Five strains of Lactococcus lactis were inoculated individually into six commercial bulk set growth media, 11% non-fat dry milk (NDM), and Elliker's broth. After growth in each medium the strains were tested for rate of acid production, and activities of proteinase, aminopeptidase, and lipase/esterase. Growth in commercial starter media significantly influenced acid production rate (P = 0.040), aminopeptidase activity (P < 0.0001), and lipase/esterase activity (P < 0.0001) . For selected strain/media combinations, the duration of induced aminopeptidase and lipase/esterase activity was followed. The chosen strains were grown in selected commercial bulk set media, reinoculated into 11% NDM, and enzyme activity was examined for five successive generations. During growth in 11% NDM, aminopeptidase and lipase/esterase activity began high and appeared to decrease after approximately two generations, as compared to the control. This study demonstrated that it is possible to select specific starter and media combinations to produce a bacterial phenotype that might not change before the cheese is pressed, thereby trapping bacteria with an altered phenotype within the cheese matrix.

The aim of this work was to use Fourier Transform Infrared Spectroscopy to characterize and identify bacteria of particular significance to the food industry. FT-IR spectroscopy is a rapid technique that can be applied to all groups of bacteria. The two objectives were to determine a suitable sampling procedure to record a spectrum and to determine a suitable statistical technique to identify characteristic regions of the spectrum associated with the genus and, potentially, the species. Pure cultures of bacteria were grown in broth, suspended in saline and dried to produce a film on a halide salt crystal. These films were then used to produce FT-IR spectra. In total, 80 spectra were recorded from seven genera, seven species and four strains of bacteria. Some of the spectra were considered to be too low in intensity to be included in statistical analysis. Data points from three specific windows of the remaining spectra were used to determine spectral distances between spectra. These spectral distances were used to perform cluster analysis using Ward's method, the Complete Linkage method and the Centroid method. The statistical analysis created successful clusters for several of the species used but was inconclusive overall in being able to distinguish between spectra at the genus, species and strain level. This may be due to inconsistent growth of bacteria and insufficient manipulation of the data. This study has shown the potential for FT-IR spectroscopy to be used to identify bacteria with significance for food but further development is needed to reproduce the consistent results demonstrated in current literature.

Listeria monocytogenes is a foodbome pathogen that can cause severe illness and even death. It is found in dairy and meat products. The focus is on rapid detection since conventional methods are time consuming (4-5 days). Pre-enrichment steps, as part of those methods, are time consuming. Our objective was to develop a detection system without a pre-enrichment step, giving a final result within 2 to 4 h. In the concept of "the need for speed," a detection system with an antibody-based capture technique, followed by polymerase chain reaction (PCR), was developed. Glass beads coated with a Listeria polyclonal antibody were added to the food sample. After a static incubation/capturing step, beads-cell complexes were separated from the food, and boiled to lyse the cells and release the DNA. In a final PCR/electrophoresis step the DNA samples were analyzed. The use of a flow-based capturing system (ImmunoFlow) was also investigated. Using a bead-antibody complex in this ImmunoFlow setup has several advantages, including the possibility of concentrating the microorganisms out of large food samples (with flow through setup), the exclusion of a pre-enrichment step, and the potential for automation. Besides buffer solution (Tris), different kinds of milk, e.g., pasteurized, Ultra High Temperature (UHT), and raw milk, were also investigated. The detection limit in buffer solution was 1 x 106 CFU/ml no matter if the ImmunoFlow system or the static incubation was used. For the different pasteurized milk samples, the detection limit varied between 1 x 107 and 1 x 108 cells/ml in the static procedure. For UHT and raw milk, however, capturing of Listeria monocytogenes cells was not possible in the static or the ImmunoFlow setup. In conclusion, we developed a rapid and specific detection system for Listeria monocytogenes at high concentration in pasteurized milk using a static capturing procedure. The total test time for this detection system is less than 4 h, which is much faster than the present detection systems (which are using an enrichment step prior to testing). Implementing a real-time PCR system after capture would further reduce this detection time.

This study compared the effects of 1.4 or 2.7% sodium levulinate or sodium lactate on aerobic plate count (APC), color, pH, and TBA value of fresh pork and turkey sausage. Both sodium lactate and Jevulinate inhibited growth of aerobic microorganisms during storage, compared to controls. Bacteriostatic effects of sodium lactate were dose dependent, wherein 2.7% lactate was significantly more antimicrobial than 1.4% lactate. This was not the case for sodium levulinate, where 1.4% sodium levulinate was as inhibitory to microbial growth as 2.7% sodium levulinate. Additionally, 1.4% sodium levulinate was as inhibitory to microbial growth as the higher level (2.7%) of sodium lactate. TBA values, color, and pH were not affected by treatment with sodium lactate or levulinate. In conclusion, sodium levulinate may have potential as an antimicrobial agent in fresh sausages if it can be obtained at a reasonable cost on a commercial basis.

The effects of micrococci on sensory characteristics of different batches of summer sausages were determined. Sixty four salt-tolerant indigenous isolates were selected from beef or mutton treated with 1.5 or 3.0% sodium chloride and 120 ppm sodium nitrite, and held at 5 or 10 C for 5 days. These isolates (61/64) were identified as staphylococci and micrococci. Summer sausages were made from several lamb, ewe, and ram carcasses which were hand deboned and blended after grinding to contain 22% fat. Six summer sausage treatments were prepared using two different sources of commercial starter cultures including Micrococcus species or Micrococcus varians and Lactobacillus plantarum, an indigenous Micrococcus isolate, a microbial lipase, or encapsulated lactic acid. Three sensory panel sessions rated these products for consumer acceptability. Sensory panel results indicated that starter culture treatments did not improve sensory characteristics of the summer sausage over the treatment containing encapsulated lactic acid. Lipase addition caused a general reduction in sensory panel ratings for flavor, texture, appearance, and overall acceptability of the summer sausage (p = 0.05).

Differences in texture at any particular stage of ripening depend upon differences in the basic structure and the extent to which the basic structure is modified by physical parameters. Thus, very young cheeses of the same variety differ in texture because of variations in pH and in salt, moisture, and fat content. How well a cheese melts and shreds depend on its texture and physical parameters. Streptococcus thermophilus MR1C produces an exopolysaccharide (EPS) that is tightly associated with the bacterial cell wall. Addition of S. thermophilus MR1C to the cheese make will increase the moisture of the cheese 2-3% and thus affect the texture, melt, and shreddability of that cheese. To determine the effect of S. thermophilus MR1C on the texture, melt, and shreddability of cheese, two stirred-curd cheeses with equivalent physical parameters using BPS-producing S. thermophilus MR1C or non-BPS-producing S. thermophilus DM10 adjunct cultures were produced. Because MR1C cheese would increase moisture, the curd size, wash water temperature, and pH at salting had to be altered in order to make the physical parameters the same for both cheeses. The MR1C cheese was harder and had a higher fracture stress than the DM10 cheese. The MRlC cheese was also more adhesive, but only for one of the two trials. Even with adjustments in the method of manufacture, the MR1C cheese still had a slightly higher SM and pH, which may be partly responsible for the differences between the two cheeses. There were no differences between the MRlC cheese and the DM1 0 cheese in shreddability as determined by fines, stickiness, and gumminess. Cheese produced without a streptoccus adjunct culture was more cohesive and had fewer fines than the MRIC or DM10 cheese.

No description available.

The primary step in the microbiological assessment of highly dynamic and complex food processing conditions is environmental sampling. The objectives of this study were to: (1) compare the efficacy of four sampling devices including Microbial-Vac system (MV), cellulose sponge (SP), polyester swab (SW) and composite tissue (CT), for the recovery of Listeria monocytogenes and Brochothrix thermosphacta on five surfaces and (2) to determine if there was a significant difference between the recovery of low (10 CFU/900cm2) and high (100 CFU/900cm2) L. monocytogenes inoculum levels using the sampling devices in a simulated food processing environment. Surfaces used for this study were stainless steel (SS), polyethylene cutting board (CB), polyurethane conveyor belt (PB), open hinge flat top conveyor belt (FT) and mesh conveyor belt (MB). Food contact surfaces were inoculated with L. monocytogenes to obtain a final cell population of 10 (low) or 100 (high) CFU/900 cm2. An average cell density of 10,000 CFU/25 cm2 was used for inoculating B. thermosphacta on each of the surfaces. Inoculated surfaces were dried and held for two hours at 4˚C then sampled and processed for detection. Because L. monocytogenes is a "zero tolerance" pathogen in ready-to-eat foods, the qualitative analysis included an enrichment step to detect presence/absence in the sample. In comparison, B. thermosphacta was directly plated in order to quantify the recovery capability of each device. Results indicated for recovery of 100 CFU/900 cm2 L. monocytogenes, there was no difference among devices on SS, CB or PB surfaces (p>0.05). However, a significant difference was detected at 10 CFU/900 cm2 on SS between MV and CT, 62.97 and 17.34%, respectively (p=0.0086). Results for FT indicated MV was superior over SP and SW (p=0.0004) for detection of high and low L. monocytogenes. There was no difference for the quantitative recovery of B. thermosphacta on PB and SS; however, there was a difference (p=0.0371) among devices on CB indicating MV was superior over SP and CT. The swab recovered 3.25 log CFU/25cm2 from flat top belts and was significantly lower (p=0.0259) than MV and SP devices, 4.29 and 4.12 log CFU/25cm2, respectively.

Self-efficacy is a proven indicator of predicting risky behaviors, but without a baseline level of adolescent food safety self-efficacy to develop targeted interventions it is difficult to produce meaningful behavior change. The research question around which this study was designed is: To what extent can a validated instrument accurately capture adolescent beliefs of food safety self-efficacy. Through rigorous field testing and statistical analysis we hypothesize a valid and reliable instrument can be created for measuring adolescents’ food safety self-efficacy. The purposes of this study included: (a) development of a high quality, food safety self-efficacy instrument, (b) validation of the instrument through expert review, and (c) field testing of the instrument to measure adolescent food safety self-efficacy. A field test of the instrument was conducted with adolescent students (n=91) using expert review and the following analyses: a) the normality, (b) the validity, and (c) the reliability. The final instrument yielded 16 items that were within the boundaries of normality, passed expert review, and/or had strong validity and reliability results. The results of this study indicate that an instrument accurately measuring and capturing adolescent food safety self-efficacy is possible to create by using proven valid and reliable methods.

Bacterial spores have remarkable resistance to a variety of harsh conditions, causing spoilage in food industry and becoming the primary bacterial agent in biowarfare and bioterrorism. In this study, inactivation mechanisms of Bacillus amyloliquefaciens (BA) spores by non-thermal plasma (NTP) were investigated by using Fourier-transform infrared spectroscopy (FTIR) as a major tool to exam spores after NTP treatment. Chemometric techniques, such as multivariate classification models based on soft independent modeling of Class Analogy (SIMCA) and Principal Component Analysis (PCA), were employed to identify functional group changes in FTIR spectra. The IR absorbance bands correlated to dipicolinic acid (DPA) decreased after NTP treatment indicating that DPA released and then reacted with reactive species generated by NTP and it was confirmed by nuclear magnetic resonance (NMR). Also IR absorbance bands corresponding to protein structure changed. FTIR combined with UV-Vis spectroscopy was used to monitor spore germination. Large amount of DPA released in a short time when spores germinated at 50°C, showing that DPA released in response to heating. NTP treated spores could germinate with little DPA release due to sub-lethal effects induced by plasma. Also an empirical model based on Weibull distribution was established to describe the spore germination process showing that NTP treated spores exhibited abnormal germination pattern. Inactivation mechanisms of NTP with air as feed gas was compared with high-pressure, wet heat, chemical treatment using chlorine dioxide (CD) and NTP with argon as feed gas. The results showed that few chemical changes in spores after autoclave and high pressure treatments, though protein structure changed. CD and NTP with air as feed gas inactivated spores by oxidation. DPA released after NTP with argon as feed gas treatment and it is possible that UV and charged particles accounts for the inactivation. This study provides in depth insight into the inactivation mechanism of NTP and information for optimizing NTP process.