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Isolation and pulsed-field gel electrophoresis typing of Listeria monocytogenes from modified atmosphere packaged fresh-cut vegetables collected in Ireland.

The incidence of Listeria monocytogenes in modified atmosphere packaged fresh-cut fruits and vegetables from chill cabinets of a supermarket in Ireland was investigated over a 2-year period. Overall, 9.58% of fresh-cut produce was contaminated with Listeria spp. Various species of Listeria were isolated from samples, including L. monocytogenes, L. seeligeri, L. innocua, L. welshimeri, and L. ivanovii. No fruit samples contained detectable L. monocytogenes. Overall, a total of 21 L. monocytogenes isolates (2.9% of samples) were recovered from a range of products, including dry coleslaw mix (80% shredded cabbage and 20% shredded carrot), bean sprouts, and leafy vegetables such iceberg, romaine, and radicchio lettuce and mixed salad leaves (curly endive, escarole, and radicchio leaves). Dry coleslaw mix appeared to have the highest incidence of Listeria contamination (20%) compared with other products. Listeria contamination was more frequent (P < 0.05) during the summer and autumn months than during the winter and spring months. The 21 L. monocytogenes isolates were subsequently subtyped by genomic macrorestriction techniques using ApaI with pulsed-field gel electrophoresis (PFGE). PFGE of digested DNA produced bands of 79 to 518 kb. Four PFGE profiles were identified, and approximately 50% of the isolates were associated with profile 1. This study indicates that fresh-cut vegetables packaged under a modified atmosphere can support growth of numerous species of Listeria, including L. monocytogenes.

Carbon Dioxide↗

Use of activated carbon inside modified atmosphere packages to maintain tomato fruit quality during cold storage.

Ethylene triggers the ripening process of tomato affecting the storage durability and shelf life (loss of quality) and inducing fruit decay. In this paper, an active packaging has been developed on the basis of the combination of modified atmosphere packaging (MAP) and the addition of granular-activated carbon (GAC) alone or impregnated with palladium as a catalyst (GAC-Pd). A steady-state atmosphere was 4 and 10 kPa for O2 and CO2 in control packages, while it was 8 and 7 kPa for O2 and CO2 in treated ones. The addition of GAC-Pd led to the lower ethylene accumulation inside packages, while the higher was obtained in controls. The parameters related to ripening showed that treated tomatoes exhibited a reduction in color evolution, softening, and weight loss, especially for GAC-Pd treatment. Moreover, these treatments were also effective in delaying tomato decay. After sensorial panel, tomatoes treated with GAC-Pd received the higher scores in terms of sweetness, firmness, juiciness, color, odor, and flavor. Results from the GC-MS analysis of the MAP headspace showed that 23 volatile compounds were identified in control packages, with these volatiles being significantly reduced in MAP-treated packages, which was correlated to the odor intensity detected by panelists after bag opening.

Adult↗

Modified atmosphere packaging for prevention of mold spoilage of bakery products with different pH and water activity levels.

A sponge cake analog was used to study the influence of pH, water activity (aw), and carbon dioxide (CO2) levels on the growth of seven fungal species commonly causing bakery product spoilage (Eurotium amstelodami, Eurotium herbariorum, Eurotium repens, Eurotium rubrum, Aspergillus niger, Aspergillus flavus, and Penicillium corylophilum). A full factorial design was used. Water activity, CO2, and their interaction were the main factors significantly affecting fungal growth. Water activity at levels of 0.80 to 0.90 had a significant influence on fungal growth and determined the concentration of CO2 needed to prevent cake analog spoilage. At an aw level of 0.85, lag phases increased twofold when the level of CO2 in the headspace increased from 0 to 70%. In general, no fungal growth was observed for up to 28 days of incubation at 25 degrees C when samples were packaged with 100% CO2, regardless of the aw level. Partial least squares projection to latent structures regression was used to build a polynomial model to predict sponge cake shelf life on the basis of the lag phases of all seven species tested. The model developed explained quite well (R2 = 79%) the growth of almost all species, which responded similarly to changes in tested factors. The results of this study emphasize the importance of combining several hurdles, such as modified atmosphere packaging, aw, and pH, that have synergistic or additive effects on the inhibition of mold growth.

Ascomycota↗

"Hotness" stability of chicken hot-wing products as affected by preparation methods and storage.

Chicken hot-drumettes containing 2% cayenne pepper were prepared using three different cooking methods and stored under two different temperatures for "hotness" evaluation. Results demonstrated that the hotness of the samples were highest when products were cooked in a microwave oven, followed by convection oven, and least hot by deep-fat frying. Regardless of the cooking method, the degree of hotness of the hot-drumette decreased drastically during refrigerated storage. Results also indicated that the loss of hotness was associated with the increase of 2-thiobarbituric acid (TBA) values in the product. The addition of antioxidants such as butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT), rosemary, and sodium nitrate during preparation or vacuum packaging retarded lipid oxidation of chicken hot-drumettes and retarded the loss of hotness of the products during refrigerated storage.

Animals↗

Influence of modified atmosphere packaging on the shelf life of prebaked pizza dough with and without preservative added.

The possible effect of different modified atmospheres on the shelf life of prebaked pizza dough, with and without added calcium propionate, was investigated. Three packaging atmospheres were tested: 20% CO2: 80% N2, 50% CO2: 50% N2, 100% CO2, and air (control). Samples were examined daily for visible mold growth and analysed after 2, 8, 17 and 31 days throughout storage (15-20 degrees C and 54-65% relative humidity, RH) for changes in gaseous composition, pH and microbial populations (mesophilic aerobic and anaerobic bacteria, lactic acid bacteria (LAB), and yeasts and molds). Microbiological results showed that molds had a greater sensitivity to CO2 than bacteria and yeasts. Products containing calcium propionate did not show mold growth throughout storage (31 days) when packaged in air or in CO2-enriched atmospheres (20, 50 and 100%). However, in pizza dough without preservative (calcium propionate), mold growth was evident after 7 days, except under 100% CO2 atmosphere (13 days) regardless of the packaging atmosphere. From these results we conclude that the addition of calcium propionate had more and decisive influence on the shelf life extension of prebaked pizza dough.

Carbon Dioxide↗

Developing microbial spoilage population in vacuum-packaged charcoal-broiled European river lamprey (Lampetra fluviatilis).

Microbiological and sensory changes in vacuum-packaged charcoal-broiled river lampreys from three lamprey processing plants were monitored as a function of time at 8 degrees C. The lampreys were examined every 7 days up to 8 weeks for aerobic plate count (APC) and lactic acid bacteria (LAB). The highest mean APC and LAB were 6.01 log CFU/g and 4.86 log CFU/g, respectively. Only 6 out of 15 lots reached an APC value of 7.0 log CFU/g during storage. The sensory scores remained at the baseline levels after 8 weeks' storage. Twenty-seven isolates were randomly picked from MRS agar and identified to species level using a 16S and 23S rDNA HindIII RFLP (ribotyping) database and sequencing of the 16S rRNA gene if no database match was obtained. Twelve of the 27 isolates were identified as Lactobacillus curvatus subsp. curvatus, and two Leuconostoc mesenteroides and one Weissella halotolerans strain were also detected. Twelve isolates were not identified by the LAB database. However, they possessed very high (99.9%) 16S gene sequence similarity with either Staphylococcus warneri or Staphylococcus pasteuri type strains. The LAB detected, with the exception of W. halotolerans, have commonly been associated with spoilage of fishery products, but in these vacuum-packaged lampreys, they were not the dominant organisms within the developing spoilage population.

Animals↗

Formation of aroma compounds during long-term frozen storage of unblanched leek (Allium ampeloprasum Var. Bulga) as affected by packaging atmosphere and slice thickness.

Content of aroma compounds and catalytic activity of lipoxygenase (LOX), hydroperoxide lyase (HPL), and alcohol dehydrogenase (ADH) were analyzed in 4- and 15-mm unblanched leek slices packed in atmospheric air (4- and 15-mm) or 100% nitrogen (N) (only 15-mm) seven times during 12 months of frozen storage (12M). Total amount of sulfur compounds was influenced by storage time, slice thickness, and atmosphere (concentration in fresh 4-mm slices = 17.8 mg/L, 4-mm 12M = 3.48 mg/L, fresh 15-mm slices = 2.48 mg/L, 15-mm 12M = 0.418 mg/L and 15-mm N 12M = 1.81 mg/L). The 4-mm slices significantly developed the most aldehydes after 12M (total amount = 9.28 mg/L) compared to 15-mm 12M (6.49 mg/L) and 15-mm N 12M (4.33 mg/L). LOX activity is positively influenced by nitrogen packaging, and HPL activity is influenced by slice thickness, whereas ADH is unaffected by both parameters.

Alcohol Dehydrogenase↗

Inhibition of Listeria monocytogenes on the surface of individually packaged hot dogs with a packaging film coating containing nisin.

The objective of this study was to determine the effectiveness of packaging films coated with a methylcellulose/hydroxypropyl methylcellulose-based solution containing 10,000, 7,500, 2,500, or 156.3 IU/ml nisin for controlling Listeria monocytogenes on the surfaces of vacuum-packaged hot dogs. Barrier film coated with a methylcellulose/hydroxypropyl methylcellulose-based solution containing nisin or no nisin (control) was heat sealed to form individual pouches. Hot dogs were placed in control and nisin-containing pouches and inoculated with a five-strain L. monocytogenes cocktail (approximately 5 log CFU per package), vacuum sealed, and stored for intervals of 2 h and 7, 15, 21, 28, and 60 d at 4 degrees C. After storage, hot dogs and packages were rinsed with 0.1% peptone water. Diluent was spiral plated on modified oxford agar and tryptic soy agar and incubated to obtain counts (CFU per package). L. monocytogenes counts on hot dogs packaged in films coated with 156.3 IU/ml nisin decreased slightly (approximately 0.5-log reduction) through day 15 of refrigerated storage but was statistically the same (P > 0.05) as hot dogs packaged in films without nisin after 60 d of storage. Packaging films coated with a cellulose-based solution containing 10,000 and 7,500 IU/ml nisin significantly decreased (P < 0.05) L. monocytogenes populations on the surface of hot dogs by greater than 2 log CFU per package throughout the 60-d study. Similar results were observed for hot dogs packaged in films coated with 2,500 IU/ml nisin; however, L. monocytogenes populations were observed to be approximately 4 log CFU per package after 60 d of refrigerated storage from plate counts on tryptic soy and modified oxford agars.

Colony Count, Microbial↗

Antioxidant properties of ready-to-drink coffee brews.

The influence of some technological variables on the changes of the antioxidant capacity of ready-to-drink coffee brews was investigated. Results showed that, depending on the roasting degree as well as on the packaging conditions adopted, redox reactions, which can take place during storage, are responsible for significant changes in the overall antioxidant capacity of the product. In particular, the redox potential of air-packaged coffee brews, obtained from light- and medium-roasted beans, showed maximum values after 2 days of storage, which corresponded to a minimum in the chain-breaking activity, while, in the case of the dark-roasted sample packaged under ordinary atmosphere, both the redox potential and the chain-breaking activity showed a maximum around 2-3 days of storage. In contrast, in the absence of oxygen, the coffee brews maintained the initial reducing properties over all the storage time, although the radical-scavenging activity values changed in a way very similar to that of the air-packaged sample. These results suggested that the changes in the antioxidant properties of the coffee brews may be attributed to a further development of the Maillard reaction during storage.

Antioxidants↗

Off-odor volatiles and pink color development in precooked, irradiated turkey breast during frozen storage.

The effect of irradiation on color, lipid oxidation, and volatile production of precooked, irradiated turkey breast during frozen storage was studied. Turkey breast muscles were precooked, aerobically or vacuum-packaged, irradiated at 0, 2.5, or 5.0 kGy using a linear accelerator (electron beam), and then frozen-stored at -40 C. Lipid oxidation, volatiles, color values, gas production, and oxidation-reduction potential (ORP) of meat were determined during 3-mo storage periods. Ionizing radiation produced characteristic off-odor volatiles (dimethyldisulfide and methylthioethane) and lipid oxidation products in precooked, frozen turkey breast. The production of volatiles was accelerated by the confounding effect of high irradiation dose, aerobic packaging, and increased storage time. Volatile production and color changes in irradiated, precooked turkey breast were induced by different mechanisms. Irradiation increased pink color in precooked, vacuum-packaged turkey breast, and the pink color was stable during frozen storage. Decreased ORP and increased CO in irradiated meat indicated that denatured CO-heme pigments could be responsible for the pink color in precooked, irradiated turkey breast. Vacuum packaging was better than aerobic packaging in preventing lipid oxidation and oxidation-dependent volatile production, but pink color in precooked, irradiated turkey breast during frozen storage was maintained.

Animals↗

Survival of Escherichia coli O157:H7 and Salmonella on chill-stored vacuum or carbon dioxide packaged primal beef cuts.

The ability of two Escherichia coli O157:H7 strains (E27, a cattle isolate, and B6-914 gfp-91, a fluorescent marker strain) and two Salmonella serotypes (S. typhimurium and S. brandenberg) to survive on chilled preservatively packaged primal beef cuts was examined. Each of the strains was inoculated separately at two dilution levels (10(3) and 10(5) cfu g(-1)) onto 500 g beef steaks, packaged under vacuum or 100% carbon dioxide, and stored, with uninoculated controls, for 6 weeks at - 1.5 degrees C, then for 2 weeks at 4 degrees C. Bacterial numbers were determined by dilution and incubation at 37 degrees C for 24 h on either Sorbitol McConkey Agar or Xylose Lysine Desoxycholate Agar for E. coli O157:H7 and Salmonella samples, respectively. Counts were corrected for background growth and their accuracy checked using immunological tests. Fluorescent E. coli O157:H7 B6-914 gfp-91 was also counted under ultra-violet light. No significant changes in numbers of the E. coli O157:H7 or Salmonella strains occurred during storage at either - 1.5 or 4 degrees C packaged under either vacuum or carbon dioxide. The ability of these pathogens to survive standard preservative packaging conditions is different from that reported from their generic counterparts and therefore a cause for public health concern.

Animals↗

Effectiveness of acidic calcium sulfate with propionic and lactic acid and lactates as postprocessing dipping solutions to control Listeria monocytogenes on frankfurters with or without potassium lactate and stored vacuum packaged at 4.5 degrees C.

The safety of ready-to-eat meat products such as frankfurters can be enhanced by treating with approved antimicrobial substances to control the growth of Listeria monocytogenes. We evaluated the effectiveness of acidic calcium sulfate with propionic and lactic acid, potassium lactate, or lactic acid postprocessing dipping solutions to control L. monocytogenes inoculated (ca. 10(8) CFU/ml) onto the surface of frankfurters with or without potassium lactate and stored in vacuum packages at 4.5 degrees C for up to 12 weeks. Two frankfurter formulations were manufactured without (control) or with potassium lactate (KL, 3.3% of a 60% [wt/wt] commercially available syrup). After cooking, chilling, and peeling, each batch was divided into inoculated (four strains of L. monocytogenes mixture) and noninoculated groups. Each group was treated with four different dips: (i) control (saline solution), (ii) acidic calcium sulfate with propionic and lactic acid (ACS, 1:2 water), (iii) KL, or (iv) lactic acid (LA, 3.4% of a 88% [wt/wt] commercially available syrup) for 30 s. Noninoculated frankfurters were periodically analyzed for pH, water activity, residual nitrite, and aerobic plate counts (APCs), and L. monocytogenes counts (modified Oxford medium) were determined on inoculated samples. Surface APC counts remained at or near the lower limit of detection (<2 log CFU per frank) on franks with or without KL and treated with ACS or LA throughout 12 weeks at 4.5 degrees C. L. monoctogenes counts remained at the minimum level of detection on all franks treated with the ACS dip, which indicated a residual bactericidal effect when L. monocytogenes populations were monitored over 12 weeks. L. monocytogenes numbers were also reduced, but not to the same degree in franks made without or with KL and treated with LA. These results revealed the effectiveness of ACS (bactericidal effect) or LA (bacteriostatic effect) as postprocessing dipping solutions to inhibit or control the growth of L. monocytogenes on vacuum-packaged frankfurters stored at 4.5 degrees C for up to 12 weeks.

Animals↗

[Color loss evaluation of a dietary formulation in function of temperature, storage time and packaging].

Color loss of a dietetic formulae based on pumpkin (Cucurbita maxima), rice, hen and vegetable oils was evaluated. The product was under an accelerated test at temperatures of 40, 50 and 70 degrees C for a month. The kinetic reaction of color loss (quality loss indicator) was obtained with n = 1 and Ea = 11.5 Kcal/mol. The product was also stored for sixth months at temperatures of 25, 30, 35 and 40 degrees C using glass containers, laminated and composite cans (non metallic). The color was measured by a colorimetric method and by sensory evaluation under the defined conditions of time, temperature and package. The statistical analyses of the color loss measured by instrument was performed by a randomized block design with a significance level of p < 0.05. The results obtained both by the instrument and by the sensory evaluation method, showed that the temperature and storage time has significant effect (p < 0.05) on the other hand, the package does not have a significant effect. It was concluded from this study that the product could be stored for 6 months at temperatures below 35 degrees C without changes in color.

Color↗

Flavor deterioration in yogurt.

Volatile components of flavored yogurt preserved at 5 degrees C in the dark for 0 day, 3 days and 10 days were recovered by simultaneous distillation extraction (SDE) and headspace (HS) procedures. Gas chromatography (GC) and GC-mass spectrometry (GC-MS) analyses of those samples showed remarkable changes in some compounds. Aldehydes which contribute to expressing citrusy notes were reduced to alcohols during fermentation process and storage. As a result, the strength of flavors which expressed well-balanced citrusy notes in yogurt were weakened, and fatty or oily notes mainly caused from alcohols were strengthened reversely. Hydrocarbons were also digested by bacteria during a fermentation process. A small amount of other compounds, such as esters and terpene alcohols changed. Fewer effects of sorption into a package material and chemical reactions, such as hydrolysis esters, hydration or oxidation of hydrocarbons, were observed.

Adsorption↗

Correlation between microbial flora, sensory changes and biogenic amines formation in fresh chicken meat stored aerobically or under modified atmosphere packaging at 4 degrees C: possible role of biogenic amines as spoilage indicators.

This study evaluated the formation of biogenic amines (BAs) in breast chicken meat during storage under aerobic and modified atmospheric packaging (MAP) conditions at 4 degrees C, the correlation of microbial and sensory changes in chicken meat with formation of BAs and the possible role of BAs as indicators of poultry meat spoilage. Poultry breast fillets were stored aerobically or under MAP (30%, CO(2), 70% N(2)) at 4 degrees C for up to 17 days. Quality evaluation was carried out using microbiological, chemical and sensory analyses. Total viable counts, Pseudomonads and Enterobacteriaceae, were in general higher for chicken samples packaged in air whereas lactic acid bacteria (LAB) and Enterobacteriaceae were among the dominant species for samples under MAP. Levels of putrescine and cadaverine increased linearly with storage time and were higher in aerobically stored chicken samples. Spermine and spermidine levels were also detected in both aerobically and MAP stored chicken meat. Levels of tyramine in both chicken samples stored aerobically and or under MAP were low (< 10 mg kg(-1)) whereas the formation of histamine was only observed after day 11 of storage when Enterobacteriaceae had reached a population of ca. 10(7) CFU g(-1). Based on sensory and microbiological analyses and also taking into account a biogenic amines index (BAI, sum of putrescine, cadaverine and tyramine), BAI values between 96 and 101 mg kg(-1) may be proposed as a quality index of MAP and aerobically-packaged fresh chicken meat. Spermine and spermidine decreased steadily throughout the entire storage period of chicken meat under aerobic and MAP packaging, and thus these two amines cannot be used as indicators of fresh chicken meat quality.

Aerobiosis↗

Evaluation of meat born lactic acid bacteria as protective cultures for the biopreservation of cooked meat products.

In this study, 91 strains, originating from meat products, were subjected to a step-by-step screening and characterisation to search for potential protective cultures to be used in the cooked cured meat industry. Strains were first tested on their homofermentative and psychrotrophic character and salt tolerance. Secondly, the antibacterial capacities towards Listeria monocytogenes, Leuconostoc mesenteroides, Leuconostoc carnosum and Brochotrix thermosphacta were determined in an agar spot test. In total, 38% of the tested strains were inhibitory towards all indicator strains. However, 91%, 88% and 74% of the strains could inhibit, respectively, L. monocytogenes, B. thermosphacta and Leuc. mesenteroides. Finally, 12 strains, with the highest antibacterial capacities, were evaluated on their competitive nature by comparing their growth rate, acidifying character and lactic acid production at 7 degrees C under anaerobic conditions in a liquid broth. All 12 strains, except for a bacteriocin producing Lactobacillus plantarum strain and the lactocin S producing Lactobacillus sakei 148, combined a fast growth rate with a deep and rapid acidification caused by the production of high levels of lactic acid. The 12 selected strains were then further investigated for their growth capacity on a model cooked ham product to establish whether the presence of these cultures on the ham did not negatively influence the sensory properties of the ham. All strains grew in 6 days at 7 degrees C from a level of 10(5)-10(6) to 10(7)-10(8) cfu/g and again the bacteriocin producing L. plantarum strain was the slowest growing strain. As the glucose level of the model cooked ham product was low (0.09+/-0.03%), growth of the putative protective cultures resulted in glucose depletion and a limited lactic acid production and accompanying pH decrease. Cooked ham inoculated with isolates 13E, 10A, 14A (all three identified as L. sakei subsp. carnosus by SDS-PAGE) and with strains L. sakei 148 (LS5) and L. sakei subsp. carnosus SAGA 777 (LS8) were not rejected by the sensory panel at the 34th day of the vacuum packaged storage at 7 degrees C. Therefore, these strains could have potential for the use as protective culture in cooked meat products.

Animals↗

Irradiation and modified atmosphere packaging effects on residual nitrite, ascorbic acid, nitrosomyoglobin, and color in sausage.

The present study was undertaken to evaluate the irradiation and modified atmosphere packaging effects on emulsion-type cooked pork sausage during storage for 4 weeks. CO(2) (100%), N(2) (100%), or 25% CO(2)/75% N(2) packaged sausage were irradiated at 0, 5, and 10 kGy, and residual nitrite, residual ascorbic acid, nitrosomyoglobin (NO-Mb), color values, and their correlation were observed. Irradiation significantly reduced the residual nitrite content and caused partial reduction of NO-Mb during storage. No difference was observed in ascorbic acid content by irradiation. Irradiation decreased the Hunter color a value of sausage. CO(2) or CO(2)/N(2) packaging were more effective for reducing residual nitrite and inhibiting the loss of the red color of sausage compared to N(2) packaging. Results indicated that the proper combination of irradiation and modified atmosphere packaging could reduce the residual nitrite in sausage with minimization of color change.

Animals↗

Spoilage microflora in fresh chicken breast stored at 4 degrees C: influence of packaging methods.

Chicken breasts with skin were packaged either in air, under vacuum or in modified atmospheres of (i) 30% CO2/70% N2 and (ii) 70% CO2/30% N2. After 3, 7, 14 and 21 days of storage at 4 degrees C, the samples were evaluated for spoilage microbial growth, odour and overall aspect. As expected, pseudomonads grew well in air or under vacuum, but growth was suppressed in both types of modified atmosphere packaging (MAP). However, growth of lactobacilli, Enterobacteriaceae and Brochothrix thermosphacta was not inhibited in MAPs. Modified atmosphere packaging (ii) extended shelf-life up to 21 days compared to 5 days for air-packed samples.

Animals↗