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Polyphenol oxidase (PPO) is the key enzyme responsible for enzymatic browning. To extend the shelf life of shredded lettuce, knowledge about biochemical PPO properties is required. The characterization of the enzyme from shredded, cold-stored lettuce was performed using pyrocatechol and the endogenous substrate (ES) (lettuce phenolics). The optimum pH and temperature for PPO activity were 5 and 50 °C, respectively. Natural infusions used as the PPO inhibitors (IC50) were ranked as follows: lovage (0.09%), marjoram (0.13%), orange peel (0.14%), oregano (0.15%), basil (0.22%), lemon peel (0.24%), parsley leaves (0.58%), and wheat bran (1.06%). Among well-recognized PPO inhibitors, kojic acid (0.00043%), ascorbic acid (0.00053%), and L-cysteine (0.00085%) were the most effective. Among the metal ions, MgCl2, FeCl2, and CaCl2 at 0.5 mM inhibited the PPO activity most effectively (by 28%, 27%, and 21%, respectively). The substrate used (pyrocatechol/ES) significantly influenced the enzyme inhibition. Using pyrocatechol, the lovage extract acted in a mixed mode (Kmi = 27.8 mM, Vmaxi = 2.03 mU), while the ES acted according to the non-competitive mode (Kmi= 0.57 mg GAE/mL, Vmax = 0.0046 U). The study confirms that natural extracts are more effective than L-cysteine when the ES is used. A pre-storage treatment with an infusion may be potentially used to improve the quality of shredded lettuce. [ABSTRACT FROM AUTHOR]

Food browning is an undesirable phenomenon that alters sensory properties and nutritional value of fresh-cut produces, which had a significant economic impact owing to decreased customer acceptability. In this study, the effect of selected spices including cinnamon bark, clove, coriander seed, cumin, fennel seed and Sichuan pepper on iceberg lettuce polyphenol oxidase (PPO) inhibition was investigated to replace synthetic browning inhibitor that often used by food manufacturers. Iceberg lettuce PPO has an enzyme activity of 13677.04 ± 21.00 EU/mL, using pyrocatechol as substrate. Ascorbic acid was used as the synthetic inhibitor of Iceberg lettuce PPO and it acted as a mixed inhibitor with the IC50 of 4.20 ± 0.19 mM. Among all the browning inhibition effect of the selected spices on Iceberg lettuce PPO, cinnamon bark was the best inhibitor among the six selected spice extracts, with the inhibition percentage of 32.39 ± 1.47 % inhibition was determined, followed by fennel seed (16.93 ± 1.47 %), Sichuan pepper (14.24 ± 0.83 %), cumin (13.72 ± 1.35 %), coriander seed (9.85 ± 0.75 %), and clove (9.64 ± 0.47 %) at 2.0 mg/mL. The present findings suggested the potential to expand the application of the spices to be used as food-based anti-browning inhibitors directly on the surface of iceberg lettuce as well as other fresh-cut produces or used as active ingredient of enzymatic browningbased active packaging of fresh-cut produces. [ABSTRACT FROM AUTHOR]

Polyphenol oxidase (PPO) is the key enzyme responsible for enzymatic browning. To extend the shelf life of shredded lettuce, knowledge about biochemical PPO properties is required. The characterization of the enzyme from shredded, cold-stored lettuce was performed using pyrocatechol and the endogenous substrate (ES) (lettuce phenolics). The optimum pH and temperature for PPO activity were 5 and 50 °C, respectively. Natural infusions used as the PPO inhibitors (IC50) were ranked as follows: lovage (0.09%), marjoram (0.13%), orange peel (0.14%), oregano (0.15%), basil (0.22%), lemon peel (0.24%), parsley leaves (0.58%), and wheat bran (1.06%). Among well-recognized PPO inhibitors, kojic acid (0.00043%), ascorbic acid (0.00053%), and L-cysteine (0.00085%) were the most effective. Among the metal ions, MgCl2, FeCl2, and CaCl2 at 0.5 mM inhibited the PPO activity most effectively (by 28%, 27%, and 21%, respectively). The substrate used (pyrocatechol/ES) significantly influenced the enzyme inhibition. Using pyrocatechol, the lovage extract acted in a mixed mode (Kmi = 27.8 mM, Vmaxi = 2.03 mU), while the ES acted according to the non-competitive mode (Kmi= 0.57 mg GAE/mL, Vmax = 0.0046 U). The study confirms that natural extracts are more effective than L-cysteine when the ES is used. A pre-storage treatment with an infusion may be potentially used to improve the quality of shredded lettuce.

The efficacy of potable water and antimicrobial agents, including turmeric extract, black pepper extract, sodium chloride and sodium bicarbonate, in reducing Listeria monocytogenes on the leaf mustard (Brassica integrifolia) and iceberg lettuce (Lactuca sativa L.) was compared. The uncontaminated samples of two raw leafy vegetables were inoculated with L. monocytogenes at a concentration of 5 log and 7 log colony-forming units (CFU) g-1 for 1 h. At the high L. monocytogenes contamination level, the treatment with black pepper extract 0.6 mg mL-1 for 5 min was found to produce the most considerable decrease in L. monocytogenes counts, resulting in 1.44 log and 1.68 log reduction on leaf mustard and iceberg lettuce, respectively. Similarly, the black pepper extract also showed the highest L. monocytogenes reduction, approximately 0.79 log CFU g-1 on two leafy vegetables at the low contamination level. However, the odour of black pepper extract was left on the vegetables after being washed.

In this study, the shelf life of fresh-cut iceberg lettuce (Lactuca sativa L.) was evaluated. Lettuce samples were washed with disinfectant agents and sodium hypochlorite and then soaked in an ascorbic acid solution. Next, samples were stored in packaging films containing three levels (1% and 3% and 0% as a control film) of nano-bentonite particles (NBPs) as a filler in a modified atmosphere for 12 days at 4 °C. Various physicochemical parameters such as color, texture, pH, titratable acidity, dehydration, moisture, dry matter, chlorophyll content, microbial quality, and sensory properties were investigated. Results indicated that nano-packaging had a significant ability to maintain the sensory physicochemical properties of lettuce at the fifth (1% nano-composite film) and ninth (3% nano-composite film) days of storage when compared to the control films. The greatest growths of molds and yeasts were observed in the control films, which demonstrates the effectiveness of the application of bentonite nanoparticle fillers. [ABSTRACT FROM AUTHOR]

ABSTRACT Iodine is essential to human metabolism, being fundamental in the production of the thyroid hormones. The consumption of biofortified foods can contribute to the increase of its intake. The objective of this study was to increase the iodine concentration in lettuce, also evaluating its effects on plant growth and production. The experiment was conducted in a greenhouse, in a hydroponic system of aerated static solution. A completely randomized design was used, in a 2 x 5 factorial scheme (variety x iodine dose), with three repetitions. Two lettuce varieties were used, the iceberg lettuce and the crispy leaf lettuce, submitted to five doses of iodine (0, 10, 20, 30 and 40 µmol L-1), having as source potassium iodide. At 40 days after transplantation, both cultivars were collected and evaluated for the weight of fresh and dry matter, iodine content and levels in the leaves and the root volume. With increased doses, the plants showed symptoms of phytotoxicity, resulting in lower productivity. However, all doses promoted elevations in the total iodine levels of plants. Therefore, it is possible to increase the iodine content in lettuce leaves, being necessary to adjust the doses to be used.

The objective of this study was to investigate the antimicrobial activities of essential oil-based microemulsions in the wash water against Escherichia coli O157:H7 and Pseudomonas fluorescens on Iceberg lettuce. Evaluated wash microemulsions included oregano oil, lemongrass oil, and cinnamon oil, along with a plant-based emulsifier for improved solubility. Iceberg lettuce was inoculated for 2 min with E. coli O157:H7 (6.0 log CFU/g) or P. fluorescens (6.0 log CFU/g) and then dip-treated in a phosphate buffered saline (PBS) control, 50 ppm chlorine, 3% hydrogen peroxide treatment or a 0.1%, 0.3%, or 0.5% microemulsion solution. Treated leaves were stored at 4 °C, and analyzed for surviving bacteria on days 0, 3, 7, 10, 14, 21, and 28. Efficacies of the antimicrobials were concentration and storage-time dependent. There was a 1.26–4.86 log CFU/g reduction in E. coli O157:H7 and significant reductions (0.32–2.35 log CFU/g) in P. fluorescens during storage at days 0–28 (p < 0.05). The 0.1% oregano oil microemulsion resulted in the best visual appeal in Iceberg leaves inoculated with E. coli O157:H7 and showed better improvement in the quality of the Iceberg leaves inoculated with spoilage bacteria P. fluorescens. The results suggest that 0.5% cinnamon and 0.3% oregano oil treatments have the potential to provide natural, eco-friendly, and effective alternatives to chemicals for the decontamination of leafy greens, eliminating E. coli O157:H7 and P. fluorescens. [ABSTRACT FROM AUTHOR]

Commercial forced-air cooling (FAC) of iceberg lettuce is usually not ideal due to multiple uncontrollable factors in the pre-cooling facility, artificial non-standardized operations and operator experience used to select the pre-cooling time. This study aimed to investigate the cooling efficiency (cooling rate, heat load and energy consumption) during commercial FAC of iceberg lettuce under two kinds of operating mode. Our field studies demonstrated that when pallets were loaded in batches with a 20 min interval (Operation A) better cooling effectiveness and less energy consumption was achieved in comparison to when all pallets were loaded and pre-cooled simultaneously (Operation B). The seven-eighths cooling time (SECT) of pallets with the lowest cooling rate in the Operation A (227 min) and Operation B (325 min) were reduced by 43.2 % and 18.8 %, respectively, compared to worker experience estimated time (400 min). In addition, the heat load analysis results indicated that Operation A was an effective way to achieve the goal of enhancing the energy efficiency of the refrigeration unit and keeping the compressor operating under the design condition. [ABSTRACT FROM AUTHOR]

Iodine is essential to human metabolism, being fundamental in the production of the thyroid hormones. The consumption of biofortified foods can contribute to the increase of its intake. The objective of this study was to increase the iodine concentration in lettuce, also evaluating its effects on plant growth and production. The experiment was conducted in a greenhouse, in a hydroponic system of aerated static solution. A completely randomized design was used, in a 2 x 5 factorial scheme (variety x iodine dose), with three repetitions. Two lettuce varieties were used, the iceberg lettuce and the crispy leaf lettuce, submitted to five doses of iodine (0, 10, 20, 30 and 40 µmol L-1), having as source potassium iodide. At 40 days after transplantation, both cultivars were collected and evaluated for the weight of fresh and dry matter, iodine content and levels in the leaves and the root volume. With increased doses, the plants showed symptoms of phytotoxicity, resulting in lower productivity. However, all doses promoted elevations in the total iodine levels of plants. Therefore, it is possible to increase the iodine content in lettuce leaves, being necessary to adjust the doses to be used. [ABSTRACT FROM AUTHOR]

The objective of this study was to investigate the antimicrobial activities of essential oil-based microemulsions in the wash water against Escherichia coli O157:H7 and Pseudomonas fluorescens on Iceberg lettuce. Evaluated wash microemulsions included oregano oil, lemongrass oil, and cinnamon oil, along with a plant-based emulsifier for improved solubility. Iceberg lettuce was inoculated for 2 min with E. coli O157:H7 (6.0 log CFU/g) or P. fluorescens (6.0 log CFU/g) and then dip-treated in a phosphate buffered saline (PBS) control, 50 ppm chlorine, 3% hydrogen peroxide treatment or a 0.1%, 0.3%, or 0.5% microemulsion solution. Treated leaves were stored at 4 °C, and analyzed for surviving bacteria on days 0, 3, 7, 10, 14, 21, and 28. Efficacies of the antimicrobials were concentration and storage-time dependent. There was a 1.26–4.86 log CFU/g reduction in E. coli O157:H7 and significant reductions (0.32–2.35 log CFU/g) in P. fluorescens during storage at days 0–28 (p < 0.05). The 0.1% oregano oil microemulsion resulted in the best visual appeal in Iceberg leaves inoculated with E. coli O157:H7 and showed better improvement in the quality of the Iceberg leaves inoculated with spoilage bacteria P. fluorescens. The results suggest that 0.5% cinnamon and 0.3% oregano oil treatments have the potential to provide natural, eco-friendly, and effective alternatives to chemicals for the decontamination of leafy greens, eliminating E. coli O157:H7 and P. fluorescens.

Context: Iceberg lettuce is a nutrient rich edible crop containing vitamin B6, thiamin and folate. The increasing demand of natural products is moving the focus towards in vitro plant sources as factories for producing important secondary metabolites. Aims: To evaluate the activities of in vitro propagated callus culture and field-grown of Iceberg lettuce, which can act as an alternate source of bioactive secondary metabolites. Methods: The extracts were made with methanol, n-hexane, ethyl acetate and water for field-grown as well as in vitro cultured Iceberg lettuce plants and evaluated for their medicinal potential both in vitro and in vivo in rats. Results: Total flavonoid and phenolic contents of plant extracts showed strong positive correlation with their antioxidant activities. The highest contents of flavonoids and phenolics were present in the methanolic extract of field-grown leaves. The antioxidant, anti-inflammatory and analgesic activities of examined samples in rats were observed as field-grown leaves extracts > callus extracts > regenerated shoots extracts. However, all of these activities in the extracts of callus culture were comparable to that of field-grown plant extracts. Conclusions: This study showed that field-grown plants are comparably rich source of secondary metabolites, which showed multiple pharmacological activities in a significant way.

Fresh-cut lettuce is a very well-known salad for today's routines because it obliges minimal preparation to minimize the loss of health beneficial vitamins, minerals, antioxidants and other phytochemicals. It is a prodigious challenge to serve its consumers fresh. Quality of freshly processed lettuce under high CO2 modified atmosphere packaging (MAP) has been investigated as a realistic alternative technique for its preservation. Storage under high CO2 atmospheric treatments exhibited a significant impact in microbial development, electrolyte leakage, volatile metabolites and sensory quality of fresh-cut iceberg lettuce. This storage condition (MAP 1: 5 kPa O2 and 20 kPa CO2 balanced by N2 at 7 °C for 6 days) inhibited the growth of mesophilic bacteria and yeasts; delayed the enzymatic browning (cut-edges and intact surface) of fresh-cut iceberg lettuce and overall visual quality was also in acceptance limit. The development of off-odors was perceived in high CO2 MAP as a consequence of volatiles (ethanol and acetaldehyde) accumulation which was persisted at an inexcusable level during 6 days of storage periods. [ABSTRACT FROM AUTHOR]

Egypt has limited agricultural land, associated with the scarcity of irrigation water and rapid population growth. Hydroponic farming, seawater desalination and magnetic treatment are among the practical solutions for sustaining rapid population growth. In this regard, the main objective of the present research study was to design and construct a hierarchical engineering unit as a hydroponic farming system (soilless) to produce an iceberg lettuce crop using magnetically treated saline water. The treatments included four types of irrigation water: common irrigation water (IW1) with an electrical conductivity (EC) of 0.96 dS/m as a control treatment, magnetically treated common irrigation water (IW2) with an EC of 0.96 dS/m, saline water (IW3) with an EC of 4.56 dS/m and magnetically treated saline water (IW4) with an EC of 4.56 dS/m; three depletion ratios (DR) of field capacity (DR0 = 50%, DR1 = 60% and DR2 = 70%) and three slopes of hydroponic pipes (S1 = 0.0%, S2 = 0.025% and S3 = 0.075%). The results revealed that seawater contributed 7.15% to produce iceberg lettuce in the hydroponic system. The geometric parameter, the slope of the pipes, influenced the obtained luminous intensity by an average increase of 21% and 71% for S2 and S3, respectively, compared with the zero slope (horizontal pipes). Magnetization of irrigation water increased the total soluble solids (TSS) and enhanced the fresh weight and water productivity of both iceberg lettuce varieties used. The maximum percentages of TSS were 5.20% and 5.10% for lemur and iceberg 077, respectively, for the combination IW4DR2S2. The highest values of fresh weight and water productivity of 3.10 kg/m and 39.15 kg/m3 were recorded with the combinations IW3DR2S3 and IW4DR1S3, respectively, for lemur and iceberg lettuce. The percentages of these increases were 109.46% and 97.78%, respectively, when compared with the combination IW1DR0S1. The highest values of iceberg lettuce 077 fresh weight and water productivity were 2.93 kg/m and 36.15 kg/m3, respectively, which were recorded with the combination IW4DR1S3. The percentages of these increases were 112.32% and 120.56%, respectively, when compared with IW1DR0S1 (the control treatment).

Summary: The impact of functional solutions (water infusions of radish sprouts, wheat bran (WBE), basil leaves (BLE) and lentil protein hydrolysate) on enzymatic browning of shredded iceberg lettuce was studied. BLE and WBE, limiting enzymatic browning in the highest degree, were tested during cold storage. The best inhibitors of PPO activity in lettuce stored for 8 days were 10% WBE (a decrease by 97%). POD activity was substantially decreased by ascorbic acid (by 75%) and 1% BLE (by 83%). POD and PPO inhibition was reflected in a decrease in enzymatic browning, that is 91% and 88% reduction was found in 8‐day stored lettuce treated with 1% BLE and 1% WBE, respectively. In the case of POD, mixed inhibition was recorded for BLE and WBE, while these solutions acted as competitive inhibitors of PPO activity. The enzymatic browning of shredded iceberg lettuce during cold storage may be effectively suppressed by natural extracts. [ABSTRACT FROM AUTHOR]

Si helps plants to mitigate with abiotic and biotic stresses because of Si-treated plants become stronger, sturdier and naturally more tolerant. The purpose of the investigations was to look the effect of Silicon on the iceberg lettuce growth and quality. There were two treatments: 1. stabilized silicic acid treatment; 2. control. The first spray, when 1 real leaf was present; the second spray was 2 weeks after spray 1; the third spray was 2 weeks after spray 2. First spray: 1 ml silicic acid was solved in 0.5 litre distilled water; second spray: 2 ml silicic acid was solved in 1 litre distilled water; third spray: 2 ml silicic acid was solved in 1 litre distilled water. pH of spray solution was 5,5. Control plants were untreated. Iceberg lettuce plants were taller and more bread in Si treatment compared to control. The content of NO3, N, P, and Ca was higher in Si-treated plants.

Minimally processed ready-to-eat (RTE) vegetables are increasingly consumed for their health benefits. However, they also pose a risk of being ingested with food-borne pathogens. The present study investigated the ability of RTE spinach and rocket to support the growth of Listeria monocytogenes as previous studies provided contradicting evidence. Findings were compared to growth on iceberg lettuce that has repeatedly been shown to support growth. Products were inoculated with a three-strain mix of L. monocytogenes at 10 and 100 cfu g−1 and stored in modified atmosphere (4 kPa O2, 8 kPa CO2) at 8 °C over 7–9 days. Spinach demonstrated the highest growth potential rate of 2 to 3 log10 cfu g−1 over a 9-day period with only marginal deterioration in its visual appearance. Growth potential on rocket was around 2 log10 cfu g−1 over 9 days with considerable deterioration in visual appearance. Growth potential of iceberg lettuce was similar to that of rocket over a 7-day period. Growth curves fitted closely to a linear growth model, indicating none to limited restrictions of growth over the duration of storage. The high growth potentials of L. monocytogenes on spinach alongside the limited visual deterioration highlight the potential risks of consuming this raw RTE food product when contaminated.

The effect of basil leaf (BLE) and wheat bran (WBE) extracts (potent anti-browning agents), on the phenolic content, antioxidant potential, microbiological quality, and consumer quality of shredded lettuce during storage were studied. Treatment of lettuce with increasing concentrations of BLE proportionally increased the total phenolic content and antioxidant properties. Compared to the control, the treatment enhanced the antiradical properties. This was especially visible during the analysis of the chemical extracts, while this effect was not retained in the potentially bioaccessible fraction. In the lettuce stored for 8 days, the highest reducing potential and ability to quench radicals were observed in samples treated with 1% BLE—33 mg Trolox equivalent/g d.m. and 2.8 mg Trolox equivalent/g d.m., respectively. Compounds exhibiting antiradical properties were easily bioaccessible in vitro. There was no negative effect of the treatments on the consumer quality. Most importantly, after 8 days of storage, lettuce treated with the studied extract, except 10% WBE, had higher microbiological quality. After 8-day storage, the coliforms count was reduced by 84% and 88% in samples treated with 0.5% BLE and 10% WBE, respectively. In conclusion, treatments of shredded lettuce with BLE and WBE maintain or even improve its quality during storage.

The aim of this study was to assess the microbiological quality of ready-to-eat (RTE) iceberg lettuce. Our investigation was based on the consumption tendency of university students considered a target market for this product. A total of 78 RTE samples were collected from chain supermarkets and analysed for the enumeration of aerobic mesophilic count (AMC), Escherichia coli and the detection of Salmonella spp. and Listeria monocytogenes. All samples were negative for the presence of pathogens. The mean value of AMC at the beginning, in the middle and after the expiration date was: 6.88, 8.51 and 8.72 log CFU g-1, respectively. The same investigation was performed on 12 samples of fresh iceberg lettuce samples. No pathogens were found and the mean value of AMC was lower than the RTE category (5.73 log CFU g-1; P

Si helps plants to mitigate with abiotic and biotic stresses because of Si-treated plants become stronger, sturdier and naturally more tolerant. The purpose of the investigations was to look the effect of Silicon on the iceberg lettuce growth and quality. There were two treatments: 1. stabilized silicic acid treatment; 2. control. The first spray, when 1 real leaf was present; the second spray was 2 weeks after spray 1; the third spray was 2 weeks after spray 2. First spray: 1 ml silicic acid was solved in 0.5 litre distilled water; second spray: 2 ml silicic acid was solved in 1 litre distilled water; third spray: 2 ml silicic acid was solved in 1 litre distilled water. pH of spray solution was 5,5. Control plants were untreated. Iceberg lettuce plants were taller and more bread in Si treatment compared to control. The content of NO3, N, P, Ca was higher in Si-treated plants. [ABSTRACT FROM AUTHOR]

We investigated the antimicrobial effects of essential oil (EO) vapors individually and in combination against Bacillus cereus. In an initial study, EO vapors were generated from 95 commercially available EOs and their antimicrobial activities against B. cereus were tested. Five EO vapors (citronella, lemongrass, may chang, oregano, and thyme thymol) showed strong inhibitory activity. Next, we determined the minimal inhibitory concentrations (MICs) and minimal lethal concentrations (MLCs) of these EOs against B. cereus cultured on nutrient agar; values were 0.0781 μL/mL and >5 μL/mL, respectively. The synergistic antimicrobial activity of combinations between EO vapors on B. cereus were evaluated using a modified checkerboard assay. Oregano and thyme thymol EO vapors showed greatest synergism (fractional inhibitory concentration index: 0.5000 at a 1:1 vol ratio). Finally, we tested for antimicrobial properties of oregano and thyme thymol EO vapors against B. cereus on iceberg lettuce individually and in combination. The growth of B. cereus was inhibited by 0.0049–0.0098 μL/mL of EO vapors at concentrations 8- to 16-fold lower than that of MICs on nutrient agar. However, a combination of oregano and thyme thymol EO vapors did not have a synergistic lethal effect. Observations provide basic information for the development of decontamination treatments to inhibit the growth of B. cereus and perhaps other spore-forming bacteria on foods and food-contact surfaces using EO vapors. • Antimicrobial effects of essential oil (EO) vapors on Bacillus cereus were investigated. • Citronella, lemongrass, may chang, oregano, thyme thymol EO vapors inhibited B. cereus. • MIC (0.0781 μL/mL) and MLC (>5 μL/mL) of EO vapors against B. cereus were determined. • Oregano and thyme thymol EO vapors showed synergistic lethal effects on nutrient agar. • Oregano and thyme thymol EO vapors inhibited B. cereus on iceberg lettuce leaves. [ABSTRACT FROM AUTHOR]

An antimicrobial sachet releasing vapor of oregano essential oil (EO) was developed and its effectiveness as an antimicrobial packaging system for fresh-cut iceberg lettuce was evaluated. Oregano EO was microencapsulated with polyvinyl alcohol (oregano EO/PVA ratio: 3/5 (w/w)) using a spray-drying technique. The sachet containing oregano microcapsules was incubated with iceberg lettuce at 20 °C and 85% RH for five days. During this storage, the reduction efficiency against growth of Dickeya chrysanthemi , molds and yeasts (MY), and total mesophilic aerobic bacteria (MAB) on the surface of iceberg lettuce was investigated. Oregano EO released from the sachet inhibited the growth of D. chrysanthemi , resulting in 3.9 log CFU/5 pieces reduction over five days storage at 20 °C. The volatile oregano EO also showed significant growth inhibitory effects against MY and total MAB that each was significantly reduced by 2.1 log CFU/5 pieces and 1.5 log CFU/5 pieces, respectively. The texture and color characteristics of the iceberg lettuce were not affected by the release of oregano EO vapor. These results may be useful for the development of antimicrobial packaging systems that are intended to increase the microbiological safety and to extend the shelf life of fresh products. [ABSTRACT FROM AUTHOR]

[Display omitted] • The proliferation stage of L. monocytogenes on iceberg lettuce was after 20 min. • L. monocytogenes aggregated more in lettuce leaf tissue than in stem. • L. monocytogenes internalized farther in stem wounds than in leaf wounds. • Biofilm formation on leaf was faster than stem, but density is opposite. Iceberg lettuce among leafy vegetables is susceptible to contamination with foodborne pathogens, posing a risk of food microbial safety. Listeria monocytogenes (L. monocytogenes) is a highly lethal pathogen that can survive and proliferate on leafy vegetables. In this paper, the contamination stage, attachment site, internalization pathway, proliferation process, extracellular substance secretion and virulence factors expression of L. monocytogenes on iceberg lettuce were researched. Results showed that the contamination stage of L. monocytogenes on iceberg lettuce was 0–20 min, the proliferation stage was after 20 min. The attachment tissues were stomata and winkles. The internalization distance of L. monocytogenes in the midrib was farther than that in the leaf blade. They enhanced the movement ability of cells by up-regulating the expression of flaA and motA genes, and enhanced the adhesion ability of cells by up-regulating the expression of actA and inla genes, which was beneficial to the proliferation. During proliferation, cells gradually secreted extracellular substances to promote the biofilm formation on iceberg lettuce. The formation of biofilms experienced: individual bacteria, cell aggregation and biofilm maturation. Biofilms were more likely to form on the leaf blade of iceberg lettuce. [ABSTRACT FROM AUTHOR]

The customers increasingly prefer fresh-cut packed vegetables which can be used at home easily. The production and trade of these products are very close for their limited shelf life. The aim of analysis is to demonstrate the relationship of expiration-date and the date of keeping quality in different storage temperature. Methods: Samples: one component fresh-cut vegetables and mixes. Storage trial: 6, 12, 20ºC, 11 days. Laboratory analysis: organoleptic evaluation, vitamin C and peroxidase enzyme activity. Results: After 3 day storage the vegetables kept their characteristic features, like fresh smell, colour, good taste, fresh habit. The time and the different temperatures induced different changes among others withering, rotting and fermentation. During the storage experiment 3 groups were found to develop. There are some which can be stored well (iceberg lettuce, endivie), can be stored badly with rotting (spinach, corn salad, rocket salad), and can be stored badly with fermentation (cabbage).