Bactericidal action of lemon grass oil vapors and negative air ions

Essential oils and essential oil compounds in animal production as antimicrobials and anthelmintics: an updated review

Several countries have shown an increased prevalence of drug resistance in animal production due to the indiscriminate use of antibiotics and antiparasitics in human and veterinary medicine. This article aims to review existing methods using naturally occurring essential oils (EOs) and their isolated compounds (EOCs) as alternatives to antimicrobials and antiparasitic compounds in animal production and, consequently, to avoid resistance. The most-reported mechanism of action of EOs and EOCs was cell membrane damage, which leads to the leakage of cytoplasmic content, increased membrane permeability, inhibition of metabolic and genetic pathways, morphologic changes, antibiofilm effects, and damage to the genetic material of infections. In parasites, anticoccidial effects, reduced motility, growth inhibition, and morphologic changes have been reported. Although these compounds regularly show a similar effect to those promoted by traditional drugs, the elucidation of their mechanisms of action is still scarce. The use of EOs and EOCs can also positively influence crucial parameters in animal production, such as body weight gain, feed conversion rate, and cholesterol reduction, which also positively impact meat quality. The application of EOs and EOCs is enhanced by their association with other natural compounds or even by the association with synthetic chemicals, which has been found to cause synergism in their antimicrobial effect. By reducing the effective therapeutical/prophylactic dose, the chances of off-flavors – the most common issue in EO and EOC application – is greatly mitigated. However, there is very little work on the combination of EOs and EOCs in large in vivo studies. In addition, research must apply the correct methodology to properly understand the observed effects; for example, the use of only high concentrations may mask potential results obtained at lower dosages. Such corrections will also allow the elucidation of finer mechanisms and promote better biotechnologic use of EOs and EOCs. This manuscript presents several information gaps to be filled before the use of EOs and EOCs are fully applicable in animal production.

Role of Litsea cubeba Essential Oil in Agricultural Products Safety: Antioxidant and Antimicrobial Applications

The essential oil from Litsea cubeba (LCEO) has good antioxidant, antimicrobial, anti-insect properties, which gives it the potential for use as a natural additive to food resources and food products in order to prevent spoilage and extend shelf life. In this study the biological activity related to food preservation was observed. The main volatile organic compounds were geranial (39.4%), neral (29.5%), and limonene (14.3%). Antioxidant activity was 30.9%, which was equal to 167.94 µg of Trolox per mL of sample. Antimicrobial activity showed the strongest inhibition against Serratia marcescens by disk diffusion method and minimum inhibitory concentrations MIC 50 and MIC 90 were the lowest for Micrococcus luteus with values 1.46 and 3.52 µL/mL, respectively. Antimicrobial activity of the LCEO vapor phase showed strong inhibition of microorganisms on apples, pears, potatoes, and kohlrabies. Over 50% of gram-positive and gram-negative bacteria and yeasts were inhibited by a concentration of 500 µL/mL. The inhibition of microorganisms was concentration dependent. Anti-insect activity was also strong, with 100% lethality of Pyrrhocoris apterus at a concentration of 25%. These results suggest that LCEO could be potentially used as a food preservative.

Effects of negative air ions treatment on the quality of fresh shiitake mushroom (Lentinus edodes) during storage

Fresh shiitake (Lentinus edodes) is prone to brown, pileus-opening and flavor-loss during storage. Therefore, it is important to find an effective preservation method for fresh shiitake. Negative air ions (NAI) are negatively-charged molecules or atoms in the air, and can affect the physiological metabolism of live cells and be conveniently used with low cost. In this study, NAI treatment was performed at different times and the physico-chemical characteristics, microstructure, membrane potential and energy metabolism of shiitake were determined during storage. Results showed that NAI treatment for 40 min could reduce 29% of browning index and maintain the hardness of shiitake. NAI treatment groups had higher content of sweetness amino acids, umami amino acids, 5'-IMP, eight-carbon alcohols compounds and cyclic sulfides compounds than the control, and comprehensive quality of the group being treated for 40 min was the best. The mitochondria of shiitake swelled and the membrane potential decreased after being treated by NAI. However, NAI treatment for 40 min could improve the contents of ATP and ADP, maintain a relatively stable energy charge level, and promote energy utilization of shiitake during storage. The results demonstrated that NAI treatment had the potential to improve the quality shiitake during storage.

A new advanced packaging system for extending the shelf life of refrigerated farmed fish fillets

BACKGROUND

An innovative pilot-plant packaging was developed and evaluated for applying oregano essential oil (OEO) vapours in conditions of high vacuum for exploring the antimicrobial effect of essential oil vapours applied immediately before packaging of fish fillets. Farmed sea bream (Sparus aurata) fresh fillets have been used as a model for validating this new technology. These fillets, as a refrigerated product under modified atmosphere packaging (MAP), have a relatively short shelf life (12-14 days) mainly due to the fast microbial growth. The effects of conventional OEO dippings [pretreatment dipping (0.1% of OEO) of whole fish (T1) and filleted sea bream (T2)] were compared with the OEO application in vapour phase (67 μL L^-1 ) under vacuum (5-10 hPa) immediately before MAP fillet packaging (T3).

RESULTS

T3/T2 samples showed the lowest microbial growth after 28 days at 4 °C, with loads up to 1/2.6 log units for Enterobacteria/lactic acid bacteria compared to untreated samples. The initial trimethylamine nitrogen (TMA-N) content (2.6 mg kg^-1 ) increased in T1 and T2/T3 samples by 9.6 and 6/7 units, respectively, after 28 days. Quality Index Method (QIM) better reflected the fish fillets shelf life than texture and colour measurements. The shelf life of T3/T2 samples was established in at least 28 days (4 °C), while the QIM threshold (6) was exceeded after 7/21 days in untreated/T1 fillets.

CONCLUSION

The fish shelf life was extended with vapour OEO treatment using this new technology, similarly to OEO dipping treatment, according to QIM, corroborated by the microbial quality and TMA-N contents. © 2020 Society of Chemical Industry.

Antimicrobial activity of gaseous Citrus limon var pompia leaf essential oil against Listeria monocytogenes on ricotta salata cheese

Contamination by Listeria monocytogenes is a particularly challenging problem in the food industry due to the ability of the bacterium to develop under conditions normally used for food preservation. Here, we show that the gaseous phase of Citrus limon var pompia leaf essential oil (hereafter PLEO) exerts specific anti-Listeria activity on ricotta salata cheese stored at 5 °C. The synergic effect of gaseous PLEO treatment and refrigeration was first confirmed in vitro on L. monocytogenes strains treated for 3 h with gaseous PLEO and then stored at 5 °C. Ricotta cheese was then inoculated with L. monocytogenes strains and subjected to hurdle technology with different concentrations of gaseous PLEO. Cell counts revealed gaseous PLEO to exert a bactericidal effect on L. monocytogenes 20600 DSMZ and a bacteriostatic effect on a mix of L. monocytogenes strains. Scanning and transmission electron microscopy analyses of L. monocytogenes cells suggested that gaseous PLEO targets the bacterial cell wall and plasma membrane. Chemical analyses of the liquid and vapor phases of PLEO indicated linalyl acetate to be the predominant compound, followed by limonene and the two isomers of citral, whereas EO composition analysis, although generally in line with previous findings, showed the presence of linalyl acetate for the first time. Solid-phase microextraction coupled with gas chromatography confirmed the presence of all crude oil components in the headspace of the box.

Development of antimicrobial nanoemulsion-based delivery systems against selected pathogenic bacteria using a thymol-rich Thymus daenensis essential oil

AIMS

Thymol-rich medicinal plants have been used in traditional medicine to relieve infectious diseases. However, the application of essential oils as medicine is limited by its low water solubility and high vapour pressure. The objective of this study was to produce stable nanoemulsions of Thymus daenensis oil in water by preventing Ostwald ripening and phase separation.

METHODS AND RESULTS

The antibacterial activity of bulk and emulsified essential oil against selected pathogenic bacteria including Gram-negative (Haemophilus influenzae, Pseudomonas aeruginosa) and Gram-positive (Streptococcus pneumoniae) were investigated in the liquid and vapour phase. The optimum formulation (L2) contained 2% Tween 80 (surfactant) and 0·1% lecithin (cosurfactant) had a mean droplet diameter of 131 nm. In the liquid phase, the optimized nanoemulsion exhibited good antibacterial activity against S. pneumonia with MIC value of 0·0039 mg mL^-1 . In the vapour phase, the MIC values against S. pneumonia were similar (<7·35 μL L^-1 ) for both bulk and emulsified essential oil. However, there was no antibacterial activity in the vapour phase against H. influenzae and P. aeruginosa. Analysis of thymol concentration in the head space indicated that the nanoemulsion retarded the release of thymol into the vapour phase.

CONCLUSIONS

These findings highlight the potential applications of nanoemulsions containing essential oils as antibacterial products.

SIGNIFICANCE AND IMPACT OF THE STUDY

The results of the current study highlight the advantages of nanoemulsification for improvement of the physicochemical properties and the antibacterial activity of T. daenensis EOs in the liquid and vapour phase for therapeutic purposes.

Beneficial Effects of Spices in Food Preservation and Safety

Spices have been used since ancient times. Although they have been employed mainly as flavoring and coloring agents, their role in food safety and preservation have also been studied in vitro and in vivo. Spices have exhibited numerous health benefits in preventing and treating a wide variety of diseases such as cancer, aging, metabolic, neurological, cardiovascular, and inflammatory diseases. The present review aims to provide a comprehensive summary of the most relevant and recent findings on spices and their active compounds in terms of targets and mode of action; in particular, their potential use in food preservation and enhancement of shelf life as a natural bioingredient.

Bioactivity of essential oils: a review on their interaction with food components

Essential oils (EOs) are liquid preparations, produced from plant materials. Although EOs showed a promising bioactivity in vitro, they could interact in foods with some components (fats, proteins, carbohydrates) and pH, thus many authors have reported that a significant effect of EOs toward spoiling and pathogenic microorganisms could be achieved in vivo by using higher amounts of oils. Different methods can be used to assess the bioactivity of EOs (disk diffusion and agar or broth dilution methods); however, there is not a standardized test and researchers propose and use different protocols (evaluating the Minimal Inhibitory Concentration, studying the survival curves, analysis through the scanning electron microscopy, etc.). Thereafter, the scope of this review is a focus on interactions of EOs with proteins, carbohydrates, oils, NaCl, and pH, as well as a brief description on the different protocols to assess their bioactivity both under in vivo and in vitro conditions.

Bioaccumulation characterization of cadmium by growing Bacillus cereus RC-1 and its mechanism

In an effort to explore the protective mechanism of growing Bacillus cereus RC-1 against the toxicity of different Cd(II) concentrations, bacterial growth, cadmium consumption, surface interactions and intra- and extra-cellular Cd(II) contents were examined. Cellular morphology and growth were evidently affected by the initial metal concentrations above 20 mg L(-1), according to the analysis of SEM, AFM, TEM and UV spectrophotometer. Surface complexation and electrostatic attraction played an important role in the different Cd(II) concentrations, as determined by the FTIR and Zeta potential analysis. Intracellular accumulation was the predominant mechanism in culture with lower metal concentrations (below 20 mg L(-1)), but was overshadowed by extracellular adsorption at higher concentrations. This suggested that the growing cells might employ one dominant mechanism at lower concentrations and then shift to another at higher concentrations. These results suggest options could be exploited for bioremediation of aqueous solution in which the Cd(II) concentration is less than 20 mg L(-1).

Morphostructural Damage in Food-Spoiling Bacteria due to the Lemon Grass Oil and Its Vapour: SEM, TEM, and AFM Investigations

In this study, antimicrobial activity and morphostructural damages due to lemon grass oil (LGO) and its vapour (LGOV) against Escherichia coli strains were investigated. Minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of LGO were determined by broth-dilution method to be 0.288 mg/mL and 0.567 mg/mL, respectively. Furthermore, the zone of inhibition (45 mm) due to the vapour phase antimicrobial efficacy evaluated using disc volatilization assay was compared with that using disc diffusion assay (i.e., 13.5 mm for the same dose of oil). The morphological and ultrastructural alterations in LGO- and LGOV-treated E. coli cells were studied using scanning electron microscopy (SEM), transmission electron microscopy (TEM), and atomic-force microscopy (AFM). In SEM observation, LGO-treated cells appeared to be aggregated and partially deformed, while LGOV-treated cells lost their turgidity, and the cytoplasmic material completely leaked from the cells. In TEM observation, extensive intracytoplasmic changes and various abnormalities were observed in LGOV-treated cells more than LGO-treated cells. Significant variations in the height and root mean square values of untreated, LGO-, and LGOV-treated E. coli cells were noticed by AFM. Present results indicate that LGO is highly effective against E. coli in vapour phase.

Housefly (Musca domestica L.) control potential of Cymbopogon citratus Stapf. (Poales: Poaceae) essential oil and monoterpenes (citral and 1,8-cineole)

In spite of being a major vector for several domestic, medical, and veterinary pests, the control aspect of the common housefly, Musca domestica L. (Diptera: Muscidae) is often neglected. In the present study, the essential oil of Cymbopogon citratus and its major components were evaluated for control of housefly. The chemical composition analysis of C. citratus oil by gas chromatographic mass spectrometry (GC-MS) revealed citral (47 %) and 1,8-cineole (7.5 %) as principal components. The analysis of oil vapor by solid phase microextraction (SPME/GC-MS) showed increase in citral (74.9 %) and 1,8-cineole (8.6 %) content. Assay of oil against housefly larvae and pupae through contact toxicity assay showed lethal concentration (LC)(50) value of 0.41 μl/cm(2) and of percentage inhibition rate (PIR) of 77.3 %, respectively. Fumigation assay was comparatively more effective with LC(50) of 48.6 μl/L against housefly larvae, and a PIR value of 100 % against housefly pupae. The monoterpenes, citral, and 1,8-cineole, when assessed for their insecticidal activity against housefly larvae, showed LC(50) of 0.002 and 0.01 μl/cm(2) (contact toxicity assay) and LC(50) of 3.3 and 2.4 μl/L (fumigation assay). For pupicidal assay, both citral and 1,8-cineole had a PIR value of 100 %. High efficacy of citral and 1,8-cineole against housefly, established them to be an active insecticidal agent of C. citratus oil. The study demonstrates potentiality of C. citratus oil as an excellent insecticide for housefly control, and the results open up the opportunity of oil/monoterpenes being developed into an eco-friendly, economical, and acceptable product.