The problem of age gelation in ultra-high temperature (U1IT) sterilized milk retentate (ultrafiltered 3x concentrated) is investigated in this work. Transmission electron microscopy (1EM), utilizing the microcube encapsulation technique and protocols for immunolocalization of milk proteins, provides insight into the phenomenon of age gelation ofUHT-sterilized, ultrafiltered (UF) milk retentate. Primary antibodies (specific for the native as well as the complexed forms of milk proteins) and secondary antibodies (conjugated to gold probes) are used to elucidate the positions of the milk proteins in various samples of milk from the stage of milking through UHT sterilization and storage for 12 months, by which time gelation had occurred. The movement of the milk proteins is charted and these data are used to determine the role of the proteins in age gelation of UHT-sterilized UF milk retentate. Heat-denatured β-lactoglobulin and α-lactalbumin form complexes within the serum as well as with the casein components of the micelles. UHT sterilization not only denatures β-lactoglobulin and α-lactalbumin, but catalyzes the reaction of these whey proteins and K-casein, leading to the successful formation of the complex. Complexing of β-lactoglobulin and K-casein competitively weakens the complex of K-casein to other casein fractions of the micelle. This leads to migration of K-casein from the micelle to the serum, compromising the role of K-casein in stabilizing the casein proteins within the micellar moiety. The time-dependent loss of K-casein from the micelle would expose the calcium-insoluble micellar αs1-casein and β-casein to the serum calcium. Subsequent to this, some αs1-casein and β-casein are also released from the micelles, and gelation of the milk occurs. No information was obtained on location of αs2-casein. The release of K-casein from the micelles thus apparently represents the critical factor in the phenomenon of age gelation in UHT-sterilized milk concentrates.

The purpose of this project was to initiate development of a nonrefrigerated dairy dessert product. Milk was concentrated by pressure-driven filtration and then sterilized using ultra-high temperature (UHT) processing. Following sterilization, samples were aseptically inoculated with rennet to coagulate the milk, which was then stored at room temperature. These processing steps produced a dairy dessert that did not require refrigeration. I investigated the influence of total solids, milk fat, rennet dosage, storage temperature, and storage time on curd firmness and syneresis. I investigated the effect on curd firmness and syneresis of giving the concentrate a heat treatment prior to UHT processing. Chocolate and vanilla dairy desserts were prepared, and a taste panel was conducted to compare the dairy dessert with a ready-to- eat starch-based pudding. Milk concentrate obtained by reverse osmosis did not form a gel, whereas concentrate obtained by ultrafiltration did gel. Increasing the solids content of the milk concentrate increased curd firmness, but increasing the fat content of the concentrate decreased curd firmness. Curd firmness and syneresis increased as the concentration of rennet was increased. Products stored at 21°C yielded firmer gels with more syneresis than products stored at 4°C. Moreover, products stored for longer periods of time produced firmer gels and greater amounts of syneresis. Concentrate that received a batch heat treatment prior to sterilization reduced syneresis. The addition of cocoa to the concentrate inhibited coagulation. Taste panelists preferred the commercial pudding over the dairy

Three batches of milk were ultrafiltered to 60, 65, or 70% volume reduction before diafiltration. Starting diafiltration at 70% volume reduction took less time and water without affecting nutrient recovery. Whole milk was heated to 60, 72, and 82°C for 16 s. Milk representing each heat treatment was divided into three batches, one unacidified (pH 6.6), the others acidified to pH 6.2 and 5.8. The milk was ultrafiltered, diafiltered, and concentrated to 5x (80% volume reduction). Retentate was inoculated with .5% lactic culture and incubated at 28°C to pH 5.1. Each lot of fermented retentate was evaporated under 76 kPa vacuum until moisture was reduced to 35-38%, then made into pasteurized process cheese food by cooking to 82°C. The final product contained 43-44% moisture, 24-28% fat, 1.7% salt, and 2.5% sodium citrate. Fat and protein recovery were not affected by heat treatment or pH adjustment of the milk. Recovery of calcium, phosphorus, and riboflavin were significantly reduced following acidification of milk. Riboflavin recovery was higher when milk was preheated to 60°C as opposed to 72 or 82°C. Effect of cooking temperature on meltability of process cheese food was evaluated by repeating the above experiment at three cooking temperatures, 70, 76, or 81 °C. Cooking temperature significantly affected meltability. Cheese cooked to 70°C melted best for all treatments. At all cooking temperatures, cheese from unacidified milk (pH 6.6) had greater meltability than cheese from milk acidified to pH 5.8 or 6.2. Cooking temperature had a greater effect on meltability of process cheese food made from ultrafiltered retentate than calcium content. Preheating milk before ultrafiltration did not significantly affect meltability of pasteurized process cheese food. Meltability of pasteurized process cheese food was best when made from retentate heated (following ultrafiltration) to 61°C for 16 sand poorest when retentate was heated to 72 or 83°C. During ultrafiltration without diafiltration, amino acid analysis was on samples taken at 0, 20, 40, 60, and 80% volume reduction. There were no differences in amino acid composition (g/100 g protein) between milk and 5x retentate. Soluble nitrogen at pH 4.6 in pasteurized process cheese food was an approximate measure of undenatgred whey protein. As processing temperature increased from 66 to 82°C, undenatured whey protein decreased. Decrease in meltability due to increased processing temperature was related to denaturation of whey protein. Process cheese food made from blends of UF curd and Cheddar cheese had acceptable meltability with up to 66% UF curd when the final processing temperature was 68°C. Milk with high bacterial numbers (7.8 x 106 CFU/ml) was heated to 72°C for 16 s, acidified to pH 5.8 and ultrafiltered to a 5x concentration. Ultrafiltration proceeded normally and no processing difficulties were encountered.

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.

Shelf life of meat and meat products depends on the quality of meat and packaging stability. Meat color change, lipid oxidation, pH, and microbial contamination are the main causes that affect the nutritional, sensory, and physical characteristics by forming toxic compounds, off flavors, off odors, and undesirable color. The first objective of this study was to examine the effect of newly developed CO2 generating absorbent pads on beef, tuna and chicken meats. The second objective was to compare the effect of Type I (radical quenching) antioxidants eugenol and rosmarinic acid (RA) to that of Type II (metal chelating) antioxidants milk mineral (MM), phytate, and sodium tri-polyphosphate (STPP) in raw ground chicken patties. In the first study samples of beef semitendinosus muscle, boneless and skinless chicken breast, and yellowfin tuna loins were chosen and packaged with four different pad types. Red meats and chicken exhibited trends as would normally be expected during storage. Specifically, color became less appealing (beef and tuna color changed from red to brown, and chicken changed from yellow–pink to grey); pH increased, microbial counts increased, and lipid oxidation (rancidity) increased. Lightness (L*) values for chicken were within 46 – 54, for tuna L* value range was 21-26. Redness/greenness (a*) is an indicator of freshness in red meats, and for beef steaks an average value of 12.32 was noted on day 8, indicative of fresh red color. Recorded average lipid oxidation (TBA values in mg/kg of meat) for chicken (< 0.19 mg/kg) and tuna were low (< 0.16 mg/kg) and for beef (1.06 mg/kg). Even though there was a significant effect of storage time (P < 0.05) as expected, no significant (P >0.05) differences were observed between the four tested pad types over the 8-day testing period. In study 2, (Chapter 4) a significant antioxidant effect (P < 0.05) was observed in L* values of ground chicken color between treatments. Milk mineral effectively preserved fresh color and slowed lipid oxidation in chicken patties by day 10. Inverse correlations (P < 0.001) were observed between pH (increasing), and lightness, redness values (decreasing) from day 1 through 10. Increased pH levels from slightly acidic to basic or physiological pH resulted in high numbers for total aerobic plate-counts. There was a significant antioxidant effect on lipid oxidation values by day 10; eugenol and MM were more effective (P < 0.05) than STPP in controlling lipid oxidation measured as thiobarbituric acid reactive substances (0.198 mg/kg, 0.198 mg/kg, and 0.268 mg/kg, respectively). In conclusion, CO2 generating absorbent pads did not have a positive effect on meat quality, while the antioxidant milk mineral efficiently maintained color, and pH, and controlled lipid oxidation and limited the growth of aerobic bacteria when compared to other antioxidants.

The cyclic nature of the beef industry is dependent on the supply and demand transaction initiated by consumers’ acceptability of quality meat products. When purchasing beef at the grocery store, consumers are dependent on USDA grades and visual appraisal; consumers expect consistency in products. Upon this appraisal, quality is determined by the color, marbling content, and texture of a particular retail cut, as well as cooked characteristics of tenderness, flavor, and juiciness. Variability in meat tenderness is a major quality defect of beef (Morgan et al., 1991b; Smith et al., 1992). A common practice used by beef processors to extend the shelf life and improve tenderness of beef products is “enhancing”. Even though enhancing products is effective for water and color retention and improved tenderness, these additives can negatively impact flavor by giving a bitter, salty or metallic taste. This experiment was conducted to determine the effect of enhancement on the eating quality of USDA Select strip loin steaks. After a training session, six students in the agriculture department at Western Kentucky University were selected to serve on a sensory panel. The panel members evaluated tenderness, juiciness, flavor, off-flavor, overall acceptability, and saltiness. The USDA Select strip loin steaks were enhanced with a 12% solution of sodium and potassium phosphate and USDA Choice strip loin steaks were non-enhanced. Results indicated the enhanced product was inferior for all palatability measures (P<.05). Enhanced USDA Select strip loin steaks were rated as being lower for tenderness, juiciness, flavor, overall acceptability, and more salty. Also, the enhanced strip loin steaks received significantly higher evaluations for off-flavor (P<.01). These data suggested that a 12% solution of sodium and potassium phosphates administered to USDA Select strip loin steaks lowered consumer satisfaction.

In this study the opportunities to recycle the phosphorus contained in food handling were identified in four municipalities in the county of Östergötland. The aim was to map the flow and find out whether there were differences between municipalities with food processing industries generating large amounts of waste or phosphorus rich wastewater, or if there were differences between municipalities of different size. It was also investigated to what extent the agricultural demand of phosphorus could be covered by recycling of phosphorus from the food handling system. The result showed that between 27% and 73% of the phosphorus was found in the sludge from wastewater treatment, and that between 13% and 49% of the phosphorus was found in the centrally collected organic waste. This corresponded to 11% of the phosphorus demand on arable land in municipalities with food processing industries generating large amounts of waste or phosphorus rich wastewater, and 8% of the phosphorus demand on arable land in municipalities without such industries.

The main objective was to determine the variation of physical properties of different cake formulations during baking in microwave and infrared-microwave combination ovens. In the first part of the study, rheological and dielectric properties of cake batter with different formulations were determined. Different concentrations of fat and different types of emulsifier and fat replacer were used. The variation of formulation had a significant effect on the apparent viscosity of the cake batter. Cake batter was found to show shear thinning and time independent behaviour for all formulations. Dielectric properties of cake batter were dependent on formulation, frequency and temperature. In the second part of the study, physical properties (dielectric properties, volume, texture, color and porosity) of cakes baked in microwave and infrared-microwave combination oven were determined. In addition, starch gelatinization during baking was investigated. For comparison, cakes were also baked in conventional oven. Formulation and baking time were found to affect physical properties and gelatinization degree of cakes. Addition of fat to the formulation was found to increase the dielectric properties and gelatinization degree of microwave and infrared-microwave combination baked cakes. For both microwave and combination baking, cake samples with SimplesseTM had the highest volume but the firmest texture. Addition of maltodextrin resulted in a more uniform structure for infrared-microwave combination baking. There was insufficient gelatinization in microwave baked cakes ranging from 70 to 78% depending on fat content. The gelatinization degree ranged from 88 to 93% in conventionally baked cakes. Combining infrared with microwaves increased gelatinization degree (80-90%).

The objective of this study was to discover the effect of high power direct contact ultrasound on drying rates of apple, celery root, carrot and potato. For this purpose ultrasonic generator with 24 kHz frequency was used and amplitude and pulse mode values were chosen as 40%, 70%, 100%, and 0.4, 0.7, 1.0, respectively. The temperature of drying air was 30&deg / C, 40&deg / C and 50&deg / C and the velocity was kept at 3.9 m/s. The samples used were 13.5 mm in diameter with 5.0 mm thickness. It is found that ultrasound assisted drying increased the drying rate for the selected produce at all the drying conditions used the degree of which depended on the structural properties of samples. Accordingly, the most suitable drying conditions were found to be amplitude 100%, pulse mode 1.0 and 30&deg / C for celery root, amplitude 100%, pulse mode 1.0 and 30&deg / C for apple, amplitude 70%, pulse mode 1.0 and 50&deg / C for carrot and amplitude 70%, pulse mode 0.7 and 50&deg / C for potato. Data obtained were treated with respect to some mathematical models that describe the drying kinetics of samples. In this respect, Page and Modified Page models were the best to represent the drying rates in all cases. Further, the results showed that the effect of ultrasound on drying rate increased in the order of apple&gt / celery root&gt / carrot&gt / potato. That order can be attributed to the structure and composition where presence of air pockets has enhancing and sugar and starch have reducing effects.

The main purpose of this thesis is to develop a model that can predict the temperature profile inside a frozen food sample during microwave tempering and infrared assisted microwave tempering processes. Another goal of the study is to compare the tempering time of frozen foods by using microwave, infrared assisted microwave, and ohmic heating methods. Frozen potato puree was used as the food sample for all studies. Three different microwave power levels (30%, 40%, and 50%) were used for microwave tempering studies. Three different microwave power levels (30%, 40%, and 50%) and three different infrared power levels (10%, 20%, and 30%) were combined for infrared assisted microwave tempering. As a control, tempering was done by keeping the sample at 4&deg / C. The increase in microwave power level and infrared power level reduced tempering time in infrared assisted microwave tempering. For the ohmic tempering studies, three different frequencies (10 kHz, 20 kHz, and 30 kHz) and three different salt contents (0.50%, 0.75%, and 1.00%) were used. The increase in frequency of ohmic heating and salt content also decreased tempering times. Microwave tempering and infrared assisted microwave tempering of frozen foods were simulated by using finite difference method. For this purpose, the change in heat capacity and the dielectric properties of frozen potato puree with respect to time were measured. The temperature distribution inside the sample was modeled, and the predicted results were compared with experimental results. The predicted temperatures showed good agreement with the experimental data (r2 &gt / 0.985). It was possible to decrease tempering times by about 75%, 90%, and 95% using ohmic, microwave, and infrared assisted microwave tempering methods, respectively as compared to control.