Effect of washing with citric acid and packaging in modified atmosphere on the sensory and microbiological quality of sliced mushrooms (Agaricus bisporus L.)

The effect of washing with citric acid before slicing and the effect of modified atmosphere packaging on the sensorial and microbiological quality of sliced mushrooms when stored at 5 °C for up to 17 days was evaluated.The atmosphere generated with the perforated PVC film was similar to that of air atmosphere. The non-perforated PVC film generated CO₂ concentrations inside the packages ranging from 6.9% to 3.1% and O₂ concentrations ranging from 2% to 6% depending on the storage time. Washing with citric acid reduced microbial counts by 2.5 log units on day 0. The anti-microbial effect of citric acid decreased during storage but remained significant on each sampling day. Modified atmospheres reduced the microbial counts by 0.8 log units throughout storage. The effect of washing with citric acid combined with packaging in modified atmosphere resulted additive. The reduction of microbial counts avoided bacterial blotch in washed mushrooms during 17 days of storage at 5 °C.     

Microbiological evaluation of an edible antimicrobial coating on minimally processed carrots

This work aimed to develop an edible antimicrobial coating based on a starch–chitosan matrix to evaluate its effect on minimally processed carrot by means of microbiological analyses. Coatings based on 4% yam starch (w/w) + 2% glycerol (w/w) and coatings based on 4% yam starch (w/w) + 2% glycerol (w/w) + chitosan in 0.5% and 1.5% concentrations were prepared. Samples of minimally processed carrot slices were immersed into these coatings. All the samples were placed in expanded polystyrene trays, wrapped in polyvinylchloride film and stored at 10 °C/15 days. During storage, all the samples had counting <100 CFU/g for Staphylococcus aureus and <3 MPN/g for Escherichia coli. Starch + 0.5% chitosan coating controlled the growth of mesophilic aerobes, yeasts and molds and psychrotrophs during the first five days of storage, ultimately presenting reductions of only 0.64, 0.11 and 0.16 log cycles, respectively, compared to the control. Starch + 1.5% chitosan coated samples showed reductions in mesophilic aerobes, mold and yeast and psychrotrophic counting of 1.34, 2.50 and 1.30 log cycles, respectively, compared to the control. The presence of 1.5% chitosan in the coatings inhibited the growth of total coliforms and lactic acid bacteria throughout the storage period. The use of edible antimicrobial yam starch and chitosan coating is a viable alternative for controlling microbiological growth in minimally processed carrot.     

Coating effects of tea polyphenol and rosemary extract combined with chitosan on the storage quality of large yellow croaker (Pseudosciaena crocea)

The coating effects of tea polyphenol (TP) and rosemary extract (R) combined with chitosan (Ch) respectively on the quality of large yellow croaker (Pseudosciaena crocea) during refrigerated storage at (4 ± 1 °C) were evaluated. A solution of TP (0.2%, w/v) and R (0.2%, w/v) was used for dip pretreatment, and Ch (1.5%, w/v) was used for the coating. Microbiological (total viable count), physicochemical (pH, TVB-N, K value, PV, TBARS), and sensory attributes were periodically assessed over 20 days. The results indicated that the two dip pretreatments combined with chitosan coating could more effectively maintain the good quality and could extend the shelf life by 8-10 days compared with the control group during the refrigerated storage.     

Effect of catechin and ferulic acid on melanosis and quality of Pacific white shrimp subjected to prior freeze–thawing during refrigerated storage

Melanosis of Pacific white shrimp (Litopenaeus vannamei) subjected to freeze–thawing with different thawing methods and various cycles were monitored during subsequent refrigerated storage (4 °C) up to 4 days. Melanosis score was lower in Pacific white shrimp thawed at 4 °C, compared with that found in samples thawed at room temperature or using tap water. Polyphenol oxidase (PPO) activity increased as freeze–thaw cycles increased (P < 0.05). Enhanced PPO activity was most likely associated with increased melanosis. Pacific white shrimp treated with catechin (0.05%, 0.1% and 0.2% (w/v)) or ferulic acid (1%, 2% and 3% (w/v)) and subjected to freeze–thawing with various cycles showed the retarded melanosis during the subsequent refrigerated storage of 4 days, compared with the control (P < 0.05). Treatment of shrimp with both phenolic compounds could impede the growth of psychrophilic bacteria and the spoilage as evidenced by the lowered psychrophilic bacteria count and total volatile base content (TVB). Sample treated with 0.2% catechin or 3% ferulic acid also exhibited the retarded lipid oxidation during the subsequent refrigerated storage, compared with the control (P < 0.05). Thus, either catechin or ferulic acid could be used as the potential additive to lower melanosis of shrimp with prior freeze–thawing.     

Effect of combined ozone and organic acid treatment for control of Escherichia coli O157:H7 and Listeria monocytogenes on enoki mushroom

This study evaluated the effects of ozonated water (1, 3, and 5 ppm) alone with different exposure times (0.5, 1, 3, or 5 min), and combinations of 3 ppm ozone with 1% organic acids (acetic, citric, or lactic acids) during 5-min exposure for control of Escherichia coli O157:H7 and Listeria monocytogenes on enoki mushroom and to observe the regrowth of these pathogenic bacteria on treated enoki mushroom during storage for 10 days at 15 °C. Results showed that ozone treatment gave less than 1.0- and 0.5-log count reductions on E. coli O157:H7 and L. monocytogenes, respectively. Efficacy was improved with combined 3 ppm ozone and 1% citric acid treatment, resulting in 2.26- and 1.32-log count reductions, respectively. During storage at 15 °C (10 days) after combined treatment and packaging, populations of E. coli O157:H7 and L. monocytogenes increased to more than 8.0 log cfu/g, indicating that the combined treatment did not have a residual antimicrobial effect during storage. Although the storage study did not show control of these pathogens, the combined ozone–organic acid treatment was more effective than individual treatments in reducing initial population levels of these pathogens on enoki mushroom.     

Effect of an argon-containing packaging atmosphere on the quality of fresh pork sausages during refrigerated storage

The effects of modified atmosphere packaging (MAP) with commercial gas mixtures made up of either CO₂ and argon or CO₂ and nitrogen on the microbiological and physico-chemical characteristics of fresh pork sausages during refrigerated storage were studied and the results compared with vacuum and over-wrap packaging. The presence of argon in the mixture of gases barely affected the growth of enterobacteria, which were at their lowest levels (P < 0.05) at the end of the preservation period. MAP with argon did not affect (P > 0.05) lactic acid bacteria or total viable counts in samples with N₂. The biogenic amine levels in all the samples remained low during storage with the exception of spermidine and spermine. There were no significant differences between the two lots in MAP respecting color parameters. MAP with argon and CO₂ had a beneficial effect on sensorial evaluation during the 28 days storage period, when compared with that of the control, which was rejected after 11 days of storage.     

Non-thermal inactivation of Escherichia coli K12 in buffered peptone water using a pilot-plant scale supercritical carbon dioxide system with a gas–liquid porous metal contactor

This study evaluated the effectiveness of a supercritical carbon dioxide (SCCO₂) system, with a gas–liquid porous metal contactor, for reducing Escherichia coli K12 in diluted buffered peptone water. 0.1% (w/v) buffered peptone water inoculated with E. coli K12 was processed using the SCCO₂ system at CO₂ concentrations of 3.1–9.5 wt%, outlet temperatures of 34, 38, and 42 °C, a system pressure of 7.6 MPa, and a flow rate of 1 L/min. Increased CO₂ concentrations and temperatures significantly (P < 0.05) enhanced microbial reduction. A maximum reduction of 5.8-log was obtained at 8.2% CO₂ and 42 °C. To achieve a 5-log reduction of E. coli K12 in 0.1% buffered peptone water, minimum CO₂ concentrations of 9.5%, 5.5%, and 5.3% were needed at 34, 38, and 42 °C, respectively. Further reductions of cells were observed after storage for 7 days at 4 °C. But storage at 25 °C increased the number of viable cells to 8-log cfu/mL after 7 days. This study showed the potential of the pilot scale SCCO₂ system with a gas–liquid porous metal contactor for microbial inactivation in liquid food.     

The potential of some spice essential oils in the control of A. parasiticus CFR 223 and aflatoxin production

Essential oils of sweet basil (Ocimum basilicum), cassia (Cinnamomum cassia), coriander (Coriandrum sativum) and bay leaf (Laurus nobilis) at 1–5% (v/v) concentration in palm kernel broth inoculated with spore suspension (10⁶/ml) of Aspergillus parasiticus CFR 223 were evaluated for their potential in the control of aflatoxigenic fungus A. parasiticus CFR 223 and aflatoxin production. Healthy sorghum grains (120/treatment) immersed in the oils and distributed in three petri dishes with wet cotton wool were also inoculated with spore suspension (10⁶/ml) of A. parasiticus CFR 223 and assayed for grain protection. Sweet basil oil at optimal protective dosage of 5% (v/v) was fungistatic on A. parasiticus CFR 223 and aflatoxins produced in vitro and on fungal development on sorghum grains (P ⩽ 0.05) with a residual effect that lasted for 32 days. In contrast, oils of cassia and bay leaf stimulated the mycelia growth of the fungus in vitro but reduced the aflatoxin concentration (B₁ + G₁) of the fungus by 97.92% and 55.21% respectively, while coriander oil did not have any effect on both the mycelia growth and aflatoxin content of the fungus. The combination of cassia and sweet basil oils at half their optimal protective dosages (2.5% v/v) completely inhibited the growth of the fungus. The feasibility of implementing the results of this study to control aflatoxins was examined by the addition of whole and ground dry basil leaves at 5% and 10% (w/w), respectively, to 10 g sorghum, groundnut, maize and melon seed after 35 days storage period. It was found that the addition of whole and ground basil leaves markedly reduced aflatoxin contamination; however, 10% (w/w) of whole leaves was more effective as the reduction in aflatoxin was between 89.05% and 91%.The findings showed that aflatoxins can be controlled by co-storing whole sweet basil leaves with aflatoxin infected foods. The economic value of the study lies in the simplified technique for control of aflatoxin contamination in agricultural products and the benefits derivable from the use of local resources.     

Microbial and quality evaluation of green peppers stored in biodegradable film packaging

The effects of polylactic acid (PLA) based biodegradable film packaging on the microbial and physicochemical quality of green peppers (Capsicum annuum L.) were compared to the effects of low-density polyethylene (LDPE) film packaging, and perforated LDPE film packaging. Each package containing green peppers was heat-sealed and stored for 7 days at 10 °C. The microbial levels (aerobic bacteria, coliform bacteria, and yeast and moulds) and physicochemical properties such as colour, weight loss, hardness, ascorbic acid concentration, O₂ and CO₂ concentrations, were monitored during storage. Results indicated that the physicochemical properties of colour, hardness, ascorbic acid concentration, and microbial levels (total aerobic bacteria, and moulds and yeasts) did not show remarkable changes during storage period. The microbial levels in coliform bacteria were increased by less than 1 log CFU/g (0.2 log CFU/g) in the biodegradable film packaging, 2.3 log CFU/g in LDPE film package, and less than 1 log CFU/g (0.9 log CFU/g) in the perforated LDPE film package, after 7 days storage period. The results suggest that the biodegradable film with higher water vapor permeability can be used to maintain the quality and sanitary conditions (protection from microbial and insect contamination) of freshly harvested green peppers in modified atmosphere packaging.     

Effect of potassium sorbate washing on the growth of Listeria monocytogenes on fresh poultry

This work evaluated the effect of potassium sorbate washing on the growth of Listeria monocytogenes on poultry legs stored at 4 °C for 7 days. Fresh inoculated chicken legs were dipped into either a 2.5% (w/v) or 5% potassium sorbate solution or distilled water (control). Changes in mesophiles, pychrotrophic counts and sensorial characteristics (odor, color, texture and overall appearance) were also evaluated.The shelf life of the samples washed with potassium sorbate was extended by at least 2 days over the control samples washed with distilled water. Legs washed with 5% potassium sorbate showed a significant (p < 0.05) inhibitory effect on L. monocytogenes compared to control legs, with a decrease of about 1.3 log units after 7 days of storage. Sensory quality was not adversely affected by potassium sorbate.     

Preventive effect of tannic acid in combination with modified atmospheric packaging on the quality losses of the refrigerated ground beef

Chemical, microbiological and sensorial changes of ground beef treated without and with tannic acid (200 mg/kg) and stored in air and under modified atmosphere packaging (MAP) (80%O₂/20%CO₂ or 10%O₂/20%CO₂/70%N₂) were monitored during 15 days of storage at 4 °C. During the storage, samples treated with tannic acid and kept under all packaging conditions contained lower peroxide value (PV) and thiobarbituric acid-reactive substances (TBARS) with coincidental lower non-haem iron content, compared with non-treated counterparts (P < 0.05). The sample packed in high oxygen MAP treated without and with tannic acid had the higher oxymyoglobin and a^* values and received the higher likeness scores for colour, whereas the samples stored in air and under low oxygen MAP showed the lower values, regardless of tannic acid treatment. After 15 days of storage, myosin heavy chain (MHC) and actin of all tannic acid treated samples underwent less degradation than those without tannic acid treatment for all packaging conditions. Degradation of MHC was more pronounced in samples kept under MAP with high oxygen. Psychrophilic bacterial count (PBC) of all tannic acid treated samples was lower, compared with that of non-treated samples (P < 0.05), irrespective of packaging condition. Therefore, tannic acid treated samples stored under high oxygen MAP could maintain the red colour and retard lipid oxidation and microbial growth of ground beef during refrigerated storage.     

Temperature distribution in Spanish domestic refrigerators and its effect on Listeria monocytogenes growth in sliced ready-to-eat ham

In order to evaluate the increase of L. monocytogenes concentration during home storage, a low level of the pathogen (<10 CFU/g) was inoculated in sliced ham. Two storage temperatures (5 °C and 9 °C) were selected from a previous study in 33 home refrigerators. Three days of storage or less were necessary to reach the regulated limited concentration (100 CFU/g), at both temperatures. When storage time was extended to 5 days, the pathogen achieved risky values (>10³ CFU/g).     

Patulin accumulation in apples during postharvest: Effect of controlled atmosphere storage and fungicide treatments

The aim of this study was to assess the opportunities of Penicillium expansum to develop and produce patulin in apples under two different CA storage methods (LOW and U-LOW) at 1 °C. Differences in lesion diameter and patulin accumulation depending on CO₂ and O₂ partial pressure were studied. Further apple rot and patulin production during a three days post-storing stage at 20 °C was also monitored so that effect of further storage at room temperature could be assesed.Two lots of apples of Golden variety with different ripeness degrees were used. Half of each lot was fungicide treated. Apples were inoculated with patulin producer P. expansum strains and stored at 1 °C for either two month or 2.5 months at both LOW and U-LOW conditions. The extent of lesions and patulin accumulation both at the end of CA cold storage and after three days at 20 °C were assessed. CA storage conditions had strong significance in P. expansum growth on apples and factors such as fruit ripeness, fungicide treatment and time at the storage room had significant influence. In general, bigger lesions were observed under U-LOW than under LOW conditions, lesions being similar or bigger when increasing the storage time from 2 to 2.5 months. P. expansum grew faster in riper apples, although fungicide application was clearly more effective for ripe rather than for underripe apples. Although lesions were evident after both storage conditions, no patulin was detected. Increase of lesion when fruits were subsequently stored at 20 °C was evident in all cases and patulin was detected at this moment. No differences in patulin content were found at this stage between LOW and U-LOW stored apples.     

Efficacy of aqueous chlorine dioxide and fumaric acid for inactivating pre-existing microorganisms and Escherichia coli O157:H7, Salmonella typhimurium,and Listeria monocytogenes on broccoli sprouts

The combined effect of aqueous chlorine dioxide (ClO₂) and fumaric acid as a chemical treatment to inactivate pre-existing microorganisms was evaluated using broccoli sprouts. Broccoli sprouts were treated with distilled water, 50 ppm ClO₂, 0.5% fumaric acid, and a combination of 0.5% fumaric acid and 50 ppm ClO₂. Treatment with 50 ppm ClO₂ and 0.5% fumaric acid reduced the initial populations of total aerobic bacteria, yeasts and molds, and coliforms in broccoli sprouts by 2.70, 2.46, and 1.71 log CFU/g, respectively. In addition, the combined treatment of 50 ppm ClO₂ and 0.5% fumaric acid reduced the initial populations of Escherichia coli O157:H7, Salmonella typhimurium, and Listeria monocytogenes inoculated on broccoli sprouts by 2.39, 2.74, and 2.65 log CFU/g, respectively, compared to the control. These results suggest that the combination of aqueous ClO₂ and fumaric acid can be useful as a hurdle for extending the shelf life of broccoli sprouts during storage.     

Antimicrobial activity of clove (Syzgium aromaticum) oil in inhibiting Listeria monocytogenes on chicken frankfurters

The ability of Listeria monocytogenes to survive and grow at refrigeration temperature in some ready to eat (RTE) poultry products is a public health concern. The inhibitory effect of clove oil (1% and 2%, v/w) applied to the surface of RTE chicken frankfurters was determined on seven strains of L. monocytogenes inoculated at low (10²–10³ cfu/g) or high cell numbers (10⁴–10⁶ cfu/g), and stored at 5 °C for 2 weeks or at 15 °C for 1 week. All strains of L. monocytogenes survived and grew on control frankfurters at 5 °C and 15 °C but growth was inhibited under both storage conditions in the presence of either 1% or 2% clove oil. Depending on the sensory considerations, the addition of clove oil to frankfurters may be an effective strategy to control L. monocytogenes in chicken frankfurters.     

Microbial profile of buffalo sausage during processing and storage

A study was made on the microbial levels of buffalo sausage during preparation and storage at 4 ± 1 °C. Microbial counts in raw minced meat were, total plate count (TPC) (log cfu/g) 5.41 ± 0.25; coliforms (MPN/g) 23.2; Staphylococcus aureus (log cfu/g) 1.57 ± 0.11; yeasts and molds (log cfu/g) 2.29 ± 0.07 and lactic acid bacteria (LAB) (log cfu/g) 0.60 ± 0.20. Sausage emulsion showed similar trend in microbial counts with minimal microbial contamination during the preparation of emulsion. Cooked buffalo sausage gave the following microbial counts: TPC (log cfu/g) 3.75 ± 0.31; coliforms (MPN/g) 0.2; LAB (log cfu/g) 0.07 ± 0.01; yeast and molds (log cfu/g) 0.72 ± 0.07. S. aureus, Clostridium perfringens and Bacillus cereus were not detected in cooked sausages. These results indicate that steam cooking for 45 min followed in the study was effective in reducing the microbial counts substantially. The investigation revealed that shelf life of cooked buffalo sausage was 31 days in either vacuum or CO₂ at 4 ± 1 °C. The results indicated that spoilage of vacuum packed cooked buffalo sausage was likely due to LAB while microflora other than LAB may be responsible for spoilage of CO₂ packed cooked buffalo sausage. The study suggests that measures such as low initial microbial counts, hygienic precautions during preparation of sausage, steam cooking for 45 min, vacuum or CO₂ packing and storage at 4 ± 1 °C would control the microbial growth and provide wholesomeness and safety to the buffalo sausage.     

Effect of combined physico-chemical treatments based on enterocin AS-48 on the control of Listeria monocytogenes and Staphylococcus aureus in a model cooked ham

Enterocin AS-48 was tested alone or in combination with chemical preservatives and/or heat against Listeria monocytogenes and Staphylococcus aureus in a cooked ham model system. AS-48 (20, 40 and 60 μg g⁻¹) alone was active against L. monocytogenes at 5 and 15 °C, but it was not sufficient to avoid regrowth of Listeria during the 60 days storage. Combination of AS-48 (40 μg g⁻¹) with nitrite/nitrate, pentasodium tripolyphosphate, sodium benzoate or potassium sorbate improved the anti-listeria effect during storage at 5 °C. The most effective combination was AS-48-nitrite/nitrate (0.007%) that reduced listeria below detection level from the beginning to end of storage. Although much more resistant, S. aureus was also inhibited by AS-48 alone at 5 °C, and especially in combinations with nitrite/nitrate, pentasodium tripolyphosphate, sodium lactate and sodium acetate. Best results against both pathogens were obtained when sodium pyrophosphate was applied in combination with 60 μg g⁻¹ AS-48. Sub-lethal heat (60 °C, 2 min) clearly increased AS-48 activity against both Listeria and Staphylococcus.     

Emerging sanitizers and Clean Room packaging for improving the microbial quality of fresh-cut ‘Galia’ melon

This study evaluated how traditional or new sanitizers, alone, or in combination with the use of a Clean Room (CR), affected the respiration rate, microbial, nutritional and sensorial quality of fresh-cut ‘Galia’ melon. Melon pieces were packed in polypropylene trays under passive modified atmosphere (7.4 kPa O₂ + 7.4 kPa CO₂) and stored up to 10 days at 5 °C. The following treatments were performed: 150 mg/l chlorine (control) for 1 min; 80 mg/l peracetic acid (PAA) for 1 min; ozonated water (0.4 mg/l) for 3 and 5 min. The combinations of: ozonated water and PAA; 150 mg/l chlorine and packaging in CR; ozonated water for 3 min and package in CR; ozonated water for 3 min + PAA and packaging in CR were also studied. Throughout the shelf-life psychrotrophic, mesophilic, Enterobactericeae, lactic acid bacteria, moulds and yeast growth were determined. The use of PAA provided the lowest microbial load, but this sanitizer decreased the total vitamin C and the antioxidant activity. Nevertheless, the combination of PAA with 0.4 mg/l of ozonated water (3 min) could be a good substitute of use of chlorine. This treatment was effective in reducing the microbial counts, maintaining the antioxidant compounds and respiration rate and maintained the sensorial quality of the product during the 10 days at 5 °C. Treated product packaged in a CR did not show increased treatment effect, probably due to air quality in the laboratory. The use of CR just for the packaging of the melon pieces did not offer any additional advantage. However, the utilization of CR in an industrial environment during all processing steps (from washing to packaging) should be investigated for potential benefits.     

The effect of packaging conditions on the quality of minimally processed celeriac flakes

The aim of the study was to select packaging conditions of minimally processed celeriac to preserve their quality during storage for 12 days at 4 and 15 °C. The quality of the product was determined on the basis of colour measured in the CIE L¹a¹b¹ system, sensory quality and total counts of mesophilic and psychrophilic bacteria, counts of moulds and yeasts, coliform counts, counts of Pseudomonas bacteria and the presence of bacteria from the genus Clostridium perfringens. Moreover, changes were determined in oxygen and carbon dioxide contents in the atmosphere within the packs, in which the product was stored. Celeriac flakes were packaged in the atmosphere with varying CO₂ contents (0%, 5%, 10%, 20%, 30%, 50% plus 2% O₂ and with balance N₂). After 12 days at 4 °C, it was found that celeriac flakes packaged in atmosphere containing 5% or 10% CO₂, 2% O₂ and balance N₂ were characterized by better quality than samples packaged in air atmosphere or in the atmosphere with CO₂ contents of 0% or higher than 10%. Modified atmosphere with the content of 5% or 10% CO₂, 2% O₂ and balance N₂, applied in the packaging of celeriac flakes, resulted in the inhibition of growth of mesophilic, psychrophilic and coliform bacteria in the tested minimally processed product.     

Antimicrobial activity of malic acid against Listeria monocytogenes,Salmonella Enteritidis and Escherichia coli O157:H7 in apple,pear and melon juices

Minimal inhibitory (MIC) and minimal bactericidal (MBC) concentrations of malic acid against Listeria monocytogenes, Salmonella Enteritidis and Escherichia coli O157:H7 inoculated in apple, pear and melon juices stored at 5, 20 and 35 °C were evaluated. MICs and MBCs against L. monocytogenes, S. Enteritidis and E. coli O157:H7 were significantly affected by storage temperature, juice characteristics and type of microorganism. Malic acid was more effective at 35 and 20 °C than at 5 °C in all studied fruit juices. E. coli O157:H7 was more resistant to malic acid than S. Enteritidis and L. monocytogenes. Apple, pear and melon juices without malic acid were inhibitory to E. coli O157:H7, S. Enteritidis and L. monocytogenes at 5 °C, whereas, MBCs of 1.5% (v/v) of malic acid in apple and pear juices, and 2% (v/v) in melon juice at 5 °C were needed to reduce E. coli O157:H7, those concentrations being higher than those required to reduce S. Enteritidis and L. monocytogenes in those fruit juices. In addition, concentrations of 2%, 2.5% and 2.5% (v/v) of malic acid added to apple, pear and melon juices, respectively, were required to inactivate the three pathogens by more than 5 log cycles after 24 h of storage at 5 °C. Transmission electron microscopy showed that malic acid produced damage in the cell cytoplasm of pathogens without apparent changes in the cell membrane.