Thesis (Ph. D.)--University of Wisconsin--Madison, 1982. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 418-430).

Milk coagulation consists of four overlapping phases: enzymic hydrolysis, micelle aggregation, gelation and syneresis. The objectives of this study were to determine the effects of added CaCl2 on milk coagulation and the relationship between enzymic hydrolysis and micelle aggregation with substrate at different concentrations. Addition of CaCl2 to milk is widely practiced in industry and in laboratories. This changes calcium concentration, pH and ionic strength. It is impossible to separate these three variables and investigate each one independently. Addition of low levels of CaCl2 shortens coagulation time and increases curd firming rate. Low levels of CaCl2 also accelerate the enzymic hydrolysis process. Calcium ions increase hydrolysis rate, but this effect is much smaller than that of lowered pH. Increase of ionic strength due to addition of CaCl2 has an adverse effect on enzymic hydrolysis. This dominates at high CaCl2 concentration, and the overall coagulation process slows down. Adding CaCl2 also promotes micelle aggregation. However, aggregation is retarded by high levels of added CaCl2. Results of this study show that about 90% of the κ-casein is hydrolyzed for diluted milk (1/3) to coagulate. Samples at normal concentration (12 g NDM/100 ml solution) require only 60% conversion of κ-casein to para-κ-casein. Addition of CaCl2 significantly decreases this percentage. This suggests a different aggregation and gelation process in samples containing added CaCl2 When pepstatin A is used to stop enzymic hydrolysis at different times, different degrees of κ-casein conversion are obtained. Micelles aggregate even at very low percentages of hydrolysis. Previous reports have stated that a micelle cannot participate in aggregation until almost all of its κ-caseins have been hydrolyzed.

Bovine plasmin activity was measured on H-D-valyl-L-leucyl-L-lysyl-4-nitroanilide by following absorbance changes at 405 nm. Steady-state kinetic parameters Vmax, Km, KI, and KI' were estimated. Bovine plasmin is competitively inhibited by casein and has a Kcat of .0158 ΔA405/min/nM, Km of .107 mM substrate, and KI of .86 mg/ml casein. Bovine plasmin can be measured directly in bovine milk without interference from casein. A total of 380 milk samples from nineteen Holstein (one herd) and nineteen Jersey (one herd) cows was collected monthly during one lactation period. Samples from each cow were analyzed for fat, protein, plasmin activity, plasminogen, pH, SCC, clotting time, curd firming rate, and final curd firmness. Three age groups form each breed/herd were chosen; first, third, and fourth and later lactations. Plasmin activity in milk was most affected by lactation number, with milk from fourth- and later-lactation cows having higher activity than milk from first- or third- lactation cows. Plasmin activity in milk increased during lactation but was not affected by breed/herd, pH, protein, or fat. Plasminogen averaged 5.4 times the plasmin activity in milk and increased during the first five months of lactation. Plasmin activity was higher in milk collected ruing summer and fall but plasminogen was higher in milk collected during fall and winter. Percentage of the total (plasmin+plasminogen) enzyme activated to plasmin increased in late-lactation milk and in milk from fourth- and later-lactation cows. Plasmin activity did not affect any milk clotting parameters in this study. Increased protein in milk resulted in shorter clotting times. When statistically adjusted for protein content, clotting time was longer in milk from the Holstein herd compared to the Jersey herd. Curd firming rate was increased in milk with higher protein and fat. Milk samples collected in the fall had faster firming rates than milk from other seasons. Firming rates remained constant during lactation but increased with higher protein and fat content. Jersey herd milk produced firmer curd than Holstein herd milk and milk collected in the fall had firmer curd than during the other seasons.

The theme of this diploma thesis is the monitoring of influences on economic aspect of the production of the blue cheese "Hermelín" in the company Pribina. The objective was to specify the dependencies of the deviations of the features of productive cow's milk and of cheese curd made from it and their economics impacts. For this purpose, the analyses of curd grain, whey and cheeses just formed were executed. The samples were taken and analyzed during the manufacturing of cheeses in the factory. Another goal was to try to design a quick operational method for measuring the firmness of curd grain, which is a factor theoretically dependent on renneting qualities of milk and indicating losses of valuable components from cheese curd to whey. The firmness of grain along with these losses may cause negative deviations from required standard of final products, especially at parametres needed for entry of cheeses on sale, such as total solids, weight or content of fat. Concerning productive pasteurize milk, the most attention was focused on the milk coagulation time and its influence on successive phases of manufacturing and on final product. Milk coagulation time is an essential technological quality of milk and it is participant on quantitative and qualitative production of cheese factory. It has been proved that milk coagulation time is notably affected by its titrating acidity, statistic analyse found this influence as very statistically significant (P

Forty-eight Holstein cows at Utah State Dairy Farm were blocked statistically according to date of calving, previous milk production, and numbers of lactation at parturition. The cattle were assigned randomly to one of four treatments within blocks. The four treatments included a base ration (control, treatment #1), base ration plus .8% of sodium bicarbonate (treatment #2), base ration plus .4% of magnesium oxide (treatment #3), and base ration plus both .8% of sodium bicarbonate and .4% of magnesium oxide (treatment #4). The research was conducted from February 1983 to November 1984. A formagraph was used to measure milk coagulation parameters and pH was determined. There was no significant difference in milk coagulation parameters or pH between the control and the buffer treatments. Milk parameters were significantly different in individual cow, week, and milk pH. Milk parameters did not appear to be dependent upon season. Curd firmness was significant in interaction of season and treatment. Significant variations in milk pH were observed in relation to week, season, and individual cow. Overall treatments, the clotting time, K20, and pH value increased each week, and A30 decreased each week. The milk parameters and pH in each treatment were significant between weeks except K20 and A30 in treatment #3, and A30 in treatment #2 (p>0.05). The clotting time and K20 were negatively correlated with firmness, and there was positive correlation between Ct and K20 as expected. Somatic cell count was positively correlated with clotting time, K20, and pH and negatively correlated with A30. Milk pH was the most significant and had positive correlation coefficient with clotting time and firming rate and negative correlation coefficient with curd firmness.

Submitted by Fabio Sobreira Campos da Costa (fabio.sobreira@ufpe.br) on 2016-12-01T12:59:09Z No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) DISSERTAÇÃO - NEUSA LYGIA VILARIM PEREIRA.pdf: 830371 bytes, checksum: 5b2e17eefc8840d24aea2dfad45d93c0 (MD5) / Made available in DSpace on 2016-12-01T12:59:09Z (GMT). No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) DISSERTAÇÃO - NEUSA LYGIA VILARIM PEREIRA.pdf: 830371 bytes, checksum: 5b2e17eefc8840d24aea2dfad45d93c0 (MD5) Previous issue date: 2016-03-22 / CNPq / O ácido siálico está presente nos leites na forma de ácido N-acetilneuramínico (Neu5Ac) e ácido N-glicolilneuramínico (Neu5Gc), desempenhando uma série de benefícios à saúde humana. O soro de queijo caprino é um bioproduto da fração solúvel do leite, obtido através da coagulação da caseína. É considerado importante para a indústria de alimentos, como ingrediente, sendo responsável por 55% de todos os nutrientes do leite. Neste estudo, objetivouse quantificar, pela primeira vez na literatura, o ácido siálico presente naturalmente no soro de queijo caprino por diferentes processos de coagulação láctea. O leite utilizado foi obtido de cabras da raça Saanen e submetidos ao processamento de coagulação enzimático e misto (enzima + cultura starter) para obtenção do soro, que foi acondicionado e congelado, sendo parte liofilizado. A identificação e quantificação do ácido siálico foi realizada por Cromatografia Líquida de Alta Eficiência por detector de fluorescência modelo RF-20A. A concentração desse nutriente variou de 23,5 a 292,1 mg/L. Foi verificado que a coagulação enzimática preserva o ácido siálico (Neu5Gc e Neu5Ac) mais eficientemente do que a coagulação mista, pois as bactérias da cultura starter possibilitaram a redução dos nutrientes presentes no soro para desempenharem o seu metabolismo, assim o ácido siálico presente como glicoconjugado, também foi reduzido. De acordo com os resultados obtidos, pode-se concluir que o soro de queijo caprino apresenta um potencial funcional, visto que contém uma quantidade relevante do nutriente estudado. / Sialic acid is present in milk in the form of N-acetylneuraminic acid (Neu5Ac) and Nglycolylneuraminic acid (Neu5Gc), performing a lot of benefits to human health. Goat cheese whey is a dairy byproduct from the soluble fraction obtained by casein coagulation. It is considered important for the food industry, as an ingredient, accounting for 55% of all milk nutrients. This study aimed to quantify the sialic acid present naturally in the goat cheese whey by different milk coagulation processes. The milk was obtained from Saanen goats and subjected to processing enzymatic and mixed coagulation (enzyme + starter culture) to obtain the whey, which was prepared and frozen, and part of it was lyophilized. The identification and quantitation of sialic acid was accomplished by High Performance Liquid Chromatography fluorescence detector RF-20A model. The sialic acid concentration ranged from 23.5 to 292.1 mg / L. It has been found that enzimatic coagulation preserves the sialic acid (Neu5Ac and Neu5Gc) more efficiently than mixed coagulation, because the bacterias of starter culture allowed the reduction of nutrients present in the whey to perform their metabolism, as well sialic acid present as glycoconjugate it was also reduced. According to the results, concluded that goat cheese whey has a functional potential, since it contains a significant quantity of the nutrient studied.

The kinetics of milk coagulation are complex and still not well understood. A deeper understanding of coagulation and the impact of the relevant factors would aid in both cheese manufacturing and also in determining the nutritional benefits of dairy products. A method using confocal microscopy was developed to follow the movement of milk fat globules and the formation of a milk protein network during the enzyme-induced coagulation of milk. Image processing methods were then used to quantify the rate of coagulation. It was found that the texture of the protein network is an indicator of the current status of the milk gelation, and hence can be used to monitor the coagulation process. The imaging experiment was performed on milk gels with different concentrations of the coagulation enzyme, chymosin. Rheological measurements were taken using free oscillation rheometry to validate the imaging results. Both methods showed an inverse relationship between rennet concentration and the coagulation time. The results from the imaging study were used to create a computational model, which created simulated images of coagulating milk. The simulated images were then analyzed using the same image analysis algorithm. The temporal protein network texture behavior in the simulated images followed the same pattern as the protein texture in the confocal imaging data. The model was developed with temperature and rennet concentration as user inputs so that it could be implemented as a predictive tool for milk coagulation.

The thesis deals with two technological properties determining the quality of milk, clotting and fermentation ability by titrable acidity, which are influenced by a large number of factors. The aim of the work was to assess the influence of milk composition, breed, order and stages of lactation on clotting and souring ability of cow and goat milk based on obtained analysis. Detailed analysis focused primarily on cow milk.