A note on shelf-life extension of British fresh sausage by vacuum packing

Vacuum packing of British fresh sausage in a low oxygen permeability film (Diolon) extended the product shelf-life at 6 degrees C to more than 20 d compared with 9-14 d in conventional packs. After 10 d storage, counts of key spoilage organisms such as yeasts and Brochothrix thermosphacta were generally 2 log cycles lower in vacuum packs. Vacuum-packed sausages also displayed a slower rate of loss of free sulphite. Variations in pack permeability to SO2 were not responsible for this. Losses of free SO2 in stored sausages are largely due to the production of sulphite-binding agents by yeasts. Selective enumeration of these yeasts showed them to be inhibited by conditions of vacuum packing. The extension of shelf-life observed is ascribed to the reduction in growth rate of the spoilage flora in vacuum packs coupled with the consequent maintenance of inhibitory levels of sulphite for a longer period.     

A note on shelf-life extension of British fresh sausage by vacuum packing

Vacuum packing of British fresh sausage in a low oxygen permeability film (Diolon) extended the product shelf-life at 6°C to more than 20 d compared with 9–14 d in conventional packs. After 10 d storage, counts of key spoilage organisms such as yeasts and Brochothrix thermosphacta were generally 2 log cycles lower in vacuum packs. Vacuum-packed sausages also displayed a slower rate of loss of free sulphite. Variations in pack permeability to SO₂ were not responsible for this. Losses of free SO₂ in stored sausages are largely due to the production of sulphite-binding agents by yeasts. Selective enumeration of these yeasts showed them to be inhibited by conditions of vacuum packing. The extension of shelf-life observed is ascribed to the reduction in growth rate of the spoilage flora in vacuum packs coupled with the consequent maintenance of inhibitory levels of sulphite for a longer period.     

Specific antibody-mediated detection of Brochothrix thermosphacta in situ in British fresh sausage

S.C. STRINGER, B.J. CHAFFEY, C.E.R. DODD, M.R.A. MORGAN AND W.M. WAITES. 1995. A rabbit polyclonal antibody-linked probe was developed which detected 76% of 800 food isolates of the spoilage bacterium Brochothrix thermosphacta when cells were bound to nitrocellulose. In slide cross-reaction tests all six environmental isolates tested were stained but the type strain was not. The antibody did not cross-react with Listeria grayi, L. monocytogenes, Lactobacillus plantarum, Lactococcus lactis, Streptococcus mutans, Bacillus cereus or B. subtilis.
The antibody-linked probe detected Br. thermosphacta in thin sections of British fresh sausage when the viable count was greater than 10⁶ g⁻¹ Cells were detected mainly within 1 or 2 mm of the surface on the loose starchy material. They were not detected within muscle blocks or in the centre of the sausage. Such results suggest that growth of this organism occurs close to the surface of the sausage.     

Thermal inactivation of Listeria monocytogenes and Yersinia enterocolitica in minced beef under laboratory conditions and in sous-vide prepared minced and solid beef cooked in a commercial retort

D-values were obtained for Listeria monocytogenes and Yersinia enterocolitica at 50, 55 and 60 degrees C in vacuum-packed minced beef samples heated in a laboratory water-bath. The experiment was repeated using vacutainers, which allowed heating of the beef to the desired temperature before inoculation. D-values of between 0.15 and 36.1 min were obtained for L. monocytogenes. Pre-heating the beef samples significantly affected (P < 0.05) the D60 value only. D-values for Y. enterocolitica ranged from 0.55 to 21.2 min and all the D-values were significantly different (P < 0.05) after pre-heating. In general, the D-values obtained for core inoculated solid beef samples were significantly higher (P < 0.05) than those generated in minced beef when heated in a Barriquand Steriflow commercial retort.     

The effect of substrate on the radiation resistance of yeasts isolated from sausage meat

J.-A, McCARTHY AND A.P. DAMOGLOU. 1996. The radiation resistance of a selection of yeasts isolated from sausages was assessed in phosphate-buffered saline and in sausage meat. The yeasts Candida zeylanoides, Debaryomyces hansenii and Trichosporon cutaneum exhibited sigmoidal survival curves in both substrates whilst the more sensitive Sporobolomyces roseus exhibited an exponential survival curve in buffer but a sigmoidal curve in meat. Irradiating C. zeylanoides, D. hansenii and T. cutaneum in sausage meat changed the shape of their survival curves to significantly alter the calculated parameters D _s (the dose in kGy that must be achieved before reduction in numbers occurs) and D ₁₀^sig(the dose in kGy required after the shoulder to achieve a 1 log cycle reduction in numbers). The D _s values were reduced while higher D ₁₀^sigvalues were obtained demonstrating that the sausage meat contributed a protective effect to these yeasts at higher irradiation doses. For the yeast S. roseus , similar numbers of survivors were recovered from both substrates at initial low irradiation doses (0–0.5 kGy) with the protective effect being demonstrated again at higher doses (> 2 kGy). These findings should be considered when defining a commercial process to reduce the numbers of yeasts in these products.     

Arcobacter contamination on pre- and post-chilled bovine carcasses and in minced beef at retail

Aims:  The present study aimed to assess the Arcobacter contamination on bovine carcasses postevisceration and postcooling in two slaughterhouses and in ready-to-eat minced beef.
Methods and Results:  Carcasses ( n  = 247) were sampled at four sites in two slaughterhouses and 100 minced beef samples were collected at retail. Isolation was performed by a quantitative and qualitative Arcobacter selective method, and the isolates were identified by multiplex PCR, after which a part of them were characterized by enterobacterial repetitive intergenic consensus (ERIC)-PCR. Although arcobacters were isolated from 37% of the bovine carcasses postevisceration with the chest and the foreleg as most contaminated sites, cooling the carcasses for at least 24 h reduced the incidence of Arcobacter (7%) on the carcass surface significantly. Arcobacter butzleri was the species most frequently isolated, although co-contamination with multiple species also occurred. At retail, arcobacters were present in 9% of the minced beef samples, with Arcobacter butzleri as the dominant species.
Conclusions:  Forced air cooling of bovine carcasses for at least 24 h decreased the number of positive carcasses, but did not eliminate all arcobacters.
Significance and Impact of the study:  This study demonstrates that maintaining good hygiene practices throughout the food supply chain is crucial to ensure safe food products at the consumer level.     

Isolation of proteolytic psychrotrophic yeasts from fresh raw seafoods

A total of 103 cultures of yeasts were isolated from seven kinds of fresh raw seafoods. The isolates comprised six genera, Candida, Cryptococcus, Debaryomyces, Rhodotorula, Sterigmatomyces and Trichosporon , and included 21 different species. All the isolates were psychrotrophic yeasts. Proteolytic activities of 50 psychrotrophic strains were studied by use of skim milk within the temperature range of 0–42°C. All the strains showed various degrees of proteolysis. In particular, Candida lipolytica. Trichosporon pullulans and Candida scottii were active species at low temperatures. Sensory spoilage due to the proteolytic yeasts were observed in mackerel homogenates stored at 10°C. C. lipolytica -inoculated homogenates caused spoilage with ammoniacal odours after 1 week of storage. Values of total volatile basic nitrogen at 10°C were highest with C. lipolytica among 35 strains tested, followed by Tr. pullans. Trichosporon cutaneum, C. scottii, Rhodotorula glutinis and Cryptococcus luteolus. Proteolytic psychrotrophic yeasts were widely distributed in raw seafoods.     

Prevalence of Escherichia coli O157:H7 in industrial minced beef

AIMS: The lack of baseline data on the prevalence of Escherichia coli O157:H7 in retail minced beef in France prompted this survey of industrial minced beef production. METHODS AND RESULTS: An automated enzyme-linked fluorescence immunoassay (ELFA), the VIDAS E. coli O157 method, was used to detect E. coli O157 in industrial minced beef samples. Confirmation of samples positive according to the ELFA was performed using an automated immunoconcentration (ICE) system, VIDAS ICE, which allows the selective capture and release of target organisms. The ICE was followed by culture on cefixime tellurite sorbitol MacConkey agar and a chromogenic medium, O157:H7 ID. Of the 3450 minced beef samples tested, 175 samples were positive with the ELFA method and, of these, four were confirmed by the ICE method. They were identified as sorbitol-negative, O157-positive, H7-positive, mobile, verotoxin-producing E. coli. CONCLUSIONS: The prevalence of E. coli O157:H7 in industrial French minced beef was 0.12%, consistent with many other reports. SIGNIFICANCE AND IMPACT OF THE STUDY: The low infective dose of E. coli O157:H7 presents a major threat. The main means of combating this organism are thermal destruction and good food hygiene covering activities on-farm, in the abattoir and in minced beef industries.     

Characterization of yeasts isolated from spontaneously fermenting fresh olive effluents

Summary Spontaneous fermentation of sugars in fresh olive oil extraction effluents was caused by yeasts tentatively identified asCandida wickerhamii, C. molischiana andSaccharomyces cerevisiae. These strains may serve to convert olive oil waste effluents into useful products.

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Caractérisation de levures isolées d'effluents d'extraction d'huile d'olive en fermentation spontanée

Résumé La fermentation spontanée des sucres dans des effluents d'extraction d'huile d'olive est due à des souches de levures tentativement identifiées commeCandida wickerhamii, C. molischiana etSaccharomyces cerevisiae. Ces souches peuvent servir à la conversion d'effluents résiduaires d'extraction d'huile d'olive en produits utiles.

     

Evaluation of methods for the isolation and detection of Escherichia coli O157 in minced beef

This study has evaluated enrichment and detection procedures for the isolation and detection of Escherichia coli O157 inoculated into minced beef. The use of a 24 h enrichment in modified EC broth containing novobiocin allowed low numbers of contaminating cells to multiply to levels detectable on culture media and by ELISA test kits. Total analysis time was reduced by the use of the Dynabead^TM immunomagnetic separation system. The use of the Petrifilm^TM Test Kit-HEC for E. coli O157: H7 and Organon Teknika EHEC-TEK system detected low numbers of contaminating cells following enrichment and reduced analysis time by 1 d. The incorporation of cefixime and tellurite into Sorbitol MacConkey Agar increased the rate and ease of isolation of E. coli O157 and its use is therefore recommended.     

Synergistic effect of heat and sodium lactate on the thermal resistance of Yersinia enterocolitica and Listeria monocytogenes in minced beef

The effect of sodium lactate (NaL) (0, 2.4 or 4.8%), in heating and recovery media, on Yersinia enterocolitica and Listeria monocytogenes numbers recovered from minced beef heated at 55 degrees C, was examined. Survivors were enumerated on selective media at pH 5.7/7.4 (Y. enterocolitica) or pH 5.7/7.2 (L. monocytogenes). Recovery of the organisms depended on the pH and NaL levels in the recovery medium. The heat resistance of Y. enterocolitica (P < 0.001) and L. monocytogenes (P < 0.01) decreased as the concentration of NaL in the minced beef increased from 0 to 2.4% or 4.8%. The thermal destruction of pathogens in foods processed using mild temperatures may be enhanced by the addition of 2.4% NaL.     

Optimization of enrichment and plating procedures for the recovery of Escherichia coli O111 and O26 from minced beef

AIM: Optimization of enrichment media and selective agars for the detection of Escherichia coli O26 and O111 from minced beef. METHODS AND RESULTS: This study compared a number of different enrichment conditions and plating media for the recovery of E. coli O26 and E. coli O111 from minced beef. The optimum enrichment conditions for E. coli O26 was observed in beef samples enriched at 41.5 degrees C in tryptone soya broth supplemented with cefixime (50 microg l(-1)), vancomycin (40 mg l(-1)) and potassium tellurite (2.5 mg l(-1)). Similar enrichment conditions were optimal for E. coli O111 with the omission of potassium tellurite. The optimum agar for recovery of E. coli O26 and giving the most effective suppression of contaminants was MacConkey agar [lactose replaced by rhamnose (20 g l(-1))] and supplemented with cefixime (50 microg ml(-1)) and potassium tellurite (2.5 mg l(-1)). Optimum recovery of E. coli O111 was on chromocult agar, supplemented with cefixime (50 microg ml(-1)), cefsulodin (5 mg l(-1)) and vancomycin (8 mg l(-1)). Minced beef samples were inoculated with a number of strains of E. coli O26 (n=9) and O111 (n=8), and the developed enrichment and plating methods, used in combination with immunomagnetic separation, were shown to be an effective method for the recovery of all strains. CONCLUSIONS: Routine cultural methods for the recovery of E. coli O26 and O111 from minced beef are described. SIGNIFICANCE AND IMPACT OF THE STUDY: The optimized enrichment and plating procedure described for the recovery of E. coli O111 and O26 from meat can be used to extend research on these emerging pathogens in beef.     

Determination of the influence of organic acids and nisin on shelf-life and microbiologicalsafety aspects of fresh pork sausage

The effect of replacing sulphur dioxide with organic acids and nisin to reduce the microbialcounts in fresh pork sausage was examined. The potential of sodium citrate or sodium lactate,used singly or in combination with nisin, was also assessed in sausage inoculated with Staphylococcus aureus MMPR 3 and Salmonella kentucky AT 1. The results indicatethat a combination of sodium lactate and nisin was particularly effective in reducing total bacterialcounts in this food product. It also appears that this combination provides an increased protectionagainst common pathogenic contaminants of fresh pork sausage, i.e. Staph. aureus and Salmonella species.