Microemulsification of clove essential oil improves its in vitro and in vivo control of Penicillium digitatum

Clove essential oil (CEO) is a promising alternative to chemical fungicides for postharvest decay control. However, relatively high concentrations required for in vivo microbial growth inhibition limit its application. Hence, this study aimed to strengthen the antifungal activity of CEO by loading it in microemulsion system. Two CEO microemulsions (ME-1, CEO/ethanol/Tween 80 = 1:2:7; ME-2, CEO/ethanol/Tween 80 = 1:3:6) were evaluated their antifungal activity against Penicillium digitatum in vitro and in navel oranges. Microemulsification of CEO caused a reduction of MIC (minimum inhibitory concentration) from 0.50 μl/ml to 0.25 μl/ml, while the MFC (minimum fungicidal concentration) remained unchanged at 0.50 μl/ml, indicating enhancement of only fungistatic activity. The decay incidence of navel oranges treated with ME-1 and ME-2 was significantly (p < 0.05) reduced by 34.51% and 20.93%, respectively, in comparison to that of pure oil treatment after 5 days' storage at 25 °C. In the vapor phase, CEO microemulsions had the best control of lesion diameter and decay development. Additionally, the improved antifungal activity of CEO microemulsions may be related to their stronger ability to suppress spore germination and germ tube elongation of P. digitatum. The enhanced control of postharvest green mold of navel oranges by CEO after microemulsification can broaden its application in food industry.     

Synergetic antibacterial efficacy of cold nitrogen plasma and clove oil against Escherichia coli O157:H7 biofilms on lettuce

This study aims to evaluate the antimicrobial effects of cold nitrogen plasma (CNP) and clove oil against Escherichia coli O157:H7 (E. coli O157:H7) biofilm on lettuce. Both clove oil (1 mg/mL, 2 mg/mL and 4 mg/mL) and CNP (400–600 W) displayed significant eradication effect on E. coli O157:H7 biofilms in vitro (p < 0.001). Subsequently, the antibiofilm effect of combined treatment was studied as well. Compared with the respective treatment, combined treatment exhibited remarkable synergistic effect on eradicating E. coli O157:H7 biofilms. The confocal laser scanning microscopy (CLSM) and scanning electron microscopy (SEM) had also visually testified that the antibacterial effects of clove oil on E. coli O157:H7 biofilms (in vitro and on lettuce) were enhanced by CNP at 400 W for short treatment duration. The results of sensory evaluation indicated that combined treatment has mild negative effect on lettuce quality. Moreover, the synergetic antibacterial mechanism of clove oil and CNP against E. coli O157:H7 was concluded as that they could damage the bacterial cell wall and the outer membrane, leading to leakage of cellular components, such as nucleic acid and ATP.     

Control of bacteria growth on ready-to-eat beef loaves by antimicrobial plastic packaging incorporated with garlic oil

This study was designated to ascertain the effectiveness of low density polyethylene (LDPE) based film incorporated with garlic oil for inhibition of food pathogen on ready-to-eat beef loaves. The blown film extrusion method was employed to produce film samples added with garlic oil in 2, 4, 6 and 8% w/w as well as sample with 0% w/w which served as control throughout the study. Besides, several analyses were also conducted to determine the water vapour barrier properties, thermal stability and bonding interaction of the plastic packaging as influenced by the incorporation of garlic oil. The outcomes of challenge test showed that regardless of the garlic oil amount (2–8% w/w), the antimicrobial plastic packaging was able to reduce the number of Listeria monocytogenes on beef loaves after 3, 6, 9 and 15 days of storage at 4 °C. However, there were insignificant effects on both Escherichia coli and Brochothrix thermosphacta. For water vapour barrier properties, films with higher amount of garlic oil proved to have weaker barrier properties. There was lack of significant difference in the thermal stability for all samples when tested with thermogravimetry analyser. Also, the infrared analysis indicated garlic oil does not change the polymer structure.     

Antimicrobial effects of modified chitosan based coating containing nanoemulsion of essential oils,modified atmosphere packaging and gamma irradiation against Escherichia coli O157:H7 and Salmonella Typhimurium on green beans

The antibacterial activity of modified chitosan-based coatings containing nanoemulsion of essential oils (EOs), gamma irradiation, modified atmosphere packaging (MAP), alone or in combinations, against Escherichia coli O157:H7 and Salmonella Typhimurium was evaluated on inoculated green bean samples. Firstly, four different nanoemulsions, made of carvacrol, mandarin, bergamot and lemon Eos, respectively, were compared in terms of minimum inhibitory concentration (MIC) against the two bacteria evaluated in vitro using the micro-broth dilution method. Carvacrol nanoemulsion resulted to be the most effective antibacterial agent and was therefore selected to be incorporated into modified chitosan (MC) to form a bioactive coating. Secondly, the radiosensitivity of E. coli and S. Typhimurium to gamma irradiation was evaluated on inoculated green beans after coating deposition and MAP. Results showed that, without MAP, MC-based coating containing carvacrol nanoemulsion significantly increased the radiosensitization of E. coli and S. Typhimurium by 1.32-fold and 1.30-fold, respectively. Remarkably, the use of bioactive coating under MAP caused a synergistic effect with an increase in radiosensitivity by 1.80-fold and 1.89-fold for E. coli and S. Typhimurium, respectively. Thirdly, the antibacterial effects of the antimicrobial coating, gamma irradiation, MAP alone and their combinations were evaluated against these two bacteria during a 13-days storage of green beans at 4 °C. Bioactive coating deposition or gamma irradiation treatment resulted effective in controlling the growth of the two bacteria during the entire shelf-life. Moreover, it was also found that the combined treatment of antimicrobial coating, gamma irradiation and MAP caused the reduction of microbial population to undetectable levels during the whole storage period for E. coli and from day 7 to the end of storage for S. Typhimurium. The obtained results can be interested to food companies aiming to ensure the food safety with a prolonged shelf life.     

Antimicrobial activity of chitosan,organic acids and nano-sized solubilisates for potential use in smart antimicrobially-active packaging for potential food applications

Antimicrobial activity of low- and medium-molecular weight chitosan and organic acids (Benzoic acid and Sorbic acid and commercially-available nano-sized benzoic- and sorbic-acid solubilisate equivalents) was investigated and compared against commercial mixtures of organic acids used as meat coatings (Articoat DLP-02^® and Sulac-01^®). From the antimicrobials tested, both low molecular weight (LMW) and medium molecular weight (MMW) chitosan exhibited the highest antimicrobial activity against all bacterial cultures tested, with mean MIC values of 0.010 and 0.015% w/v, respectively. The results suggested that the MW of the chitosan used effected antimicrobial activity of the chitosan. Nano-sized solubilisates of benzoic acid and sorbic acid had significantly (P < 0.05) higher antimicrobial properties than their non-nano equivalents. The results found in this study open opportunities for the nano-sized solubilisates, derived from food compatible sources, to be used in smart and active antimicrobial packaging applications, as less of the antimicrobial substances in question is required to deliver the same antimicrobial effect.     

Evaluation of two antimicrobial packaging films against Escherichia coli O157:H7 strains in vitro and during storage of a Spanish ripened sheep cheese (Zamorano)

The antimicrobial activity of two packaging films (polypropylene – PP- and polyethylene terephthalate – PET-) coated with different concentrations (0, 4, 6 and 8%) of essential oil from Origanum vulgare (OR) and Ethyl Lauroyl Arginate HCl (LAE) was tested against two Escherichia coli O157:H7 strains using in vitro systems and a raw milk sheep cheese model (Zamorano). The influence of the antimicrobials on the sensory attributes of cheese was also evaluated. For both strains, the MBC (minimum bactericidal concentration) values were identical to their respective MIC (minimum inhibitory concentration) values and lower for LAE (25 mg/l) than for OR (200–400 mg/l). PP and PET films coated with OR were tested by a vapour phase assay and the Japanese Standard method (JIS Z 2801:2000). Both films coated with LAE were tested by an agar diffusion method. Overall, in vitro tests were effective against both strains. The inhibitory activity depended on the active compound concentration, the target strain and the packaging material, PET being more effective than PP. For inoculated cheese slices, OR and LAE PP films did not effectively decrease E. coli O157:H7 counts after 7-days cold storage. PET films incorporating 6 and 8% of OR and LAE significantly (p < 0.05) decreased the numbers of both strains and also did 4% for the reference and wild strain depending on the antimicrobial. LAE PP, OR PET and LAE PET did not significantly (p > 0.05) affect sensorial characteristics of Zamorano cheese. Packaging with PET films coated with ≥6% LAE concentrations might be useful in reducing E. coli O157:H7 numbers in sheep cheese.     

Antibacterial activity of plant essential oils and extracts: The role of thyme essential oil,nisin, and their combination to control Listeria monocytogenes inoculated in minced fish meat

Food poisoning caused by Listeria monocytogenes leads to a 30% rate of mortality among patients. The antibacterial activity of cinnamon, thyme, and rosemary essential oils (EOs) and shallot and turmeric extracts was tested against L. monocytogenes using agar well and disc diffusion techniques. Results showed that thyme EO had the highest antimicrobial activity, followed by cinnamon and rosemary EOs, respectively. The antilisterial activity of thyme EO at 0.4%, 0.8%, and 1.2% levels, nisin at 500 or 1000 IU/g level, and their combination against L. monocytogenes was examined in minced fish samples. The antilisterial properties of nisin were also investigated in cooked minced fish treatments. Nisin at 500 or 1000 IU/g in the minced fish meat demonstrated bacteriostatic activity against L. monocytogenes. The use of thyme EO at 0.8% and 1.2% reduced the L. monocytogenes viable count below 2 log cfu/g after 6 days. Furthermore, simultaneous use of thyme EO at 0.8% and 1.2%, and nisin at 500 or 1000 IU/g level, reduced the L. monocytogenes viable count below 2 log cfu/g after the second day of storage. The antilisterial activity of nisin in the cooked minced fish samples was slightly stronger than that of the raw group.     

Thermo-mechanical,structural characterization and antibacterial performance of solvent casted polylactide/cinnamon oil composite films

Polylactic acid (PLA) based composite films were prepared by incorporating polyethylene glycol (PEG) and cinnamon oil (CIN) (25 and 50% w/w of PLA) via solution casting method. Morphological, structural, thermo-mechanical, spectral, and antibacterial properties of PLA/PEG/CIN films were investigated. Tensile strength (TS) and tensile modulus (TM) of the film decreased, while the elongation at break (EAB) increased by increasing CIN concentration. Using the principle of time-temperature superposition, the viscous modulus and the complex viscosity of composite films at selected temperatures and frequencies (time scales) were superimposed well in an extended frequency range. Thermal properties decreased substantially with incorporation of CIN. Significant changes in molecular organisation and intermolecular interactions between CIN and PLA/PEG matrix were observed through the FTIR spectroscopy. Scanning electron microscopic (SEM) revealed rough surfaces of the composite films. The effectiveness of composite films was tested against Listeria monocytogenes and Salmonella typhimurium inoculated in chicken samples, and it was found that the film containing 50% CIN showed an antibacterial activity during 16 days storage at refrigerated condition. The developed film has a potential for packaging of chicken samples with extended storage.     

柴油吸附脱硫活性炭改性吸附剂研究

研究了用不同金属离子以及糠醛、糠醇、浓硫酸、浓硝酸对活性炭进行改性对活性炭吸附剂对FCC柴油和由正癸烷和二苯并噻吩(DBT)组成的模拟柴油的脱硫率的影响。实验结果表明:金属离子改性中Fe离子改性活性炭脱硫率好;活性炭浸涂糠醛、糠醇也可以提高吸附脱硫性能;浓硫酸、浓硝酸氧化可以增加活性炭表面酸性基团的量,改进脱硫性能,浓硫酸优于浓硝酸。进行了活性炭复合改性实验,结果表明,浓硫酸氧化后再进行Fe改性,脱硫率最高,吸附DBT模型物的脱硫率可达到100%。     

Application of high-pressure processing and polylactide/cinnamon oil packaging on chicken sample for inactivation and inhibition of Listeria monocytogenes and Salmonella Typhimurium,and post-processing film properties

The synergistic effects of combined high-pressure (HP) treatment and active packaging consisting of polylactide (PLA), polyethylene glycol (PEG) and cinnamon oil (CIN) on the inactivation and inhibition of Listeria monocytogenes and Salmonella Typhimurium in chicken samples during the refrigerated storage were assessed. The target was to decrease the treatment pressure intensity of the traditional HP technology and cinnamon oil concentration so that the process becomes more economically viable. The CIN concentration was varied from 7 to 17% in the plasticized film (PLA/PEG 80/20). It was observed that the most effective treatment was the combination of a pressure treatment at a level of 300 MPa, and packaging the chicken sample in an active packaging containing 17% CIN, which reduced the population of the pathogens to a safe level during 21 days of refrigerated storage. Furthermore, the impact of HP and CIN on the thermal, rheological and mechanical properties of those films was evaluated. Time-temperature superposition principle indicated that the mechanical properties of those films remained intact after the HP-treatment, and at high temperature. Therefore, the developed films could be used for packaging of chicken samples under high-pressure, and high-temperature with maintaining the packaging integrity and the food safety at the highest level.     

Development and performance of whey protein active coatings with Origanum virens essential oils in the quality and shelf life improvement of processed meat products

Active coating development for prevention and control of microbial contamination is an extremely challenging technology. In this field, the potential of plant-based compounds to be used as a complement or an alternative to the synthetic preservatives have drawn increasing attention from the food industry.In this study, an active coating containing Origanum virens essential oil (EO-WPC) was applied on the surface of two traditional Portuguese sausages (paínhos and alheiras) during industrial production. For 4 months, both products were regularly monitored for their physicochemical properties and total microbial load. Sensory evaluation was also carried out for each sausage type.The application of the EO-WPC caused little variations on the moisture content and texture profile. Higher acidity and protection against color fading was observed particularly in paínhos, while coated alheiras had a significant reduction of the lipid peroxidation. Inhibition of the total microbial load was observed for both coated sausages, resulting in an extension of the shelf life of approximately 20 and 15 days for paínhos and alheiras, respectively. Sensory analysis revealed an overall positive acceptance. These results support the great potential of O. virens EO to be used as food preservative in processed meat products.