Liselot Steen

The application of staphylococci with flavour-generating potential is affected by acidification in fermented dry sausages

Differences in the production of bacterial metabolites with potential impact on fermented sausage flavour were found in meat simulation medium when comparing different strains of Staphylococcus xylosus and Staphylococcus carnosus as starter cultures. Overall, higher levels of 3-methyl-1-butanol and acetoin were found for S. xylosus, with some intraspecies variability. In addition, sausage fermentation parameters affected staphylococcal growth and metabolism. Strong acidification, as in Northern-European types of fermented dry sausage, inhibited S. xylosus 3PA6 but not S. carnosus 833. During a milder, Southern-European type of acidification, both strains displayed survival over time. During in situ sausage trials, variations in the degree of acidification and the choice of starter microorganisms were of importance, whereas modifications in fat and salt contents had no effects. Staphylococcus sciuri alphaSg2, Staphylococcus succinus 4PB1, and S. xylosus 3PA6 were unable to survive the fermentation of a Northern-European type of fermented dry sausage, characterized by low or no 3-methyl-1-butanol and acetoin production. Inoculation with S. sciuri alphaSg2, S. succinus 4PB1, or S. xylosus 3PA6 led to 3-methyl-1-butanol and acetoin production in Southern-European type of fermented dry sausages, which was not observed with S. carnosus 833.

Influence of NaCl reduction and replacement on the growth of Lactobacillus sakei in broth, cooked ham and white sauce

The growth inhibiting effects of NaCl and selected simple salt replacers (CaCl(2), MgCl(2), KCl and MgSO(4)) on the growth of Lactobacillus sakei were studied in de Man Rogosa Sharpe broth at 7 degrees C over a water phase concentration of 0 to 6.4%. The divalent chloride salts (CaCl(2) in particular) generally had the largest antimicrobial activities at equivalent water phase concentrations, molalities or water activity (a(w)) values. MgSO(4) had not only the least antimicrobial activity but also the smallest a(w) depressing capacity. The results also showed that the antimicrobial effects of CaCl(2) were not fully accounted for by its a(w) depressing effects. Challenge tests performed on cooked ham and white sauce showed that reduction of NaCl levels by 28 and 33%, respectively, had no influence on the microbial stability of these products to L. sakei. Ultimately the study concluded that the microbiological consequences of the full or partial replacement of NaCl on the growth of L. sakei largely depend on the initial level of NaCl, the level of replacement and the nature of the salt replacer used. Altered stability to L. sakei is most likely given a high initial NaCl level, combined with a large level of partial replacement with either CaCl(2) (increased stability) or MgSO(4) (reduced stability) as the replacer.

Phosphate Reduction in Emulsified Meat Products: Impact of Phosphate Type and Dosage on Quality Characteristics

Phosphate reduction is of important industrial relevance in the manufacturing of emulsified meat products because it may give rise to a healthier product. The effect of seven different phosphate types was tested on the physicochemical and quality characteristics to select the most promising phosphate type for further cooked sausage manufacturing. Next, phosphate mass fraction was gradually reduced. Tetrasodium di- or pyrophosphate (TSPP) and sodium tripolyphosphate (STPP) increased pH, reduced structural properties, resulted in the highest emulsion stability, lowest cooking loss and had little effect on hardness. Based on the viscoelastic properties, a minimum mass fraction of 0.06% TSPP was sufficient to obtain an acceptable quality product. Rheology proved to be a very useful tool to evaluate the quality of meat products, as it gives insight in the structure of the meat product and especially the functional properties of meat proteins. Based on the obtained results, it can be concluded that the current amount of phosphate added to emulsified meat products can be significantly reduced with minimal loss of product quality.

Thermal inactivation kinetics of surface contaminating Listeria monocytogenes on vacuum-packaged agar surface and ready-to-eat sliced ham and sausage

The aim of this work was to study thermal inactivation kinetics of Listeria monocytogenes on vacuum-packaged food surfaces. The kinetics were first determined on model agar systems (BHI agar plates), mimicking cooked meat products, which have the same characteristics (pH, sodium chloride (NaCl) or sodium lactate (NaL) content and thickness) as the cooked meat products. Then, in order to validate how well the thermal inactivation on the model agar system simulated inactivation on real products, inactivation kinetics of L. monocytogenes on slices of cooked ham and cooked sausage were examined. BHI agar plates (pH6.2 or 7.2) were prepared with and without the addition of 3% NaCl or NaL. They were initially inoculated with approximately 109CFU/plate culture, aseptically packaged in linear low-density polyethylene pouches, and vacuum-sealed. Thermal treatments were performed by submerging packages in a water bath maintained at 60°C. For most of the conditions studied, the inactivation curves were linear; shoulders were only observed for curves at conditions of pH6.2 with 3.0% NaL. The t4D values (time needed to obtain an inactivation of four-log reduction) were calculated based on the best fitting models included in GInaFit. The observed t4D values for L. monocytogenes on agar surfaces ranged from 6.8 (pH6.2) to 13.7min (pH7.2 with 3.0% NaCl). At pH6.2 addition of NaCl or NaL significantly increased the heat resistance of L. monocytogenes while at pH7.2 this effect was not significant. NaL seemed to affect the heat resistance to the same extent as NaCl. Inactivation curves of L. monocytogenes on slices of cooked ham at pH6.2 with or without addition of NaCl or NaL appeared to be log-linear in shape. However, the curves obtained from cooked sausages were markedly concave and the Weibull model was used for fitting. Concerning heat resistance of L. monocytogenes on meat products, t4D values increased approximately two-fold compared to those corresponding on model agar surfaces. The addition of 3.0% NaCl and NaL in cooked ham increased t4D values of L. monocytogenes from 11.8 to 24.9min and 24.3min, respectively. Similar effects were observed on cooked sausage. Survival on the cooked sausage, containing about 33% of fat, was not significantly different from that on cooked ham. Meanwhile, the addition of NaCl or NaL decreased the average proportions of injured cells substantially. The results of this study can be used by food processors to validate thermal processes with regard to the expected inactivation of L. monocytogenes post-contaminating meat product surfaces.