Ultrasonication enhanced low concentration electrolyzed water efficacy on bacteria inactivation and shelf life extension on lettuce

Effect of ultrasonication (40 kHz) to enhance low concentration electrolyzed water (LcEW) efficacy for microbial decontamination on lettuce leaves was investigated. Lettuce was separately treated with LcEW, ultrasonication, LcEW combined with ultrasonication, LcEW followed by ultrasonication, and ultrasonication followed by LcEW for 1, 3, and 5 min for each step at room temperature. The highest reduction (2.3 log CFU/g) in total bacteria count (TBC) was resulted from ultrasonication followed by LcEW. Subsequently, the effect of temperature was studied resulting in 2.6 and 3.18 log CFU/g reduction of TBC and Escherichia coli O157:H7 respectively, in 3 min ultrasonication followed by 3 min LcEW treatment at 40°C. This optimum treatment also prevented lettuce from reaching 7.0 log CFU/g in TBC until the end of the 6 day storage at 10°C. Therefore, this newly developed approach may result in improved microbiological safety and enhanced shelf life of produce.     

Effect of warm,chlorinated water on the microbial flora of shredded iceberg lettuce

An optimization technique was used to determine suitable times of exposure and temperatures for maximum destruction of microorganisms in shredded iceberg lettuce dipped in warm, chlorinated (100 μg/ml) water in a model system. Shredded lettuce washed for 3 min at 47°C and packaged in high oxygen transmission rate (6000–8000 cc m² 24 h) bags maintained an acceptable appearance after 7 days in storage at 1±1°C. Initial microbial loads were reduced by approximately 3 log cfu g⁻¹ in lettuce washed in chlorinated water at 47°C, and 1 log cfu g⁻¹ at 4°C. Pilot plant scale studies confirmed observations in the model system. The microbial flora of shredded lettuce packaged in the raw state and after a 3 min wash in 100 g ml⁻¹ chlorine at 4 or 47°C was dominated by psychrotrophic bacteria, particularly species of Pseudomonas, throughout the storage period. Numbers of these microorganisms were significantly lower than in raw lettuce or lettuce washed at 4°C until the 15th day in storage. Gas composition inside the bags was not affected by the washes.     

Antilisterial Properties of Marinades during Refrigerated Storage and Microwave Oven Reheating against Post‐Cooking Inoculated Chicken Breast Meat

This study evaluated growth of Listeria monocytogenes inoculated on cooked chicken meat with different marinades and survival of the pathogen as affected by microwave oven reheating. During aerobic storage at 7 °C, on days 0, 1, 2, 4, and 7, samples were reheated by microwave oven (1100 W) for 45 or 90 s and analyzed microbiologically. L. monocytogenes counts on nonmarinated (control) samples increased (P < 0.05) from 2.7 ± 0.1 (day‐0) to 6.9 ± 0.1 (day‐7) log CFU/g during storage. Initial (day‐0) pathogen counts of marinated samples were <0.5 log CFU/g lower than those of the control, irrespective of marinating treatment. At 7 d of storage, pathogen levels on samples marinated with tomato juice were not different (P ≥ 0.05; 6.9 ± 0.1 log CFU/g) from those of the control, whereas for samples treated with the remaining marinades, pathogen counts were 0.7 (soy sauce) to 2.0 (lemon juice) log CFU/g lower (P < 0.05) than those of the control. Microwave oven reheating reduced L. monocytogenes counts by 1.9 to 4.1 (45 s) and >2.4 to 5.0 (90 s) log CFU/g. With similar trends across different marinates, the high levels of L. monocytogenes survivors found after microwave reheating, especially after storage for more than 2 d, indicate that length of storage and reheating time need to be considered for safe consumption of leftover cooked chicken.     

Effects of Frozen Storage on Survival of Staphylococcus aureus and Enterotoxin Production in Precooked Tuna Meat

This study investigated the survival of Staphylococcus aureus in precooked tuna meat for producing canned products during frozen storage (?20 ± 2 °C) as well as its growth and enterotoxin production at 35 to 37 °C after the storage. Samples (50 ± 5 g) of precooked albacore (loin, chunk, and flake) and skipjack (chunk and flake) tuna were inoculated with 5 enterotoxin‐producing strains of S. aureus at a level of approximately 3.5 log CFU/g and individually packed in a vacuum bag after 3 h incubation at 35 to 37 °C. Vacuum‐packed samples were stored in a freezer (?20 ± 2 °C) for 4 wk. The frozen samples were then thawed in 37 °C circulating water for 2 h and incubated at 35 to 37 °C for 22 h. Populations of S. aureus in all precooked tuna samples decreased slightly (<0.7 log CFU/g) after 4 wk of storage at ?20 ± 2 °C, but increased rapidly once the samples were thawed and held at 35 to 37 °C. Total S. aureus counts in albacore and skipjack samples increased by greater than 3 log CFU/g after 6 and 8 h of exposure to 35 to 37 °C, respectively. All samples became spoiled after 10 h of exposure to 35 to 37 °C, while no enterotoxin was detected in any samples. However, enterotoxins were detected in albacore loin and other samples after 12 and 24 h of incubation at 35 to 37 °C, respectively. Frozen precooked tuna meat should be used for producing canned tuna within 6 to 8 h of thawing to avoid product spoilage and potential enterotoxin production by S. aureus in contaminated precooked tuna meat.     

Evaluation of Changes in Listeria monocytogenes Populations on Frankfurters at Different Stages from Manufacturing to Consumption

ABSTRACT: This study evaluated the fate of inoculated Listeria monocytogenes on frankfurters stored under conditions simulating those that may be encountered between manufacturing and consumption. Frankfurters with or without 1.5% potassium lactate and 0.1% sodium diacetate (PL/SD) were inoculated (1.8 ± 0.1 log CFU/cm²) with a 10‐strain composite of L. monocytogenes, vacuum‐packaged, and stored under conditions simulating predistribution storage (24 h, 4 °C), temperature abuse during transportation (7 h, 7 °C followed by 7 h, 12 °C), and storage before purchase (60 d, 4 °C; SBP). At 0, 20, 40, and 60 d of SBP, samples were exposed to conditions simulating delivery from stores to homes or food establishments (3 h, 23 °C), and then opened or held vacuum‐packaged at 4 or 7 °C for 14 d (SHF). Pathogen counts remained relatively constant on frankfurters with PL/SD regardless of product age and storage conditions; however, they increased on product without antimicrobials. In vacuum‐packaged samples, during SHF at 4 °C, the pathogen grew faster (P < 0.05) on older product (20 d of SBP) compared to product that was fresh (0 d of SBP); a similar trend was observed in opened packages. At 7 °C, the fastest growth (0.35 ± 0.02 log CFU/cm²/d) was observed on fresh product in opened packages; in vacuum‐packages, growth rates on fresh and aged products were similar. By day 40 of SBP the pathogen reached high numbers and increased slowly or remained unchanged during SHF. This information may be valuable in L. monocytogenes risk assessments and in development of guidelines for storage of frankfurters between package opening and product consumption.     

MICROBIAL QUALITY OF FRESH‐CUT ICEBERG LETTUCE WASHED IN WARM OR COLD WATER AND IRRADIATED IN A MODIFIED ATMOSPHERE PACKAGE*

ABSTRACT

The microbial keeping quality of fresh‐cut iceberg lettuce was determined after being washed in either cold water (5C) for 3 min or warm water (47C) for 2 min followed by a cold water rinse (5C) and packaged in a modified atmosphere film bag. The lettuce samples were treated with gamma radiation to 0, 1 or 2 kGy while maintaining a refrigerated temperature (4C). The samples were analyzed for total aerobic, total coliform and Enterobacteriaceae counts after refrigerated storage up to 12 days. No difference in aerobic counts was observed between the hot‐ and cold‐washed samples immediately after washing. The coliform and Enterobacteriaceae counts were reduced by 2 log after the warm water wash and no difference for the cold water‐washed sample. The irradiation treatment at 1 kGy reduced the aerobic, coliform and Enterobacteriaceae counts by 2 log for the warm‐washed samples. At the 2‐kGy treatment level, the aerobic and coliform counts were reduced by 3 log for the cold‐washed lettuce, whereas the Enterobacteriaceae counts were reduced by only 2 log. The observed log reductions in bacterial counts after irradiation were maintained for 12 days when stored at 4C. The combination of a cold water wash and irradiation to 2 kGy had the best microbial keeping quality.

PRACTICAL APPLICATIONS

Fresh‐cut lettuce, when washed in either cold or warm water, shows neither an appreciable removal of the microbial load nor a significant increase in the keeping quality when compared with unwashed fresh‐cut controls. Placing the washed lettuce into modified atmosphere packaging (MAP) did not lessen the overall bacteriologic load, and after 12 days of storage at 4C, the microbial counts increased. However, gamma irradiation of the washed, MAP‐stored lettuce to a dose of 2 kGy significantly reduces the overall microbe count, thereby increasing both the shelf life and the safety of the produce. A 2‐kGy dose of gamma irradiation provides a pathogen‐free, long shelf life, fresh‐cut lettuce that is bacteriologically safer and sensorially indistinguishable from bagged, nonirradiated, fresh‐cut lettuce.     

Effects of Soaking with Natural Additives in Combinations with Vacuum or Modified Atmosphere Packaging on Microbial Populations and Shelf Life of Fresh Truffles (Chinese Tuber Indicum)

The objective of this study was to evaluate the relative effects and interactions of combined soaking treatment using citric acid (CTA) and apple polyphenol (APP) at mild heating temperatures for the inactivation of the external and internal microflora (mesophilic aerobic bacteria, mesophilic anaerobic bacteria, and fungi) in Chinese Tuber indicum, as well as to analyze the microbiological and sensory changes under modified atmosphere packaging (MAP)‐ and vacuum atmosphere packaging (VAC)‐packed Chinese T. indicum stored at 4 °C for up to 55 d. Chinese T. indicum was soaked with CTA and APP alone or in combination for 10, 20, and 30 min at 35, 45, and 55 °C. A disinfection method using CTA and APP (3% CTA + 3% APP for 20 min at 45 °C) was obtained. Under this set of combination, the experimental values of microbial counts of mesophilic aerobic bacteria, mesophilic anaerobic bacteria, and fungi were 2.31 ± 0.4 log CFU/g, <1.0 log CFU/g, and <1.0 log CFU/g, respectively. Through the analysis of sensory qualities and microbial populations for MAP‐ or VAC‐packed Chinese T. indicum, the shelf life of soaked truffles was prolonged to 45 or 40 d, respectively. The synergistic effect of CTA and APP may provide valuable insight into the reduction of microorganisms on fresh truffles.     

Soluble protein content in minimally processed vegetables during storage

Soluble protein content (SPC) and electrophoretic protein profile in minimally processed broccoli, Dutch carrot and Cos lettuce were determined after 0, 3, 5, 7, 10 and 12 days of storage at 12 °C and 95±2% relative humidity. An increase in SPC in broccoli tissues (florets, stems and whole) was observed on day 3, followed by a slight fluctuation thereafter. Similar observations were recorded in shredded carrot, which showed a significant (P<0.05) increase in SPC after 3 days at 12 °C. However, changes in SPC in Cos lettuce were different from broccoli and carrot, and showed a significant (P<0.05) decrease after 3 days. The SDS-PAGE profile revealed a continuous decrease in the band intensity of soluble proteins from broccoli, Dutch carrot and Cos lettuce throughout the storage period. Complete disappearance of some bands was observed in Cos lettuce leaves and shredded carrot after 12 days of storage at 12 °C.     

Effect of Single‐ and Two‐Cycle High Hydrostatic Pressure Treatments on Water Properties,Physicochemical and Microbial Qualities of Minimally Processed Squids (Todarodes pacificus)

This study investigated the effect of single‐ and two‐cycle high hydrostatic pressure (HHP) treatments on water properties, physicochemical, and microbial qualities of squids (Todarodes pacificus) during 4 °C storage for up to 10 d. Single‐cycle treatments were applied at 200, 400, or 600 MPa for 20 min (S‐200, S‐400, and S‐600), and two‐cycle treatments consisted of two 10 min cycles at 200, 400, or 600 MPa, respectively (T‐200, T‐400, and T‐600). HHP‐treated samples had higher (P < 0.05) content of P_2b (immobilized water) and P₂₁ (myofibril water), but lower P₂₂ (free water) than those of control. The single‐ and two‐cycle HHP treatments at the same pressure level caused no significant difference in water state of squids. The two‐cycle HHP treatment was more effective in controlling total volatile basic nitrogen, pH, and total plate counts (TPC) of squids during storage, in which TPC of S‐600 and T‐600 was 2.9 and 1.8 log CFU/g at 10 d, respectively, compared with 7.5 log CFU/g in control. HHP treatments delayed browning discoloration of the squids during storage, and the higher pressure level and two‐cycle HHP were more effective. Water properties highly corresponded with color and texture indices of squids. This study demonstrated that the two‐cycle HHP treatment was more effective in controlling microbial growth and quality deterioration while having similar impact on the physicochemical and water properties of squids in comparison with the single‐cycle treatment, thus more desirable for extending shelf‐life of fresh squids.     

Pathogen Reduction and Quality of Lettuce Treated with Electrolyzed Oxidizing and Acidified Chlorinated Water

ABSTRACT: The efficacy of electrolyzed oxidizing (EO) and acidified chlorinated water (45 ppm residual chlorine) was evaluated in killing Escherichia coli O157:H7 and Listeria monocytogenes on lettuce. After surface inoculation, each leaf was immersed in 1.5 L of EO or acidified chlorinated water for 1 or 3 min at 22 °C. Compared to a water wash only, the EO water washes significantly decreased mean populations of E. coli O157:H7 and L. monocytogenes by 2.41 and 2.65 log10 CFU per lettuce leaf for 3 min treatments, respectively (p < 0.05). However, the difference between the bactericidal activity of EO and acidified chlorinated waters was not significant (p > 0.05). Change in the quality of lettuce subjected to the different wash treatments was not significant at the end of 2 wk of storage.     

Changes in appearance and natural microflora on iceberg lettuce treated in warm,chlorinated water and then stored at refrigeration temperature

The objective of this study was to determine the effect of warm, chlorinated water on the survival and subsequent growth of naturally occurring microorganisms and visual quality of fresh-cut iceberg lettuce. After dipping cut lettuce leaves in water containing 20 mg l⁻¹free chlorine for 90 s at 50°C, samples were stored at 5 or 15°C for up to 18 or 7 days, respectively. Populations of aerobic mesophiles, psychrotrophs, Enterobacteriaceae, lactic acid bacteria, and yeasts and molds were determined. The visual appearance and development of brown discoloration were monitored. Treatment of lettuce in warm (50°C) chlorinated water delayed browning of lettuce. Shelf life of lettuce stored at 5°C, as determined by subjective evaluation of color and general appearance, was about 5 days longer than that of lettuce stored at 15°C. Treatment in warm (50°) water, with or without 20 mg l⁻¹chlorine, and in chlorinated water at 20°C significantly (α= 0·05) reduced the initial population of mesophilic aerobic microflora by 1·73–1·96 log₁₀cfu g⁻¹. Populations increased, regardless of treatment, as storage time at 5°C and 15°C increased. The same trends were observed in populations of psychrotrophs and Enterobacteriaceae. Yeast populations increased slightly in lettuce stored at 5°C but were consistently about 3 logs lower than mesophilic aerobes. Populations of molds and lactic acid bacteria were less than 2 log₁₀cfu g⁻¹throughout storage at 5 or 15°C. Results suggest that heat (50°C) treatment may have delayed browning and reduced initial populations of some groups of micro-organisms naturally occurring on iceberg lettuce, but enhanced microbial growth during subsequent storage.     

Determination of Spoilage Microbiota of Pacific White Shrimp During Ambient and Cold Storage Using Next‐Generation Sequencing and Culture‐Dependent Method

This study was conducted to determine the initial and spoilage microbiota of Pacific white shrimp during ambient and cold storage using next‐generation sequencing (NGS) and a culture‐dependent method. The quality changes were also evaluated by sensory analysis and total volatile basic nitrogen (TVB‐N) values. After 1 d of storage, the psychrotrophic bacteria were only 5.97 log CFU/g, accounting for 1.1% of the mesophilic bacteria counts (7.94 log CFU/g). The psychrotrophic bacteria counts exceeded the counts of mesophilic bacteria for shrimp stored at 4 °C after 6 d of storage, indicating that psychrotrophic bacteria became predominant. The NGS was used to identify the bacterial species in samples stored at 25 and 4 °C. The results showed that the dominant microorganisms were Vibrio at 25 °C, and Acinetobacter, Psychrobacter, and Shewanella at 4 °C. By the culture‐dependent method based on 16S rRNA gene and VITEK®2 CompactA system, it showed that the dominant microorganisms were Proteus spp. at 25 °C, and Shewanella putrefaciens, Acinetobacter johnsonii, and Aeromonas sobria at 4 °C. In conclusion, differences in results of microbiota analyzed by culture dependent and independent approaches were observed. The combination of both methodologies may provide more comprehensive information about the dominant spoilage microbiota in Pacific white shrimp during ambient and cold storage.     

Evaluation of Shelf Life of Superchilled Cod (Gadus morhua) Fillets and the Influence of Temperature Fluctuations During Storage on Microbial and Chemical Quality Indicators

Quality changes of aerobically packed cod fillets stored under superchilling and abusive temperature conditions were characterized by the growth of specific spoilage organisms (SSO) and the production of microbial metabolites measured by an electronic nose along with traditional sensory and chemical analysis (total volatile basic nitrogen [TVB‐N], pH). A new process based on quick contact freezing and cold air blasting was used to achieve superchilling of fillets before chilled (0.5 °C) or superchilled (‐1.5 °C) storage. Photobacterium phosphoreum dominated under temperature abusive conditions coinciding with high levels of TVB‐N and increased electronic nose responses indicating increased levels of alcohols and aldehydes at sensory rejection. Dominating growth of Pseudomonas spp. in 1 batch was associated with the origin, the catching method, and the cooling conditions during processing. The superchilling process followed by superchilled storage (‐1.5 °C) extended the sensory shelf life of the fillets for at least 3 d compared with traditional process, resulting in a total shelf life of 15 d. High content of TVB‐N was observed in superchilled fillets at sensory rejection. P. phosphoreum counts were lower under superchilling conditions (6.0 to 6.8 log colony‐forming units [CFU]/g), compared with the traditionally processed chilled fillets (7.2 log CFU/g). However, H₂S‐producing bacteria appeared to grow steadily under superchilling conditions reaching counts as high as 7.6 log CFU/g at sensory rejection.     

Effect of Hops Beta Acids on the Survival of Unstressed‐ or Acid‐Stress‐Adapted‐Listeria Monocytogenes and on the Quality and Sensory Attributes of Commercially Cured Ham Slices

This study evaluated the antilisterial activity of hops beta acids (HBA) and their impact on the quality and sensory attributes of ham. Commercially cured ham slices were inoculated with unstressed‐ and acid‐stress‐adapted (ASA)‐L. monocytogenes (2.2 to 2.5 log CFU/cm²), followed by no dipping (control), dipping in deionized (DI) water, or dipping in a 0.11% HBA solution. This was followed by vacuum or aerobic packaging and storage (7.2 °C, 35 or 20 d). Samples were taken periodically during storage to check for pH changes and analyze the microbial populations. Color measurements were obtained by dipping noninoculated ham slices in a 0.11% HBA solution, followed by vacuum packaging and storage (4.0 °C, 42 d). Sensory evaluations were performed on ham slices treated with 0.05% to 0.23% HBA solutions, followed by vacuum packaging and storage (4.0 °C, 30 d). HBA caused immediate reductions of 1.2 to 1.5 log CFU/cm² (P < 0.05) in unstressed‐ and ASA‐L. monocytogenes populations on ham slices. During storage, the unstressed‐L. monocytogenes populations on HBA‐treated samples were 0.5 to 2.0 log CFU/cm² lower (P < 0.05) than control samples and those dipped in DI water. The lag‐phase of the unstressed‐L. monocytogenes population was extended from 3.396 to 7.125 d (control) to 7.194 to 10.920 d in the HBA‐treated samples. However, the ASA‐L. monocytogenes population showed resistance to HBA because they had a higher growth rate than control samples and had similar growth variables to DI water‐treated samples during storage. Dipping in HBA solution did not adversely affect the color or sensory attributes of the ham slices stored in vacuum packages. These results are useful for helping ready‐to‐eat meat processors develop operational procedures for applying HBA on ham slices.     

Microbiological hazards involved in fresh‐cut lettuce processing

BACKGROUND: The increasing consumption of produce all over the world has resulted in increasing concern by the regulatory agencies with respect to the level of safety performed by the processors. The objective of the present study was to investigate the hazards involved in the various steps of fresh‐cut lettuce processing (reception/selection of raw material, washing, rinsing, sanitisation and final product) by means of microbiological analyses of microbial groups used as indicators of hygienic conditions and of pathogens. RESULTS: High microbial loads of mesophilic and psychrotrophic bacteria and Pseudomonas spp. were found in the ram reception (～6 log colony‐forming units (CFU) g^?1), which were reduced by a single logarithmic cycle for the last two microbial groups after the sanitisation step (P < 0.05), the latter being ineffective against the first microbial group (P > 0.05). Lower counts of yeasts and moulds, total coliforms (35 °C) and faecal coliforms (44 °C) were observed in the initial step (3.49–4.53 log CFU g^?1, 0.65–1.55 log most probable number (MPN) g^?1 and 0.50–0.90 log MPN g^?1 respectively), these values increasing significantly after the sanitisation step for yeasts and moulds (～5 log CFU g^?1) but remaining unaltered for coliforms (P > 0.05). Salmonella spp. were not found in any of the experiments carried out, while the presence of Escherichia coli was observed in the final product. CONCLUSIONS : Practices compromising the hygienic quality of the final product during commercial storage were observed and corrective measures suggested. To the best of the authors' knowledge, these are the first data on microbiological safety in Brazilian fresh‐cut processing plants. Copyright © 2008 Society of Chemical Industry     

MODEL OF MICROBIAL GROWTH ON FRESH-CUT LETTUCE TREATED WITH CHLORINATED WATER DURING STORAGE UNDER DIFFERENT TEMPERATURES

Various Gompertz models of the growth of bacteria on fresh‐cut lettuce were established in order to predict the shelf life of fresh‐cut lettuce untreated and treated with chlorinated water in storage under different temperatures. The sensory quality of fresh‐cut lettuce treated with water containing 75 µg/L of available chlorine was also examined during storage at 0, 4 and 25C, respectively. Bacteria growth on fresh‐cut lettuce in storage was analyzed to evaluate the effect of temperature, and the established model of predictive bacteria growth on fresh‐cut lettuce fitted the Gompertz modified model best. The lag time λ, the asymptote A and maximum specific growth rate μ_m of the bacteria were calculated, according to Gompertz models. The value of μ_m and A at 0C were lower than that at 4 and 25C, and the lag time was longer at a low temperature than at a higher temperature, indicating that the lower the storage temperature, the slower the growth of bacteria on lettuce, and the smaller the maximum bacteria number reached on the lettuce. The efficacy of preservation of fresh‐cut lettuce treated with chlorinated water was significantly better than that of nontreated lettuce under the same storage temperature. It was found that the final bacteria number predicted (S) on lettuce treated with chlorinated water was lower than that on nontreated lettuce, and that the higher the storage temperature, the higher the final bacteria number predicted (S). The established growth models at different temperature were able to predict the shelf life of fresh‐cut lettuce.     

A Comparative Study of Natural Antimicrobial Delivery Systems for Microbial Safety and Quality of Fresh‐Cut Lettuce

Nanoencapsulation can provide a means to effectively deliver antimicrobial compounds and enhance the safety of fresh produce. However, to date there are no studies which directly compares how different nanoencapsulation systems affect fresh produce safety and quality. This study compared the effects on quality and safety of fresh‐cut lettuce treated with free and nanoencapsulated natural antimicrobial, cinnamon bark extract (CBE). A challenge study compared antimicrobial efficacy of 3 different nanoencapsulated CBE systems. The most effective antimicrobial treatment against Listeria monocytogenes was chitosan‐co‐poly‐N‐isopropylacrylamide (chitosan‐PNIPAAM) encapsulated CBE, with a reduction on bacterial load up to 2 log₁₀ CFU/g (P < 0.05) compared to the other encapsulation systems when fresh‐cut lettuce was stored at 5 °C and 10 °C for 15 d. Subsequently, chitosan‐PNIPAAM‐CBE nanoparticles (20, 40, and 80 mg/mL) were compared to a control and free CBE (400, 800, and 1600 μg/mL) for its effects on fresh‐cut lettuce quality over 15 d at 5 °C. By the 10th day, the most effective antimicrobial concentration was 80 mg/mL for chitosan‐PNIPAAM‐CBE, up to 2 log₁₀ CFU/g reduction (P < 0.05), compared with the other treatments. There was no significant difference between control and treated samples up to day 10 for the quality attributes evaluated. Chitosan‐PNIPAAM‐CBE nanoparticles effectively inhibited spoilage microorganisms’ growth and extended fresh‐cut lettuce shelf‐life. Overall, nanoencapsulation provided a method to effectively deliver essential oil and enhanced produce safety, while creating little to no detrimental quality changes on the fresh‐cut lettuce.     

The Effect of pH on Inactivation of Pathogenic Bacteria on Fresh-cut Lettuce by Dipping Treatment with Electrolyzed Water

Fresh‐cut lettuce samples inoculated with S. Typhimurium, E. coli O157:H7 or L. monocytogenes were dipped into 300 ppm electrolyzed water (EW) at pH 4 to 9 and 30 °C for 5 min. The effects of treatment pH on bacterial reduction and visual quality of the lettuce were determined. The treatments at pH 4 and 8 resulted in the most effective inactivation of E. coli O157:H7, but the effect of pH was not significant (P > 0.05) for S. Typhimurium and L. monocytogenes. The treatment at pH 7 retained the best visual quality of lettuce, and achieved a reduction of approximately 2 log CFU/g for above 3 bacteria.     

Thermal Destruction of Listeria monocytogenes in a Meat Slurry and in Ground Beef

Thermal destruction of Listeria monocytogenes cells was determined in phosphate buffer, a meat slurry (20% ground beef/80% water) and in ground beef. D-values at 60°C, 65°C and 70°C in phosphate buffer, and in the meat slurry were 0.63, 0.29 and 0.15, and 2.54, 0.75 and 0.23 min, respectively. Heating of ground beef (80% lean) in a 75°C water bath to 50°C, 60°C or 65°C required 6.2, 8.4 and 10.6 min, respectively, and resulted in 0.2-0.9, 1.6-3.4 and 4.4-6.1 log reductions in L. monocytogenes cells, from the initial inoculation level of 8.08 log CFU/g. Viable cells were also detected after cold (21 days) or selective enrichment (24 hr) in eight out of nine samples of ground beef inoculated with 7.84-8.08 log CFU/g and cooked to 70°C.     

Oscillatory High Pressure Processing Applied to Mechanically Recovered Poultry Meat for Bacterial Inactivation

The effect of oscillatory high pressure processing on mesophile and psychrotroph populations of mechanically recovered poultry meat (MRPM) was evaluated. Vacuum‐packaged samples were subjected to cycles by alternating moderate pressure (60 MPa) and high pressure (450 MPa) at 20 °C, once or several times so that the total time under high pressure was 15 min. A continuous treatment at 450 MPa for 15 min at 20 °C was also performed. Oscillatory treatments did not generate significantly higher decreases in counts of both populations than continuous pressurization. Reductions from 3.2 to 3.8 log CFU g^–1 were found for mesophiles. Psychrotrophs proved more sensitive: one of the cyclic treatments induced a lethality of 5.2 log CFU g ^–1. Pressurization improves the microbiological quality of MRPM.