Vacuum-packaged Ham Research Articles

Optimal experimental design to model spoilage bacteria growth in vacuum-packaged ham

Proper mathematical models with trustworthy estimated parameters are essential to accurately predict the shelf life of foodstuffs. Traditionally, many isothermal experiments are performed to estimate these parameters and their temperature dependence. Alternatively, Optimal Experimental Design (OED) of non-isothermal experiments reduces the experimental workload and costs. The objective of this study was to apply OED to estimate the growth parameters of Weissella viridescens in vacuum-packaged ham under non-isothermal conditions. Results of non-isothermal experiments (temperature ranging from 4 to 25 °C) were used for parameters estimation and independent data for model validation. Baranyi and Roberts primary model and the Square Root secondary model fitted well to the data, as verified by R2, greater than 0.986, RMSE, lower than 0.470, and by narrow confidence interval of the estimated parameters. In the model validation, a good agreement between predicted values and experimental data was observed (RMSE = 0.344, bias = 0.997 and accuracy = 1.017), indicating that the growth parameters of W. viridescens in vacuum-packaged ham were successfully estimated with OED.

Characterization of specific spoilage organisms (SSOs) in vacuum-packed ham by culture-plating techniques and MiSeq next-generation sequencing technologies.

Knowledge regarding microaerophilic and anaerobic specific spoilage organisms (SSOs) is crucial for an appropriate evaluation of vacuum-packed ham. The objective of this study was to characterize the SSO community in vacuum-packed ham by a culture-dependent technique and MiSeq next-generation sequencing (NGS) platform. The relation between changes among the SSO group in the ham and changes in sensory characteristics of the product was also assessed. In the study, conventional microbiological analyses were employed in order to establish the participation of several groups of microorganisms in the deterioration of vacuum-packed ham. The diversity of the SSO group in the product was further assessed with the use of MiSeq NGS technology. The bacteria identified in sliced cooked ham belonged mostly to four phyla, namely Actinobacteria, Proteobacteria, Firmicutes and Bacteroidetes. A temperature of 4 °C favoured the development of mesophilic and psychrophilic/psychrotrophic flora, mainly Lactobacillaceae, Enterobacteriaceae and Micrococcaceae families. A high ratio of Brochothrix thermosphacta species and new, cold-tolerant Clostridium spp. was also observed. The growth of these microorganisms facilitated changes in the pH value and organoleptic characteristics of the product. This study confirms that the combination of culturing and MiSeq NGS technology improves the microbial evaluation of food. © 2016 Society of Chemical Industry.

Modeling the growth of Lactobacillus viridescens under non-isothermal conditions in vacuum-packed sliced ham

Lactic acid bacteria (LAB) are responsible for spoiling vacuum-packed meat products, such as ham. Since the temperature is the main factor affecting the microbial dynamic, the use of mathematical models describing the microbial behavior into a non-isothermal environment can be very useful for predicting food shelf life. In this study, the growth of Lactobacillus viridescens was measured in vacuum-packed sliced ham under non-isothermal conditions, and the predictive ability of primary (Baranyi and Roberts, 1994) and secondary (Square Root) models were assessed using parameters estimated in MRS culture medium under isothermal conditions (between 4 and 30°C). Fresh ham piece was sterilized, sliced, inoculated, vacuum-packed, and stored in a temperature-controlled incubator at five different non-isothermal conditions (between 4 and 25°C) and one isothermal condition (8°C). The mathematical models obtained in MRS medium were assessed by comparing predicted values with L. viridescens growth data in vacuum-packed ham. Its predictive ability was assessed through statistical indexes, with good results (bias factor between 0.95 and 1.03; accuracy factor between 1.04 and 1.07, and RMSE between 0.76 and 1.33), especially in increasing temperature, which predictions were safe. The model parameters obtained from isothermal growth data in MRS medium enabled to estimate the shelf life of a commercial ham under non-isothermal conditions in the temperature range analyzed.

Reduction of Listeria Innocua Contamination in Vacuum-Packaged Dry-Cured Italian Pork Products After High Hydrostatic Pressure Treatment.

The present work aims to present the results of the application of a treatment with high hydrostatic pressure (HHP) on Italian fermented and dry-cured pork products. The products used in this study were portioned cured ham, portioned bacon and salami, vacuumpackaged and produced by a single processing company. Two studies were conducted on a single batch of the three products by means of an artificial contamination with Listeria innocua as a surrogate of L. monocytogenes. In the first trial a superficial contamination was obtained by immersion for 3 min in the culture broth with a concentration of approximately 9 log cfu/mL. At the end of the inoculum step, the pieces were dred at room temperature and vacuum packaged. In the second trial 50 kg of minced pork meat were contaminated before production of salami. In both cases the inoculum contained 5 strains of L. innocua. Subsequently, in both trials, 10 samples were randomly divided into two groups of 5 pieces each: i) TH group, samples treated with HHP; ii) group C, control samples, not subjected to any treatment. All samples were stored at refrigeration temperature at the end of HHP treatments (if applied), and analyzed for the determination of the surface (1st trial) and deep (2nd trial) quantitative contamination of L. innocua. pH and aW were also determined on 3 pieces of each products belonging to group C. The difference between the medians of the log cfu/cm2 or g established between controls and treated were compared using the non-parametric test (Kruskal-Wallis test) with P<0.01. In all products and in both trials the level of contamination detected in treatment groups was always significantly lower than in controls (P<0.01). In particular, in vacuum-packaged ham, bacon and salami viability logarithmic viability reductions equal to -2.29, -2.54 and -2.51 were observed, respectively. This study aimed to evaluate a not-thermal treatment on Italian cured or fermented pork products. The results of this study need to be confirmed in different products and in a greater number of lots, but they appear promising, also because of the considerable literature available for different categories of products (cheese, vegetables and fruit).

Sodium chloride-induced filamentation and alternative gene expression of fts, murZ, and gnd in Listeria monocytogenes 08-5923 on vacuum-packaged ham.

The aim of this study was to examine the filament formation and differential gene expression of Listeria monocytogenes 08-5923 grown on refrigerated vacuum-packaged ham products with various NaCl concentrations. Filament formation of L. monocytogenes was observed on ham products with 1.35% and 2.35% NaCl, which was monitored using flow cytometry by measuring forward light scatter. Quantitative real-time PCR was used to study the differential expression of genes in filamented cells of L. monocytogenes grown on hams following 2 or 3 months of storage at 4 °C. The genes involved in cell division (ftsX/lmo2506), cell wall synthesis (murZ/lmo2552), and NADPH production (gnd/lmo1376) were significantly downregulated in filamented cells of L. monocytogenes grown on ham with 2.35% NaCl stored at 4 °C. To our knowledge, this study reports the first evidence of filament formation of Listeria grown on meat products, which could impact the food safety risk and tolerance levels of L. monocytogenes set by regulatory agencies.

Inhibition of Listeria monocytogenes ATCC 19115 on ham steak by tea bioactive compounds incorporated into chitosan-coated plastic films.

BackgroundThe consumer demands for better quality and safety of food products have given rise to the development and implementation of edible films. The use of antimicrobial films can be a promising tool for controlling L. monocytogenes on ready to eat products. The aim of this study was to develop effective antimicrobial films incorporating bioactive compounds from green and black teas into chitosan, for controlling L. monocytogenes ATCC 19115 on vacuum-packaged ham steak. The effectiveness of these antimicrobial films was evaluated at room temperature (20°C) for 10 days and at refrigerated temperature (4°C) for 8 weeks.ResultsThe HPLC results clearly show that relative concentrations of catechins and caffeine in green tea ranked EGCG>EGC>CAF>ECG>EC>C while in black tea extracts ranked CAF>EGCG>ECG>EGC>EC>C. The chitosan-coated plastic films incorporating green tea and black tea extracts shows specific markers identified by FTIR. Incorporating natural extracts into chitosan showed that the growth of L monocytogenes ATCC 19115 was inhibited. The efficacy of antimicrobial effect of tea extracts incorporated into chitosan-coated plastic film was dose dependent. However, chitosan-coated films without addition of tea extracts did not inhibit the growth of L. monocytogenes ATCC 19115. Chitosan-coated plastic films incorporating 4% Green tea extract was the most effective antimicrobial, reducing the initial counts from 3.2 to 2.65 log CFU/cm2 during room temperature storage and from 3.2 to 1–1.5 log CFU/cm2 during refrigerated storage.ConclusionsIncorporation of tea extracts into the chitosan-coated films considerably enhanced their effectiveness against L. monocytogenes ATCC 19115. 4% Green tea incorporated into chitosan-coated plastic film had a better antilisterial effect than 2% green tea or 2% and 4% black tea. Data from this study would provide new formulation options for developing antimicrobial packaging films using tea extracts to improve the microbiological safety and quality of ham steak during room and refrigerated storage.

Efficacy of pulsed light for shelf-life extension and inactivation of Listeria monocytogenes on ready-to-eat cooked meat products

Pulsed light (PL) was tested for its utility to improve the microbial quality and safety of ready-to-eat cooked meat products. Vacuum-packaged ham and bologna slices were superficially inoculated with Listeria monocytogenes and treated with 0.7, 2.1, 4.2 and 8.4 J/cm2. PL treatment at 8.4 J/cm2 reduced L. monocytogenes by 1.78 cfu/cm2 in cooked ham and by 1.11 cfu/cm2 in bologna. The effect of PL on lipid oxidation and sensory properties was also investigated. The 2-thiobarbituric acid values were very low and chromaticity parameters were within the normal values reported for cooked meat products. PL at 8.4 J/cm2 did not affect the sensory quality of cooked ham, while treatments above 2.1 J/cm2 negatively influenced the sensory properties of bologna. The combination of PL and vacuum packaging provided ham with an additional shelf-life extension of 30 days compared with only vacuum packaging. The shelf-life of bologna was not extended by PL. The efficacy of pulsed light for the decontamination of surfaces offers excellent possibilities to ensure food safety and to extend shelf-life of ready-to-eat (RTE) products. The results of this study indicate that Listeria monocytogenes can be reduced by approximately 2 log cfu/cm2 in RTE cooked ham and 1 log cfu/cm2 in bologna using a fluence of 8.4 J/cm2. This dose does not affect the sensory properties of ham and triples its shelf-life when compared with conventional RTE products. On the contrary, fluences above 2.1 J/cm2 are not suitable for the treatment of bologna since sensory quality is modified.

Growth characteristics of Listeria monocytogenes as affected by a native microflora in cooked ham under refrigerated and temperature abuse conditions

This study examined the growth characteristics of Listeria monocytogenes as affected by a native microflora in cooked ham at refrigerated and abuse temperatures. A five-strain mixture of L. monocytogenes and a native microflora, consisting of Brochothrix spp., isolated from cooked meat were inoculated alone (monocultured) or co-inoculated (co-cultured) onto cooked ham slices. The growth characteristics, lag phase duration (LPD, h), growth rate (GR, log 10 cfu/h), and maximum population density (MPD, log 10 cfu/g), of L. monocytogenes and the native microflora in vacuum-packed ham slices stored at 4, 6, 8, 10, and 12 °C for up to 5 weeks were determined. At 4–12 °C, the LPDs of co-cultured L. monocytogenes were not significantly different from those of monocultured L. monocytogenes in ham, indicating the LPDs of L. monocytogenes at 4–12 °C were not influenced by the presence of the native microflora. At 4–8 °C, the GRs of co-cultured L. monocytogenes (0.0114–0.0130 log 10 cfu/h) were statistically but marginally lower than those of monocultured L. monocytogenes (0.0132–0.0145 log 10 cfu/h), indicating the GRs of L. monocytogenes at 4–8 °C were reduced by the presence of the native microflora. The GRs of L. monocytogenes were reduced by 8–7% with the presence of the native microflora at 4–8 °C, whereas there was less influence of the native microflora on the GRs of L. monocytogenes at 10 and 12 °C. The MPDs of L. monocytogenes at 4–8 °C were also reduced by the presence of the native microflora. Data from this study provide additional information regarding the growth suppression of L. monocytogenes by the native microflora for assessing the survival and growth of L. monocytogenes in ready-to-eat meat products.

Modeling the growth of lactic acid bacteria in sliced ham processed by high hydrostatic pressure

The main responsible for the spoilage of cooked cured meat products stored under refrigerated and anaerobic conditions are lactic acid bacteria. The application of high hydrostatic pressure (HHP) reduces the lactic acid bacterial growth extending the product shelf-life and preserving natural taste, texture, color and vitamin content. This work studied the influence of pressure level and holding time on the lactic acid bacterial growth in vacuum-packaged sliced ham. Modified Gompertz and Logistic models were used to fit experimental data obtained from post-treatment microbial counts carried out along the product storage. Samples of sliced vacuum-packaged ham treated by HHP and control samples (non-treated) were stored at 8 °C until the microorganism population reached 10 7 CFU/g. An experimental planning 2 2 with triplicate at the central point was designed to determine the influence of pressure level (200, 300, and 400 MPa) and holding time (5, 10, and 15 min) on the product shelf-life. The results have shown that the pressure intensity and the holding time significantly influenced microbial population over the product storage. Shelf-life of ham treated at 400 MPa for 15 min was extended from 19 (control samples) to 85 days.

Effect of the inoculation of a starter culture and vacuum packaging during the resting stage on sensory traits of dry-cured ham

The effects of the inoculation of a mixed starter culture and vacuum packaging (during resting stage) on odour, appearance, texture and flavour of dry-cured ham were studied. After salting, half of the 36 processed hams were inoculated with a commercial starter culture containing lactic-acid bacteria, Gram-positive catalase-positive cocci and yeasts. Nine hams per group (inoculated and non-inoculated) remained vacuum-packaged during resting. External odour during the process, as well as appearance of the cut surface, texture and flavour on semimembranosus and biceps femoris of the final product were assessed. Vacuum packaging during resting caused an increase in white film and feedstuff flavour, as well as a decrease in aged flavour, hardness, fibrousness and overall liking. The use of the starter culture brought about an increase in feedstuff flavour, a decrease in sweetness, aged flavour, nutty flavour and overall liking and, only in vacuum-packaged hams, the development of a floral flavour, but had no significant effect on texture descriptors. The starter culture studied is considered inappropriate for the production of traditional Spanish dry-cured ham regardless of the type of resting used.

Antilisterial activity of lactic acid bacteria inoculated on cooked ham

This study was conducted to evaluate the ability of Lactobacillus sakei 1, a bacteriocin-producing (bac +) lactic acid bacterium (LAB), isolated from Brazilian fresh pork sausage to inhibit two Listeria monocytogenes strains (serotypes 4b and 1/2a) on cooked, sliced vacuum-packaged ham. L. sakei ATCC 15521 was used as a non-bacteriocin producer (bac −). L. monocytogenes (ca. 2 log CFU/mL) and LAB (ca. 6 log CFU/ml) were inoculated on the sterilized ham, vacuum-sealed and incubated at 8 °C for 10 days. A treatment with the bacteriocin Chrisin (UI/ml) was included. Both L. monocytogenes strains were significantly inhibited in the presence of either bac + and bac − LAB in comparison to the control ( L. monocytogenes alone). Using a bacteriocinogenic strain of LAB did not offer an additional barrier to listerial growth in the studied meat system. The application of Chrisin did not affect at all the growth of L. monocytogenes.

Evaluation of antilisterial action of cilantro oil on vacuum packed ham

Cilantro oil is an essential oil preparation extracted from the plant Coriandrum sativium. A series of experiments were conducted to evaluate the ability of cilantro oil to control the growth of Listeria monocytogenes on vacuum-packed ham. The in vitro minimal inhibitory concentration for five strains of L. monocytogenes was found to vary from 0.074% to 0.018% depending on strain. Cilantro oil treatments were then tested on ham disks inoculated with a cocktail of the five L. monocytogenes strains. The treatments studied were 0.1%, 0.5%, and 6% cilantro oil diluted in sterile canola oil or incorporated into a gelatin gel in which lecithin was used to enhance incorporation of the cilantro oil. Gelatin gel treatments were also conducted with 1.4% monolaurin with or without 6% cilantro oil to determine if an interaction between the antimicrobials could increase inhibition of L. monocytogenes. Treated ham was then vacuum-packed and stored at 10 °C for up to 4 weeks. The only cilantro oil treatment which inhibited growth of L. monocytogenes on the ham samples was 6% cilantro oil gel. Samples receiving this treatment had populations of L. monocytogenes 1.3 log CFU/ml lower than controls at week 1 of storage, though there was no difference between treatments from week 2 onward. It appears that immobilization of the antimicrobial in a gel enhanced the effect of treatments. Cilantro oil does not appear to be a suitable agent for the control of L. monocytogenes on ham. The possible reasons for reduced effectiveness of cilantro oil against L. monocytogenes on ham are discussed.

Protective cultures inhibit growth of Listeria monocytogenes and Escherichia coli O157:H7 in cooked, sliced, vacuum- and gas-packaged meat

Contamination of cooked meat products with Listeria monocytogenes poses a constant threat to the meat industry. The aim of this study was therefore to investigate the use of indigenous lactic acid bacteria (LAB) as protective cultures in cooked meat products. Cooked, sliced, vacuum- or gas-packaged ham and servelat sausage from nine meat factories in Norway were inoculated with 10 3 cfu/g of a mixture of three rifampicin resistant ( rif-mutant) strains of L. monocytogenes and stored at 8°C for four weeks. Growth of L. monocytogenes and indigenous lactic acid flora was followed throughout the storage period. LAB were isolated from samples where L. monocytogenes failed to grow. Five different strains growing well at 3°C, pH 6.2, with 3% NaCl, and producing moderate amounts of acid were selected for challenge experiments with the rif-resistant strains of L. monocytogenes, a nalidixic acid/streptomycin sulphate-resistant strain of Escherichia coli O157:H7 and a mixture of three rif-resistant strains of Yersinia enterocolitica O:3. All five LAB strains inhibited growth of both L. monocytogenes and E. coli O157:H7. No inhibition of Y. enterocolitica O:3 was observed. A professional taste panel evaluated cooked, sliced, vacuum-packaged ham inoculated with each of the five test strains after storage for 21 days at 8°C. All samples had acceptable sensory properties. The five LAB strains hybridised to a 23S rRNA oligonucleotide probe specific for Lactobacillus sakei. These indigenous LAB may be used as protective cultures to inhibit growth of L. monocytogenes and E. coli O157:H7 in cooked meat products.

Chilling and Trimming Effects on the Microbial Populations of Pork Carcasses

The effects of chilling (normal chill or freeze chill) and trimming (hot fat trim or no fat trim) on the microbial populations of pork carcasses were evaluated. In a two-part study, composited ham, loin, belly, and shoulder samples from 30 pork carcasses had similar aerobic plate counts, averaging 5.5 log10 CFU/cm2. The nofat trim, normal chill procedure typically used in the industry, however, produced higher coliform and Staphylococcus spp. counts (P < 0.05). The hot fat trim, freeze chill treatment had the lowest lactic acid bacteria counts. Only 1 sample in 60 tested positive for Salmonella spp. Vacuum-packaged hams and loins stored at 4°C for 14 days had similar (P > 0.05) aerobic plate counts, lactic acid bacteria and Staphylococcus spp. counts regardless of trim, chill, or the location of treatment, averaging 5.7, 6.3 and 1.4 log10 CFU/cm2, respectively. Hams had higher counts than loins all three days; however, only the difference on day 2 was significant. The desire to reduce microbial populations on pork carcasses as a food-safety issue and the coming implementation of hazard analysis critical control points (HACCP) programs warrants the use of trimming and chilling methods as critical control points or good manufacturing practices and standard operating procedures in the pork slaughter, processing, and packaging industry.

Characterization of Leuconostoc species isolated from vacuum-packaged ham.

Thirty-six isolates of Leuconostoc spp. were isolated from yellow spots that occurred on the surface of vacuum-packaged ham. All isolates were Gram-positive, catalase-negative cocci that produced gas from glucose and formed more than 90% of their lactate as D(-) isomer. These isolates could grow at 4 degrees C but not above 30 degrees C and most strains produced yellow spots on the ham. The isolates were divided into three groups by sugar fermentation patterns. Representative strains from three groups showed intergroup DNA homology values of above 88.8%, showing that these groups were composed of a single species. This organism was positioned at a separate branch in the genus Leuconostoc on the phylogenetic tree based on 16S rRNA sequences, which was assigned to Leuconostoc gelidum on the basis of DNA-DNA relatedness.

Fate of Selected Pathogens in Vacuum-Packaged Dry-Cured (Country-Style) Ham Slices Stored at 2 and 25°C

Whole dry-cured (country-style) hams from six manufacturers were sliced and the slices randomly allotted into five treatment groups per manufacturer. One treatment group served as a control and slices in the four other treatment groups were inoculated with approximately 105 CFU/g of ham of either Escherichia coli O157:H7, Listeria monocytogenes, a mixture of three Salmonella spp. (Salmonella typhimurium, Salmonella enteritidis and Salmonella choleraesuis), or Staphylococcus aureus. All ham slices were vacuum-packaged with half of the packages in each treatment group stored at 25°C and half stored at 2°C. Two packages from each manufacturer for each treatment and storage temperature were examined after storage for 0,7, 14,21, and 28 days. S. aureus was detected in 2 of 60 control slices, Salmonella in 2 of 120, L. monocytogenes in 4 of 120, and E. coli O157:H7 was not detected in any of the 120 control ham slices analyzed before or after storage. Aerobic (26 and 35°C) populations of the control vacuum-packaged hams slices increased (P < 0.05) with storage time and the increase in populations was greater (P < 0.05) in vacuum-packaged hams slices at 25 than at 2°C. The extent of the decreases in populations of the inoculated pathogens during storage of vacuum-packaged dry-cured ham slices varied with manufacturer (P < 0.05) and storage temperature (P < 0.05). Decreases in Salmonella spp. and E. coli O157:H7 populations were greater (P < 0.05) in slices stored at 25 than at 2°C, while decreases in L. monocytogenes were similar at both storage temperatures. Staphylococcus aureus enterotoxin was not detected in either S. aureus-inoculated or control ham slices after storage for 28 days. Survival of these pathogens in vacuum-packaged dry-cured ham slices suggests that contaminated hams may pose a safety risk to consumers if consumed without adequate cooking.

Asymmetric Distribution and Growth of Bacteria in Sliced Vacuum-Packaged Ham and Bologna

Commercially sliced vacuum-packaged cooked ham and bologna were found to contain significantly greater numbers of total and lactic acid bacteria (LAB) on package surface slices than on internal slices. This asymmetric distribution persisted in most samples to beyond the manufacturer's “best before” date. Enterobacteriaceae and bacterial spores were detected infrequently. Bacterial spores were found most often on the surface slices of commercially packaged sliced bologna. Where they occurred, aerobic and anaerobic spores were detected in equal numbers. Center slices of bologna were less hospitable sites for spores and LAB than were surface slices in vacuum packages. When freshly cooked ham and bologna were sliced together with uncooked fermented sausage, LAB from the sausage (pediococci and thermo-tolerant homofermentative lactobacilli) contaminated the cooked meats immediately causing an equal distribution of bacteria throughout the slices. Pediococci did not survive in the vacuum-packaged cooked meats more than 2 weeks at 7°C. The pH of co-sliced bologna prematurely dropped. The shelf life of refrigerated co-sliced ham was reduced by 44%, probably because of adventitious lactobacilli from the sausage. Brochothrix thermosphacta was not present in co-sliced or sliced control meats. Homofermentative lactobacilli predominated in co-sliced and control samples packaged in the laboratory, but in commercially packaged sliced cooked ham and bologna heterofermentative LAB species were dominant. Prolonging cooked ham and bologna shelf life is possible if handling of uncooked fermented sausage is kept separate from the slicing and packaging of cooked cured products.

Destruction of Listeria monocytogenes during a Ham Cooking Process

Two batches of uncooked whole hams were inoculated with Listeria monocytogenes phagovar 2389/2425/3274/2671/47/108/340 during brining. One batch of hams was contaminated with a high level (3.9 × 105CFU/g), and the second batch was contaminated with a low level of L. monoytogenes (<10 CFU/g). These vacuum-packaged hams were then cooked according to the minimum standards allowed to obtain technologically and organoleptically acceptable hams, i.e., to a core temperature of 58.8°C and an F70-value of 32 min. They were then maintained undisturbed for 2 months at 9°C, which is consistent with the worst conditions typically found in practice. Enumeration of the spoilage flora (30°C mesophilic flora, lactic flora, and Enterobacteriaceae) during storage demonstrated that this treatment yielded a microbiologically satisfactory food product. In the case of L. monocytogenes, the heat treatment applied would in theory reduce the contamination level by 52 to 77 log units (assuming a D-value in the range of 1.82 to 3.38 min at 60°C and a z-value in the range of 5.05 to 6.74°C). No Listeria spp. was found during storage in the batch of hams contaminated with the low level. However, a very small number of L. monocytogenes was found in the highly contaminated batch of hams at the end of the storage period. These results should alert the commercial sector to the importance of cooking their products to a minimum core temperature of 65°C, with an F70-value of at least 40 min. If weakly contaminated products are cooked according to this protocol, the risk of L. monocytogenes surviving should be diminished.

Modified packaging as protection against photodegradation of the colour of pasteurized, sliced ham

Carbon dioxide flushing and packaging under slight overpressure has been found to eliminate discoloration of vacuum-packed ham, normally encountered as a result of photooxidation of nitric oxide pigments during the first 24 h of display in illuminated cabinets. On exposure to light, even when the product is packed in high-vacuum, residual oxygen invariably present in the product gives rise to significant photochemical pigment degradation and general poor oxidative stability, and has warranted up to 4 days of dark storage prior to display. Replacement of the atmosphere with carbon dioxide, even when repeated, followed by the establishment of vacuum, does not yield a similar protection.

Schmeißfliegen (Calliphoridae) und vakuumverpackter Schinken

Blowflies (Calliphoridae) and vacuum-packed ham In a few cases blowfly maggots have been reported from vacuum-packed ham. The possibility of egg-hatching and larval development in the product was analysed. In experiments no hatching of blowfly eggs on vacuum-packed, boiled, sliced ham occurred. However, the eggs are not killed immediately; 1–4 days after the packing, they are still viable and when the wrapping is broken, hatching may occur. After a stay of 7–10 days on vacuum-packed ham, the viability of the eggs seems lost. In the actual case the risk of oviposition by blowflies on ham in the cannery and succeeding larval development in the product is considered to be very low.