Essential oils (EOs) or their isolated components, such as eugenol and carvacrol, have strong antimicrobial activities against both Gram-positive and Gram-negative bacteria and are generally recognized as safe by the FDA. However their hydrophobic properties limit their dispersion and stabilization in aqueous food systems. This requires higher concentrations, which in turn negatively affect the quality of foods. The objective here was to determine the effect of the natural emulsifier lecithin on the antimicrobial activity of eugenol and carvacrol and possible food applications. Escherichia coli K12 and E. coli O157:H7 strains ‘Cider’ and ATCC 43889 were used. Homogenized eugenol and carvacrol, with and without lecithin, were screened for antimicrobial activity. The stability of the samples measured by particle size and zeta potential was not affected by different concentrations of lecithin. For all strains, the antimicrobial activity of carvacrol and eugenol was enhanced significantly (P<0.05) by low concentration of lecithin. The D-value (time at a specific concentration of antimicrobial necessary to cause a 90% reduction in viable cells) for E. coli K12 exposed to 0.047% v/v eugenol or 0.015 % v/v carvacrol was reduced from 13.3 to 6.3 min and 17.4 to 9.7 min, respectively, with the addition of 0.0025% lecithin (w/v). Similarly 0.0025% w/v lecithin in the presence of 0.058% v/v eugenol or 0.0188% v/v carvacrol, caused the D-value to decrease from 4.0 to 1.2 min and 10.2 to 6.9 min, respectively, for E. coli strain ‘Cider’ and from 6.2 min to 3.6 min and 9.9 to 5.4 min, respectively, for E. coli ATCC 43889. Higher lecithin concentrations (> 0.005% w/v) increased D-values compared to lower concentrations. Similar results were found in vegetable juice. The results showed that a small amount of lecithin can enhance the antimicrobial activities of essential oils. Addition of lecithin had no effect on oil-water emulsion droplet particle size and the stability of the samples was not affected by different concentration of lecithin. We believe that lecithin enhances the antimicrobial activity of eugenol and carvacrol droplets by improving the ionic interactions between the positively charged lecithin-containing essential oil components and negatively charged bacterial cells.

Listeriosis has the highest fatality and hospitalization rate among foodborne illnesses. Listeria monocytogenes causes listeriosis and is a difficult bacterium for ready-to-eat food processors to eliminate because of its ability to grow in the absence of oxygen and under refrigeration. Recently, milk and its proteins have gained recognition as the largest source of biologically active peptides, and, it stands reason that several antimicrobial peptides (AMP) can be released from casein as it is the most abundant milk protein. AMPs are commonly obtained by cutting the whole protein into peptide fragments using enzymes or by acidification. The objective of this study was to predict potential AMPs through computer aided tools, improve hydrolysate preparation, and determine trypsin and pepsin-casein hydrolysate antimicrobial activity in growth media and on frankfurters against two strains of Listeria monocytogenes (Scott A and 310) and Escherichia coli O157:H7 (Salami strain). The prediction study procedure was to identify the most common variants of primary peptide sequences. The sequences were analyzed for greatest possible enzyme cuts on the protein, peptide masses, isoelectric point, net charge and percent hydrophilic residues using online proteomics programs. The fragments were explored for AMP commonalities: fragment length of 3 to 50 amino acids, positive (cationic) net charge, and hydrophilic residues between 25 and 50%. This technique identified 16 potential AMPs which proved that it is possible to screen for AMPs. The method used to determine the trypsin-casein hydrolysate (TCH) and pepsin-casein hydrolysate (PCH) antimicrobial activity was to hydrolyze sodium caseinate with pepsin or trypsin. L. monocytogenes (strains Scott A and 310) were incubated in 0, 10, 20, and 40% PCH and 0 and 50% TCH concentrations over a 24 hour period. PCH suppressed growth of L. monocytogenes Scott A by 1.76 log CFU/mL and reduced initial populations of L. monocytogenes 310 and E. coli O157:H7 by 0.52 and 0.62 log CFU/ml, respectively. TCH had little or no effect on growth suppression of any of the three test organisms. The frankfurter study was conducted by spot inoculating frankfurters with L. monocytogenes Scott A and then dipping frankfurters into one of five treatments (deionized water, pH 2.7 buffer, pH 5.1 buffer, pH 2.7 PCH, and pH 5.1 PCH) for 30 seconds; inoculated frankfurters that were not dipped served as controls. Frankfurters were incubated at 32°C for seven days. The results showed that there was no significant difference (p>0.05) in antimicrobial effectiveness among the treatments and control. This study demonstrated that enzymatically derived casein hydrolysates somewhat inhibit growth of L. monocytogenes and E. coli O157:H7 in culture media, but were ineffective when applied to frankfurters. Casein hydrolysate solutions can be easily made in a processing facility for application in fluid systems such as an antimicrobial spray on beef carcasses and in milk, juice, sports drinks, soda, soups, and yogurt. It also could be used in solid systems such as frankfurters, cheese, ground beef, and processed or RTE foods.

Community-acquired Clostridium difficile infections have recently been increasing in incidence and severity. Several studies have isolated C. difficile spores from livestock and retail meats, suggesting that food may play a role in transmission. No research has been done, however, on what food conditions might allow for the survival and/or growth of the bacterium. We therefore modelled the minimum thresholds for C. difficile growth under low pH, water activity (aw), and temperature. We also sampled retail ground meats, cheese, and milk for the presence of C. difficile spores and subtyped food isolates for comparison with clinical strains. We found that C. difficile growth could be prevented by refrigeration temperatures. C. difficile spores were also detected for the first time in Canada in ground lamb, ground turkey, ground chicken, cheese and milk. The majority of these food isolates were genetically similar to epidemic strain NAP7/078, suggesting that food may not be a direct vector for C. difficile transmission, but could still be clinically relevant.

High pressure (HP) sterilization of low acid foods is a process involving HP at elevated temperatures. Data available on HP destruction kinetics of pressure resistant pathogenic, spoilage-causing and surrogate bacterial spores are limited, but essential for establishing such a process. While compression heating could be employed to provide the elevated temperature, accurate data gathering under such conditions is difficult due to rapid heat loss during the treatment. The objectives of this research were to first standardize the set up carrying out HP tests at elevated and stabilized temperatures, and subsequently to evaluate HP destruction kinetics of selected bacterial spores under HP elevated temperature processing conditions. / The set-up consisted of a thick insulated chamber for holding samples during the test. A relationship was established for the adiabatic temperature rise milk which was used as the main low acid food medium: DeltaTP = -0.306 + 0.0224Ti + 0.0423P + 4.49x10-4T i2 + 1.31x10-4TiP -- 1.24x10 -5P2 (R2 =0.999, n = 50, SE = 0.20&deg;C, p&lt;0.05). Initial temperatures at 83.5, 91.7, 95.8&deg;C and 80.7, 88.9, 93.0&deg;C provided operating process temperature 121, 130, 135&deg;C, at 800, 900MPa, respectively. / Destruction kinetics tests were carried with two strains of Clostridium sporogenes (11437, 7955) and Geobacillus stearothermophilus 10149 spores suspended in milk at 700-900 MPa and 70-100&deg;C. These strains were selected for their relatively high pressue and thermal resistance. The survival counts were well fitted by first order linear models. The D values C. sporogenes 11437 varied from 0.73 min at 900 MPa 100&deg;C to 17.0 min at 700 MPa 80&deg;C HP treatments while they ranged from 6.0 to 833 min at 80-100&deg;C under thermal processing conditions. The D values associated with of C. sporogenes 7955 spores were higher and varied from 1.3 min at 900 MPa 100&deg;C to 38.2 min at 700 MPa 80&deg;C HP treatments, and from 12.1 to 156 min at 80-100&deg;C during thermal treatments. The D values of Geobacillus stearothermophilus 10149 spores varied from 0.6 min at 900 MPa 90C to 20.9 min at 500 MPa 70&deg;C HP treatments with 6.3 to 49.4 min for thermal treatments at 110-120&deg;C. Hence C. sporogenes 7955 spores were the most resistant among those studied. The HP destruction kinetics of C. sporogenes 7955 spores were also studied in salmon and were lower than in milk. / Pressure resistance screening of selected group I C. botulinum spores was carried out at 800-900 MPa at 90-100&deg;C. Nominal D values of each strain were evaluated which demonstrated that PA9508B, H09504A and CK2-A were the more resistant spores (PA9508B > HO9504A > CK2-A). HP destruction kinetics of C. botulinum PA9508B spores in milk were evaluated in detail at 700-900 MPa at 90-100&deg;C and parallel thermal treatment at 90-100&deg;C. The survival counts were again described by first order linear models (R2 >0.86). The D values varied from 0.35 min at 900 MPa 110&deg;C to 38.9 min at 700 MPa 90&deg;C for HP treatments and 14.4 to 273 min at 90-100&deg;C for thermal treatments. These demonstrated that HP processing combined with elevated temperatures will accelerate the spore destruction rate. However, the associated D values of C. botulinum PA9508B spores in milk were more resistant than those of C. sporogenes 7955 at 90, 100&deg;C, which indicated that the surrogate may not be very effective for using as a target for verification HP at elevated temperature processing conditions. / Overall, this work has demonstrated several findings. The non-pathogenic C. sporogenes 7955 spore was the most resistant surrogate but the pathogenic C. botulinum PA9508B spore was even more resistant. D values associated with HP at elevated temperatures were higher than under conventional thermal treatments, and hence provide accelerated destruction kinetics at least for the non-pathogenic spores and hence better spoilage control. However, from safety point of view the conventional thermal sterility requirements would still persist even under HP processing conditions. Milk as a low acid food medium provided more resistance for HP destruction than fish.

The infrared spectra of 14 bacteria were recorded by Fourier Transform Infrared (FTIR) spectroscopy. The effects of changes in growth conditions, such as temperature, growth medium, and incubation time, sampling conditions on the reproducibility of the spectra were investigated. The spectra of bacteria suspended in saline solution, in D$ sb2$O-saline and on plate films were obtained and stored in separate spectral libraries. The application of library search routines for differentiation and identification of the 14 bacteria was investigated. The spectral regions used for the library search include 1750-1560 cm$ sp{-1}$ and 1480-960 cm$ sp{-1}$, which contain bands mainly associated with proteins (secondary structure), lipids, and polysaccharides. An index produced by the library search, which indicates how much an "unknown spectrum" matches a library spectrum, is suggested as a criterion for the differentiation and identification of bacteria. A correct identification of five unknown samples shows the feasibility of using spectral library searching routines for identification of bacteria down to the species level by FTIR spectroscopy. This technique is rapid, easier, and more efficient than conventional microbiological and biochemical methods. Quantitative analysis of a mixture of Escherichia coli and Staphylococcus aureus by the partial-lest-square (PLS) technique was also evaluated. The analytical error was about 10%.

Raw and processed foods are vulnerable to contamination during their production, distribution and sale. Thus, a wide variety of chemical preservatives are used in the food industry to prevent the growth of food spoilage and pathogenic bacteria. However, health and economic concerns have led to an intensive search for natural alternatives, such as plant extracts, that can safely be used as substitutes for synthetic antimicrobials and preservatives to partially or completely inhibit the growth of bacteria. This study evaluated the antimicrobial effects of natural phenolic compounds extracted from vegetables, fruits, herbs and spices. The main objective was to determine the lowest concentration of phenolics to inhibit the visible growth of the pathogenic bacteria which is defined as the minimum inhibitory concentration (MIC). Some of the most common Gram-positive and Gram-negative foodborne pathogens were treated with several natural phenolic compounds. Concentrations of 5, 10, 15, and 20 ppm (pH 5-6) of each compound were evaluated by broth micro-dilution method and the MICs were determined by using official density (OD) assay. The results demonstrated that the phenolic compounds have varying antimicrobial activities against foodborne pathogens. Natural sources of phenolic compounds contain major antibacterial components and have great potential to be used as natural antimicrobials and food preservatives.

This study explored the in vitro and in situ antilisterial inhibitory activity of 16 essential oils during indirect exposure: Spanish Basil oil (Ocimum basilicum), Bay oil (Pimenta racemosa), Italian Bergamot oil (Citrus bergamia), Roman Chamomile oil (Anthemis nobilis), Sir Lanka Cinnamon oil (Cinnamomum zeylanicum), Citral, Clove Bud oil (Syzygium aromaticum), Cumin Seed oil (cuminum cyminum), Eucalyptus oil (Eucalyptus globulus), Eugenol, Geranium extract (Pelargonium graveolens), Marjoram oil (Origanum majorana), Neroli extract (Citrus aurantium), Peppermint oil (Mentha piperita L.), Rosemary oil (Rosmarinus officinalis L.),and Spanish Sage oil (Salvia officinalis L.). All essential oils were tested against Listeria monocytogenes (ATCC 4644). In vitro inhibitory activity was determined using the microatmosphere method at three temperatures (37°C, 24°C, 4°C) and six possible volumes (0, 10µl, 25µl, 50µl, 100µl, 150µl, or 200µl). In situ inhibitory activity was determined using inoculated bologna slices packaged in Modified Atmosphere Packaging (80% O2, 20% CO2). Essential oils (0, 0.13ml, 1.35ml, or 2.70ml) were injected into the sample packages adjacent, but not touching, the bologna slices and stored at 24°C for 24h. Basil oil displayed the least antilisterial activity across the three temperature applications in vitro. Peppermint, Cumin Seed, and Citral consistently exhibited the greatest antilisterial activity among the temperature applications in vitro. However, only Eugenol applied at 1.35ml achieved a mean one log10 CFU/ml reduction in LM in situ, which could not be replicated. Peppermint (P < 0.048) displayed significant differences between application volumes (0.13ml, 1.35ml) but did not attain a mean one log10 CFU/ml reduction in LM. This study suggests that while various essential oils can display antilisterial activity in vitro, transitioning into a MAP food system warrants further research in mode of actions and application volumes.

Community-acquired Clostridium difficile infections have recently been increasing in incidence and severity. Several studies have isolated C. difficile spores from livestock and retail meats, suggesting that food may play a role in transmission. No research has been done, however, on what food conditions might allow for the survival and/or growth of the bacterium. We therefore modelled the minimum thresholds for C. difficile growth under low pH, water activity (aw), and temperature. We also sampled retail ground meats, cheese, and milk for the presence of C. difficile spores and subtyped food isolates for comparison with clinical strains. We found that C. difficile growth could be prevented by refrigeration temperatures. C. difficile spores were also detected for the first time in Canada in ground lamb, ground turkey, ground chicken, cheese and milk. The majority of these food isolates were genetically similar to epidemic strain NAP7/078, suggesting that food may not be a direct vector for C. difficile transmission, but could still be clinically relevant.

Diss. (sammanfattning) Uppsala : Sveriges lantbruksuniv. / Härtill 6 uppsatser.

Diss. (sammanfattning) Stockholm : Karolinska institutet, 2005. / Härtill 6 uppsatser.