The effect of fat and pH on the best estimate threshold (BET) of 3 prominent dairy product flavor compounds with varying physicochemical properties: diacetyl, delta-decalactone, and furaneol, in water, oil and oil-in-water model emulsions (at 10 and 20 % fat at neutral and acidified pH 5.5) were investigated. The headspace-matrix partition coefficients (KHS/matrix) of each compound in the different matrixes were established. The rheology and particle size of the emulsions used in this study were also investigated. The particle size and the viscosity of the emulsions did not affect the BET or the partition coefficients. Reducing fat from 20 to 0 % did not affect the BET value or partition coefficient of diacetyl (P>0.05). Increasing fat content increased the BET value and decreased the partition coefficient (P<0.05) of the most lipophilic compound in the study, delta-decalactone. Fat did not affect the BET of furaneol (P>0.05) but did have an effect on the partition coefficient (P<0.05). At pH 7, addition of fat decreased the partition coefficient of furaneol whereas at pH 5.5, addition of fat increased the partition coefficient of furaneol. Adjustment of pH from 7.0 to 5.5 did not impact the BET values of delta-decalactone, but did affect the partition coefficients of furaneol at all fat levels and impacted diacetyl at 0 % fat. The partition coefficient results generally agreed with the BET values on the effect of fat and pH, although, the partition coefficient test was more sensitive to the differences in the matrix composition than a threshold test.

Aseptic processing of low-acid foods containing large particles is an emerging technology. Most multiphase process validation methods employ simulated particles to contain residence time tags, thermo-sensitive implants and/or bio-loads for temperature detection, time-temperature integration, and bactericidal efficacy confirmation. Such particles need to have conservative (fast-moving and slow-heating) characteristics to compare them with real food particles for thermal treatment. This study was conducted to fabricate and test (by heat penetration studies) conservative simulated particles which serve as carriers for thermo-sensitive implants and bio-loads in the validation procedure required for aseptic processing of shelf stable low-acid multiphase foods. A custom developed CPD (Conservative Particle Design) software was used to determine the minimum wall thickness (~ 2 mm) and cavity dimensions of half inch cubic particles for validation of aseptic processing of foods containing half inch cubic potato, carrot and other vegetable pieces. These particles were fabricated from PP (polypropylene) and PMP (polymethylpentene) polymers and they exhibited conservative heat penetration characteristics when compared with various real food particles. Duplicate samples of simulated and real food particles were fitted with thermocouples and heated (< 127 degree C) under pressurized (autoclave, 24 psi) conditions. The method developed in this study can be used for experimental validation of the safety of aseptic processing of multiphase foods and would reduce the cost and complexity of process documentation and filing with regulatory agencies and bring aseptic multiphase foods closer to commercial reality.

<i>Listeria monocytogenes</i>, a food-borne pathogen of humans and animals, can cause severe listeriosis with relatively high mortality. A cluster of closely related strains of <i>L. monocytogenes</i> (designated Epidemic Clone I) have been implicated in numerous outbreaks in Europe and North America, including the California outbreak of 1985. <i>L. monocytogenes</i> strains implicated in the 1998-1999 and the 2002 multistate outbreaks in the USA represent a unique epidemic-associated clonal group, designated Epidemic Clone II (ECII). Comparative genomic analyses across five genomes from different <i>L. monocytogenes</i> isolates and <i>Listeria</i> species identified a genomic region (region-18) in serotype 4b strains that may have been acquired by horizontal gene transfer. Region-18 is either absent or markedly divergent in ECII strains but conserved among other serotype 4b strains. Region-18 is flanked by a large gene encoding a putative cell-wall associated protein (<i>wap</i>) on one side and a well-known virulence gene internalin A (<i>inlA</i>) on the other side in serotype 4b strains. PCR primers and DNA probes derived from this ECII-specific region-18 can readily differentiate ECII strains from other serotype 4b strains. This facilitates the detection and monitoring of these strains belonging to ECII clonal group in foods, clinical samples, and the environment. Genetic characterization of <i>wap</i> by the construction of deletion mutants suggested that the ECII <i>wap</i> mutant but not the ECI <i>wap</i> mutant may be involved in specific environmental adaptations such as surface adherence and possibly biofilm formation in ECII strains. Mutational and functional analyses showed that the deletion mutant of region-18 in ECII had an enhanced death rate during post-stationary incubation at 42℃,suggesting that the ECII-specific region-18 may be implicated in post-stationary stress responses.Two c72.44-negative variants of epidemic-associated <i>L. monocytogenes</i> serotype 4b strains were isolated from laboratory cultures. Naturally occurring c74.22-negative variants that exist under laboratory conditions without any noticeable phenotypic differences from their original forms may complicate the analysis of phage sensitivity and pathogenic characteristics.

<p><META [NAME="keywords" CONTENT="bacterial-pathogens, bacteriocins, Citric acid, EDTA, foodborne illnesses, formulation, growth curve, nisin, poultry, Salmonella, salmonella typhimurium, Salmonellosis, shelf-life, shelflife, simplex search algorithm, treatment optimization" NAME="copyright" CONTENT="© Sarid M. Shefet 1994"]><b>SHEFET, SARID M.<br><p><p><p>    More than 10% of the U.S. population experience at least one incident of foodborne disease annually (Todd, 1989). From 1983 to 1987, infections contribute to at least 1,000 deaths per year in the United States. <p>     Poultry products are considered to be the single most important food source of contamination rates for live chickens can vary from about 13% to 80% of the flock and are invariably higher after processing (Mead, 1976; Roberts, 1988; Budnik, 1990). In 1992, the U.S. was ranked first in the world in poultry consumption with 94.8 pounds per capita, followed by Israel with 83.7 pounds, and Hong Kong with 79.3 pounds (Brown, 1993). In 1993 over 27.6 billion pounds of ready-to-cook poultry products were produced in the U.S. Per capita consumption of poultry products has increased substantially over the last two decades relative to other meat products; therefore, exposure of the consumer to poultry product-associated microorganisms including pathogens has correspondingly increased and no doubt contributes to these foodborne disease statistics.<p>    Besides bacterial pathogens, poultry products are also contaminated with a variety of spoilage microorganisms which can contribute to the development of strong off odors and/or slime formation and shortened product shelf life. These organisms, however, are not generally associated with human illness. A reduction in the population of these microorganisms or suppression of their growth often results in increased product shelf life and greater consumer acceptability. Some reports have estimated that the presence of pathogenic and spoilage microorganisms on poultry may cost the American public over two billion dollars annually in foodborne disease-related expenditures and spoiled products (Roberts, 1988; Todd, 1989). <p>     The bacteriocin nisin was approved by the United States Food and Drug Administration in 1988 as a GRAS (general recognized as safe) substance for use in pasteurized cheese spreads to control outgrowth and toxin production by Clostridium botulinum. Blackburn when combined with chelating agents such as disodium ethylenediamine tetraacetate (EDTA) and citrate. Perturbation of the outer membrane of gram-negative bacteria via chelation of divalent cations located in the lipopolysaccharide layer is believed to sensitize the cells by providing access to the cytoplasmic membrane where nisin-mediated inactivation occurs. <p>    The initial focus of this study was to optimize the inhibitory activity of nisin against a NAR skin population, as observed with broiler drumstick skin, were detected following treatment with the four nisin-containing treatments.<p>     Experiments were also conducted to determine the efficacy of the nisin-based treatments against NAR-infected drumstick skin under varying exposure times and concentrations of nisin. Exposure time significantly influenced the lethality of the treatments and depending on the treatment, nisin concentrations could be reduced from 100 µg/ml to 50 or 25 µg/ml without loss of significant biocidal activity. In other studies, the refrigerated shelf life of broiler drumsticks was extended by 1.5 to 3 days following immersion for 30 minutes in one of the optimized nisin-containing treatments in comparison to drumsticks immersed in distilled, deionized water.<p>     These findings indicate that treatments containing nisin and varying concentrations of chelating agents and/or surfactant at an acidic pH are capable of significantly inhibiting the population of -free poultry products, the identification and implementation of effective preservation methods could result in several long term benefits including greater public confidence in poultry products, an increased market potential, and increased profits for the poultry industry.<P>

<p><META [NAME="keywords" CONTENT="aseptic, sterilizers, flow, particulates, food, food-particles, heat-transfer, heat transfer, flow-visualization, flow visualization, visualization" NAME="copyright" CONTENT="© Sarid M. Shefet 1998"]><b>SHEFET, SARID M.<br><p><p><p>     Presently, conventional continuous pasteurization systems which were designed primarily for liquids and semi-liquids do not satisfy either product quality specifications or safety requirements of U.S. regulatory agencies when applied to food containing particulates. One potential solution to the above problem was suggested in a recently issued patent by this author entitled 'Hydrostatic Heating Apparatus'. <p>     The objectives of this study were to develop a quantitative visualization tool for evaluating flow behavior of particles in a model hydrostatic heating apparatus or other flow systems and to estimate process paramenters (Reynolds numbers, Nusselt numbers, Biot numbers, heat transfer coefficients, holding tube length and process times) of a simulated aseptic process for potato spheres, based on the quantitative data collected during the study.<p>    The three dimensional movement of polystyrene balls as influenced by ball diameter (0.95 and 1.9 cm), flow rate (10, 20 and 30 l/min) and conveyor disk design (2 configurations) were recorded in the model heating apparatus and analyzed using motion analysis software. Ball speed and net-to-gross-displacement (NGDR) ratio values were calculated for ball movement in the 0.9) indicating that either statistic could be used to describe the flow behavior of particles. In addition, a high correlation(r). The average speed derived from the quantitative visualization method was subsequently used to calculate heat transfer and related properties in the model hydrostatic heating apparatus.<p>    Based on the successful assessment of the quantitative flow visualization tool in this study, it is anticipated that this method may be useful for comparing flow characteristics of particles in other food conveying systems (i.e. continuous aseptic pasteurizers). The fact that the movement of a particle in a given system can be documented and characterized suggests that similar comparisons of particle movements can be achieved in other systems or factors influencing flow can be readily evaluated. Furthermore, this method will allow process engineers to make recommendations on specifications (i.e. conveyor disk design, liquid velocity, particulate load, etc.) of future designs of the hydrostatic heating apparatus or any other system designed for conveying particulates.<P>

<p>This study investigated the static and dynamic physical properties of protein foams and cake batters made from egg white protein and whey protein isolate. A method of rheological evaluation (vane method) initially employed in the study of soils was used to evaluate protein foam rheology. The method was shown to be a reliable method for determining large-scale rheological properties of protein foams. Egg white protein produced foams with higher yield stress at lower concentrations and shorter whip times than did whey protein isolate. Short lifetime decreases in yield stress were observed in foams of higher protein concentration of both types, which were both concentration and whip time dependent. This is considered to be the result of a restructuring of the system as opposed to collapse of the foam. Cakes made from foams of both types showed different performance properties as well. Cakes produced from egg white protein exhibited a minimum concentration of protein (between 5 and 10% w/w of foam) necessary to form a cake of satisfactory volume. Whey protein isolate was unable to form a satisfactory cake regardless of the concentration studied. Phase contrast microscopy, fluorescence microscopy and differential scanning calorimetry studies suggested that the difference in behaviors might be due to a high degree of phase separation between egg white protein and soluble starch that was not seen in whey protein containing systems. This phase separation appears to allow significant matrix development in egg white protein containing cakes that can support the volume of the final product. <P>

<p>Whey protein isolate (WPI) forms particulate, heat-induced gels under conditions of low electrostatic repulsion among proteins. Particulate gels appear opaque, release water when deformed, and can be formed by 1) adjusting the pH to near the isoelectric point (pI) of beta-lactoglobulin (?pH treatment?), and 2) addition of >200 mM NaCl at pH 7.0 (?NaCl treatment?). The objective of our research was to understand the electrostatic contribution to particulate gel formation, using large strain rheology and microstructural techniques to characterize gel properties.Gels of WPI (10% protein w/v) were formed by heating at 80 degrees C for 30 minutes. The large strain fracture properties of shear strain at fracture, shear stress at fracture, and slope ratio (R0.3) (indication of non-linear stress/strain behavior) were measured with a torsion gelometer. Gel microstructure was observed using scanning electron microscopy (SEM). Gel permeability (Bgel) was evaluated by measuring the flow of solvent through a fixed gel matrix and calculating the permeability coefficient based on Darcy's Law. Fracture properties for both treatments were determined from pH 5.2 to 5.8 and NaCl concentration from 0.2 to 0.6 M (pH 7). When fracture stress and fracture strain curves for pH and NaCl treatments were overlaid, there was a distinct overlap. Based on this, treatment pairs were formulated to match rheological properties. The "high stress" pair was matched at pH 5.47 and 0.25 M NaCl, pH 7.0 (fracture stress=23 kPa and fracture strain=1.86) and the "low stress" pair at pH 5.68 and 0.6 M NaCl, pH 7.0 (fracture stress=13 kPa and fracture strain=1.90). Each pair was not significantly different for fracture stress(p>0.05), and there was no significant difference among all treatment pair values for fracture strain (p>0.05). However, the R0.3 was treatment, not pair specific. The NaCl treatments (0.25 M NaCl, pH 7 and 0.6 M, pH 7) had R0.3 values of 1.23 and 1.26, respectively, which were not significantly different (p>0.05). The gels formed at pH 5.47 and 5.68 had R0.3 values of 1.05 and 1.11, respectively, which were significantly different (p1) have been related to the presence of more than one structural component in the gel network (Bot et al., 1996). The increased strain hardening for NaCl treatments may be largely due to intermolecular disulfide bond formation, which is preferred at pH 7 relative to isoelectric pH due to the pKa of the thiol group. Random coil structure may be the other structural component that contributes to strain hardening in WPI gels, but more research is needed in this area.With the fracture properties normalized, no relationships were observed with the permeability or the microstructure between treatments. Lower permeability values were found for the treatment values (0.25 M NaCl, pH 7 and pH 5.68) near the fine-stranded transition regions (~pH 6 and 0.2 M NaCl, pH 7). These networks had more of a stranded-type structure with smaller, less defined aggregates as observed in SEM. This further demonstrates that there is little relationship between fracture rheology and microstructure of particulate gels. <P>

<p>Listeria monocytogenes is the cause of human listeriosis, a food borne disease with high mortality. Serotypes 1/2a, 1/2b, and 4b account for most cause of illness. Serotype 4b is of special interest, for its high implication in foodborne outbreaks. Two loci were previously found to be involved in serotype-specific surface antigen expression of L. monocytogenes serotype 4b. One mutant, 27B6, derived from L.monocytogenes serotype 4b strain 2381L (Jalisco cheese outbreak), was found to be negative in immunoblot reactions with all three serotype 4b-specific MAbs C74.22, C74.33, and C74.180. Chromatographic analysis showed markedly reduced levels of two sugar substituents on the teichoic acid backbone, compared with the wild type strain. The mutant was furthermore resistant to Listeria species-specific phage A511, while still sensitive to serotype 4b-specific phage 2671. In this study, the transposon localized in a new genomic region (locus III). The genes in this region had homologues in the database involved in galactose metabolism, including galM, galE, and pgm. The transposon in 27B6 was found to be in the putative pgm. Interestingly, although inactivation of the putative pgm affected the presentation of both serotype-specific sugar substituents on the teichoic acid, the gene was not found to be unique to serotype 4b. The gene pgm was present in L.monocytogenes serotypes other than 4b, while it was absent or highly divergent in other species. An in-frame deletion of pgm was constructed, showing similar phenotypes as those of the initial transposon mutant 27B6. The wild type pgm sequence could successfully complement mutant 27B6 in-trans, restoring wild-type reactivity with MAbs, as well as phage A511 sensitivity. In conclusion, this newly characterized genomic region of L.monocytogenes may function in sugar metabolism and is possibly associated with cell wall teichoic acid glycosylation in serotype 4b, being required for expression of serotype 4b-specific antigenic determinants as well as receptors for phage A511. <P>

<p>Common and important cosolutes of whey proteins include NaCl, CaCl and NaCl at pH 3.0 and 7.0. In the first study, the dynamic surface tension of at levels up to 0.1 M increased the initial rate of adsorption due to a reduction of the electrostatic barrier to protein adsorption. The effect of lactose concentration was minimal.For the second study, the addition of CaCl when compared to equivalent concentrations of NaCl. At pH 3.0, neither salt at any concentration significantly affected yield stress; however, overrun was generally higher at pH 3.0 as compared to pH 7.0. The relationship between overrun and surface tension with yield stress as predicted by a previously described theoretical model did not hold for this data. Specific divalent cationic effects were thought to be partially responsible for improved yield stress values. Dynamic surface tension measurements of the foaming solutions lent credence to this ion specific hypothesis. <P>

Apple cider/juice contaminated with Escherichia coli O157:H7 has been implicated in several foodborne illness outbreaks, but due to the presence of reaction inhibitors, detection by polymerase chain reaction (PCR) is often difficult. The studies presented in this dissertation were conducted to evaluate techniques to improve detection of E. coli O157:H7 in apple juice using a fluorogenic probe-based real-time PCR assay without prior enrichment. Two commercial DNA extraction and purification procedures, GenEluteTM Bacterial Genomic DNA Kit and PrepMan® Ultra Sample Preparation Reagent, were combined with two real-time PCR chemistries, SYBR® Green I dye and TaqMan® probes for potential use in the apple juice assay. After real-time PCR, no significant differences were observed in cycle threshold values (Ct) (p>0.05) among the methods. The PrepMan/TaqMan method was subsequently combined with a real-time PCR assay based on detection of the stx1, stx2, and uidA genes. Apple juice was inoculated individually with nine strains of E. coli O157:H7 (1.0 log CFU/ml to 4.0 log CFU/ml) and plated to verify initial inocula. For particulate removal, apple juice was vacuum filtered twice (Whatman No. 4 and Whatman No. 1), followed by a distilled water wash. Samples were plated again to obtain post-filtration inocula. Filtered juice was centrifuged, pellets were resuspended in 1 ml phosphate buffer, and E. coli O157:H7 cells were concentrated by immunomagnetic separation. PrepMan Ultra was added to the magnetic bead/E. coli O157:H7 complex for DNA extraction. Extracts were combined as appropriate with primers, probe and other reagents, and real-time PCR was performed. Average E. coli O157:H7 inoculum levels of 0.3, 2.2, 3.3 and 4.3 log CFU/ml in apple juice were detected at average Ct values of 41.22, 37.54, 34.69 and 31.81 (stx1); 43.13, 38.74, 35.21 and 32.58 (stx2); and 44.13, 41.54, 37.81 and 34.06 (uidA). Across all E. coli O157:H7 strains, populations as low as 1.6 (44 CFU/ml) (stx1), 1.6 (43 CFU/ml) (stx2), and 1.5 (33 CFU/ml) (uidA) log CFU/ml could be quantified using the cell concentration/real-time PCR assay. However, E. coli O157:H7 was detected on occasion below the quantifiable level at the lowest inoculum level for all strains. This method can be used for rapid detection and quantification (<5 h) of E. coli O157:H7 in apple cider/juice and potentially other foods.