistance rate (≥89.28%) to vancomycin, tetracycline, streptomycin, or nalidixic acid was found. Trimethoprim‐sulfamethoxazole resistance was present in 32.14%. Relatively lower incidence of resistance (≤8.33%) to gentamicin, chloramphenicol, ampicillin, and ceftriaxone was observed. Concurrent resistance to at least 4 antibiotics was detected in 92.85% of the isolates. Cls1 integrons and Int1 were positive in 80.95% and 95.23% of the isolates, respectively. However, Int1 alone was detected in 15.47% (n = 13). In conclusion, the high prevalence of Salmonella spp. in chicken meat may pose a potential public health risk, and the presence of antibiotic‐resistant Salmonella spp. isolate together with Cls1 integron and/or integrase might play an important role in horizontal antibiotic gene transfer.     

Growth/survival of natural flora and Aeromonas hydrophila on refrigerated uncooked pork and turkey packaged in modified atmospheres

To evaluate the growth/survival of natural flora and Aeromonas hydrophila on refrigerated normal low (pork) and high (turkey) pH meats packaged in modified atmospheres, A. hydrophila was inoculated onto fresh pork and turkey meat slices. Inoculated and control samples were packaged in modified atmospheres (100% N₂, 20/80 and 40/60 CO₂/O₂) or in air in plastic bags and kept at 1 and 7°C. Samples packaged in air showed a similar microbiological pattern to that usually observed in fresh meat stored aerobically. Packaging in modified atmosphere produced a strong inhibition of bacterial growth at 1°C, particularly in samples stored in CO₂/O₂enriched atmospheres. Aeromonas hydrophila grew on turkey and pork meat stored in 100% N₂at 1 and 7°C. Likewise, growth of this bacterium was detected on turkey stored in 20/80 CO₂/O₂at 7°C. No growth was observed in 40/60 CO₂/O₂in any meat at both temperatures assayed.     

STUDIES ON OCCURRENCE AND CHARACTERIZATION OF CLOSTRIDIUM PERFRINGENS FROM SELECT MEATS

A study was undertaken to assess the prevalence of Clostridium perfringens in meat and to characterize the isolates obtained in the study for virulence factors. A total of 211 meat samples of different animals (70 each of buffalo and goat and 71 of poultry) were screened and the highest occurrence of C. perfringens was observed in goat (91.4%) followed by poultry (70.4%) and buffalo (65.7%). Among the 116 isolates (buffalo‐32, goat‐37 and poultry‐45) of C. perfringens screened for the presence of enterotoxin gene by PCR, 9.3, 32.4 and 15.5% isolates of buffalo, goat and poultry, respectively, were found to possess enterotoxin gene. Screening of 15 enterotoxin gene possessing isolates for verocytotoxicity revealed that 12 isolates exhibited cytopathic effect while 3 isolates did not show any cytopathic effect in spite of the presence of enterotoxin gene. A total of 115 C. perfringens isolates were screened for other virulence markers, i.e., lecithinase and hemolysin. The results revealed that the majority of the isolates expressed these activities. Antibiogram studies of C. perfringens isolates using 16 antibiotics displayed multidrug resistance. The isolates showed resistance to streptomycin, ceftazidime, colistin sulfate, cephalothin, ampicillin and gentamicin. Whereas 100% sensitivity to ciprofloxacin, ofloxacin and nitrofurantoin was seen, moderate sensitivity was observed with tetracycline and sulfatriad.     

The microflora of Tilsit cheese. Part 1. Variability of the smear flora

The microflora of 25 Tilsit cheeses from 2 cheese plants was analysed. Debaryomyces hansenii was found to be the predominant yeast in all stages of ripening. 75–95% of the bacterial flora consisted of coryneform bacteria. Several of the isolates were identified as Arthrobacter. Brevibacterium linens was found at 0-15%. In all cheeses tested, 5-15% of total cell counts were made up by staphylococci. They were determined as being not Staphylococcus aureus or other pathogenic staphylococci since all isolates were negative with respect to thermo-nuclease, clumping, coagulase, and hemagglutination. Most of the isolates were hemolysis negative. By genetical analysis, several selected isolates were classified as Staphylococcus equorum, one isolate as S. sciuri. Contamination of cheeses with Fusarium moulds indicated the influence of the smearing strategy on spreading of undesirable microorganisms. In plant A, old cheeses were smeared first, then young cheeses were smeared with the same smear liquid. Fusarium contamination could be detected in all stages of ripening. In plant B, young cheeses (0-3 weeks) were smeared with a commercial surface starter cocktail. In all cheeses of this age, problems with Penicillium contaminations were observed. Older cheeses (>3 weeks) were smeared according to the strategy applied in plant A. Consequently, Fusarium moulds were detected in cheeses 4-8 weeks of age.     

Molecular identification and osmotolerant profile of wine yeasts that ferment a high sugar grape must

The objective of this study was to examine the Saccharomyces and non-Saccharomyces yeast populations involved in a spontaneous fermentation of a traditional high sugar must (Vino cotto) produced in central Italy. Molecular identification of a total of 78 isolates was achieved by a combination of PCR-RFLP of the 5.8S ITS rRNA region and sequencing of the D1/D2 domain of the 26S rRNA gene. In addition, the isolates were differentiated by RAPD-PCR. Only a restricted number of osmotolerant yeast species, i.e. Candida apicola, Candida zemplinina and Zygosaccharomyces bailii, were found throughout all the fermentation process, while Saccharomyces cerevisiae prevailed after 15 days of fermentation. A physiological characterization of isolates was performed in relation to the resistance to osmotic stress and ethanol concentration. The osmotolerant features of C. apicola, C. zemplinina and Z. bailii were confirmed, while S. cerevisiae strains showed three patterns of growth in response to different glucose concentrations (2%, 20%, 40% and 60% w/v). The ability of some C. apicola and C. zemplinina strains to grow at 14% v/v ethanol is noteworthy. The finding that some yeast biotypes with higher multiple stress tolerance can persist in the entire winemaking process suggests possible future candidates as starter for Vino cotto production.     

Survey of Clostridium difficile in retail seafood in College Station,Texas

The incidence and severity of disease associated with toxigenic Clostridium difficile have increased in hospitals in North America with the emergence of newer, more virulent strains. Toxigenic C. difficile has been isolated from food animals and retail meat with potential implications of transfer to humans. The objective of the present study was to investigate the prevalence of C. difficile in retail seafood from grocery stores in College Station, Texas. C. difficile was found in 4.5% (3/67) of shellfish and finfish samples. The positive samples included one each from fresh mussel, frozen salmon and frozen shrimp. The mussel and salmon isolates were characterized as toxinotype V and pulsed-field gel electrophoresis (PFGE) type-NAP7. The shrimp isolate was identified as toxinotype XII, but had an unknown PFGE type. Susceptibilities to 11 antimicrobial agents were identical for the mussel and salmon isolates and were sensitive to eight of 11 antimicrobials (including ampicillin) and intermediate to clindamycin. However, the shrimp isolate was resistant to clindamycin and ampicillin. This study demonstrates that seafood, like other food commodities, can be contaminated by C. difficile.