Influence of heat shrink treatments on the onset of clostridial “blown pack” spoilage of vacuum packed chilled meat

Storage trials were conducted to determine if short duration high temperature treatments applied in commercial heat shrinking of vacuum barrier packs affect the onset of clostridial blown pack spoilage. Spore suspensions of six significant gas producers were used: Clostridium estertheticum NCIMB 12511, and five local psychrotolerant clostridial isolates. Beef striploins, pH 5.5 and 6.0, were cut into steaks and placed into vacuum pouches. Duplicate pouches were inoculated with each test spore suspension for each meat pH/heat treatment/storage temperature combination. After vacuum packaging and heat shrinking, packs were stored at −1.5, 1 or 4°C. Based on time to first-phase gas production (small bubbles in drip), the test strains were considered statistically as representing two groups. With both groups, post-packaging heat treatment had a significant effect on time to gas production. Mean times, pooled for the three storage temperatures, to gas production with Group A were 49, 39, 36 and 35 days for the no heat, 70, 80 and 90°C treatments, respectively. With Group B these times were 77, 42, 39 and 36 days, respectively. Post-packaging heat shrink treatments of vacuum packaged meat accelerate the onset of Clostridium spp. mediated blown pack spoilage during chilled storage. Possible mechanisms for accelerated onset of blown pack spoilage following heat shrinking of vacuum packs are discussed.     

Effects of meat pH and the initial numbers of spores of Clostridium estertheticum on the development of blown pack spoilage of vacuum‐packaged beef

To understand how the initial numbers of Clostridium estertheticum spores on, and the concentration of glucose in meat affect the development of blown pack spoilage, beef of pH ≤5.6 and of pH ≥5.8 was inoculated with the spores at various numbers, vacuum‐packaged and stored at 2 °C. For beef of pH ≤5.6, the volumes of packs inoculated with ≤10 spores did not change; and packs inoculated with ≥30 spores started swelling after 35 days, and the rate of volume increase increased with increasing number of inoculated spores. For beef of pH ≥5.8, packs inoculated 0, three or ten spores slackened, and packs inoculated with ≥30 spores became swollen at the end of storage, but to a much lesser degree than the corresponding packs of beef of pH ≤5.6. Glucose was reduced by 21 mm and depleted in the rinse fluids from swollen packs of beef of pH ≤5.6 and of pH ≥5.8, respectively.     

A CASE OF "BLOWN PACK" MEAT LINKED TO CLOSTRIDIUM ESTERTHETICUM IN IRELAND

The objective of this study was to determine whether Clostridium estertheticum can be linked to the "blown pack" of vacuum-packed beef and lamb. Vacuum-packed chilled beef and lamb samples that had been spoiled by gross gas distension were obtained from two Irish meat processing plants. A sample of purged liquid from each sample was removed from the each meat pack and divided into 3 replicate samples. Both polymerase chain reaction amplification and conventional culturing methods was used to detect C. estertheticum in each purge sample. DNA sequencing was used to confirm its detection. C. estertheticum DNA was detected in beef but not detected in lamb. C. estertheticum was not isolated from the beef or lamb purge samples. This study represents the first confirmed link between C. estertheticum and the blown pack vacuum-packed beef in Ireland.

PRACTICAL APPLICATIONS

Blown pack spoilage of vacuum packed meat is a significant problem in the meat industry and has the potential to cause considerable economic loss to meat processors. This study found, the first evidence of Clostridium estertheticum in vacuum packed meat in Ireland. This research will contribute to a better understanding of blown pack spoilage of vacuum packed meat caused by C. estertheticum .     

Effects of vacuum,modified atmospheres and storage temperature on the microbial flora of packaged beef

The flora growing on beef stored in vacuum and 100% CO₂at 2 or 6°C (experiment 1) and in vacuum and different mixtures of CO₂and N₂at −1 or 2°C (experiment 2) was determined in two separate experiments. Both a high concentration of CO₂and a low storage temperature inhibited bacterial growth, especially of the spoilage bacteria pseudomonads andBrochothrix thermosphacta. No packaging conditions gave growth of coliforms. High numbers (log₈5–6) of lactic acid bacteria after storage in vacuum or gas packs, inhibited growth of pseudomonads andB. thermosphactaduring subsequent storage under retail conditions. Samples of the lactic acid bacteria obtained in experiment 2 were identified by genus-specific rRNA probes. Leuconostocs dominated in vacuum and CO₂packs at both temperatures, whereas carnobacteria dominated in N₂at −1°C.     

Influence of peroxyacetic acid-based carcass rinse on the onset of "blown pack" spoilage in artificially inoculated vacuum-packed chilled beef

"Blown pack" spoilage is an increasingly reported spoilage condition of vacuum-packed chilled meats. This spoilage condition is primarily caused by a psychrophilic obligately anaerobic microorganism, Clostridium estertheticum. The present study investigated whether peroxyacetic acid (POAA)-based carcass rinse can delay the onset of gas production in chilled vacuum-packed beef artificially inoculated with C. estertheticum spores. The variables studied were (i) two prepackaging meat rinses (water and POAA-based rinse); (ii) three levels of C. estertheticum spores (0, 4, and 40 spores per cm2); and (iii) three postpackaging storage temperatures (-1.5, 0, and 2 degrees C). Treatment with POAA-based rinse marginally delayed the onset of pack blowing in packs carrying high numbers of C. estertheticum spores but not in packs carrying low levels of inoculum or in uninoculated controls. The presence of as few as 4 spores per cm2 of meat surface effectively decreased by two-thirds the nominal shelf life of vacuum-packed chilled beef. Increasing the inoculum by 10-fold to 40 spores per cm2 resulted in the additional acceleration of the onset of pack blowing. The onset of gas production was significantly delayed by storing the packaged product at -1.5 degrees C rather than at 0 degrees C. The results of this study indicate that the POAA-based rinse tested will not eliminate the spoilage threat posed by clostridial blown pack spoilage spores present on meat surfaces. POAA-based rinse can be used alone to achieve some extension of shelf life of beef cuts heavily contaminated with C. estertheticum spores. Alternatively, the rinse may offer an opportunity for a more substantial extension of shelf life of contaminated cuts when used with additional hurdles.     

Extension of the chilled storage life of smoked blue cod (Parapercis colias) by carbon dioxide packaging

Commercially prepared smoked blue cod ( Parapercis colias ), packaged aerobically, under vacuum and in carbon dioxide controlled atmosphere packs, was stored at + 3°C and - 1.5°C. Product stored aerobically on overwrapped polystyrene trays spoiled by 14 and 28 days respectively, and that in vacuum packs spoiled by 14 and 35 days respectively, when held at 3°C and - 1.5°C. In contrast, product in carbon dioxide packs remained acceptable until the 3°C and - 1.5°C storage trials ended after 49 and 113 days respectively. Microbial spoilage was first evident in overwrapped product stored aerobically and in vacuum-packed product as offensive putrid amine-like odours on pack opening. These odours were associated with the development of a predominantly Gram-negative spoilage microflora. Extension of product life afforded by the use of carbon dioxide controlled atmosphere packaging is attributable to a significant extension of the lag phase before spoilage microflora proliferation commenced and to the selection of a low-spoilage-potential lactic-acid-bacteria-dominated flora. Although the use of carbon dioxide packaging offers an export potential for chilled smoked blue cod, caution must be advocated until product safety, in respect to the growth of cold tolerant pathogens in the case of temperature abuse (>3°C), can be more fully evaluated.     

Sensory and microbiological quality assessment of beef fillets using a portable electronic nose in tandem with support vector machine analysis

The performance of a portable quartz microbalance based electronic nose has been evaluated in monitoring aerobically packaged beef fillet spoilage at different storage temperatures (0, 4, 8, 12, and 16 °C). Electronic nose data were collected from the headspace of meat samples in parallel with data from microbiological analysis for the enumeration of the population dynamics of total viable counts, Pseudomonas spp., Brochothrix thermosphacta, lactic acid bacteria and Enterobacteriaceae. Qualitative interpretation of electronic nose data was based on sensory evaluation discriminating samples in three quality classes (fresh, semi-fresh, and spoiled). Support Vector Machine (SVM) classification and regression models using radial basis kernel function were developed to classify beef fillet samples in the respective quality class, and correlate the population dynamics of the microbial association with electronic nose sensor responses. The obtained results demonstrated good performance in discriminating meat samples in one of the three pre-defined quality classes. Overall classification accuracies of prediction above 89% were obtained for the three sensory classes regardless of storage temperature. For SVM regression model development, correlations above 0.96 and 0.86 were obtained between observed and predicted microbial counts for the training and test data sets, respectively.     

Microbial Growth on Fat and Lean Surfaces of Vacuum-Packaged Chilled Beef

Brochothrix thermosphacta, Enterobacteriaceae and the Pseudomonas-Moraxella group grew more rapidly on the fat than on the lean surfaces of chilled vacuum-packaged beef striploins of pH 5.45–5.85. On the fat, both B. thermosphacta and Enterobacteriaceae grew to outnumber the Pseudomonas-Moraxella. When Enterobacteriaceae and B. thermosphacta were present initially in about equal numbers, Enterobacteriaceae outgrew B. thermosphacta on both the fat and the lean surfaces of packs stored at 5°C. At 1°C the growth rate of the Enterobacteriaceae was greatly reduced. As a result, on the fat at 1°C, B. thermosphacta grew considerably faster than did the Enterobacteriaceae.     

High‐Throughput Sequencing of Viable Microbial Communities in Raw Pork Subjected to a Fast Cooling Process

This study aimed to investigate the effect of the fast cooling process on the microbiological community in chilled fresh pork during storage. We established a culture‐independent method to study viable microbes in raw pork. Tray‐packaged fresh pork and chilled fresh pork were completely spoiled after 18 and 49 d in aseptic bags at 4 °C, respectively. 16S/18S ribosomal RNAs were reverse transcribed to cDNA to characterize the activity of viable bacteria/fungi in the 2 types of pork. Both cDNA and total DNA were analyzed by high‐throughput sequencing, which revealed that viable Bacteroides sp. were the most active genus in rotten pork, although viable Myroides sp. and Pseudomonas sp. were also active. Moreover, viable fungi were only detected in chilled fresh pork. The sequencing results revealed that the fast cooling process could suppress the growth of microbes present initially in the raw meat to extend its shelf life. Our results also suggested that fungi associated with pork spoilage could not grow well in aseptic tray‐packaged conditions.     

Significance of Lactobacilli and Film Permeability in the Spoilage of Vacuum-Packaged Beef

The spoilage of vacuum-packaged fresh beef during storage at 5°C was studied using analytical taste panels. In the absence of contaminating micro-organisms, meat spoiled due to the development of an “off” flavor described as “liver-like.” This occurred even when the meat was packaged in bags made of film of very low oxygen permeability, but the rate of spoilage increased as the film permeability increased. Thus, vacuum-packaged beef has a limited shelf life even in the absence of a significant population of contaminating microorganisms. Pure cultures of lactic acid bacteria increased the rate of spoilage, which was then due largely to the development of flavor defects described as sour, acid and bitter. Depending upon the strain of bacteria chosen, off flavor became significant 13—28 days after the population reached 10⁸/cm².     

Proteolytic and Lipolytic Changes in Beef Inoculated with Spoilage Microorganisms and Bioprotective Lactic Acid Bacteria

Abstract

The use of a controlled lactic fermentation has been studied by several authors as a means to extend meat shelf‐life without notably altering its sensory quality. Growth and metabolite production by spoilage microorganisms as well as by bioprotective strains are influenced by storage conditions. The objective of this work was to study the effect of temperature and storage time upon the growth and metabolite production of four spoilage bacteria and three bioprotective lactic acid strains in vacuum packaged, finely cut beef. Lipolysis was mainly due to the presence of Brochothrix thermosphacta at 4°C and at 20°C, whereas proteolysis was mainly caused by pseudomonads. Presence of Lactobacillus minor, a heterofermentative strain, did not promote proteolysis nor lipolysis at either temperature. No considerable lipolysis was observed until day 8 of storage in samples inoculated with bioprotective strains, but increased at day 12 when stored at 20°C; no proteolysis was observed at any storage temperature.     

Influence of storage temperature on the quality of beef liver; pH as a reliable indicator of beef liver spoilage

The development of the microbial flora specifically involved in the spoilage of sliced beef livers packaged and stored under aerobic conditions at 0 and 3 °C for 14 days was studied. Changes in the pH value of the product were also determined. The possibility that pH value could be considered as a quick and reliable indicator of incipient spoilage was particularly considered. All microbial groups (except micrococci) showed differences in their rates of growth between 0 and 3 °C. Pseudomonads and lactic acid bacteria were the main components of the spoilage flora. When the 37 °C aerobic plate counts (APCs) reached 10⁵–10⁶ CFU g⁻¹ and the 20 °C APCs and pseudomonad counts reached 10⁶–10⁷ CFU g⁻¹, visible surface colonies (VSCs) were observed. The presence of VSCs is the most important criterion to determine organoleptic beef liver spoilage and has hence enabled us to establish a shelf-life of up to 8–10 and 5.5–6.5 days for samples stored at 0 and 3 °C respectively. Our study shows that the determination of pH, which is simple, economical and rapid, is capable of giving a reliable estimate of the spoilage status of beef livers. pH values lower than 6.15 may be considered as indicative of beef liver spoilage. © 1999 Society of Chemical Industry     

Volatile compounds associated with the spoilage of normal and high pH vacuum-packed pork

Pork of normal (5.5–5.6) and high (6.3–6.6) pH was stored in vacuum packs at 5°C until spoiled. At spoilage the bacterial flora of the normal pH meat was dominated by lactic acid bacteria, that of the high pH meat by Gram-negative organisms. Volatile compounds in the packs were analysed by a headspace entrainment technique and gas chromatography-mass spectrometry. Major differences between the two types of meat were confined mainly to a series of sulphur-containing compounds which were more numerous, and present in higher concentrations, in the headspaces above high pH meat.     

Microbiological and Sensory Changes in Minced Beef Treated with Potassium Lactate and Sodium Diacetate during Refrigerated Storage

The effect of potassium lactate and sodium diacetate on the microbiological changes and sensory properties of vacuum-packaged minced beef was investigated. The meat samples both with a preservative (in the amounts 0.65% and 1.3%) and without were stored at temperatures of 0–1°C and 5–6°C. The influence of storage time on changes in total bacteria count (TBC), lactic acid bacteria (LAB), Brochothrix thermosphacta, and the microbes of the Enterobacteriaceae family was investigated, as well as changes in pH and sensory quality. It was found that the addition of the preservative to the minced meat caused a significant extension (p < 0.05) of the lag phase and an inhibition of microbial growth rate, depending on temperature, storage time, and its concentration. The antibacterial effect was significantly higher (p < 0.05) at a temperature of 0–1°C than at 5–6°C and most susceptible to it were the bacteria belonging to the Enterobacteriaceae. The study results showed that the minced beef containing the preservative which had been vacuum stored at 0–1°C, presented a better sensory quality and had a shelf-life of about 6 days longer, in relation to the quality and shelf-life of the control samples. For each of the refrigeration storage temperatures however, there was no statistically significant change (p < 0.05) in the pH for the various storage periods and preservative quantities present.     

Spoilage-related microbiota associated with chilled beef stored in air or vacuum pack

In order to study the spoilage-related microbiota of beef at species level, a combination of culture-independent and culture-dependent methods was used to analyse nine different beef samples stored at 4 °C in air or in vacuum pack. Plate counts on selective agars after 0, 7 and 20 days of storage showed that vacuum packaging reduced the viable counts of Brochothrix thermosphacta, Pseudomonas spp. and Enterobacteriaceae, whereas the growth of lactic acid bacteria (LAB) was unaffected. Storage in vacuum pack mainly affected viable counts and not necessarily the species diversity of microbial populations on meat. Such populations were studied by PCR-DGGE of DNA directly extracted from meat and from bulk cells from culture media, followed by sequencing of DGGE fragments. Pseudomonas spp., Carnobacterium divergens, B. thermosphacta, Rahnella spp. and Serratia grimesii, or close relatives were detected in the meat at time zero. The use of the culture-independent method highlighted the occurrence of species that were not detected by plating. Photobacterium spp. occurred in most meat samples stored in air or in vacuum pack, which indicates this organism probably has a role in spoilage. In contrast, culture-dependent analysis allowed detection of bacterial species that were not found in DNA extracted directly from meat. This was the case for several species of Serratia or Rhanella among the enterobacteria, and Leuconostoc spp. among the LAB. Besides advancing our knowledge of the species involved in the spoilage of vacuum-packaged meat, this study shows the benefits of combining culture-based and direct approaches to enhance understanding of populations of spoilage bacteria.     

The spoilage characteristics of Brochothrix thermosphacta and two psychrotolerant Enterobacteriacae in vacuum packed lamb and the comparison between high and low pH cuts

The spoilage potential of Brochothrix thermosphacta, Serratia proteamaculans and Rahnella aquatilis was investigated in vacuum packaged high (5.9 to 6.4) and low (5.4 to 5.8) pH lamb. Vacuum packaged fore shank (m. extensor carpi radialis) and striploins (m. longissimus dorsi) (n = 306) inoculated with ~ 100 CFU of individual bacteria were stored for twelve weeks at temperatures − 1.5, 0, 2 and 7 °C. Spoilage characteristics and bacterial numbers were recorded and analysed in comparison to un-inoculated control samples. All three bacterial species were shown to grow in vacuum packaged lamb of pH values between 5.4 and 6.4, when stored at chilled temperatures (− 1.5 to 7 °C) for up to 84 days. B. thermosphacta and S. proteamaculans caused spoilage to the meat under these conditions whilst R. aquatilis spoiled high pH meat at 7 °C. These results go against previous beef models stipulating that Brochothrix and Enterobacteriacae species cannot grow on or cause spoilage of low pH meat in the absence of oxygen.     

Modified Atmosphere Packaging of Fresh, "Ready-to-use" Grated Carrots in Polymeric Films

“Ready-to-use” grated carrots were packaged in different films (oxygen permeability from 950 to 22,000 cc/m²/day/atm at 25°C) and stored at 2, 6 or 10°C for 10 days. Gaseous atmosphere in packs and the following were monitored: lactic acid bacteria, yeast counts, exudate and potassium ion released, sugars, carotene, ethanol and lactic acid. The respiration rate of the packaged carrots was measured. Films with very low oxygen permeability resulted in anaerobic respiration, high leakage of potassium, and high lactic acid bacteria. With high-permeability films (between 10,000 and 20,000 cc/m²/day/atm at 25°C), grated carrots showed aerobic respiration and retained good quality. At 10°C, in carrots packed in the most permeable film, sucrose decreased markedly during storage. The gas permeabilities required for packaging grated carrots were evaluated in relation to storage temperature.     

Microbial, physical-chemical and sensory spoilage during the refrigerated storage of cooked pork loin processed by the sous vide method

The aim was to study spoilage during the refrigerated storage of cooked pork loin processed by the sous vide method. Samples were packaged under vacuum into polyamide-polypropylene pouches, cooked at an oven temperature/time of 70 °C/12 h, chilled at 3 °C and stored at 2 °C for 0, 5 or 10 weeks. Microbial (psychrotrophs, lactic acid bacteria, Enterobacteriaceae, moulds and yeasts), physical–chemical (pH, water activity, TBARS, acidity, L^*a^*b^* colour, texture profile analysis and shear force) and sensory (appearance, odour, flavour, texture and acceptance) parameters were determined. The results showed that sensory spoilage preceded microbiological spoilage of sous vide pork loin. Counts bellow 1 log cfu/g of psychrotrophs, anaerobic psychrotrophs, Enterobacteriaceae and lactic acid bacteria were detected in any control week, while moderate counts (2–3 log cfu/g) of moulds and yeasts were found. Minor changes in water activity, lipid oxidation, CIELab colour, hardness, cohesiveness or gumminess were associated with spoilage of pork loin, only decreases of lactic acid, springiness and shear force were observed. The pork loin was unacceptable after 10 weeks. This loss of acceptance was mainly due to the deterioration of meaty flavour and odour, although the loss of appearance, juiciness and firmness also contributed. Moderate warmed-over and rancidity were detected. The sensory analysis was the most effective method for determining the shelf life of the sous vide pork-based dishes.     

The effect of vacuum packaging on the microbial spoilage and shelf-life of ‚ready-to-use’︁ sliced carrots

The effect of vacuum packaging on the microbial spoilage of ?ready-to-use’? carrot slices and on the effect on shelf-life of the product is reported. The microbial development on vacuum packaged carrots was slower than that of non-vacuum packaged material. The predominant organisms present were Leuconostoc spp. in the vacuum packs as opposed to Erwinia spp. in the aerobic packs. Vacuum packaging of the sliced carrots significantly extended the shelf-life of the product when stored at 4°C from 5 to 8 days.     

Psychrophilic and psychrotrophic clostridia: sporulation and germination processes and their role in the spoilage of chilled,vacuum‐packaged beef,lamb and venison

Spoilage of beef, lamb and venison by psychrophilic and psychrotrophic clostridial species renders meat unacceptable resulting in financial losses and reduced consumer confidence. A number of clostridial strains, including Clostridium algidicarnis, Clostridium algidixylanolyticum, Clostridium estertheticum, Clostridium frigidicarnis and Clostridium gasigenes, have been implicated in red meat spoilage. Unlike other spoilers, these clostridia are able to grow in anaerobic conditions and at chilled temperatures (some at ?1.5 °C the optimal storage temperature for chilled red meat). The spoilage they cause is characterised by softening of the meat, production of large amounts of drip (exudates), offensive odours and in the case of C. estertheticum and C. gasigenes production of gas. Spoilage occurs following the introduction of clostridial spores into vacuum packages during processing. Germination of spores is necessary for the growth of vegetative cells, which cause spoilage. Current mitigation strategies focus on good management practice within meat processing plants. However, this is not always sufficient to prevent spoilage. This review summarises the issues associated with meat spoilage because of psychrotolerant clostridia and discusses areas that require further study.