Effect of E-beam treatment on expression of virulence and stress-response genes of Listeria monocytogenes in dry-cured ham.

Various adverse conditions can trigger defensive mechanisms in Listeria monocytogenes that can increase the virulence of surviving cells. The objective of this study was to evaluate the expression of one stress-response (sigB) and three virulence (plcA, hly, and iap) genes in L. monocytogenes exposed to a sub lethal dose of E-beam irradiation in dry-cured ham. To accomplish this, dry-cured ham slices (10 g) were immersed in a 109 CFU/mL suspension of L. monocytogenes strain S4-2 and subsequently irradiated with 1, 2, or 3 kGy. After irradiation, samples were stored at 7 °C or 15 °C for 30 days. Absolute gene expression levels were determined by RT-qPCR, and numbers of surviving Listeria cells were assessed by microbial counts after different storage times (0, 7, 15, and 30 days). At 7 °C, after E-beam treatment at doses of 2 or 3 kGy, Listeria gene expression significantly increased (p ≤ 0.05) up to day 15. Listeria counts decreased with increasing dosage. The relationship between absolute gene expression and the number of surviving Listeria cells could indicate that sublethal doses of E-beam irradiation can increase expression of the genes studied. We observed no significant influence of storage time or temperature on gene expression (p > 0.05). Listeria that survives E-beam treatment may display increased virulence, constituting a significant potential public health risk.

Effects of irradiation on hamburgers enriched with folic acid.

Hamburgers enriched with different amounts of folic acid (0.6, 1.2 and 2.4 mg/100g) were manufactured. They were then treated with doses of 2-4 kGy of ionizing radiation in order to increase their safety. The effects of these treatments on the colour, texture parameters, and sensory quality of the meat, as well as on the stability of folic acid, were studied in both raw and cooked hamburgers. The presence of folic acid negligibly influenced the quality of these meat products, with irradiation treatments causing most of the loss of sensory quality and so, the treatment with 4 kGy was not adequate. Folic acid levels decreased 20-30% following irradiation with 2 kGy, and no additional decrease was observed at higher doses of radiation. This new functional meat product may help consumers achieve the RDA for this vitamin in a normal diet.

Usefulness of calcium lactate, citrate and gluconate for calcium enrichment of dry fermented sausages.

Food manufacturers are interested in new ways to improve the nutritional value of their meat products. In this study, calcium lactate, gluconate and citrate have been added to dry fermented sausages in an attempt to determine whether they are useful for enriching these meat products with calcium. The sausages were manufactured with different amounts of pork backfat (6, 15, and 30%) and the salts were added in sufficient amounts to 100g of sausage to give 20% and 30% of the recommended daily allowance (RDA) of calcium established by the Institute of Medicine of the USA (1000mg/day). The lower concentration of whichever calcium salt (20% of RDA), was the most sensorially adequate. With this amount these sausages can be considered a "source of calcium". In addition, we found that the lower backfat percentage (6%) compromises the acceptability of the product.

Dry fermented sausages enriched with lycopene from tomato peel.

Tomato industries yield a high amount of by-products mainly tomato peel and seeds. Since tomato peel is rich in lycopene, the direct addition of peel to food products could be a way to use this by-product to obtain a new products enriched in lycopene. This work describes experiments performed to develop dry fermented sausages (salchichón) containing this carotene. 0%, 0.6%, 0.9% and 1.2% (w/w) of dry tomato peel was added to the meat mixture used in sausage manufacture. A slight losts of lycopene was detected after 21 days ripening, however, levels remained between 0.26 and 0.58mg of lycopene/100g of sausage. The sensory and textural properties and overall acceptability of all sausages were good, indicating that tomato peel could be added to dry fermented sausages to produce a meat product enriched in lycopene.

Design of a new cooked meat sausage enriched with calcium.

The effect of calcium lactate, calcium gluconate and calcium citrate addition on the sensory properties of cooked meat sausages has been studied. Conventional and reduced-fat products (approx. 40%) were manufactured. The calcium salts studied were added in sufficient amounts to 100g of final product to give 20% and 25% of calcium RDA (1200mg). The energy value reduction in the final products was close to 30%. The instrumental measurement of colour and texture was performed. The presence of calcium salts only slightly decrease the lightness of the sausage and few changes were observed in relation to the texture. These were mainly related to increased hardness, observed at levels of calcium at 25% RDA. Sensory properties were estimated by a hedonic test. In general terms, they were very acceptable, which indicated that it is possible to manufacture conventional and reduced-fat cooked meat products enriched with calcium as a new healthier meat product.

The effect of fructooligosaccharides on the sensory characteristics of cooked sausages.

The effect of a short chain fructooligosaccharide on the sensory properties of conventional and reduced-fat cooked meat sausages has been studied in products in which a fat reduction of close to 40% was obtained. The fibre assayed was used in sufficient amounts to constitute between 2% and 12% of the final product. The energy value reduction of the final products was close to 35%. Instrumental measurements of colour and texture were performed. Sensory properties were estimated by a hedonic test. A correlation principal component analysis was performed. The results showed that the sensory and textural properties and the overall acceptability were very good, which indicated that this fibre can be considered a good fat replacer in meat products. Thus, with its addition, a reduced calorie product enriched with soluble dietetic fibre is obtained.

Utilization of cereal and fruit fibres in low fat dry fermented sausages.

The effect of addition of cereal and fruit dietary fibres on the sensory properties of reduced-fat, dry fermented sausages was studied. Dry fermented sausages with 6 and 10% pork backfat were manufactured, with addition of cereal (wheat and oat) and fruit (peach, apple and orange) dietary fibres, at 1.5 and 3% concentrations. The energy value reduction of the final products was close to 35% and their final fibre contents, after ripening, were 2 and 4%, respectively. The ripening process was monitored by physico-chemical and microbiological analysis. Sensory properties were analyzed using triangular and hedonic tests and, a texture profile analysis was carried out. A correlation principal component analysis was performed. The results showed that the sensory and textural properties of batches with 3% dietary fibre were the worst, due to their hardness and cohesiveness. The best results were obtained with sausages containing 10% pork backfat and 1.5% fruit fibre especially those with orange fibre, which gave organoleptic characteristics similar to conventional high fat products. Thus, reduced fat sausages fortified with dietary fibre can be obtained with an acceptable sensory profile.

Inulin as fat substitute in low fat, dry fermented sausages.

Low fat, dry fermented sausages were prepared with a fat content close to 50% and 25% of the original amount. The batch with the smallest proportion of fat was less tender, less springy and was gummier than the batch with the highest proportion. However, it was still considered acceptable by the panel of judges. The 25% batch was supplemented with different amounts of soluble dietetic fibre (inulin) as both a powder and in aqueous solution. Ripening was followed by physico-chemical and microbiological analysis. Sensory analysis and texture profile analysis were performed to evaluate the effect of the inulin addition. Results obtained indicated an overall improvement in the sensory properties due to a softer texture and tenderness, springiness and adhesiveness similar to the conventional high fat sausage. Thus, with the addition of inulin a low calorie product (30% of the original), enriched with soluble dietetic fibre (10% approximatively) can be obtained.

Lactic acid bacteria: hydrophobicity and strength of attachment to meat surfaces.

The hydrophobicity and strength of attachment of several lactic acid bacteria with antimicrobial activity were studied. Hydrophobicity was determined by bacterial adherence to hydrocarbons (BATH; octane or xylene), adhesion to nitrocellulose filters (NCF), salt aggregation test (SAT) and adherence to phenyl-Sepharose beads (PSB). The relative hydrophobicity of lactic acid bacteria depended markedly on the method used. No correlation between either SAT or BATH (octane) and strength of attachment (Sr value) existed. However, a significant relationship between strength of attachment and BATH (xylene), NCF and PSB, respectively, was observed, showing the highest correlation coefficient (r = 0.778) for BATH (xylene).

Virulence factors-pathogenicity relationships for Aeromonas species from clinical and food isolates.

The presence of virulence factors in 96 Aeromonas strains isolated from food and clinical samples was studied. Neither cytotoxic activity and hydrophobicity, not the presence of pili or an extra surface layer made it possible to establish differences between food and clinical strains. Statistical studies showed that cytotoxin production was associated with a positive Voges-Proskauer reaction, inability to ferment arabinose and a positive lysine decarboxylation. Therefore, when comparing cytotoxic clinical and food strains with lysine decarboxylation phenotype, there was a significant difference (p < 0.05) between the two groups. The association of a cytotoxin production and lysine decarboxylation character should thus be considered as a possible virulence marker.

Cell surface hydrophobicity and attachment of pathogenic and spoilage bacteria to meat surfaces.

Cell surface hydrophobicity of several pathogenic and spoilage bacteria was determined by hydrocarbon adherence, adhesion to nitrocellulose filter, salt aggregation and adherence to phenyl-sepharose beads. Hydrophobicity of each bacterium was dependent on the method of measurement. Hydrophobicity was compared with the strength of attachment (Sr) of the bacteria to beef muscle surfaces. Bacterial cell surface hydrophobicity, as determined by the bacterial adherence to xylene correlated well with attachment strength (r = 0.800, P < 0.05). Staphylococcus aureus, Clostridium perfringens and Yersinia enterocolitica showed the highest values of attachment strength.

Attachment of lactic acid bacteria to beef-muscle surfaces.

The effect of immersion time and cell concentration in the attachment of several lactic acid bacteria with antibacterial activity to beef-muscle surface was studied. The number of firmly attached bacteria increased with immersion time in the case of Pediococcus acidilacti, Lactobacillus sake, Lactococcus cremoris (two strains) and Pediococcus acidilacti. Pediococcus pentosaceus, Lactococcus lactis and Lactobacillus curvatus reached maximum adhesion after 15-30 min. The highest strength of attachment (Sr values) were observed after 15-30 min of contact time except for P. pentosaceus. For all strains, the number of bacteria adhering to meat increased with increasing cell concentration in the adhesion medium. The highest strength of attachment was observed at a cell concentration of 10(5)/mL mainly for L. sake, L. lactis and L. cremoris. Due to their attachment characteristics, L. sake, L. lactis and L. cremoris are proposed as potential biocontrol agents because they could grow on meat surface and limit the potential attachment of pathogenic microorganisms.

Incidence of motile Aeromonas spp. in foods.

A total of 80 food samples were purchased from local retail consumer shops and examined for the presence of motile Aeromonas spp. Of the food categories tested, poultry had the highest incidence, with 100% positive. This was followed by lamb samples, with 60% positive. Raw milk and cheese samples had very low incidence (20%). No motile Aeromonas spp. were found in pre-prepared salads. Shellfish, fish, pork and beef samples had incidences of 40%. Most of the strains isolated were Aeromonas hydrophila, and for most of the food categories, no Aeromonas caviae isolates were obtained.

Virulence factors in clinical and food isolates of Aeromonas species.

Virulence factors were compared in 15 Aeromonas spp. isolated from faeces of patients with Aeromonas-associated gastroenteritis and in 81 strains isolated from food. Strains from food did not show differences in the distribution of virulence factors when compared with strains isolated from faeces. However, 88.8% of Aeromonas strains isolated from food were capable of producing possible virulence factors. Characterization of 28 autoagglutinating (AA+) Aeromonas spp. indicated that the human strains differed from the food strains in hemagglutinating and hemolytic capacities. These results suggest that autoagglutination associated with hemagglutinating and hemolytic capacities in food strains may be a helpful indicator of potential pathogenicity.

Actual identity of six micrococcal strains selected as potential starter for dry fermented sausages production.

The DNA guanine + cytosine contents of six strains previously selected as potential starters for their use for the dry fermented sausages production have been determined. Five strains were characterized as Micrococcus spp. and the remainder as incertae sedis.