SUMMARYProteolytic activity in mastitic skim-milk was often 5–10 fold higher than in normal milk, its level being related to somatic cell count but not precisely correlated with it. In milks with the highest levels of activity plasmin accounted for about one third of the total proteinase. A further third was sedimented with the micellar fraction together with the plasmin, but unlike plasmin, was not inhibited by addition of soyabean trypsin inhibitor (SBTI). The final third remained in the serum phase.Polyacrylamide gel electrophoresis (PAGE) showed that αsl- and β-caseins were degraded at about the same overall rate. The plasmin produced the usual readily identified fragments from β-casein, but incubation of mastitic milk also produced changes in patterns in the γ-casein region differing from plasmin-induced changes which were also apparent when the micellar fraction was incubated. As they were inhibited by SBTI, a second trypsin-like enzyme in addition to plasmin may also have been present. Other proteinase(s) not inhibited by SBTI was also associated with casein micelles and produced at least 3 characteristic protein fragments seen on PAGE. The serum phase proteinase(s) was likewise not inhibited by SBTI, and did not produce any well-defined electrophoretic bands, suggesting a rather non-specific breakdown of caseins. After separation of mastitic whole milk, a considerable proportion of the proteolytic activity was found in the cream phase. The proportion was enhanced by freezing and thawing, and the enzyme appeared to be identical to the SBTI-resistant micellar proteinase.Because of the considerable proteolysis likely to occur under the time and temperature conditions involved, our results may provide some explanation for the problems encountered in cheesemaking with mastitic milks (e.g. yield losses, poor curd strength and off-flavour development).

Table 1 -Analysis of the defatted soy flourThe solubility of phytate and protein in soy extracts as influenced by pH, NaCl, calcium and EDTA was measured. The behavior of phytate is explained in terms of its binding to calcium-magnesium and/or to proteins. Three processes for preparing low-phytate soy protein products were derived from this theory, at both the laboratory and pilot plant scale. The nutritional properties of isolates prepared with these processes were examined. moisture protein (N X 6.25) fat phytate Ca Mg Ne K P ash NSI pH (5% suspension) 7.6 % 50.0 % 0.9 % 1.5 % 0.24% 0.32 % 0.01 % 0.05 % 0.7 % 4.2 % higher than 90 6.7

Proteolysis was measured quantitatively in normal bulk milk, either raw, pasteurized or heated (95 °C, 15 min). During incubation at 37 °C for 24 h, about 0 -7 mM of peptide bonds were split in raw milk, and 1-8 HIM after activation of the zymogen with urokinase. The same values were observed in pasteurized milk, and no significant activity was present in heated milk. When compared with a commercial plasmin preparation, these levels correspond to.about 1*4 and 3 -6/*g/ml of plasmin respectively. Most of this activity was separated in the micellar fraction, and it was suppressed by addition of soyabean trypsin inhibitor (SBTI). The remaining activity in the serum phase was not inhibited by SBTI and gave a rather non-specific breakdown with few well-defined casein fragments being produced. Upon further incubation, after the first 24 h, the activity increased, indicating that activation of the zymogen (plasminogen) occurred spontaneously. The rate of this activation was independent of the addition of more plasminogen and was higher in pasteurized than in raw milk. In pasteurized milk, all the native milk proteinase was in the form of the zymogen at the time of secretion. /?-Casein was the preferred substrate for the milk proteinase (plasmin) and produced y-caseins and proteose-peptone components 5 and 8-fast; other fragments were clearly visible on polyacrylamide gel electrophoresis, and included degradation products of a sl -casein. The formation of all these fragments was enhanced by addition of urokinase alone, or of plasminogen and urokinase, or by increasing the incubation time. They were also produced by incubating the micellar fraction alone, but not the serum fraction. Additional fragments were produced when porcine plasmin was added presumably due to differences in specificity between the porcine and bovine enzymes or to contaminating enzymes. Proteolysis induced by additions of plasminogen alone, or of plasminogen plus urokinase, was closer to that observed for the native milk proteinase, and must be recommended for future work in which it is desired to enhance the level of proteinase without altering breakdown patterns, unless a very pure bovine plasmin is available.

No abstract

Bovine serum IgG1, colostral IgG1 and serum IgG2 with anti-ferritin activity were digested with pepsin or trypsin. Their fragments were characterized by immunoelectrophoresis, gel electrophoresis and gel filtration; their ferritin-binding ability was determined. The kinetics of proteolysis were established by measuring the appearance of free amino groups. No differences were observed between serum and colostrum IgG1. IgG1 was more susceptible to pepsin, and IgG2 to trypsin. This became evident from both the amount of intact IgG determined by gel electrophoresis, immunoelectrophoresis or gel filtration, and from the kinetics of the appearance of amino groups. A model is presented to explain the size, mobilities and properties of the obtained fragments.

Use of soy protein in a complex fluid food model containing carbohydrate, fat, minerals and 8-10% protein was investigated. Soy protein at this concentration yielded a product that gelified upon heating. Gelation was inhibited if the protein was previously hydrolyzed utilizing food grade proteases. Removal of the high-molecular weight fraction of the hydrolysate by precipitation with calcium further helped to decrease viscosity. Bitterness was reduced without affecting viscosity, through elimination of small peptides and free amino acids by ultrafiltration. Stable and long shelf-life samples of the model could be manufactured if the proteolytic process was carefully controlled in order to avoid losing the stabilization of the emulsion by the soy protein. Nutritional value of the hydrolysate was higher than that of the isolate used.

SUMMARY. Analysis of retentates of milk or whey, ultrafiltered and diafiltered by a pilot batch process with DDS Lab module equipment or (whey only) ultrafiltered by an industrial continuous process showed that nitrogen and ionic contents could not be described mathematically by the use of any value of the retention coefficient K. Analytical data suggested a new concept called segregation for nitrogen and ions in which each of these components consists of a completely permeable fraction and a totally retained fraction that do not exchange. A segregation coefficient Y is then defined as the ratio of the totally retained fraction to the total concentration of the species in the product fed to the equipment. However, this concept does not apply to lactose, where the classic retention concept (K) is retained. The two models are equivalent when K = Y = 0 or K = Y = 1. A first mathematical expression of this model was elaborated for batch ultrafiltration and/or constant volume diafiltration. Another set of equations was established for industrial conditions. These empirical models predict the retentate and permeate composition at any time during processing as well as after drying. The fit of analytical data with computed values was generally fair, with K being 01-0-4 in the pilot plant, and 0-1 in the factory. The nitrogen Y value was ~ 0-95 for milk, and 0-85 for whey. In whey, the calcium Y value varied greatly from 0 -06-0 -71 depending on the pH, citrate content and heat treatment; in milk it was fairly constant at 0-5 at pH 67-5 -8.Ultrafiltration (UF) and diafiltration (DF) of milk and/or whey yield retentates with various lactose: protein: ash ratios. It is of value to be able to monitor the process to a given composition of the retentate. This needs a model accommodating various raw materials, pretreatments and processing conditions.Mathematical descriptions of the behaviour of the individual components during UF and DF do exist, but they have usually been derived theoretically, or from small laboratory equipment, and do not apply satisfactorily to pilot or industrial processes. In addition, often they do not describe both UF and DF.The aim of this work was to establish an empirical model to describe the retentate composition during UF and DF of milk and whey, and to test this model under a variety of conditions. available at https:/www.cambridge.org/core/terms. https://doi