In vitro antioxidant and antibacterial activities of essentials oils obtained from Egyptian aromatic plants

The aim of this work was to (i) determine the chemical composition of the essential oils (EOs) of five spices widely cultivated in Egypt as: Fennel (Foeniculum vulgare), parsley (Petroselinum crispum), lavender (Lavandula officinalis), black cumin (Nigella sativa) and thyme (Thymus vulgaris); (ii) determine the total phenolic compound (TPC) content (iii) determine the antioxidant activity of the Egyptian essentials oils by means of three different antioxidant test and (iv) determine the effectiveness of the Egyptian essentials oils on the inhibition of the growth of some indicators of spoilage bacteria strains. There is a great variability in the chemical composition of EOs obtained from the five Egyptian aromatic plants. Thyme EO had the highest content of total phenols (913.17 mg GAE/L). Black cumin (highest % of inhibition of DPPH radical: 95.89% and highest FRAC values 3.33 mmol/L Trolox) and thyme (highest % of inhibition of TBARS: 80.76) essential oils presented the best antioxidant profile. Only the essential oil of thyme showed inhibitory effects on the three tested bacteria at all added doses.     

Inactivation of foodborne pathogens on gala apples by application of antimicrobial waxes

There is a need for effective postharvest controls capable of inactivating bacterial foodborne pathogens, which can be applied to the organic and conventional apple industries. This study evaluated the efficacy of natural antimicrobials (essential oils or cultured dextrose) when incorporated into carnauba wax and applied to apples. Organic Gala apples were spot inoculated with a five strains/serovars cocktail (∼9 Log CFU/mL) of Listeria monocytogenes, Shiga-toxigenic E. coli O157:H7, or Salmonella. Inoculated apples were coated with organic carnauba wax containing a 1% and 2% (v/v) mixture of essential oils (EOs) in equal proportions (oregano, clove bud, cinnamon bark, and coriander seed) or commercially cultured dextrose at 0.5% (w/v). Apples coated with carnauba wax only and uncoated apples were used as control treatments. Apples were stored at 20 °C and sampled for up to 40 days. Five treatments with three biological replicates and three samples per replicate were used for each treatment (n = 9). A sensory discrimination test was used to identify differences between waxed apples for treatments with the greatest efficacy. Carnauba wax containing 2% EOs was the most effective treatment for inactivating target foodborne pathogens inoculated on apples for 40 days. This treatment showed 4.05, 1.38 and 2.81 Log CFU/apple reduction in L. monocytogenes, E. coli O157:H7, and Salmonella, respectively, compared to uncoated apples. Carnauba wax containing 2% EOs showed significantly (P ≤ 0.001) lower populations of L. monocytogenes and Salmonella compared with 1% EOs, 0.5% cultured dextrose, or wax-only control. In contrast, there were no significant differences (P > 0.05) for E. coli O157:H7. Sensory evaluation showed that panelists could detect differences for apples treated with wax containing 2% EOs, but not for 1% EOs compared to wax-only control. This study provides information to the organic and conventional apple industry about the efficacy of antimicrobial waxes to inactivate bacterial foodborne pathogens.     

Efficacy of the combined application of oregano and rosemary essential oils for the control of Escherichia coli,Listeria monocytogenes and Salmonella Enteritidis in leafy vegetables

This study assessed the effect of the combined application of essential oils (EOs) from Origanum vulgare L. – oregano (OVEO) and Rosmarinus officinalis L. – rosemary (ROEO), alone or in combination at subinhibitory concentrations, against three pathogenic bacteria that are associated with fresh leafy vegetables: Listeria monocytogenes (L. monocytogenes), Escherichia coli (E. coli) and Salmonella enterica Serovar Enteritidis (S. Enteritidis). The inhibitory effects were evaluated by determining the minimum inhibitory concentration (MIC) and the fractional inhibitory concentration index (FICI) and assessing the viable cell counts in vegetable broth and artificially infected vegetables over time. Still, the effects of the EOs on native spoilage native flora were assessed. The MIC of OVEO was 0.6 μL/mL against the test strains either in single and mixed inoculum. The MIC of ROEO was 5 μL/mL against L. monocytogenes and E. coli and 10 μL/mL against S. Enteritidis in single inocula, whereas it was 10 μL/mL against the mixed inoculum. The FICI of the combined EOs was 0.5 against the mixed bacterial inoculum, which suggested a synergic interaction. The incorporation of OVEO and ROEO alone (MIC) or combined at different subinhibitory concentrations in vegetable broth resulted in a decrease in the viable cell counts of all test strains over 24 h. Similarly, the EOs alone or in the tested combinations reduced the viable cell counts of all test strains in experimentally infected fresh vegetables, besides to decrease the counts of spoiling native flora (mesophilic bacteria, enterobacteria and fungi). These findings reinforce the rational for the use of OVEO and ROEO in combination at subinhibitory concentrations to guarantee the safety and extend the shelf life of fresh vegetables.     

Antimicrobial properties of selected essential oils in vapour phase against foodborne bacteria

The aim of this study was to identify antimicrobial properties of essential oils in vapour phase. In vitro antibacterial activity against five foodborne bacteria (Escherichia coli, Listeria monocytogenes, Pseudomonas aeruginosa, Salmonella enteritidis, Staphylococcus aureus) was evaluated by disc volatilization method. The results were expressed as minimum inhibitory concentrations (MIC) in μl/cm³ of air. Thirteen of the 27 essential oils were active at least against one bacterial strain in the range of tested concentrations (0.0083–0.53 μl/cm³). The best results were shown by Armoracia rusticana (MIC 0.0083 μl/cm³) against all of the strains, followed by Allium sativum > Origanum vulgare > Thymus vulgaris > Satureja montana, Thymus pulegioides > Thymus serpyllum > Origanum majorana > Caryopteris x clandonensis, Hyssopus officinalis, Mentha villosa, Nepeta x faassenii, Ocimum basilicum var. grant verte. In conclusion, certain essential oils are highly effective in vapour phase and could be used in control of foodborne bacterial pathogens.     

Evaluation of Zataria multiflora Boiss. essential oil activity against Escherichia coli O157:H7, Salmonella enterica and Listeria monocytogenes by propidium monoazide quantitative PCR in vegetables

Essential oils (EOs) have long been applied as flavoring agents in foods, and due to their content in antimicrobial compounds, they have potential as natural agents for food preservation. Recently, real-time PCR in combination with PMA has successfully been applied to discriminate between live Escherichia coli O157:H7 and dead bacteria killed by cumin, clove, oregano and cinnamon EOs. In this study, initial experiments were performed in order to elucidate the minimum bactericidal concentration of Zataria multiflora EOs on E. coli O157:H7, Salmonella enterica and Listeria monocytogenes. Thereafter PMA-qPCR was applied in order to selectively quantify life cells within a bacterial population treated with Z. multiflora EO. Inactivation was obtained at EO concentrations of 0.02, 0.035, 0.045 for L. monocytogenes, E. coli O157:H7 and S. enterica, respectively. L. monocytogenes were totally killed in 30 min while it took 1 h 30 min for the gram negative pathogens. As a conclusion Z. multiflora EO has potential as natural food additive or biopreservative since it was able to irreversibly inactivate the three pathogens tested, at lower concentrations than other EOs and short exposition times. In addition, the PMA-qPCR approach proved efficient to selectively detect live pathogenic bacteria in vegetables following inactivation with Z. multiflora EO.     

Antimicrobial herb and spice compounds in food

Herbs and spices containing essential oils (EOs) in the range of 0.05–0.1% have demonstrated activity against pathogens, such as Salmonella typhimurium, Escherichia coli O157:H7, Listeria monocytogenes, Bacillus cereus and Staphylococcus aureus, in food systems. Application of herbs, spices and EOs with antimicrobial effects comparable to synthetic additives is still remote for three major reasons: limited data about their effects in food, strong odor, and high cost. Combinations of techniques have been successfully applied in several in-food and in vitro experiments. This paper aims to review recent in-food applications of EOs and plant-origin natural antimicrobials and recent techniques for screening such compounds.     

Preservative effectiveness of essential oils in vapor phase combined with modified atmosphere packaging against spoilage bacteria on fresh cabbage

This study was conducted to investigate the antibacterial effects of various essential oils (EOs) against pathogens using the disc volatilization method. Also, combined effects of EOs in vapor phase and MAP were evaluated for reducing levels of total mesophilic microorganisms on fresh cabbage. The vapor phase activities of EOs (thyme-1, oregano-1, lemongrass-1, and lemongrass-2 oils) observed strong inhibitory effects. The MAP results showed that 100% CO₂ gas packaging reduced significantly levels of total mesophilic microorganisms on cabbage and radish sprouts, and their reduction level was 1.55 and 2.26 log₁₀ CFU/g compared to control after 21 days of storage (p ≤ 0.05). Based on previous results, combined effects of EOs in vapor phase and MAP (100% CO₂) showed that lemongrass-2 oil with 20 discs showed complete inactivation by <1.0 log₁₀ CFU/g after 14 days of storage. These results could provide useful information for developing alternative preservation method to improve the freshness and shelf-life of fresh produce using natural antimicrobials.     

Efficacy of Fir and Qysoom essential oils,alone and in combination,in controlling Listeria monocytogenes in vitro and in RTE meat products model

Listeria monocytogenes, frequently associated with ready-to-eat meat products (RTE-MP), is the causal agent of listeriosis, the virulent foodborne disease. Accordingly, this work aimed to study the effectiveness of essential oils (EOs) of different plants to control growth of L. monocytogenes in RTE-MP model. EOs antilisteric activities were screened by disk diffusion method. Then, efficacy of EOs (1% v/w) with strong inhibition activities were further examined in meat luncheon model, against 2 levels of L. monocytogenes strains cocktail (3 and 6 log CFU/g) coupled with storage at 4 °C for 14 days. The EOs of Fir and Qysoom showed to have the highest significant (p < 0.05) antilisteric activity. In the food model, L. monocytogenes populations in control samples increased by 4 log cycles after 14 days of storage at 4 °C. At the end of storage, for samples with low contamination; Fir, Qysoom, and EOs mixture had approximately 6.37, 6.04, and 5.53 log CFU/g of L. monocytogenes respectively, compared to 6.90 log of control. Whereas in the samples with high contamination level, populations reached to 8.43, 8.88 and 6.75 log CFU/g for Fir, Qysoom, and EOs mixture respectively, compared to 9.90 log of the control. The application of 1% EOs (v/w) to RTE-MP surfaces significantly showed to reduce (p < 0.05) the L. monocytogenes populations growth rate as compared to control in the 2 levels treatments after 14 days of storage at 4 °C. Accordingly, our results suggest that these EOs could be used as natural bio-preservatives in many food products produced in Jordan and worldwide, particularly in RTE-MP.     

Synergistic action between fractions of essential oils from Cymbopogon citratus, Ocimum gratissimum and Thymus vulgaris against Penicillium expansum

Penicillium expansum is a mould that causes the rotting of several fruits and vegetables, especially apples onto which it also synthesizes some dangerous mycotoxins. The degree of synergism between fractions of essential from Cymbopogon citratus, Ocimum gratissimum and Thymus vulgaris was evaluated against two mycotoxin producing strains of P. expansum. The antifungal activity determined by dilution method and expressed as a Number of Decimal Reduction of the colony forming units per ml (NDR cfu) showed that the essential oils extracted from O. gratissimum was significantly (P < 0.05) more active against P. expansum than those extracted from C. citratus and T. vulgaris. Fractions enriched with oxygenated terpenes were significantly (P < 0.05) more active than their respective essential oils, whereas most of the fractions enriched with terpene hydrocarbons, were significantly (P < 0.05) less active. The fungicidal activity of mixtures of fractions from the same essential oils or from two different essential oils showed that there exist synergistic, additive and antagonistic effects between fractions of the three essential oils tested against both fungal strains. The synergistic effects observed could be exploited in order to maximize the antimicrobial activity of essential oils and to minimize the concentrations of essential oil required to produce a given antimicrobial effect without any alteration of the food test.     

Antimicrobial activity of essential oils against Escherichia coli O157:H7 in organic soil

Soil can be a significant source of preharvest contamination of produce by pathogens. Demand for natural pesticides such as essential oils for organic farming continues to increase. We examined the antimicrobial activity of several essential oils against Escherichia coli O157:H7 in soil. Two essential oils (cinnamaldehyde and eugenol), two bio-pesticides (Ecotrol and Sporan) containing essential oils, and an organic acid (acetic acid) at 0.5%, 1.0%, 1.5% and 2.0%, were mixed with organic sandy soil and inoculated with five different strains of E. coli O157:H7. Soils were incubated at room temperature (22 °C) and samples obtained at 1, 7 and 28 days were enumerated to determine survival. E. coli O157:H7 populations in soil were reduced by up to 5 log cfu/g after 24 h incubation at room temperature with 2% cinnamanaldehyde, Ecotrol, Sporan or vinegar. Reduction in E. coli O157:H7 by eugenol was not significantly different from control. Overall, E. coli O157:H7 strain 4406 was the most sensitive of all the five strains tested and cinnamaldehyde was superior to other treatments in reducing E. coli O157:H7 in soil. In general, increases in essential oil concentrations corresponded to reduced survival of E. coli O157:H7 with all oils used in this study. The results suggest that oils can reduce potential contamination of fresh organic produce inadvertently contaminated by soil.     

Spinning cone column isolation of rosemary essential oil

Chemical compositions of rosemary (Rosmarinus officinalis L.) essential oil isolated using different processes, steam distillation and a spinning cone column (SCC), and harvested at different times, spring and autumn, were compared. The effect SCC operating parameters had on yields was also studied. The method used for isolating the oil influenced its composition and yield. The main components found were: camphor, β-myrcene and 1,8-cineole. SCC derived oils were more consistent and richer, on average, in oxygenated compounds than steam distilled oils. Furthermore, citronellol, chrysanthenone, piperitone and thymol were detected in SCC oils but not in their steam distilled counterparts. SCC yields were more consistent at a 1/40 dilution while higher yields were achieved at the same dilution spinning at 570 rpm.     

Chemical composition and antiaflatoxigenic activity of Carum carvi L., Thymus vulgaris and Citrus aurantifolia essential oils

In order to find out plants useful to controlling aflatoxins (AFs) production, the essential oils (EOs) from 12 medicinal plants prepared by hydrodistillation were studied with special reference to the inhibition of Aspergillus parasiticus growth and AFs production. The toxigenic fungus was cultured in presence of various oils in 6-well microplates using a microbioassay technique. The mycelial mass was estimated as an index of fungal growth, while the aflatoxins B₁ (AFB₁) and G₁ (AFG₁) were measured by high performance liquid chromatography (HPLC). Among plants tested, Thymus vulgari and Citrus aurantifolia were found to inhibit both A. parasiticus and AF production. The EOs from Mentha spicata L., Foeniculum miller, Azadirachta indica A. Juss, Conium maculatum and Artemisia dracunculus were only inhibited fungal growth, while Carum carvi L. effectively inhibited AF production without any obvious effect on fungal growth. The other plants including Ferula gummosa, Citrus sinensis, Mentha longifolia and Eucalyptus camaldulensis had no effect on A. parasiticus growth and AF production at all concentrations used. The IC₅₀ values of T. vulgaris, C. aurantifolia and C. carvi for AF inhibition were reported as 93.5, 285.6, and 621.9 μg/ml for AFB₁, while they were calculated as 11.7, 50.1, and 56.0 μg/ml for AFG₁. These results indicate that the EOs of some medicinal plants may be considered as potential candidates to protect foods and feeds from toxigenic fungus growth and subsequent AF contamination.     

The antifungal activity of essential oils in combination with warm air flow against postharvest phytopathogenic fungi in apples

Essential oils (EOs) are strong plant-derived antimicrobials. For their efficient use in the agri-food industry, the problems with technology of their application have to be solved. In vitro antifungal activity of cinnamon, oregano, lemongrass and clove essential oils (EOs) was tested by innovative method using EO in combination with warm air flow (WAF). EOs in concentrations from 0.25 to 512 μL/L of air were tested against eleven phytopathogenic fungi. Application of EOs in concentration of 4 and 16 μL/L by WAF method was used for treatment of apples inoculated with Penicillium expansum. Detailed sensory analysis of treated apples was performed. The WAF was more effective compare to standard disc volatilization method (DVM), the average minimum inhibitory concentrations in vitro were 5.6 μL/L during 5 min WAF treatment, compared to 136 μL/L during the DVM 24 h treatment. EOs applied by WAF delayed the incidence and development of P. expansum on apples with minimal adverse effect on their sensory profile. The WAF treatment could be considered for the development of antifungal treatments in the agri-food industry.     

Antimicrobial activity of Pistacia lentiscus and Satureja montana essential oils against Listeria monocytogenes CECT 935 using laboratory media: Efficacy and synergistic potential in minced beef

The aim of this study was to optimize the antimicrobial efficacy of plant essential oils (EOs) for control of Listeria monocytogenes (L. monocytogenes) serovar 4b CECT 935 using laboratory media and minced beef stored at 5 ± 1 °C. Commercial EOs obtained from leave parts of Mediterranean Pistacia lentiscus (P. lentiscus) and Satureja montana (S. montana) were analyzed by gas chromatography–mass spectrometry (GC–MS). The main components of EOs obtained were β-myrcene (15.18%) and carvacrol (29.19%), respectively for P. lentiscus and S. montana. The in vitro antimicrobial activity of both EOs was evaluated against L. monocytogenes using the agar diffusion technique, the minimum inhibitory concentrations (MIC) were also determined against the same microorganism using the broth microdilution method. According to the diameters of inhibition, S. montana EO had more antibacterial effects than that from P. lentiscus. MICs showed a range of 0.03 and 0.10% (vol/vol) respectively for S. montana and P. lentiscus. S. montana and P. lentiscus EOs were added respectively in minced beef (twofold MIC values) at 0.06 and 0.20%, experimentally inoculated with L. monocytogenes at a level of 3 × 10⁵ CFU/g and stored at 5 ± 1 °C during one week. S. montana EO was the more effective (P < 0.05) against target bacteria. P. lentiscus EO also demonstrated antibacterial effect against the same bacterium. EO combinations were also investigated in minced beef and P. lentiscus combined with S. montana had synergistic effects. This work shows that the combined EOs might be more effective against L. monocytogenes when applied to minced beef at the ratio of 1/1 to 2/2 according to the MIC values. Sensory evaluation revealed that minced beef treated with EOs was acceptable by panelists at the levels used.     

Enhanced antibacterial effectiveness of essential oils vapors in low pressure environment

Due to their antimicrobial activity, essential oils (EOs) have potential to alternate conventional food preservatives. Relatively high doses of EOs necessary for microbial growth inhibition indicate that they should be used in combination with other preservation techniques rather than alone. Therefore, new combinations of preservative methods with EOs are still investigated. In our study, oregano, clove, cinnamon, and lemongrass EO vapors were tested in vitro in atmospheric and low pressure against Escherichia coli and Salmonella enteritidis at different times of treatment ranging from 5 min to 4 h. Combination of EO-low pressure shortened up to 48 times the time necessary for total inhibition of microorganism growth compared to the same treatment in atmospheric pressure. Minimal inhibitory times of EOs vapors ranged mostly from 15 to 60 min in low pressure and were equal to or more than 4 h in atmospheric pressure. Possible decrease of MICs of EOs in low pressure was also investigated. Microorganisms demonstrated increased susceptibility to oregano, lemongrass and cinnamon EOs in low pressure e.g. the MIC of cinnamon vapors for S. enteritidis decreased from 512 μL/L to 128 μL/L.     

The sanitizing action of essential oil-based solutions against Salmonella enterica serotype Enteritidis S64 biofilm formation on AISI 304 stainless steel

Bacterial adhesion and biofilm formation by Salmonella enterica serovar Enteritidis is a serious concern in the food processing industry; organism persistence in biofilms represents a continual source of contamination. Due to unsuccessful disinfection processes and emerging resistance, conventional control methods are rapidly becoming ineffective, necessitating the development of new control strategies. The following study evaluated the anti-biofilm effect of disinfectant solutions formulated with essential oils (EOs) of peppermint (Mentha piperita) and lemongrass (Cymbopogon citratus) against biofilm formation by S. enterica serotype Enteritidis S64 on stainless steel surface AISI 304 (#4) after 10, 20 and 40 min of contact. A minimum inhibitory concentration (MIC) of 7.8 μL/mL was found for both EOs and disinfectant solutions were formulated based on these MIC values. Ten minutes of sanitizing solution contact significantly reduced (p ≤ 0.05) adhered bacterial populations for both EOs tested. After 20 and 40 min of treatment, cell counts were not detected. Thus, M. piperita and C. citratus EOs can be considered convenient, quality alternatives to the application of conventional sanitizing agents in the food industry; further, use of these EOs addresses the increasing consumer demand for natural products.     

Highly enhanced bactericidal effects of medium chain fatty acids (caprylic,capric, and lauric acid) combined with edible plant essential oils (carvacrol,eugenol, β-resorcylic acid,trans-cinnamaldehyde,thymol, and vanillin) against Escherichia coli O157:H7

Medium chain fatty acids (MCFAs) and essential oils (EOs) are known to be natural antimicrobials, but their combined effects have not been fully investigated. The objective of the present study was to examine the bactericidal effects of various combined treatments of MCFAs [caprylic (CA), capric (CPA), and lauric acid (LRA)] and EOs [carvacrol (CAR), eugenol (EUG), β-resorcylic acid (RA), trans-cinnamaldehyde (TC), thymol (TM), and vanillin (VNL)]. Escherichia coli O157:H7, was treated with 1) control (2% ethanol), 2) MCFA alone, 3) EO alone, and 4) different combinations of MCFAs and EOs at 37 °C for 5 and 10 min. Synergistic bactericidal effects were observed with combined treatments; the log reduction in viable bacteria in response to the combined treatments was much greater than the sum of the effects of the two compounds applied individually. For example, individual treatment with 0.2 mM CPA (0.004%) and 0.4 mM RA (0.006%) for 5 min resulted in a negligible reduction in bacterial load (0.25 and 0.21 log reduction, respectively), whereas combined treatment at the same concentrations and for the same time reduced the bacterial population in the test sample to an undetectable level (initial population: 7.51 log CFU/ml; detection limit: 1 CFU/ml). The ranking of EOs showing the highest bacterial killing activities when combined with MCFAs was generally RA, CAR, TM > EUG > TC > VNL. All the antimicrobials used in this study are natural compounds that have been widely used in industry, so they are both consumer- and user-friendly. Combined treatment can overcome the disadvantages of MCFAs and EOs such as unpleasant odor and high cost because the required concentrations can be reduced. Our results indicate that the combined treatments used here could be successfully used to eliminate foodborne pathogens, significantly improving the microbiological safety of foods.     

Determination of antimicrobial effect of mint and basil essential oils on survival of E. coli O157:H7 and S. typhimurium in fresh-cut lettuce and purslane

In this research, mint and basil essential oils at concentrations of 0.01 ml/L, 0.032 ml/L or 0.08 ml/L were used for disinfection treatments of fresh-cut lettuce and purslane samples inoculated with Salmonella typhimurium or Escherichia coli 0157:H7. Disinfection treatment time was applied as 10 min (short) or 15 min (long). Disinfected samples were packaged aerobically and stored at refrigerator +4 °C for 7 days. It was observed that mint and basil essential oils showed antimicrobial effect on the survival of E. coli O157:H7 and S. typhimurium inoculated into lettuce and purslane samples during refrigerated storage. Mint essential oil showed higher antimicrobial effect on pathogens when compared to basil essential oil. Mint and basil essential oils at concentration of 0.08 ml/L were the most effective antimicrobial treatment against pathogens in two different vegetable. S. typhimurium was more resistant against basil oil in lettuce samples when compared to its resistance against basil oil in purslane samples, whereas E. coli O157:H7 was more resistant to mint oil in purslane samples when compared to its resistance against mint oil in lettuce samples.     

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.     

Behaviour of food-borne pathogens on dry cured sausage manufactured with herbs and spices essential oils and their sensorial acceptability

Dry cured sausages such as Portuguese chouriço de vinho are made generally with roughly minced pork and fat and seasoned with a large variety of herbs and spices. It is a particular sausage because meat is marinated in wine with other seasonings during 24–48 h before stuffing. Nowadays, health concerns of consumers have left food processors with less flexibility to choose preservative substances and methods. Thus, the objective of this study was to assess the antimicrobial effect of essential oils (EOs) of herbs and spices traditionally used in seasoning dry cured sausage chouriço against Salmonella spp., Listeria monocytogenes and Staphylococcus aureus. First, antibacterial activity of 14 EOs was screened by disk diffusion assay. Those EOs that displayed antimicrobial activity were further characterized by GC–MS and added as natural antimicrobial substances to the manufacture of chouriço at two concentrations (0.005% and 0.05%). Samples were analyzed 24 h after the preparation of the batter and after 3, 8, 15 and 21 days.After 15 days of drying, Salmonella spp. and L. monocytogenes counts decreased by ca. 2 log cfu/g in all samples. At 3 days, Salmonella spp. was already undetectable in chouriço made with 0.05% of garlic and oregano EOs. Both Salmonella spp. and L. monocytogenes were not detected after 8 and 15 days of drying respectively. S. aureus was still presented after 21 days of drying although its counts were not high enough to a potential enterotoxins presence. Utilization of EOs in manufacture of dry cured sausage resulted in an interesting strategy to improve its safety against Salmonella spp, L. monocytogenes and S. aureus, but with sensory limitations, that does not allow its use in high concentrations, that are those more interesting for pathogen inhibition.However, results with good potential to be applied by the industry were found, once the level of addition of 0.005% contributed for significant reductions on the pathogen's counts and for a shorter period to achieve the not detectable level, allowing the industry to shorten the drying period and, thereafter increasing yield production.