Milk protein polymorphisms have a significant influence on milk quantity and composition. Kappa-casein is of special interest due to its known relationship with milk quality. In goats, a number of allelic variants have been identified, primarily classified into two groups. Group BIEF alleles (D, E, K, and M) have been shown to have a positive effect on milk yield and technological properties, while group AIEF, the remaining alleles, have a less positive influence on milk composition. The aim of this study was to investigate genetic variation in the kappa-casein genotype of South African goats. PCR-RFLP and DNA sequencing were performed on 68 and 77 samples, respectively. In addition, 84 milk samples were analyzed for milk composition. RFLP analysis revealed that the A and/or B alleles were the most frequent in the populations studied. A frequency of 0.00 was observed for the BIEF variants using DNA sequencing. In all goat types included, the B allele was the most common, with frequencies ranging from 60% in SA Boer goats to 100% in Saanens. The B’ allele had lower frequencies of 0.357 and 0.207 in SA Boer goats and local goat types, respectively. The H allele was present at low frequencies in local goat types (10.3%) and in SA Boer goats (3.6%), but was absent in Saanens. AMOVA results indicated that most of the total variation occurred within populations (80.66%) with the remainder of the variation (FST = 0.1934; p < 0.01) occurring due to genetic differences between populations. / Dissertation (MSc(Agric))--University of Pretoria, 2009. / Animal and Wildlife Sciences / unrestricted

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The Technicon AutoAnalyzer II was evaluated for automatic quantitation of non-casein protein (NCP) in milk. The Lowry method f or colorimetric measurement of proteins was adapted to the automated method and found to be accurate in the determination of non-casein protein in milk. The automated Lowry method obeyed Beer's law. Casein content was calculated by difference between total protein determined by infrared milk analysis (IRMA) and non-casein protein. In the analysis of twenty-five replicate milk samples, the standard deviation was 0.32 and the coefficient of variability was 0.90. The casein content as a percentage of total protein in the milk of cows in the Utah State University dairy herd was found to vary from 41.0 to 81.3%. The automated or continuous flow method was affected by as little as 0.05% (w/w) mercuric chloride, a chemical preservative used in milk, whereas potassium dichromate and formaldehyde had insignificant effects upon the assay.

The purpose of this study was to determine if size exclusion chromatography could be used to separate casein micelles from whey proteins for a rapid, direct test to measure percent casein in milk. A size exclusion chromatography column was developed for the separation having dimensions 100 by .4 cm. Packing material selected was glycophase coated porous glass supports. A Beckman DU-8B spectrophotometer monitored the casein and whey protein peaks as they eluted and a Tektronix 4052 computer accepted data points every 4 sec, storing these on tape. Absorbances and areas of each peak were used in the evaluation of samples. Treatments of temperature, pH and calcium addition were performed on a commingled milk sample from Utah State University Dairy Laboratory. It was determined that addition of calcium and pre-warming to 40 C before injection is important for good separation. Several samples of milk from individual cows were run through the column and parameters obtained. For each sample, percent casein was measured using the standard method of acid precipitation and Kjeldahl nitrogen determination. Percent casein was then estimated using area and absorbance of each casein peak from the elution plots of milk from individual cows. A regression line of predicted vs actual percent casein resulted in a correlation coefficient (r) of .92.

Cheddar cheese was made by the traditional 4.5-h method from three experimental lots of milk, each standardized to casein/fat ratios of approximately 0.64, 0.67 and 0.70. The effect of casein/fat ratio on milk fat recovery was determined. The effects of milk composition on curd firmness at cutting, cheese composition and resulting yield of cheese were evaluated. Correlations between milk constituents and various cheese components were obtained. Milk fat recovery was unaffected by casein/fat ratios within the limits of 0.64 and 0.71. Average milk fat recovery was 91.58 ± 1.73%. Cheese yield was a function of milk protein, milk fat and cheese moisture; and a modified Van Slyke equation predicted cheese yield better than the original equation within the limits of casein/fat ratio studied. Strong negative correlations were observed between casein/fat ratio and cheese fat and cheese fat in the dry matter whereas positive correlations were observed between casein/fat ratio and cheese protein. At constant protein levels curd firmness increased directly with the amount of fat in cheese milk.

This work reviews studies of bovine K-casein and specifically K-casein macropeptide. Properties of K-casein, its structure and heterogeneity, proteolytic activity of some milk clotting enzymes on K-casein, and K-casein sensitive bonds are discussed. Macropeptides of other species are also presented. The carbohydrate moieties of bovine macropeptide together with their biological and physiological functions are reviewed. Macropeptides were produced by enzymic hydrolysis from whole casein solution using crystalline chymosin (EC 3.4.23.4). Trichloroacetic acid (final concentrations 2, 8 and 12%) was added after 5, 30 and 60 min of incubation to precipitate protein and inactivate the enzyme. The filtrate was then exhaustively dialyzed against distilled water to remove trichloroacetic acid and small molecules. The dialyzate was lyophilized and stored at -20deg;c until required for analysis. These macropeptides were then compared using RP-HPLC with macropeptides obtained from purified K-casein isolates by the same method (15 min incubation). Proteolytic activity of some milk-clotting enzymes (chymosin, Mucor miehei rennet and Endothia parasitica rennet) and some proteinases (trypsin and chymotrypsin) on K-casein and macropeptide isolated from K-casein was followed by RP-HPLC. The milk-clotting enzymes were standardized to the same clotting activity using a Formagraph. Each enzyme was incubated with .5 mix-casein and macropeptide solutions (10 mg in 1 ml .05 MpH 6.6 phosphate buffer) at 37°C for various incubation times. Reactions were stopped by addition .5 ml of 8 Murea containing 10-5 Mpepstatin or .025 ml pepstatin (1 mg pepstatin in 1 ml methanol). These reaction mixtures were separated into fractions using RP-HPLC and chromatograms of the different enzymes compared.

Orientador: João Carlos Pinheiro Ferreira / Resumo: O uso do sêmen refrigerado proporciona maiores taxas de prenhez se comparado ao do sêmen congelado. Essa diferença parece estar relacionada às lesões mais severas das membranas espermáticas desencadeadas pelo processo de congelação. Por sua habilidade de se ligar às proteínas ligadoras de espermatozoides e ao íon cálcio, o caseinato de sódio vem sendo estudado como uma substância capaz de inibir a capacitação espermática precoce, uma importante causa de diminuição da taxa de prenhez quando do uso de sêmen congelado. O primeiro objetivo deste estudo foi avaliar a possibilidade de um diluente comercial a base de gema de ovo, destinado à congelação de sêmen bovino, ser empregado para a criopreservação de sêmen bubalino; o segundo objetivo foi investigar o efeito do uso desse diluente, suplementado com caseinato de sódio, na criopreservação de espermatozoides bubalinos, por meio da avaliação dos espermatozoides, por citometria de fluxo, e da cinética espermática, empregando-se o sistema CASA. Na primeira parte do estudo, quando comparados os resultados das avaliações da cinética espermática e integridade das membranas plasmática e acrossomal, observou-se que o processo de congelação seminal promoveu mais danos celulares que o processo de refrigeração. Na segunda parte do estudo, não foram observados efeitos da adição do caseinato de sódio ao diluente a base de gema de ovo. A partir dos resultados do presente estudo foi possível concluir que o diluente a base de gema de ovo testad... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: The use of cooled semen results in higher pregnancy rates compared than the use of frozen semen. This result seems to be related to the more severe damages triggered by the freezing process, when compared to those observed during the refrigeration. Due to its ability to bind to sperm-binding proteins and calcium ions, sodium caseinate has been studied as a ubstance capable to prevent early sperm capacitation, a major cause of decreased pregnancy rate after using frozen semen. The first objective of this study was to evaluate if a commercial egg yolk diluent developed for freezing bovine semen could be used for buffalo semen cryopreservation; the second objective was to investigate the effect of this diluent, added with sodium caseinate, during the procedures of buffalo sperm cryopreservation, using flow cytometry and computer-assisted sperm analysis. In the first part of the study, comparing the results of spermatic kinetics and plasma and acrosomal membranes integrity, it was observed that the freezing process resulted in more cell damage than the cooling process. In the second part of the study, no effects of the addition of sodium caseinate to the egg yolk diluent were observed. From the results of the present study it was possible to conclude that the egg yolk-based diluent was suitable for buffalo semen cryopreservation and that the addition of sodium caseinate did not decrease the deleterious effects related to seminal cryopreservation. / Mestre

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No description available.

<p>  </p> <p><strong>Background information:</strong> </p> <p>Lactose is a disaccharide found in milk and milk products. Lactose is digested by the enzyme lactase. Lactase non-persistence is a genetic trait in which individuals have low lactase activity. Approximately 70 percent of the world population is lactase non-persistent. It is a major cause of lactose maldigestion. An increase of 20 ppm hydrogen in breath within six hours of a lactose challenge dose (0.5 g of lactose per kg bodyweight) indicates lactose maldigestion. On the other hand, lactose intolerant individuals experience abdominal pain, bloating, diarrhea, and flatulence on consuming dairy. Therefore, lactose intolerant individuals avoid milk, which is a rich source of calcium. Consequently, lactose intolerance has been associated with reduced calcium intake and low bone mineral density. There are two mechanisms for lactose intolerance. The first mechanism is dependent on lactose dose and the second one is independent of lactose. Recently, A1 and A2 β-caseins have been associated with lactose intolerance. Studies conducted in China, New Zealand and Australia demonstrated fewer symptoms on consumption of milk containing only A2 β-casein as compared to milk containing both A1 and A2 β-casein. However, no study was conducted in the population residing in United States, where crossbred cows producing milk containing both A1 and A2 β-casein is the norm. Moreover, no study compared tolerance and digestion on consuming milk with different proportions of A1 and A2 β-casein. Lactose intolerant individuals can include A2 milk in their diet to meet the calcium requirement, if milk containing only A2 β-casein causes fewer symptoms and less maldigestion. </p> <p><strong>Objectives:</strong></p> <p>1. To determine if a single meal of A2 milk containing only A2 β-casein would be better tolerated, producing fewer GI symptoms and less maldigestion, than conventional milk containing 75 percent A1 β-casein and 25 percent A2 β-casein</p> <p>2. To determine if a single meal of Jersey milk containing 25 percent A1 β-casein and 75 percent A2 β-casein would produce less maldigestion and intolerance, than conventional milk containing 75 percent A1 β-casein and 25 percent A2 β-casein</p> <p>3. To determine if the gastric emptying time of milk containing only A2 β-casein and milk containing 75 percent A1 β-casein and 25 percent A2 β-casein was different </p> <p>4. To determine if inflammation, maldigestion and intolerance is lower with a two-week daily consumption of milk containing only A2 β-casein as compared to milk containing 75 percent A1 β-casein and 25 percent A2 β-casein</p> <p><strong>Methods:</strong> </p> <p>Three randomized, double-blinded, crossover trials were conducted. The first study was conducted to determine tolerance and digestion of milk containing different proportions of A1 β-casein and A2 β-casein in subjects residing in the United States. There were four milk interventions in the study: A2 milk (milk containing 100% A2 β-casein), Jersey milk (milk containing 25%/75% A1/A2 β-casein), conventional milk (milk containing 75%/25% A1/A2 β-casein) and lactose-free milk (milk containing 60%/40% A1/A2 β-casein). Lactose intolerance in subjects was determined using a Qualifying Lactose Challenge Symptom Score after a challenge milk dose of 0.5 g of lactose/kg bodyweight. Subjects were screened for lactose maldigestion with a six-hour Hydrogen Breath Test. Symptoms and madigestion response to a single meal of milk (dose calculated as 0.5 g of lactose/kg bodyweight) containing different proportions of A1 and A2 β-casein were determined in lactose intolerant subjects and lactose maldigesters. </p> <p>The second study was conducted to examine the difference in gastric transit between A2 milk and conventional milk in lactose maldigesters. Magnetic Resonance Imaging (MRI) technique was used to observe gastric emptying. Subjects rated abdominal pain after consumption of the two milk interventions using a six-point Likert scale.</p> <p>The final study was conducted to determine symptoms, maldigestion and inflammation due to consumption of A2 milk and conventional milk for fourteen days on a daily basis in lactose maldigesters. Subjects rated lactose intolerance symptoms every day during the fourteen days using a six-point Likert scale. Breath hydrogen, serum inflammatory markers and serum antioxidant concentrations were measured on day 15 after the two-week milk consumption.  All the studies were registered at clinicaltrials.gov. </p> <p><strong>Results: </strong></p> <p>Results from the first study indicated that abdominal pain due to a single meal of A2 milk in lactose intolerant subjects was lower by twenty-three percent as compared to conventional milk (p=0.004, n=25). Similarly, there was a twenty-eight percent decrease in abdominal pain score on consumption of A2 milk as compared to conventional milk in lactose maldigesters (p=0.001, n=33). All the other symptoms were not different between A2 and conventional milk in lactose intolerant subjects and lactose maldigesters. A single meal of A2 milk reduced the total hydrogen production (p=0.04, n=33) by sixteen percent and total symptoms production (p=0.04, n=33) by eighteen percent in lactose maldigesters as compared to conventional milk. However, the total hydrogen and total symptoms produced were not different in lactose intolerant subjects between A2 and conventional milk. Similarly, individual GI symptoms, total symptoms and total hydrogen were not different between jersey and conventional milk in lactose intolerant subjects and lactose maldigesters.</p> <p>Results from gastric transit study indicated that volume of A2 milk in the stomach was higher by twenty-four percent at 30 (p=0.01, n=10), forty-six percent at 60 (p=0.002, n=10) and one hundred and sixty-one percent at 120 (p<0.001, n=10) minutes as compared to conventional milk in lactose maldigesters. </p> <p>Results from the last study suggested a fecal urgency score lower by thirty-three percent (p=0.033, n=10) in lactose maldigesters due to daily consumption of A2 milk for two weeks as compared to conventional milk. The other symptoms, inflammation markers, antioxidant and breath hydrogen production were not different between A2 and conventional milk due to two-week milk consumption.</p> <p><strong>Conclusion:</strong> </p> <p>Total intolerance symptoms and total hydrogen production were lower due to consumption of a single meal of A2 milk than conventional milk in lactose maldigesters. Gastric transit of A2 milk was slower as compared to conventional milk in lactose maldigesters. Daily consumption of A2 milk for two-weeks reduced fecal urgency as compared to conventional milk in lactose maldigesters. </p> <p>  </p>