A study of the variation with time of the compositions of the essential leaf oils of 16Eucalyptus species

Anti-Listerial Activity of Four Seaweed Essential Oils Against Listeria monocytogenes

Background

Listeria monocytogenes is one of the most virulent types of bacteria and causes severe foodborne illness, such as listeriosis. Because this pathogen has become resistant to sanitizers and other disinfectants that are used to clean utensils and surfaces during food processing, it poses a serious threat to the food industry.

Objectives

The study was conducted to determine the anti-listerial potential of essential oils extracted from four edible seaweeds against L. monocytogenes.

Materials and Methods

Essential oil was extracted from four edible seaweeds (Enteromorpha linza, Undaria pinnatifida, Laminaria japonica, and Porphyra tenera) against L. monocytogenes using the microwave hydrodistillation method. The anti-listerial activity of the essential oil was determined using the standard disc diffusion method.

Results

Among the four essential oils, E. linza (ELEO) was most effective against all three strains of L. monocytogenes (11.3 - 16.0 mm). The other three essential oils were only effective against two strains, L. monocytogenes ATCC 19115 (10.0 - 10.5 mm) and L. monocytogenes ATCC 7644 (11.0 - 15.0 mm). The minimum inhibitory concentration and the minimum bactericidal concentration of all four essential oils varied from 12.5 - 25.0 mg/mL. Further, the mode of action of ELEO against L. monocytogenes was investigated by examining its effect on cell viability, the release of 260-nm absorbing materials, the number of K+ ions, the relative electrical conductivity, and the salt tolerance capacity. The results indicated that the essential oils exhibited strong anti-listerial activity against multiple strains of L. monocytogenes. It displayed potential inhibitory effects on the viability of bacterial cells and loss of integrity as indicated by an increase in the relative electrical conductivity, leakage of K+ ions and other 260-nm absorbing materials, and a loss of the salt tolerance capacity.

Conclusions

The results presented herein provided insight into a possible explanation for the modes of action of essential oils on L. monocytogenes. The outcome of the present study may aid the food industry in locating the most promising potential anti-listerial agents from edible seaweed sources to control L. monocytogenes and also in facilitating their application in food processing and preservation techniques in a nontoxic and environmental friendly manner.

Responses to mild water deficit and rewatering differ among secondary metabolites but are similar among provenances within Eucalyptus species

Water deficit associated with drought can severely affect plants and influence ecological interactions involving plant secondary metabolites. We tested the effect of mild water deficit and rewatering on physiological, morphological and chemical traits of juvenile Eucalyptus globulus Labill. and Eucalyptus viminalis Labill. We also tested if responses of juvenile eucalypts to water deficit and rewatering varied within species using provenances across a rainfall gradient. Both species and all provenances were similarly affected by mild water deficit and rewatering, as only foliar abscisic acid levels differed among provenances during water deficit. Across species and provenances, water deficit decreased leaf water potential, above-ground biomass and formylated phloroglucinol compound concentrations, and increased condensed tannin concentrations. Rewatering reduced leaf carbon : nitrogen, and total phenolic and chlorogenic acid concentrations. Water deficit and rewatering had no effect on total oil or individual terpene concentrations. Levels of trait plasticity due to water deficit and rewatering were less than levels of constitutive trait variation among provenances. The overall uniformity of responses to the treatments regardless of native provenance indicates limited diversification of plastic responses when compared with the larger quantitative variation of constitutive traits within these species. These responses to mild water deficit may differ from responses to more extreme water deficit or to responses of juvenile/mature eucalypts growing at each locality.

Properties of 1,8-Cineole: A Thermophysical and Theoretical Study

This paper reports on an experimental and theoretical study of 1,8-cineole, one of the main components of essential oils in different plants. The pressure-volume-temperature behavior of this fluid was evaluated accurately over wide temperature and pressure ranges and correlated successfully with the empirical TRIDEN equation. From the measured data, the relevant derived coefficients isothermal compressibility, isobaric expansibility, and internal pressure were calculated. The isobaric heat capacities at high pressure were extrapolated from the data measured at atmospheric pressure. The cubic equations of state by Soave, Peng-Robinson, Stryjek-Vera modification of Peng-Robinson, Patel-Teja, Sako-Wu-Prausnitz, and the SAFT and PC-SAFT molecularly based equations of state were used to predict the PVT behavior. The SAFT and PC-SAFT parameters for 1,8-cineole were obtained from correlation of available saturation literature data; the best results were provided by Sako-Wu-Prausnitz and PC-SAFT equations of state, whereas the classical ones were shown to be inadequate. The molecular structure was studied by quantum computations at the B3LYP/6-311++g(d) level and classical molecular dynamics simulations in the NPT ensemble with the OPLS-AA forcefield. On the basis of both macroscopic and microscopic studies, a complex fluid structure was inferred.

Eucalyptus camaldulensis: volatiles from immature flowers and high production of 1,8-cineole and beta-pinene by in vitro cultures

Calli of Eucalyptus camaldulensis Dehn were induced, for the first time, from immature flowers and stamens and established in the presence of 2,4-D and BA, under dark and light conditions. Immature flowers, of the same type used for callus induction, were submitted to hydrodistillation while the induced calli were extracted with n-pentane. The constituents of the n-pentane extracts and of the hydrodistillate were identified by GC-MS. The main constituents of the hydrodistillate from immature flowers were 1,8-cineole (34.7%), beta-pinene (7.7%), and spathulenol (9.5%). The n-pentane extract from calli developed from stamens consisted only of alkanes, alkenes and alcohols, while that of calli developed from immature flowers consisted mainly of monoterpenes (92.08-96.56%). The main monoterpenes produced in these calli, cultured in darkness and under light conditions, were 1,8-cineole, 62.70 and 69.26% as well as beta-pinene, 27.09 and the 25.31%, respectively.