Skim milk powder (SMP) is commonly used as a food ingredient. Both processing procedures and storage conditions have been noted as important contributors to SMP flavor. Research has not addressed how or if SMP flavor variability impacts consumer acceptance of ingredient applications. Further, many studies have addressed the importance and impact of SMP storage on flavor variability, but the impact of SMP processing on flavor formation has not been extensively researched. In this study, we examined both the impact of SMP flavor variability on consumer acceptability in SMP ingredient applications as well as the flavor formation of SMP throughout production, with emphasis on steps where heat was applied.

The purpose of the research has been to develop an experimental biofilm ecocystem for the characterization of Listeria monocytogenes biofilms in a simulated food processing (SFP) environment. Individual strains of L. monocytogenes were initially surveyed for their ability to attach to surfaces and form biofilms under a variety of conditions. Five strains of L. monocytogenes were then screened for optimal cell attachment and biofilm formation. Significant differences in surface attachment and biofilm formation were observed among the different strains of L. monocytogenes. The biofilms of the five-strain mixture of L. monocytogenes were formed on surfaces that are commonly used in food processing facilities, such as stainless steel and Teflon®. The biofilms were subjected to the SFP system in sequential 24-h daily cycles. Conditions of the SFP system included: starvation, washing, rinsing, and sanitation that routinely occur in a food processing plant. Cell survival in biofilms was determined during the time course of the experiment. The susceptibility of the cells in biofilms and detached cells to different sanitizers was measured. The morphology of the cells in biofilms and the planktonic cells detached from biofilms was observed. The study indicated that the progressive resistance developed by L. monocytogenes biofilms to a sanitizer could protect the cells in biofilms from this and other sanitizing agents. The progressive resistance and cross protection was observed in biofilms, but not in detached cells. These findings could provide a basis for further research on the mechanism of progressive resistance to stresses by L. monocytogenes in biofilms under food processing conditions. The data may help to establish effective sanitation programs for food processing and related industries.

MICROWAVE-ASEPTIC PROCESSING OF SWEETPOTATO PUREES: DIELECTRIC PROPERTIES AND MICROBIAL INACTIVATION EVALUATION

The development of reduced fat foods is a continual challenge in the food industry. Among the many attributes fat contributes to food products is flavor. Fat replacers are used to regain some of these lost attributes as fat is removed from foods. These fat substitutes affect the rate and concentration at which flavor molecules are released during mastication. Whey is a source of protein for protein-based fat replacers. The effects this ingredient has on flavor intensity was studied utilizing 2,4-Dimethylbenzaldehyde (DMB) and Ethyl Butyrate (EB). The objective of this project was to develop a headspace gas chromatography method to measure the changes in volatility of these two flavor compounds in various concentrations of WPI solutions and to compare these results to sensory findings. There was a significant decrease in the volatility of DMB with increases of protein concentration from 0 to 2%. Aroma and taste intensity also decreased with increasing protein concentration. The volatility of EB and taste intensity showed no significant differences with successive increases in protein concentration. However, aroma shows significant decreases in intensity with increases in protein concentration at the 0 to 2% and 4 to 6% levels. There was significant positive correlations between volatility and sensory results.

<i>Campylobacter</i> is the most common bacterial agent causing human gastroenteritis and is mainly transmitted through foods. <i>Campylobacter</i> is a zoonotic agent, and commonly colonizes poultry and other meat animals. Whereas erythromycin resistance in <i>Campylobacter jejuni</i> rarely occurs, erythromycin resistance in <i>Campylobacter coli</i> from meat animals is frequently encountered, and could represent a substantial barrier to antibiotic treatment of human infections. Erythromycin resistance in <i>C. coli</i> has been associated with a point mutation (A2075G) in the 23S rRNA gene, acting synergistically with the CmeABC efflux pump. However, the mechanisms responsible for possible dissemination of erythromycin resistance in <i>C. coli</i> remain poorly understood. In this study we investigated transformation-mediated acquisition of erythromycin resistance by genotypically diverse <i>C. coli</i> strains from turkeys and swine, with total genomic DNA from erythromycin-resistant <i>C. coli</i> used as donor. In addition, we studied the effects of environmental factors and species (<i>C. coli</i> vs. <i>C. jejuni</i>), and fitness costs of erythromycin resistance in transformants. Overall, transformation to erythromycin resistance was significantly more frequent in <i>C. coli</i> from turkeys than in swine-derived strains (P<0.01) with frequency of transformation 10^-4 to 10^-6 in turkey-derived strains, but 10^-7 or less in <i>C. coli</i> from swine. Transformants harbored the point mutation, A2075G in the 23S rRNA gene. Erythromycin resistance was stable in transformants following serial transfers, and most transformants had high MIC values (>256µg/ml), as did the <i>C. coli</i> donor strains. In contrast to results obtained with transformation, spontaneous mutants had relatively low erythromycin MIC (32-64µg/ml) and lacked the A2075G mutation. Temperature profoundly affected frequency of transformation to erythromycin resistance in <i>C. coli</i> and transformation frequency at 42°C was significantly higher than at 25°C, 32°C and even 37°C. However, transformation to nalidixic acid resistance was not significantly affected by temperature. No significant difference in transformation frequency was detected between microaerobic (5-10% CO₂) and aerobic conditions. Starvation conditions did not affect transformation frequency to nalidixic acid resistance. Increasing incubation time from 3-4h to 15-17h significantly increased transformation frequency to erythromycin resistance (P<0.05). Transformation of <i>C. jejuni</i> using genomic DNA from erythromycin resistant <i>C. coli</i> revealed that transformation frequency of <i>C. jejuni</i> to erythromycin resistance was lower than <i>C. coli</i>, suggesting that erythromycin resistance in <i>C. coli</i> may not be disseminated via transformation in <i>C. jejuni</i> as frequently as in <i>C. coli</i>. Transformants derived from <i>C. jejuni</i>, however, had high erythromycin MIC values (>256µg/ml) and harbored the A2075G transition, similarly to <i>C. coli</i> transformants. When grown separately at 42°C, an erythromycin-resistant transformant derived from <i>C. coli</i> strain 961 had a similar growth rate as its erythromycin-sensitive parental strain, whereas an erythromycin-resistant transformant derived from <i>C. jejuni</i> strain SC49 had a significantly longer generation time compared to its parental strain. In competitive growth studies, however, the <i>C. coli</i> transformant was at competitive disadvantage in relation to its parental strain in stationary phase, whereas the <i>C. jejuni</i> transformant was at a slight fitness advantage after 14days. Furthermore, in the mixed culture the generation time of the <i>C. jejuni</i> transformant was not significantly different from that of the parental strain. In conclusion, natural transformation has the potential to contribute to dissemination of high-level resistance to erythromycin among <i>C. coli</i> strains colonizing meat animals and temperature can greatly affect transformation to erythromycin resistance, but not to nalidixic acid resistance. These findings suggest that ecological attributes may play an important role and exert differential impact on the potential of the organism to acquire antimicrobial resistance determinants via natural transformation. However, further study is necessary to characterize the fitness of erythromycin resistant transformants in <i>Campylobacter</i> and identify possible mechanisms underlying the relatively low frequency of erythromycin resistance in <i>C. jejuni</i>.

Campylobacter is considered to be a leading bacterial cause of acute enteritis in the United States. Campylobacter is found in the fecal material and the gastrointestinal tract of a broad range of animals. It has been suggested that the greatest cause of human infection is cross-contamination and/or the consumption of undercooked meat and poultry products. In the United States there are limited data on the presence of Campylobacter in cattle. This study investigated the prevalence of Campylobacter (C. jejuni and C. coli) as well as the presence of antibiotic resistant strains in mature cattle at slaughter. Representative fecal samples (n = 610) of the day¡¯s harvest were taken from the colon of mature cattle older than 30 months of age, over a period of 17 months. Species of Campylobacter isolates were determined by polymerase chain reaction. Pure cultures of Campylobacter were obtained from 143 of the 610 samples (23.4%, SE 1.7%). Of the confirmed Campylobacter-positive samples, the majority (93.0%) yielded C. jejuni, with C. coli recovered from the rest (7.0%). Seasonal data showed that Campylobacter prevalence is somewhat greater during the winter (29.4%) as compared to summer months (20.7%) (P ¡Ü 0.05). Some of the isolates were resistant to selected antibiotics, with the greatest incidence being resistance to ampicillin (49.7%). The data imply that there may be a human health risk from the colonization of mature cattle at harvest by Campylobacter. Further research needs to be done to evaluate the food safety impact of Campylobacter colonization of cattle.

Determining the redox potential of a system can be a useful tool in evaluating the thermodynamic changes that occur over a period of time. Currently, fermentation industries use pH measurements to assess the progress of fermentation and growth of lactic acid bacteria (LAB). Redox potential (Eh) measures the transfer of electrons within a system, rather than solely the concentration of hydrogen ions, as measured by pH. Continuous monitoring of fermentation by Eh may allow for more descriptive analysis of the metabolic process and could offer a method for the earlier prediction of spoilage by yeasts. The trends in redox potential of fermenting cucumbers were observed to evaluate the possible application of this parameter in monitoring the development of fermentation. Additionally, an evaluation of the effect of gas purging on microbial growth during the fermentation was conducted using redox potential trends as a monitoring tool. Cucumbers were packed and brined using sodium chloride, calcium chloride, and acetic acid and the redox potential monitored during fermentation. Examination of both pasteurized-inoculated jars and non-pasteurized jars was conducted in this study. In addition, changes in redox potential were measured in fermentations that were purged with nitrogen, oxygen, hydrogen, or left untreated. Brine samples were analyzed for microbial counts, pH and substrates and products of fermentation. Under conditions representative of a standard cucumber fermentation, a dramatic decrease in the redox potential was observed during the first day, concomitantly with the initiation of the log phase of bacterial growth. However, in the presence of spoilage yeast, redox potential remained low over this initial period. The progress of a fermentation sparged with nitrogen, oxygen, or no treatment produced similar Eh trends. The Eh trend was more reduced under hydrogen sparging. A heightened growth rate for LAB, more efficient production of lactic acid, and lower production of ethanol occurred with nitrogen sparging. The evidence suggests that the growth of yeasts in a cucumber fermentation could be detected based upon differences in the redox potential. Distinct variations in Eh were still recorded after pH values decreased and remained constant, suggesting the valuable possible application of Eh to monitor industrial cucumber fermentations. Additionally, changes in redox potential were affected by gases introduced during cucumber fermentations and sparging with nitrogen could have substantial benefits to the industry.

Computation of overall heat transfer coefficients in a triple tube heat exchanger (TTHE) is complicated when compared to a double tube heat exchanger (DTHE) since the two overall heat transfer coefficients are not independent of each other and must be solved for simultaneously. Previous methods established towards calculation of these parameters either include assumptions that are not valid for all flow conditions and fluid flow rates or use empirical correlations which may cause significant deviations from actual values of these parameters. A more generic technique was developed for calculation of overall heat transfer coefficients and axial temperature distribution of fluids in a triple tube heat exchanger. The developed procedure has been used for calculation of these parameters at various fluid flow rates and product inlet temperatures. Theoretical double tube heat exchanger results were also tabulated for comparison purposes. The advantages of using a TTHE over a DTHE has been both conceptually explained and demonstrated using the results obtained. However, it was also shown that design of TTHE experiments is critical, especially in the co-current flow arrangement, since the relative flow rates of the fluids may result in a decrease in the effectiveness. The effect of fluid flow rates, product inlet temperature, and flow arrangement on values of overall heat transfer coefficients, total amount of heat transferred, and effectiveness were also investigated. These results were analyzed using SAS and interpreted for the consistency of the obtained results with the literature.

Lactobacillus acidophilus NCFM is a probiotic culture widely added to dairy products and dietary supplements. The bacterium has been linked with immune modulation, cold prevention in humans, and relief of gut pain via a morphine like mechanism in animals. Industrially, the target for delivery of viable cells in a 6 oz. serving of yogurt at the end of a 52 day shelf-life is 2 x 106 CFU/g. Survival studies with an industrial yogurt formulation showed that counts of NCFM fell to less than 102 CFU/g at the end of shelf-life. The objective of this study was to investigate the reasons for the dramatic loss of viability during shelf-life, and define a solution that could maintain viability throughout shelf-life. Levels of NCFM were followed in fermented yogurts at pH 4.1, 4.7 and 5.0. Results showed that with inoculation levels of 108 CFU/ml, NCFM added at the outset of fermentation maintained survival in yogurts acidified at pH 4.7 and 5.0. NCFM showed poor survival in yogurts acidified to pH 4.1, exhibiting a 3 log loss after 48 days. The possible effects of cell injury in lyophilized Lb. acidophilus NCFM cells were also investigated. Cells subjected to a 60 minute resuscitation period in MRS media, prior to addition to acidified yogurt base at pH 4.1, showed only a ~1.5 log loss after 42 days. Survival of NCFM in yogurt was compromised at acidic conditions below pH 4.7 and a recovery period of the lyophilized cells can greatly improve survival.

Drying is a unit operation where water is removed from a material by means of evaporation and mass transfer. It is widely used in industrial manufacturing processes. Many of these processes involve drying of porous materials. Porous media are, in general, heterogeneous systems. The microstructure of the pore space influences transport properties and hence, drying rates. Thus, a quantitative geometrical characterization of the pore space is crucial for accurate prediction of porous media drying rates. Simulation of porous media structure, given a specific size distribution of constituent particles, followed by pore-space characterization is a powerful as well as economical predictive tool for product design. Realistic unconsolidated porous media were reconstructed through Monte Carlo gravitational particle packing simulation. The porous media simulation was validated by comparison with extracted transport related micro-structural parameters from x-ray micro-CT (computed tomographic) images. A mathematical morphology based three-dimensional image processing algorithm was developed to characterize the pore space in the simulated porous media. This realistic pore-throat network information was utilized in an invasion percolation based simulation of porous media drying and showed satisfactory agreement with quantitative data extracted from in-situ NMR (nuclear magnetic resonance) imaging experiments.