New approach to study the mechanism of antimicrobial protection of an active packaging.

This article reports on the antimicrobial efficiency of a new active packaging concept based on the use of two essential oils (cinnamon and oregano) and their chemical descriptors (cinnamaldehyde, thymol, and carvacrol) against the Gram-positive bacterium Listeria monocytogenes, the Gram-negative bacterium Salmonella choleraesuis, the yeast Candida albicans, and the mold Aspergillus flavus. Complete inhibition of these microorganisms with either bactericidal or bacteriostatic effect has been demonstrated. It has been proven that the inhibition provided by these solutions is related not to the total amount of the active chemical released but to the amount of active compounds that reach the agar surface at a critical time. This critical time is notably related with the duration of the lag phase, as demonstrated for the bacteria, and shows that kinetic behavior has a critical role in the antimicrobial properties of the active packaging. Two different active films, polypropylene and the complex polyethylene-ethylenvynil alcohol, have been studied and a higher efficiency was found for polypropylene, mainly because of the mentioned kinetic reasons. These results can be used to understand the mechanism of action of the chemicals and provide valuable data for the development of the active packaging concept.

Active paraffin-based paper packaging for extending the shelf life of cherry tomatoes.

A new active paraffin coating for paper and board was evaluated for antimicrobial protection and decay retardation for cherry tomatoes. Different active agents were evaluated against Alternaria alternata fungus both in vitro and in vivo using artificially inoculated cherry tomatoes. Bark cinnamon and oregano essential oil showed the best performance (versus clove and leaf cinnamon essential oils) when incorporated to active paper or board used for packaging at nominal concentrations of 3 and 6% (w/w), respectively. Almost total inhibition of the fungus was obtained when 6% of bark cinnamon essential oil was applied to the packaging material. A number of physicochemical parameters such as pH, weight loss, water activity, and color were monitored, and no significant differences between active, blank, and control samples were found for weight loss and color difference. The maximum transfer of trans-cinnamaldehyde and carvacrol to the food was detected after 1 or 2 days of storage. Sensorial analysis was performed, and panelists were not able to detect changes in cinnamon-based packaged tomatoes but they could in the oregano-based tomatoes.

Effect of mixed antimicrobial agents and flavors in active packaging films.

Active packaging is an emerging food technology to improve the quality and safety of food products. Many works have been developed to study the antimicrobial activity of essential oils. Essential oils have been traditionally used as flavorings in food, so they have an important odor impact but they have as well antimicrobial properties that could be used to protect the food. Recent developments in antimicrobial active packaging showed the efficiency of essential oils versus bread and bakery products among other applications. However, one of the main problems to face is the odor and taste they could provide to the packaged food. Using some aromas to mask the odor could be a good approach. That is why the main objective of this paper is to develop an antimicrobial packaging material based on the combination of the most active compounds of essential oils (hydrocinnamaldehyde, oregano essential oil, cinnamaldehyde, thymol, and carvacrol) together with some aromas commonly used in the food industry. A study of the concentration required to get the antimicrobial properties, the organoleptic compatibility with typical aroma present in many food systems (vanilla, banana, and strawberry), and the right combination of both systems has been carried out. Antimicrobial tests of both the mentioned aromas, the main components of some essential oils, and the combination of both groups were carried out against bacteria (Enterococcus faecalis, Listeria monocytogenes, Bacillus cereus, Staphylococcus aureus, Salmonella choleraesuis, Yersinia enterocolitica, Escherichia coli), yeasts (Candida albicans, Debaryomyces hansenii, Zygosaccharomyces rouxii), and molds (Botrytis cinerae, Aspergillus flavus, Penicillium roqueforti, Eurotium repens, Penicillium islandicum, Penicillium commune, Penicillium nalgiovensis). The sensory properties of the combinations were evaluated with a triangular test and classification was by an order test; the odor threshold of the aroma compounds was also studied. The results reveal that none of the aromas had antimicrobial properties. The most antimicrobial compounds are thymol, carvacrol, and cinnamaldehyde, but none of them could be combined with banana aroma, whereas only thymol with strawberry aroma gave the right combined organoleptic profile. All of the antimicrobials under study could be combined with vanilla aroma, providing both antimicrobial property and the odor expected.

Determination of fifteen active compounds released from paraffin-based active packaging in tomato samples via microextraction techniques.

Automated headspace solid-phase microextraction (HS-SPME) and hollow-fibre liquid-phase microextraction (HFLPME) methods for the determination of 15 active chemicals released from essential-oil-based active packaging have been considered. The HS-SPME procedure demonstrates good performance and was therefore optimised and validated, providing detection limits in the low microgram per kilogramme range and wide and convenient linear ranges from 40.0 to 900.0 microg/kg. Extraction temperature has been demonstrated to be the most critical experimental parameter requiring accurate monitoring.

Active single-drop microextraction for the determination of gaseous diisocyanates.

This paper presents a novel application of active single-drop microextraction (SDME) for the determination of mixtures of four gaseous diisocyanates: 2,4- and 2,6-toluene diisocyanate (TDI), hexamethylene diisocyanate (HDI) and methylene diphenyl diisocyanate (MDI). The optimised simultaneous extraction, preconcentration and derivatization method utilizes a 2.3-microL Milli-Q water drop containing dibutylamine (DBA) as a derivatization reagent and phenylisocyanate (PHI) as an injection standard. A type III screening design, combined with Box-Behnken surface modelling and Simplex optimisation was applied to optimise the method. Several SDME approaches--standard SDME, automatic organic solvent film (OSF) and use of a supported-drop (SD) device--were compared with solid-phase microextraction (SPME) in terms of sensitivity and robustness under varied conditions. Of these SDME alternatives, SD proved to be the most suitable for diisocyanate sampling. The detection limits using SDME followed by UPLC-MS-MS analysis were 0.9 and 0.8 microg m(-3) for 2,4- and 2,6-TDI, respectively, 1.0 microg m(-3) for HDI and 0.2 microg m(-3) for MDI.

Strategies for single-drop microextraction optimisation and validation. Application to the detection of potential antimicrobial agents.

Convenient methods that are capable of determining potentially antimicrobial compounds in both vapour and liquid phases are required (inter alia) to facilitate the development of active packaging materials using natural substances. The suitability of single-drop microextraction (SDME) coupled with gas chromatography-mass spectrometry (GC-MS) for this purpose has been assessed by evaluating its ability to determine a range of analytes (mainly terpenes) in vapour samples and three liquid food simulants - distilled water, 10% (v/v) water/ethanol, and 3% (w/v) acetic acid - by headspace-SDME (HS-SDME) and direct immersion-SDME (DI-SDME), respectively. In this contribution, a screening strategy based on the Hildebrand solubility parameter has been used to build a solvent priority list. Solvents were then tested following the list, taking into account additional factors such as low volatility for HS-SDME or buoyancy and relative miscibility for DI-SDME. Other experimental parameters affecting the performance of SDME (such as drop volume, sampling time and temperature, drop position in the sample vial, sample vial size, stirring rate, filling rate and ionic strength of the sample) were investigated using a Plackett-Burman screening design. The method optimisation was completed by means of response surface modelling (RSM). The methods were validated by characterising relevant performance parameters including their robustness, linear range, accuracy (trueness and precision) and capability of detection as described by the International Organization for Standardization.

Vapor-phase activities of cinnamon, thyme, and oregano essential oils and key constituents against foodborne microorganisms.

The aim of the study presented here was to gain knowledge about the vapor-phase antimicrobial activity of selected essential oils and their major putatively active constituents against a range of foodborne bacterial and fungal strains. In a first step, the vapor-phase antimicrobial activities of three commercially available essential oils (EOs)-cinnamon (Cinnamomum zeylanicum), thyme (Thymus vulgaris), and oregano (Origanum vulgare)-were evaluated against a wide range of microorganisms, including Gram-negative bacteria (Escherichia coli, Yersinia enterocolitica, Pseudomonas aeruginosa, and Salmonella choleraesuis), Gram-positive bacteria (Listeria monocytogenes, Staphylococcus aureus, Bacillus cereus, and Enterococcus faecalis), molds (Penicillium islandicum and Aspergillus flavus), and a yeast (Candida albicans). The minimum inhibitory concentrations (MICs) were generally lower for oregano EO than for the thyme and cinnamon EOs, especially against the relatively resistant Gram-negative. The persistence of the EOs' antimicrobial activities over time was assessed, and changes in the composition of the atmosphere they generated over time were determined using single-drop microextraction (SDME) in combination with gas chromatography-mass spectrometry (GC-MS) and subsequent analysis of the data by principal component analysis (PCA). More relevant chemicals were selected. In addition, the vapor-phase activities of putatively key constituents of the oils were screened against representative Gram-positive (L. monocytogenes) and Gram-negative (S. choleraesuis) bacteria, a mold (A. flavus), and a yeast (C. albicans). Of the tested compounds, cinnamaldehyde, thymol, and carvacrol showed the strongest antimicrobial effectiveness, so their MICs, defined as the minimum vapor concentrations that completely inhibited detectable growth of the microorganisms, were calculated. To check for possible interactions between components present in the EOs, cinnamon EO was fortified with cinnamaldehyde and thyme EO with thymol, and then the antimicrobial activities of the fortified oils were compared to those of the respective unfortified EOs using fractional inhibitory concentration (FIC) indices and by plotting inhibition curves as functions of the vapor-phase concentrations. Synergistic effects were detected for cinnamaldehyde on A. flavus and for thymol on L. monocytogenes, S. choleraesuis, and A. flavus. In all other cases the fortification had additive effects, except for cinnamaldehyde's activity against S. choleraesuis, for which the effect was antagonistic. Finally, various microorganisms were found to cause slight changes over time to the atmospheres generated by all of the EOs (fortified and unfortified) except the fortified cinnamon EO.

Use of new generation poly(styrene-divinylbenzene) resins for gas-phase trapping-thermal desorption. Application to the retention of seven volatile organic compounds.

Two new generation polymeric resins, Bond Elut ENV (styrene-divinylbenzene) from Varian and LiChrolut EN (ethylvinylbenzene-divinylbenzene) from Merck, commonly used in liquid--solid-phase extraction (SPE) were evaluated as sorbents for gas-phase sampling followed by thermal desorption and compared to Tenax TA, a reference sorbent in this kind of applications. The three resins were tested against seven volatile organic compounds (VOCs): 1-octene, ethylbenzene, (p-, m-, o-)xylenes, styrene and 1,4-dichlorobenzene. Elution curves for all compounds were determined at temperatures from 120 to 180 degrees C, and from such curves, different parameters, such as retention factor (k), distribution coefficient (K), height equivalent to a theoretical plate (H), asymmetry factor (Fa) and breakthrough volume (VB) were calculated and extrapolated at room (25 degrees C) and desorption (220 degrees C) temperatures in order to estimate breakthrough and elution volumes. In average, retention in LiChrolut EN is 10 and 200 times stronger than in Bond Elut ENV and Tenax TA, respectively, but its chromatographic behavior is rather poor giving quite asymmetric elution profiles (Fa >1.8 at 120 degrees C). Bond Elut ENV exhibited the best chromatographic behavior, with H values two or five times lower than those of LiChrolut EN or Tenax TA. An additional advantage of the new sorbents is that retention decreases with T much faster than it does in Tenax (8 or 20 times for Bond Elut ENV or LiChrolut EN). Modeling has finally shown that beds with 60-80 (for Bond Elut ENV) or 300-400 (for LiChrolut EN) times less of sorbent have the same retention properties than standard Tenax TA tubes and similar (LiChrolut EN) or five to six times smaller (Bond Elut ENV) elution volumes. These predictions have been experimentally confirmed.

Subcritical water and dynamic sonication-assisted solvent extraction of fluorescent whitening agents and azo dyes in paper samples.

Two low-volume solvent continuous extraction methods are applied to the extraction of paper matrices. In the methods reported here, a complex mixture of fluorescent whitening agents (FWAs) and azo dyes (AZOs) used in paper materials intended to come into contact with foodstuffs was extracted by using subcritical water extraction (SWE) and dynamic sonication-assisted solvent extraction (DSASE). Rationale for the work is based upon migration concerns of these groups of analytes from the packaging to the packaged items, thus compromising their subjective and/or objective quality. In SWE, sample was extracted in 21 min with 0.5 mL of water, whereas the DSASE method required 11 min and used 7 mL of water. DSASE was further developed by incorporating an organic modifier in order to change water polarity, thus improving extraction of moderately polar analytes. This way, modified-DSASE used a total organic volume of 0.9 mL which represents a reduction of 200 times in organic solvent consumption (200 mL versus approximately 1.0 mL) and 11 times in extraction time (2h versus 11 min) compared to the existing methods. SWE was able to extract only 9 out of 12 test analytes with average recoveries between 10 and 25% whereas modified-DSASE succeed in extracting all the target analytes with an average recovery of 89%. Complete discussion and explanation concerning these differences are provided in the text.

Application of single-drop microextraction to the determination of dialkyl phthalate esters in food simulants.

A fast and simple method, using static single-drop microextraction (SDME), has been developed to facilitate the identification and quantification of seven dialkyl phthalate esters in the three aqueous food simulants. The simulants were: A, distilled water; B, 3% (w/v) acetic acid/water; and C, 15% (v/v) ethanol/water. The extraction is performed by simply suspending a drop of organic solvent in the aqueous sample using a conventional gas chromatography (GC) microsyringe. Following extraction, the organic phase is withdrawn into the syringe and analyzed by gas chromatography and flame ionization detection (FID). The optimized method yields a linear calibration curve over three orders of magnitude for all the simulants, and method detection limits (MDLs) allowing detection of all the studied compounds at concentrations below migration limits established by the European Union. The accuracy of the SDME method was tested and compared to that of solid-phase microextraction (SPME) by recovery experiments using spiked samples, with results ranging from 85 to 115% in most cases.

Enhanced detection of nitroaromatic explosive vapors combining solid-phase extraction-air sampling, supercritical fluid extraction, and large-volume injection-GC.

A complete method for sampling and analyzing of energetic compounds in the atmosphere is described. The method consists of the hyphenation of several techniques: active air sampling using a solid-phase extraction cartridge to collect the analytes, extraction of the sorbed analytes by toluene/methyl tert-butyl ether modified supercritical fluid extraction (SFE), and analysis of the extract by large-volume injection GC-nitrogen/phosphorus detection. The GC system is equipped with a loop-type injection interface with an early solvent vapor exit, a utilizing concurrent solvent evaporation technique. Chemometric approaches, based on a Plackett-Burman screening design and a central composite design for response surface modeling, were used to determine the optimum SFE conditions. The relative standard deviations of the optimized method were determined to be 4.3 to 7.7%, giving raise to method detection limits ranging from 0.06 to 0.36 ng in the sampling cartridge, equivalent to 6.2-36.4 pg/L in the atmosphere, standard sampling volume 10 L. The analytical method was applied to characterize headspace composition above military grade trinitrotoluene (TNT). Results confirm that 2,4-dinitrotoluene (DNT) and 1,3-dinitrobenzene (DNB) constitute the largest vapor flux, but TNT, 2,6-DNT, and trinitrobenzene TNB were also consistently detected in all the samples.

On-line coupling of supercritical fluid extraction with high-performance liquid chromatography for the determination of explosives in vapour phases.

An analytical method for determining nitroaromatic explosives in vapour phases is presented. Samples were collected by pumping air through glass fibre filters and polyurethane foam adsorbents, and an on-line extraction system combining supercritical fluid extraction (SFE) and high-performance liquid chromatography (HPLC) was developed. This allows analytes to be transferred from the adsorbent to the HPLC system via a porous graphitic carbon trap. When using gradient elution with a suitable mobile phase, most of the nitroaromatic isomers tested were separated. The proposed method is fully automated, allows a complete analysis to be processed in less than 30 min, and it is compatible with most of the organic solvents commonly used as SFE modifiers or additives. The method has been applied to the analysis of real samples obtained from headspace sampling of military-grade 2,4,6-trinitrotoluene and has been shown to constitute a promising alternative for assessing whether areas are mined in landmine-clearing operations.