Shelf-life extension of fresh-cut iceberg lettuce (Lactuca sativa L) by different antimicrobial films

This study was conducted to investigate the antibacterial activity and shelf-life extension effect of iceberg lettuce packed in BN/PE film. The BN/PE film has a strong microbial suppression effect on pathogenic bacteria such as Escherichia coli, Salmonella enteritidis, and S. typhimurium. The number of psychrophiles and mesophiles during 5 days of cold storage of fresh-cut iceberg lettuce at 10 degrees C packaged in BN/PE film was strictly suppressed in comparison with other tested films (OPP, PE, and PET film). When fresh processed iceberg lettuce was processed and stored under the current conditions, the shelf-life of the product was longer than 5 days in the BN/PE film package, whereas the shelf-life when using the other films tested, PE, OPP and PET, was no longer than 3-4 days. The decay rates of the iceberg lettuce packed in the BN/PE film was maintained at 29.8 +/- 2.1% on the 5th day of preservation. The samples packed in BN/PE film maintained an excellent visual quality during the 3 days of storage without significant differences in comparison with the initial visual quality. No browning was observed in the samples packed in BN/PE film for up to 3 days. The texture of shredded iceberg lettuce packaged in BN/PE film remained unchanged up to 3 days, and then a moderate decrease in texture was observed after 4 days of storage. In addition, the overall acceptability of fresh-cut iceberg lettuce packaged in BN/PE film did not change for up to 3 days, whereas the samples packaged in the other films were inedible by 3 days of storage. In conclusion, the shelf-life of fresh-cut iceberg lettuce packaged in the BN/PE film was extended to more than 5 days at 10 degres C, whereas that in the other films was 2 days at 10 degrees C. Therefore, the shelf-life extension effect of the fresh-cut iceberg lettuce in BN/PE film packaging was very effective compared with the other films tested.     

Evidence of an antilisterial factor induced by wounding of iceberg lettuce tissues

AIMS: To examine the influence of wound-associated reactions in cut iceberg lettuce (Lactuca sativa L.) tissues on the fate of Listeria monocytogenes. METHODS AND RESULTS: Aqueous extracts prepared from shredded iceberg lettuce before and after storage in high oxygen permeability film were inoculated with L. monocytogenes. Listeria monocytogenes grew in extracts prepared from fresh lettuce. In contrast, inhibition ranging from arrested growth to a decline in cell viability was observed in extracts prepared from samples stored for 1-3 days. Similar behaviour was evident in lettuce shreds inoculated with 10(5) CFU g(-1)L. monocytogenes immediately after processing or after 3 days in storage. Heat treatment of the cut tissues at 47 degrees C for 3 min before storage diminished the inhibitory effect. CONCLUSIONS: The results provided evidence that an antilisterial factor or factors are released by wounded iceberg lettuce tissues. Antilisterial activity was mitigated by heat treatment of the lettuce. SIGNIFICANCE AND IMPACT OF STUDY: This study indicates that intrinsic factors associated with plant metabolism could play a significant role in the ecology of human pathogens in packaged horticultural products.     

Inactivation of Escherichia coli and Listeria monocytogenes on iceberg lettuce by dip wash treatments with organic acids

AIMS: To study and compare the efficacy of organic acids and chlorine dipping in inactivation of Escherichia coli and Listeria monocytogenes on fresh-cut iceberg lettuce. METHODS AND RESULTS: Fresh-cut iceberg lettuce leaves were inoculated with E. coli or L. monocytogenes. After inoculation, samples were stored at 4 degrees C for 24 h and dipped in organic acid or chlorine solutions for 2 and 5 min. E. coli and L. monocytogenes were enumerated on selective media. Treatment of fresh-cut iceberg lettuce with chlorine solution caused 1.0 and 2.0 log(10) CFU g(-1) reductions in the number of L. monocytogenes and E. coli, respectively. Maximum reduction for E. coli (about 2.0 log(10) CFU g(-1)) was obtained for samples dipped in lactic or citric acids while maximum reduction for L. monocytogenes (about 1.5 log(10) CFU g(-1)) was attained for samples dipped in lactic acid. CONCLUSIONS: Dipping of iceberg lettuce in 0.5% citric acid or 0.5% lactic acid solution for 2 min could be as effective as chlorine for reducing microbial populations on fresh-cut iceberg lettuce. SIGNIFICANCE AND IMPACT OF THE STUDY: Dipping in solutions containing organic acids is shown to be effective to reduce E. coli and L. monocytogenes on fresh-cut iceberg lettuce.     

Mild heat treatment of lettuce enhances growth of Listeria monocytogenes during subsequent storage at 5 degrees C or 15 degrees C

AIMS: The objective of this study was to determine the influence of mild heat treatment, storage temperature and storage time on the survival and growth of Listeria monocytogenes inoculated onto cut iceberg lettuce leaves. METHODS AND RESULTS: Before or after inoculation with L. monocytogenes, cut iceberg lettuce leaves were dipped in water (20 or 50 degrees C) containing or not 20 mg l(-1) chlorine, for 90 s, then stored at 5 degrees C for up to 18 days or 15 degrees C for up to 7 days. The presence of 20 mg l(-1) chlorine in the treatment water did not significantly (alpha=0.05) affect populations of the pathogen, regardless of other test parameters. The population of L. monocytogenes on lettuce treated at 50 degrees C steadily increased throughout storage at 5 degrees C for up to 18 days. At day 10 and thereafter, populations were 1.7-2.3 log10 cfu g(-1) higher on lettuce treated at 50 degrees C after inoculation compared with untreated lettuce or lettuce treated at 20 degrees C, regardless of chlorine treatment. The population of L. monocytogenes increased rapidly on lettuce stored at 15 degrees C. At 2 and 4 days, significantly higher populations were detected on lettuce that had been treated at 50 degrees C, compared with respective samples that had been treated at 20 degrees C, regardless of inoculation before or after treatment, or the presence of 20 mg l(-1) chlorine in the treatment water. CONCLUSIONS: The results clearly demonstrated that mild heat treatment of cut lettuce leaves enhances the growth of L. monocytogenes during subsequent storage at 5 or 15 degrees C. SIGNIFICANCE AND IMPACT OF THE STUDY: Mild heat treatment of cut lettuce may result in a prolonged shelf life as a result of delaying the development of brown discoloration. However, heat treatment also facilitates the growth of L. monocytogenes during storage at refrigeration temperature, thereby increasing the potential risk of causing listeriosis.     

Microbial and sensory quality of "Lollo verde" lettuce and rocket salad stored under active atmosphere packaging

Samples of fresh rocket “Eruca Sativa” were stored either alone or with the addition of lettuce “Lollo verde” leaves under two different atmosphere modifications (5% O₂ and 10% CO₂ for MAP A and 2% O₂ and 5% CO₂ for MAP B). Throughout the storage period of 10 days the microbial (mesophilic, psychrotrophic bacteria and Enterobacteriacae) populations, firmness, color and organoleptic parameters were monitored. Elevated CO₂ levels created by both atmosphere modifications inhibited mesophile and psychrophile growth (p < 0.05). Color was better maintained in MAP samples. Shelf life of rocket leaves was extended by 4 days under MAP A while mixed salads shelf life was limited to 9 days.     

Shelf life and safety aspects of chilled cooked and peeled shrimps (Pandalus borealis) in modified atmosphere packaging

AIMS: To evaluate the growth of Listeria monocytogenes and shelf life of cooked and peeled shrimps in modified atmosphere packaging (MAP). METHODS AND RESULTS: Storage trials with naturally contaminated cooked and peeled MAP shrimps (Pandalus borealis) were carried out at 2, 5 and 8 degrees C. Challenge tests at the same conditions were performed after inoculation with Listeria monocytogenes. Both storage trials and challenge tests were repeated after 4 months of frozen storage (-22 degrees C). Brochothrix thermosphacta and Carnobacterium maltaromaticum were responsible for sensory spoilage of cooked and peeled MAP shrimps. In challenge tests, growth of L. monocytogenes was observed at all of the storage temperatures studied. At 5 and 8 degrees C the concentration of L. monocytogenes increased more than a 1000-fold before the product became sensory spoiled whereas this was not observed at 2 degrees C. Frozen storage had only a minor inhibiting effect on growth of L. monocytogenes in the thawed product. CONCLUSIONS: To prevent L. monocytogenes becoming a safety problem, cooked and peeled MAP shrimps should be distributed at 2 degrees C and with a maximum shelf life of 20-21 d. At higher temperatures shelf life is significantly reduced. SIGNIFICANCE AND IMPACT OF THE STUDY: Information is provided to establish shelf life of cooked and peeled MAP shrimps.     

Behaviour of Listeria monocytogenes in packaged fresh mushrooms (Agaricus bisporus)

AIMS: The aim of this study was to evaluate the potential of Listeria monocytogenes to grow in mushrooms packaged in two different types of PVC films when stored at 4 degrees C and 10 degrees C. METHODS AND RESULTS: Mushrooms were packed in two polymeric films (perforated and nonperforated PVC) and stored at 4 degrees C and 10 degrees C. The carbon dioxide and oxygen content inside the packages, aerobic mesophiles, psychrotrophs, Pseudomonas spp., Listeria monocytogenes, faecal coliforms, Escherichia coli, anaerobic spores and major sensory factors were determined. The mushrooms packaged in nonperforated film and stored at 4 degrees C had the most desirable quality parameters (texture, development stage and absence of moulds). Listeria monocytogenes was able to grow at 4 degrees C and 10 degrees C in inoculated mushrooms packaged in perforated and nonperforated films between 1 and 2 log units during the first 48 h. After 10 d of storage, the populations of L. monocytogenes were higher in mushrooms packaged in nonperforated film and stored at 10 degrees C. CONCLUSIONS: MAP followed by storage at 4 degrees C or 10 degrees C extends the shelf life by maintaining an acceptable appearance, but allows the growth and survival of L. monocytogenes. SIGNIFICANCE AND IMPACT OF THE STUDY: According to this study additional hurdles must be studied in order to prevent the growth of L. monocytogenes.     

Quality of cut lettuce treated by heat shock: prevention of enzymatic browning, repression of phenylalanine ammonia-lyase activity, and improvement on sensory evaluation during storage

Stored cut lettuce gradually turns brown on the cut section after several days of storage, because cutting induces phenylalanine ammonia-lyase (PAL) activity, the biosynthesis of polyphenol is promoted, and the polyphenols are oxidized by polyphenol oxidase. Here, the effect of heat shock treatment at 50 degrees C for 90 s on the quality of cut lettuce during cold storage was examined. The heat shock treatment significantly repressed the induction of PAL activity and phenolics accumulation in cut lettuce during storage, and prevented the browning of cut lettuce. Ascorbic acid content was not affected by the heat shock treatment. The sensory analysis showed that the organoleptic quality of cut lettuce treated by heat shock was significantly better than that of the control cut lettuce. These results show that heat shock treatment is useful for prolonging the shelf life of cut lettuce.     

Determination of the shelf life of sliced cooked ham based on the growth of lactic acid bacteria in different steps of the chain

Aims: Development of a predictive model for the determination of the shelf life of modified atmosphere‐packed (MAP) cooked sliced ham in each step of the cold chain. Methods and Results: The growth of lactic acid bacteria (LAB), as well as the development of the total viable count and changes of sensory and pH value parameters in MAP cooked sliced ham, stored under different constant temperature conditions from 2 to 15°C was investigated. As a result of the measurements, the end of the shelf life could be considered as the time when LAB reach more than 7 log₁₀ CFU g^?1. Different primary and secondary models were tested and analysed to find the best way to calculate the shelf life. For primary modelling, the modified Gompertz Function and the modified Logistic Function were compared. There was no substantial difference between either model. The effect of temperature on the growth rate was modelled by using the Arrhenius and the Square root model, whereas the Arrhenius equation gave a better result. A combination of the primary and secondary model was used for shelf‐life prediction under dynamic conditions. This combination showed the best prediction of microbial counts using the modified Logistic model and the Arrhenius equation. Conclusions: With the developed model, it is possible to predict the shelf life of MAP cooked sliced ham based on the growth of LAB under different temperature conditions. Significance and Impact of the Study: The developed model can be used to calculate the remaining shelf life in different steps of the chain. Thus, it can deliver an important contribution to improve food quality by optimizing the storage management.     

Reducing CO2 accumulation and its phytotoxicity to lettuce with absorbent in hermetic storage as a simulation of long-term fumigation

Long-term fumigation with pure phosphine at low-temperature injures lettuce and the injury is likely caused by a potential accumulation of CO₂. In this study, iceberg and romaine lettuce were stored hermetically in fumigation chambers with and without absorbents for CO₂ and ethylene for 3 days at 2 ºC as a simulation of long-term fumigation to determine the effects of the absorbents on accumulations of CO₂ and ethylene and postharvest quality of lettuce. In the absence of absorbents, CO₂ level increased from 0.08% at the start to 3.36% at the end of the 3-day hermetic storage. No accumulation of ethylene was detected. Hermetic storage resulted in significant CO₂ injuries to both iceberg and romaine lettuce and quality degradation as compared with the controls at 14 days after treatment. In the storage with absorbents, the CO₂ level remained low throughout the storage and ethylene was undetectable, and the CO₂ injury level was the same or lower than the control. Lettuce quality scores were either the same or better than lettuce in the control. Our findings suggest that the accumulation of CO₂ alone caused injuries associated with long-term phosphine fumigation and CO₂ absorbent has the potential to prevent such injuries.     

Microbial spoilage and formation of biogenic amines in fresh and thawed modified atmosphere-packed salmon (Salmo salar) at 2 degrees C

AIMS: To evaluate the microbial spoilage, formation of biogenic amines and shelf life of chilled fresh and frozen/thawed salmon packed in a modified atmosphere and stored at 2 degrees C. METHODS AND RESULTS: The dominating microflora, formation of biogenic amines and shelf life were studied in two series of storage trials with naturally contaminated fresh and thawed modified atmosphere-packed (MAP) salmon at 2 degrees C. Photobacterium phosphoreum dominated the spoilage microflora of fresh MAP salmon at more than 10(6) cfu g(-1) and the activity of this specific spoilage organism (SSO) limited the shelf life of the product to ca 14 and 21 d in the two experiments. Despite the high levels of P. phosphoreum, less than 20 mg kg(-1) histamine was observed in fresh MAP salmon prior to sensory spoilage. Freezing eliminated P. phosphoreum and extended the shelf life of MAP salmon at 2 degrees C by 1-2 weeks. Carnobacterium piscicola dominated the spoilage microflora of thawed MAP salmon and probably produced the ca 40 mg kg(-1) tyramine detected in this product at the end of its shelf life. CONCLUSIONS: Photobacterium phosphoreum dominated the spoilage microflora of fresh MAP salmon but produced only small amounts of biogenic amines in this product. The elimination of P. phosphoreum by freezing allowed this bacteria to be identified as the SSO in fresh MAP salmon. SIGNIFICANCE AND IMPACT OF THE STUDY: The identification of P. phosphoreum as the SSO in fresh MAP salmon facilitates the development of methods to determine and predict the shelf life of this product, as previously shown with fresh MAP cod.     

A combination of chitosan,coating and modified atmosphere packaging for prolonging Fior di latte cheese shelf life

In this work, the addition of chitosan into cheese making, combined with either coating or active coating (lysozyme and ethylenediamine tetraacetic acid, disodium salt) and MAP (modified atmosphere packaging) was used to prolong the shelf life of “Fior di latte” cheese. On the packaged cheese stored at 4 °C microbiological, pH, gas composition and sensory changes were monitored over an 8-day period. Results showed that the combination of chitosan, active coating and MAP improved “Fior di latte” cheese preservation by increasing the shelf life in comparison with the traditional packaging. In fact, the latter showed a very short shelf life limited to more or less 1 day, whereas the integrated approach developed in this study allowed us to obtain a significant shelf life prolongation to 5 days, most probably due to the synergic effect between the active compounds and the atmospheric conditions in the package headspace.     

Microbiological, biochemical and sensory assessment of mussels (Mytilus galloprovincialis) stored under modified atmosphere packaging

AIMS: To determine the microbiological, biochemical and sensory changes of mussels during storage under aerobic, vacuum packaging (VP) and modified atmosphere packaging (MAP) conditions at 4 degrees C, and to determine shelf-life of mussels under the same packaging conditions using the above assessment parameters. METHODS AND RESULTS: Aqua-cultured mussels (Mytilus galloprovincialis) were obtained from a local culture farm, packaged aerobically under VP and MAP (50%/50% CO2/N2: M1, 80%/20% CO2/N2: M2, 40%/30%/30% CO2/N2/O2: M3), and stored at 4 degrees C. Quality evaluation was carried out using microbiological, chemical and sensory analyses. Microbiological results revealed that the M2 and VP delayed microbial growth compared with that of air-packaged samples. The effect was more pronounced for total viable count (TVC), Pseudomonas spp., lactic acid bacteria (LAB) and H2S-producing bacteria. TVC was reduced by 0.9-1.0, Pseudomonas spp. by 0.7-0.8, LAB by 1.0-2.2, H2S-producing bacteria by 0.7-1.2. Enterobacteriaceae were not significantly affected by MAP conditions. Of the chemical indices determined, the total volatile basic nitrogen and trimethylamine nitrogen values remained lower than the proposed acceptability limits of 35 mg N 100 g(-1) and 12 mg N 100 g(-1), respectively, after 15 days of storage. Both the VP and air-packaged mussel samples exceeded these limits. The thiobarbituric acid value of all MAP and VP mussels remained lower than the proposed acceptability limit of 1 mg malondialdehyde kg(-1). The air-packaged samples exceeded this limit. All samples retained desirable sensory characteristics during the first 8 days of storage. CONCLUSIONS: Based on odour and taste evaluation, the M1 and M3 samples remained acceptable until ca day 11-12, the M2 samples remained acceptable until ca day 14-15 days while the VP and air-packaged mussel samples remained acceptable until ca days 10-11 and 8-9 of storage respectively. Based primarily on sensory, but also on biochemical and microbiological parameters determined, M2 gas mixture was the most effective for mussel preservation achieving a shelf-life of ca 14-15 days. SIGNIFICANCE AND IMPACT OF THE STUDY: MAP (M2) can be used to increase the shelf-life of refrigerated mussels. A shelf-life extension of refrigerated mussels by ca 5-6 days under MAP may be obtained.     

FRESH-CUT ANNURCA APPLES: ACCEPTABILITY STUDY AND SHELF-LIFE DETERMINATION

To establish the likelihood of purchase and acceptability level of new fresh-cut apples, the responses of two categories of consumers, children and adults, were evaluated. The effect of storage time on acceptability was investigated and the shelf life of fresh-cut apples was determined by using a Weibull hazard model.
The samples were distributed at different storage time (from second to fifth day) at the Science Museum of Naples as part of an educational program for children to evaluate the likelihood of buying and the acceptability level of the product. The data were collected over 5 weeks, and the test was performed in 2,421 children and 224 adults. The product was distributed at the University of Naples at different storage time (time 0 to 10 days) to perform the Weibull test using 63 consumers.
The adults and children appreciated the product, and the adults were generally willing to buy it. The Weibull analysis proved an appropriate method to evaluate product shelf life, which was estimated at 7.5 days at 4C.

PRACTICAL APPLICATIONS

This study contributes to enhance the competitiveness of a traditional food as Protected Geographical Indication Annurca apples. In fact, an attractive way to improve the consumption of this variety of apple is to market it as a ready-to-eat product. Also, the research allows for a better understanding of the children's acceptability level of new fresh-cut apples in order to improve the intake of apples among primary schoolchildren. In fact, an interesting way to increase the children's consumption of fruit is to distribute it at school level and also to increase the convenience for children. Finally, the fact that the product was distributed to the Science Museum of Naples can be considered as a premarket test for a new product launch.     

Longevity of cryogenically stored seeds

Though cryogenic storage is presumed to provide nearly infinite longevity to cells, the actual shelf life achieved under ultra-cold temperatures has not been addressed theoretically or empirically. Here, we report measurable changes in germination of dried seeds stored under liquid nitrogen conditions for >10 years. There was considerable variability in the extent of deterioration among species and accessions within a species. Aging time courses for lettuce seeds stored at temperatures between 50 and -196 degrees C were fit to a form of the Avrami equation to determine rate coefficients and predict half-life of accessions. A reduction in the temperature dependency on aging rate, determined as a break in the Arrhenius plot, occurred at about -15 degrees C, and this resulted in faster deterioration than anticipated from extrapolation of kinetics measured at higher temperatures. The break in Arrhenius behavior occurred at temperatures in between the glass transition temperature (28 degrees C) and the Kauzmann temperature (-42 degrees C) and also coincided with a major triacylglycerol phase change (-40 to -7 degrees C). In spite of the faster than anticipated deterioration, cryogenic storage clearly prolonged shelf life of lettuce seeds with half-lives projected as approximately 500 and approximately 3400 years for fresh lettuce seeds stored in the vapor and liquid phases of liquid nitrogen, respectively. The benefit of low temperature storage (-18 or -135 degrees C) on seed longevity was progressively lost if seeds were first stored at 5 degrees C. Collectively, these results demonstrate that lowering storage temperature progressively increases longevity of seeds. However, cryogenic temperatures were not sufficient to stop deterioration, especially if initial stages of aging were allowed to progress at higher storage temperatures. This work contributes to reliable assessments of the potential benefit and cost of different genebanking strategies.     

Bacteriological quality and shelf life of ground beef.

The bacteriological quality of unfrozen raw ground beef was evaluated after 0, 3, 6, 9, 12, 15, and 18 days of storage at 29 +/- 1 F (-1.7 +/- 0.6 C). At the time of fabrication, all of the ground beef samples contained 10(6) or fewer total aerobic and psychrotrophic bacteria/g; 81% contained 100 or fewer coliforms/g; 94% contained 100 or fewer Escherichia coli/g; and all of the samples contained 100 or fewer coagulase-positive Staphylococcus aureus and Clostridium perfringens/g. Total aerobic and psychrotrophic bacteria increased by 1 log between 3 and 18 days of storage. Coliform and E. coli counts decreased during storage, whereas coagulase-positive S. aureus and C. perfringens counts did not change significantly. These data indicate that meat processors, wholesalers, and retailers could improve the bacteriological quality and prolong the shelf life of ground beef packaged in oxygen-impermeable film if the temperature of product never exceeded 29 +/- 1 F (-1.7 +/- 0.6 C).     

Monitoring of microbial metabolites and bacterial diversity in beef stored under different packaging conditions

Beef chops were stored at 4°C under different conditions: in air (A), modified-atmosphere packaging (MAP), vacuum packaging (V), or bacteriocin-activated antimicrobial packaging (AV). After 0 to 45 days of storage, analyses were performed to determine loads of spoilage microorganisms, microbial metabolites (by solid-phase microextraction [SPME]-gas chromatography [GC]-mass spectrometry [MS] and proton nuclear magnetic resonance [(1)H NMR]), and microbial diversity (by PCR-denaturing gradient gel electrophoresis [DGGE] and pyrosequencing). The microbiological shelf life of meat increased with increasing selectivity of storage conditions. Culture-independent analysis by pyrosequencing of DNA extracted directly from meat showed that Brochothrix thermosphacta dominated during the early stages of storage in A and MAP, while Pseudomonas spp. took over during further storage in A. Many different bacteria, several of which are usually associated with soil rather than meat, were identified in V and AV; however, lactic acid bacteria (LAB) dominated during the late phases of storage, and Carnobacterium divergens was the most frequent microorganism in AV. Among the volatile metabolites, butanoic acid was associated with the growth of LAB under V and AV storage conditions, while acetoin was related to the other spoilage microbial groups and storage conditions. (1)H NMR analysis showed that storage in air was associated with decreases in lactate, glycogen, IMP, and ADP levels and with selective increases in levels of 3-methylindole, betaine, creatine, and other amino acids. The meat microbiota is significantly affected by storage conditions, and its changes during storage determine complex shifts in the metabolites produced, with a potential impact on meat quality.     

Bacteriological quality and shelf life of ground beef.

The bacteriological quality of unfrozen raw ground beef was evaluated after 0, 3, 6, 9, 12, 15, and 18 days of storage at 29 +/- 1 F (-1.7 +/- 0.6 C). At the time of fabrication, all of the ground beef samples contained 10(6) or fewer total aerobic and psychrotrophic bacteria/g; 81% contained 100 or fewer coliforms/g; 94% contained 100 or fewer Escherichia coli/g; and all of the samples contained 100 or fewer coagulase-positive Staphylococcus aureus and Clostridium perfringens/g. Total aerobic and psychrotrophic bacteria increased by 1 log between 3 and 18 days of storage. Coliform and E. coli counts decreased during storage, whereas coagulase-positive S. aureus and C. perfringens counts did not change significantly. These data indicate that meat processors, wholesalers, and retailers could improve the bacteriological quality and prolong the shelf life of ground beef packaged in oxygen-impermeable film if the temperature of product never exceeded 29 +/- 1 F (-1.7 +/- 0.6 C).     

Effect of various gas atmospheres on the growth and survival of Campylobacter jejuni on beef

Pieces of fresh beef were inoculated with three strains of Campylobacter jejuni . The meat was then allocated to three treatments: (a) vacuum packaged, (b) packaged in an atmosphere of 20% CO₂+ 80% N₂, and (c) packaged into sterile Petri dishes in anaerobic cultivation boxes, which were filled with a gas mixture of 5% O₂+ 10% CO₂+ 85% N₂. The packaging material in the first two treatments was PA 80/PE 100–PE 100/PA 80/PE 100. The survival of Campylobacter cells was followed at 37°C, 20°C and 4°C for 48 h, 4 days and 25 days, respectively. At 37°C the counts of two Campylobacter strains increased in each package treatment for 48 h. At 20°C and at 4°C the counts of the same two strains decreased by 1 to 2 log units and 0.5 to 1 log unit, respectively, during storage. The survival of the two strains was about the same in all package treatments. The third strain was the most sensitive of the strains studied. At 37°C its numbers increased only in the optimal gas atmosphere; at 20°C the strain was not detectable after 24 to 48 h storage and at 4°C after 4 days storage. The aerobic plate counts were determined for all samples at the same time as Campylobacter counts. The high indigenous bacterial numbers of the meat samples did not appear to have a great effect on the survival or growth of campylobacters.     

Evaluating extraction and storage of a recombinant protein produced in agroinfiltrated lettuce

Extraction and storage of a recombinant protein produced by transient expression following agroinfiltration of lettuce were investigated. Lettuce leaves expressing beta-glucuronidase (GUS) were extracted by homogenization in several buffer combinations, and the yield and stability were assessed. The reducing agent dithiothreitol (DTT) was found to be the most important (significant) component in the extraction buffer. An extraction buffer consisting of 50 mM sodium phosphate at pH 7.0 with 10 mM DTT produced a good yield and stabilized GUS. Leaching of GUS through intact agroinfiltrated lettuce leaves was determined to be infeasible, with a maximum flux of 10 microg GUS/h/m2 and recovery of 1.7% of the GUS content in 24 h. Freeze-drying was evaluated as a method to extend the shelf life of the perishable leaf material containing GUS. First- and second-order kinetic models and the Weibull distribution were compared to describe inactivation of GUS in the freeze-dried leaves and leaf extracts. The first-order model best fit the inactivation data. An Arrhenius model fit the first-order inactivation data with respect to temperature with R2 = 1.00. Freeze-drying the lettuce leaves extended the estimated half-life of GUS to 69 days at 21 degrees C versus 11 days at 4 degrees C for fresh lettuce.