Coagulation Of Milk Proteins Research Articles

Magnetization transfer MRI of intragastric milk digestion: A feasibility study in humans

Gastric milk protein coagulation has been extensively studied using in vitro and animal models. Yet, verifying these results in humans remains essential. In this study, we assessed the feasibility of using MT MRI for monitoring milk protein coagulation in vivo in humans. Twelve adults underwent MRI scans before and after ingesting 300 g of milk with low- or high-protein denaturation (LPD or HPD, respectively). We assessed coagulation and gastric emptying dynamics by deriving the MT ratio (MTR), total gastric content (TGC), semi-solid, and liquid volumes. The MTR values increased during digestion for both milk products, indicating an increase in the degree of coagulation. Prolonged heating of milk did not affect the MTR (MD = 16 %, 95 % CI [10–21], p = 0.15), but resulted in higher TGC volumes (MD 40.3 mL, 95 % CI [25.5–55.1], p = 0.044), indicating slower gastric emptying. We thus showed that by combining MT with conventional anatomical MRI both milk protein coagulation and gastric emptying dynamics, and thereby the impact of heating on gastric milk digestion, can be assessed in vivo in humans. Our work underpins the feasibility of using MRI as a non-invasive imaging tool for studying the effects of food processing and composition on gastric digestion.

Probing structural modification of milk proteins in the presence of pepsin and/or acid using small- and ultra-small-angle neutron scattering

Acid- and pepsin-induced milk protein coagulation plays a crucial role in the gastric digestion of milk. Real-time structural evolution at a nano- (e.g. colloidal calcium phosphate (CCP) and micelle) and micro- (gel network) level of unheated and heated (85 °C for 30 min) bovine milk was examined under acidic conditions and at low and high concentrations of pepsin using ultra-small- and small-angle neutron scattering (USANS and SANS), small-amplitude oscillatory rheometry and confocal scanning laser microscopy. Milk was treated with glucono-δ-lactone (GDL), pepsin or a combination of GDL and pepsin to induce coagulation. Heat-treated milk showed a faster increase in elastic storage modulus (G′) and scattering intensity (USANS and SANS) compared with unheated milk when coagulated with GDL or the combination of GDL and pepsin. At pH 6.3, heat treatment retarded pepsin (1.10 U/mL)-induced milk coagulation, with slower increases in G′ and scattering intensity. At a high concentration of pepsin (2000 U/mL) that mimics the concentration found in the stomach, general proteolysis followed coagulation. Heat treatment retarded coagulation but accelerated curd proteolysis. This study demonstrates how time-resolved USANS and SANS can be used to investigate the structural evolution of protein coagulation and degradation under gastric environment conditions at nano- and micro-metre length scales.

Factors affecting the coagulation of milk protein during quark cheese processing in Vietnam

In recent years, cheese consumption in Vietnam is markedly rising, leading to the attention of local milk processors on cheese making. Quark-type cheese, a traditional food in Central Europe, is a type of well-known acid-coagulated cheese product. Milk coagulation properties (MCPs) play an important role to the success of the cheese-making process and are influenced by different parameters. In this study, the quality of raw milk for cheese making and the coagulation conditions in quark-type cheese processing were investigated. Raw milk collected from Phu Dong dairy farm met the requirement of Vietnamese standard for cheese making. The appropriate conditions for coagulation were identified: the heat treatment of milk at 60°C for 15 minutes, coagulation temperature at 40oC and pH 5.5, CaCl2 concentration at 0.04g/l. Under these conditions, a short coagulation time (72.33 seconds) and high curd yields (50.70%) were obtained. These results suggested that quark-type cheese using raw milk in Vietnam could be successfully developed at larger scale.

Yogurt Production.

Yogurt is a widely consumed dairy product that is obtained through the fermentation of lactic acid bacteria. During fermentation, these bacteria produce lactic acid, which lowers the pH and causes the coagulation of milk proteins. Metabolites of lactic acid bacteria, such as carbonyl compounds, nonvolatile or volatile acids, and exopolysaccharides, significantly affect the quality of yogurt. The production method also greatly influences yogurt characteristics. Yogurt can be produced in various forms, including solid, fluid, and soft-drinking types, depending on the manufacturing method employed. In addition, the raw materials, sterilization, homogenization, fermentation, and other conditions in each manufacturing method greatly affect yogurt's physical properties and flavor. This chapter summarizes common and modern methods of yogurt production.

Biotechnology factors influence on formation of curd cheese quality indicators

Considering the growing interest of the Russian society in fermented dairy products, in particular, cream cheese enriched with probiotic cultures and biologically active substances (BAS), it is relevant to conduct research aimed at scientifically justifying the choice of biotechnology of curd production as a raw material for cream cheese by studying the influence of biotechnological and technological factors on the formation of properties of the used curd. The generally accepted methods of qualitative prediction were used. The study of consumer opinion revealed the demand of Russian buyers for curd products enriched with BAS and probiotic cultures. The analysis of the regulatory documentation allowed us to form a set of mandatory requirements for the quality of curd cheese and the curd used, as well as a list of raw materials, biotechnological and technological factors required in the technology of curd cheese production. The study of the influence of each type of biotechnological and technological factors on the properties of the finished product has shown that in the biotechnology of enriched cream cheese it is necessary to use starter from pure cultures of lactococci or a mixture of lactococci and thermophilic lactic acid streptococci, acid method of coagulation of milk protein, whey separation by separation or ultrafiltration, introduction of BAS and flavoring fillers with cream in a separate method of normalization, as well as to exclude the use of milkclotting enzyme, and also to eliminate the use of milk-clotting enzymes. The results obtained are the basis for the development of new biotechnologies of curd cheese enriched with BAS and/or probiotic cultures.

Technologies for Reducing Biowaste in the Dairy Industry

The work is devoted to the development of a technology for reducing the release of whey into the environment, which is produced in large volumes during traditional cheese and cottage cheese manufacturing processes. The proposed technology is based on the process of thermoacid coagulation of milk proteins, ensuring low-waste production and environmental protection by minimizing whey protein emissions and maximizing their extraction in combination with casein in the resulting protein masses. Research shows that increasing the heating temperature to 95°C decreases the mass fraction of proteins and solids in the released whey by 30.95% and 11.72%, respectively, compared to heating at 80°C. The mass fraction of whey proteins in the whey also decreases with increasing duration of heat exposure to 5 and 20 minutes by 0.36% and 2.6%, respectively. Furthermore, it was found that when the coagulation temperature of proteins in heat-treated milk (95°C, held for 5 minutes) is reduced from 95°C to 65°C, the degree of utilization of the solids in the protein masses remains at the same level. This indicates a significant reduction in the release of whey proteins into the environment. The improvement in consistency observed is important for expanding the range of protein products.

PELATIHAN PEMBUATAN YOGHURT SUSU SAPI DENGAN METODE SEDERHANA MENGGUNAKAN LACTOBACILLUS BULGARICUS DAN STREPTOCOCCUS THERMOPHILUS

Yogurt is a dairy product that is fermented using Lactobacillus bulgaricus and Streptococcus thermophilus bacteria which are good for digestion so that they can reduce toxic substances. The combination of the two bacteria functions to convert lactose (milk sugar) into lactic acid which can lower pH and can form clots caused by coagulation of milk protein by acid, resulting in a distinctive taste because it contains flavor components such as diacetyl, acetaldehyde and carbon dioxide. The process of making yogurt begins with heating the milk to be fermented at a temperature of 90°C for 15-30 minutes, after which the milk is cooled to a temperature of 40°C, then packaged in bottles or other places. The activity process was carried out in the Yoghurt making training (presentation and demonstration), by Dharma Wanita members at SMA Negeri 6 Malang. This training was conducted to increase the productivity and skills of Dharma Wanita members at SMA Negeri 6 Malang through the use of cow's milk in yogurt. Processing cow's milk will increase the nutritional and economic value of milk. The training on milk processing into yogurt consisted of presentations on the use and processing of milk and training on making yogurt. With the implementation of this training, it is hoped that it can create side jobs for Dharma Wanita members in SMA Negeri 6 Malang so that they can increase income and have an impact on the economic welfare of the family.

Растительные компоненты в продуктах для геродиетического питания

Aim. To explore some of the theoretical and practical possibilities of using vegetable powders in dairy products and beverages for older people. Materials and Methods. As raw materials, sterilized cow's milk with a mass fraction of fat of 1.5% (GOST 31450-2013), drinking water (SanPiN 3.3686-21), vegetable powders: rosehip, cranberry, baobab pulp, blueberry, sea buckthorn were used. For research, plant powders in the amount of 1.0 and 1.5% were dissolved in milk or water at a temperature of 20°C. Organoleptic parameters were determined according to GOST ISO 6658-2016. Temperature processing of experimental samples was carried out at 75; 80 and 85оС. Active acidity was determined with a testo 206-pH1 instrument. Results. The organoleptic characteristics of the samples were evaluated when combining vegetable powders in an amount of 1.0% with milk of 1.5% fat content, on the basis of which a powder from baobab pulp and a powder from rosehip fruits were selected for further research. The studies of some organoleptic, physico-chemical and technological properties of mixtures of baobab fruit powder and rosehip fruit powder with drinking water and milk with a fat mass fraction of 1.5% showed that when these powders were added, a decrease in the hydrogen index (pH) was noted, which can lead to coagulation of milk proteins during heat treatment. During thermal treatment of experimental samples with milk, the amount of vegetable powder was established, at which it is possible to apply the pasteurization temperature regime of 85оC. Conclusion. The choice is justified and the possibility and expediency of including powder from the pulp of baobab and powder from rosehip fruits in the formulations of milk-based products and beverages for herodietic nutrition is established.

Kinetics of pepsin-induced hydrolysis and the coagulation of milk proteins

Hydrolysis-induced coagulation of casein micelles by pepsin occurs during the digestion of milk. In this study, the effect of pH (6.7-5.3) and pepsin concentration (0.110-2.75 U/mL) on the hydrolysis of κ-casein and the coagulation of the casein micelles in bovine skim milk was investigated at 37°C using reverse-phase HPLC, oscillatory rheology, and confocal laser scanning microscopy. The hydrolysis of κ-casein followed a combined kinetic model of first-order hydrolysis and putative pepsin denaturation. The hydrolysis rate increased with increasing pepsin concentration at a given pH, was pH dependent, and reached a maximum at pH ∼6.0. Both the increase in pepsin concentration and decrease in pH resulted in a shorter coagulation time. The extent of κ-casein hydrolysis required for coagulation was independent of the pepsin concentration at a given pH and, because of the lower electrostatic repulsion between para-casein micelles at lower pH, decreased markedly from ∼73% to ∼33% when pH decreased from 6.3 to 5.3. In addition, the rheological properties and the microstructures of the coagulum were markedly affected by the pH and the pepsin concentration. The knowledge obtained from this study provides further understanding on the mechanism of milk coagulation, occurring at the initial stage of transiting into gastric conditions with high pH and low pepsin concentration.

Effect of stage of lactation and dietary starch content on endocrine-metabolic status, blood amino acid concentrations, milk yield, and composition in Holstein dairy cows

Milk yield and composition are modified by level and chemical characteristics of dietary energy and protein. Those factors determine nutrient availability from a given diet, and once absorbed, they interact with the endocrine system and together determine availability of metabolites to the mammary gland. Four multiparous dairy cows in early lactation and subsequently in late lactation were fed 2 diets for 28 d in a changeover design that provided, within the same stage of lactation, similar amounts of rumen fermentable feed with either high (HS) or low starch (LS). All diets had similar dietary crude protein (15.5% dry matter) and rumen-undegradable protein (∼40% of crude protein) content. Profiles of AA were calculated to be similar to that of casein. On d 28, [1-13C] Leu was infused into one jugular vein with blood samples taken at 0, 2, 4, 6, and 8 h, and cows milked at 0, 2, 4, 5, 6, 7, and 8 h from start of infusion. Isotopic enrichments of plasma Leu, keto-isocaproic acid, and milk casein were determined for calculation of Leu kinetics. Data were subjected to ANOVA using the MIXED procedure of SAS (SAS Institute Inc.), with time as repeated factor and cow as the random effect. Dry matter intake within each stage of lactation was similar between groups. Feeding LS resulted in lower blood glucose and greater ratio of bovine somatotropin to insulin. This response was associated with greater blood concentrations of nonesterified fatty acids and β-hydroxybutyrate, which might have contributed to greater milk fat content in LS-fed cows. Except for His, average concentrations of all AA in blood were higher in late than early lactation. Diet did not alter average plasma concentrations of AA. However, for most of the essential AA (particularly branched-chain), the HS diet led to a marked decrease in concentrations after the forage meal, resulting in significant differences between dietary groups in early lactation. In early-lactating cows fed HS, a greater reduction in plasma concentrations at 8 h relative to pre-feeding values (time zero) was observed for Met, Lys, and His, resulting in decreases of 27.9%, 33.6%, and 38.5%, respectively. A higher bovine somatotropin/insulin ratio in early lactation and in cows fed LS could possibly have led to greater breakdown and, consequently, higher AA flux from peripheral tissues. In LS-fed cows, higher mobilization of body fat and protein was confirmed by the greater body weight loss in both stages of lactation. Higher irreversible loss of [1-13C] Leu in early lactation suggested lower protein retention in peripheral tissues during early compared with late lactation. Milk yield, protein output, and composition were similar between groups at both stages of lactation, whereas milk coagulation was faster (lower curd firming rate) and with higher curd firmness in response to feeding HS in late lactation. Overall, data indicated that rate of carbohydrate fermentability in the rumen can modify the availability of metabolites to the mammary gland and consequently modify milk protein coagulation.

Методы оценки свертываемости белков молока в системе прогнозирования технологических свойств

Introduction. An integrated monitoring of raw milk’s contents, quality, and security is a key factor that guarantees the high-quality dairy production. As a result, new research methods of rennet clotting are a topical and urgent area of study. The research objective was to systemize and analyze the basic criteria and assessment methods of rennet-induced protein gels in milk systems. Study objects and methods. The authors reviewed the official Russian criteria and methods of raw milk assessment by its rennet coagulation properties. The research also featured the most widespread instrumental approaches used in best practices from around the world. Results and discussion. In Russian and foreign cheese production, milk is always tested for its physicochemical and microbiological indicators, with a mandatory check of its coagulation characteristics. Russian cheese-makers use different modifications of rennet and rennet-fermenting tests based on subjective sensory evaluation, while international scientific trends in this area aim at developing and improving instrumental methods by using a complex indicator MCP. This indicator characterizes the parameters of rennet coagulation with the help of such devices as Formagraph, Lattodinamografo, Optigraph, etc. Formagraph is a simple instrument for measuring rheological properties of milk clotting. It was popular in the late XX century. The resent years saw the development of other methods of instrumental control, including those based on optical measurements. For instance, Ortigraph is one such instrument that receives unified data on coagulation properties of raw milk by using near-infrared waves. Sensory and instrumental methods have their advantages and disadvantages. However, the most significant criteria for a quick test of cheeseability, yield, and quality are the speed of analysis and the comparability and reproducibility of results. Conclusion. To improve cheeseability testing, Russian cheese-makers need to use the international experience, which offers standardized evaluation criteria in combination with various instrumental approaches. However, the integration of foreign regulations and methods into Russian studies is not the only option. The improvement and development of national instrumental methods of evaluating milk protein coagulation is also crucial.

Research of quality indicators in protein-blueberry concentrates

The effect of blueberry coagulant in the form of specially processed blueberry paste on the building-up process of protein-blueberry concentrates has been considered in the article and the change in their physical-chemical indicators during storage has been determined. A study of blueberry coagulant application in the amount of up to 12% provides the effective running to process of thermo acid coagulation of milk proteins with a maximum clot yield (excluding limiting factors – organoleptic indicators and active acidity). It has been found that with an increase in the amount of blueberry paste adding from 2% to 10%, the yield of protein-blueberry concentrates increases from 5% to 40%, and the moisture mass fraction in clots decreases, on the contrary, from 73.4% to 67.1%. Other quality indicators of protein-blueberry concentrates were recorded: active acidity (from 5.0 pH at the beginning to 4.7 pH at the end of the storage life), and the water-retaining capacity at the level of (75.44 ±0.5%). Based on chromatographic studies, the degree of polyphenolic compounds transition (including anthocyanins) to protein-blueberry concentrates at the level of 52.26% has been determined by the calculation method and analyzed compared with control sample (blueberry paste) and colored whey. Based on the researches, protein-blueberry concentrates obtained by thermo acid coagulation of milk proteins are suggested to be used as basis in the cheese products recipes.

Technological properties of cow's milk: correlations with milk composition, effect of interactions of genes and other factors

We analysed the correlations of milk fermentability (yogurt test acidity), renneting (time to rennet coagulation of milk protein) and results of ethanol tests (indirect indicator of milk thermostability) with the percentages of the milk components. The correlations of the milk component percentages with renneting were mostly weak, while the correlations with the ethanol test were even poorer. The CSN3 and LGB genotypes did not show a significant interaction in their influence on milk fermentability, renneting or ethanol test results. For the ethanol test, many significant interactions were observed between the DGAT1, LEP, FASN, SCD1, CSN2, CSN3 and LGB genotypes. DGAT1 interacted significantly with all genes for milk fermentability. For renneting that was measured instrumentally, CSN3 interacted significantly with DGAT1, FASN, SCD1, CSN2 A/B, CSN2 A1/A2; SCD1 interacted significantly with LEP and FASN. The breed and genotypes did not show any interactions. Farm and genotypes interacted significantly for all the technological properties studied; similar results were observed for the protein percentage and the genotypes, except that no interactions influenced the ethanol test results.

Effect of the protein coagulation on heat and shape stability of cultured milk ice cream

The paper deals with the investigation of the effect of the degree of milk protein coagulation on cultured milk ice cream quality indices (mixture viscosity, heat stability, shape stability and overrun). It was defined that the capability of mixture to be saturated with air decreased as its acidity increased because of the increase of the protein coagulation degree. Due to this the capability of protein to stabilize the air phase decreased. The positive effect of the process and the degree of protein coagulation on the product resistivity to thawing was proved experimentally; it was due to the product dense consistency and air low content.

The use of laminaria in the manufacture of soft cheeses

This article presents a reserarch on the use of iodine-containing dietary supplements – kelp in the formulation of soft cheese. The kelp brought in experienced options formula before thermocycling coagulation in the amount of 0.2 % by weight of the formula. In control supplement laminaria has not imposed. All kinds of cheese, both a control, and test samples were manufactured from the same batch of milk as raw material. Technological process of establishing fortified with iodine thermocycling cheese included the following operations: preparation of the milk to thermocycling coagulation; heating; the introduction of the flavoring component and thermocycling coagulation of milk proteins; formation; selfpressing the curd; salting; form of pale malt; cooling; packaging; storage. The results showed that the introduction of kelp powder does not degrade the quality of the cheese but gives it a certain spicy flavour peculiar to seaweed and is a product of functional purpose.

The nfluence of microparticulate on acid coagulation of milk proteins in curd manufacture

One of the important trends of whey processing is the modification of its composition and properties for the applications in curd technology. Modification of whey composition and properties included ultrafiltration concentration and subsequent microparticulation of the concentrate obtained. Selected modes allowed to obtain particles of microparticulate of whey proteins similar to fat globules in shape and size. Whey proteins microparticulate was proposed to use in curd technology. The influence of mass fraction of whey proteins microparticulate on the process of fermentation and acid clot formation in the production of low-fat curd was investigated. The most intensive growth and titratable and active acidity was observed in samples of curd clots with a mass fraction of whey proteins microparticulate from 10 to 15%. The analysis of organoleptic characteristics of curd clots led to the conclusion that the introduction _ of whey proteins microparticulate gives a smooth appearance to the clot, increases the density, adds a creamy taste. In the process of self-pressing _ of whey proteins microparticulate particles embedded inside impede the process of densification, and the mass fraction of moisture in the curd increases. Application _ of whey proteins microparticulate intensifies the process of curd clot formation and increases the yield of the finished product by 20 - 30%. Application of whey proteins microparticulate for enrichment of normalized mixture in the production of curd allows to expand the range of low-calorie protein products contributes to the intensification of the process of ripening of enriched normalized mixture, increases the yield of curd and its biological value.

The nfluence of microparticulate on acid coagulation of milk proteins in curd manufacture

The nfluence of microparticulate on acid coagulation of milk proteins in curd manufacture

Proteomic profiling of the coagulation of milk proteins induced by glucono-delta-lactone

This study investigated the glucono-delta-lactone (GDL)-induced coagulation of milk proteins at 30 °C. The addition of 0.5 M GDL caused milk proteins to coagulate following a 1 h incubation period. Approximately 90.7% of milk proteins were coagulated into the milk pellet fraction (MPF), and the protein concentration of the milk supernatant fraction (MSF) decreased from 29.2 ± 1.1 mg mL−1 (control) to 2.7 ± 1.1 mg mL−1. The SDS-PAGE analysis demonstrated that the protein bands corresponding to αS-casein, β-casein and κ-casein in the MSF decreased to 0.2 ± 0.1, 0.5 ± 0.2 and 0.5 ± 0.3% of their original levels, respectively. However, only 29.5% of the β-lactoglobulin was coagulated into the MPF following the treatment with 0.5 M GDL. Two-dimensional electrophoresis analysis indicated that isomers of αS1-casein, αS2-casein, β-casein and κ-casein, as well as a fraction of β-lactoglobulin and α-lactalbumin, were coagulated from the MSF into the MPF following incubation with 0.5 M GDL.

Vlivy nadmořskÉ výšky lokality na některé chemické, zdravotní, mikrobiologické, fyzikální a technologické ukazatele kravského mléka a senzorické vlastnosti sýrů

Obecně je nadmořskĂĄ výťka chovu dojnic inherentnĂ­m a kumulativnĂ­m faktorem, kterĂ˝ mĹŻĹže ovlivnit vĂ˝znamně faremnĂ­ podmĂ­nky a tĂ­m produkci i kvalitu mlĂŠka. Je tvořen prĹŻměrnou ročnĂ­ teplotou, Ăşhrnem ročnĂ­ch srĂĄĹžek, dĂŠlkou doby slunečnĂ­ho svitu a dalĹĄĂ­mi poloĹžkami ve smyslu klimatu a počasĂ­. Celkově mĹŻĹže mĂ­t přímĂ˝ vliv na tepelnĂŠ stresy dojnic a rezistenci např. vůči mastitidĂĄm a nepřímĂ˝ na mléčnou uĹžitkovost prostřednictvĂ­m pĹŻdnĂ­ch podmĂ­nek a skladby krmnĂ˝ch pĂ­cnin. Jako faktor ji lze ovĹĄem jen omezeně ovlivňovat, vystupuje vĹĄak vĹždy do popředĂ­ zĂĄjmu v rĂĄmci diskusĂ­ o struktuře stĂĄtnĂ­ch podpor do chovu dojnic a jejich přerozdělenĂ­. ZĂĄroveň je zahrnuta nepřímo v diskusi o udrĹžitelnĂŠm, ĹĄetrnĂŠm zemědělstvĂ­ v tzv. LFA (mĂŠně příznivĂ˝ch oblastech). Jako příspěvek k tĂŠto diskusi bylo srovnĂĄno sloĹženĂ­ a kvalita mlĂŠka ze sedmi modelovĂ˝ch chovĹŻ v nĂ­ĹžinnĂ˝ch (N, ≤ 350 m n. m.) a podhorskĂ˝ch (P > 350 m n. m.) oblastech ČR. Z hlediska plemennĂŠho vlivu byl soubor vyrovnanĂ˝, tzn. v kaĹždĂŠ oblasti polovina zvířat nĂĄleĹžela k plemeni HolĹĄtĂ˝n a polovina k plemeni ČeskĂŠ strakatĂŠ. VýŞiva zvířat modelovĂ˝ch chovĹŻ odpovĂ­dala oblastem a typickĂŠmu profilu výŞivy dojnic v ČR. Byla sledovĂĄna celĂĄ řada sloĹžkovĂ˝ch a technologickĂ˝ch (24) ukazatelĹŻ v individuĂĄlnĂ­m mlĂŠce, hygienickĂ˝ch v bazĂŠnovĂŠm mlĂŠce, směsnĂŠ krmnĂŠ dĂĄvce, vĂ˝kalech dojnic a senzorickĂŠ vlastnosti sĂ˝rĹŻ ĹĄvĂ˝carskĂŠho typu z modelovĂ˝ch vĂ˝rob. Celkem bylo odebrĂĄno za tři roky, vĹždy v letnĂ­ a zimnĂ­ krmnĂŠ sezoně, 240 (N) a 444 (P) individuĂĄlnĂ­ch vzorkĹŻ mlĂŠka, 31 a 39 bazĂŠnovĂ˝ch vzorkĹŻ mlĂŠka, prĹŻměrnĂ˝ch vzorkĹŻ vĂ˝kalĹŻ a vzorkĹŻ směsnĂ˝ch krmnĂ˝ch dĂĄvek z krmnĂŠho Ĺžlabu a bylo provedeno 30 modelovĂ˝ch vĂ˝rob tvrdĂ˝ch, přírodně zranĂ˝ch sĂ˝rĹŻ. Ve smyslu klimatu se chovy dojnic N a P statisticky vĂ˝znamně (P < 0,01) liĹĄily v prĹŻměrnĂŠm ročnĂ­m Ăşhrnu srĂĄĹžek (572 a 776 mm) a v prĹŻměrnĂŠ ročnĂ­ teplotě (P < 0,001; 9,7 a 7,1 °C), zatĂ­mco se vĂ˝znamně neliĹĄily v prĹŻměrnĂŠ ročnĂ­ době slunečnĂ­ho svitu (1851 a 1650 hod.; P > 0,05). VĂ˝znamnějĹĄĂ­ rozdĂ­ly byly pozorovĂĄny u technologickĂ˝ch ukazatelĹŻ mlĂŠka jako alkoholovĂŠ stability, času sýřenĂ­ a pevnosti sýřeniny s vĂ˝hodou pro N oblast pro posledně dva jmenovanĂŠ a pro P oblast pro alkoholovou stabilitu mléčnĂ˝ch bĂ­lkovin. VĂ˝znamnějĹĄĂ­ rozdĂ­ly byly takĂŠ u nebĂ­lkovinnĂ˝ch dusĂ­katĂ˝ch lĂĄtek, avĹĄak bez praktickĂŠho vĂ˝znamu. VětĹĄinou vĹĄak byly rozdĂ­ly v dojivosti a ve sloĹženĂ­ a vlastnostech mlĂŠka jako obsazĂ­ch tuku, laktĂłzy, tukuprostĂŠ suĹĄiny, frakcĂ­ bĂ­lkovin (hrubĂ˝ch a čistĂ˝ch bĂ­lkovin, kaseinu a syrovĂĄtkovĂ˝ch bĂ­lkovin), močoviny, acetonu, elektrickĂŠ konduktivitě, titračnĂ­ kyselosti atd. mezi N a P nevĂ˝znamnĂŠ (P > 0,05). VĂ˝skyty termorezistentnĂ­ch mikroorganismĹŻ a bacilĹŻ by mohly bĂ˝t vztaĹženy mezi kvalitou krmiv, kontaminacĂ­ vĂ˝kalĹŻ a nĂĄsledně mlĂŠka, přičemĹž kvalita krmiv (jejich konzervace) mĹŻĹže zĂĄviset např. na srĂĄĹžkĂĄch. VĂ˝znamnĂŠ rozdĂ­ly uvnitř sledovanĂ˝ch hygienickĂ˝ch ukazatelĹŻ a materiĂĄlĹŻ (krmivo, vĂ˝kaly, mlĂŠko) mezi N a P oblastmi vĹĄak nebyly pozorovĂĄny, tedy nebyly potvrzeny předchozĂ­ hypotĂŠzy. SenzorickĂĄ kvalita sĂ˝rĹŻ byla nevĂ˝znamně vyĹĄĹĄĂ­ v oblasti P při mnohem větĹĄĂ­ variabilitě, kdy nejlepĹĄĂ­ byla na jednĂŠ z P farem charakterizovanĂŠ vysokou kvalitou sklizně a konzervace travnĂ­ch senåŞí o vysokĂŠ suĹĄině. VĂ˝sledky umoŞňujĂ­ svĂ˝m charakterem doporučenĂ­ pro udrĹženĂ­ chovu dojnic takĂŠ v podhorskĂ˝ch oblastech, ve kterĂ˝ch byl mnohde zaznamenĂĄn jeho vĂ˝raznějĹĄĂ­ Ăşstup, pro jejich vhodnost k produkci mlĂŠka srovnatelnĂŠ kvality a moĹžnĂŠ vĂ˝hody v sĂ˝rařstvĂ­.

Effect of high pressures on the enzymatic activity of commercial milk protein coagulants

This study was aimed at determining the effect of high pressures in the range of 100–1000 MPa/15 min, applied in 100 MPa increments, on the coagulating and proteolytic activity of commercial coagulants produced with genetic engineering methods: Maxiren, Chymogen, Chymax and of a natural rennin preparation, Hala. The coagulating activity of Hala preparation differed compared with the other preparations, due to greater resistance to high pressures, especially in the range of 500–600 MPa. The preparations produced with genetic engineering methods lost their capability for milk protein coagulation by 500 MPa. Pressurization at 200 MPa contributed to their reduced capability for casein macroproteolysis. In contrast, an increase in Chymax, Chymogen, Maxiren and Hala preparations’ hydrolytic capability for the macroproteolysis of isoelectric casein was observed upon pressure treatment at 100 and 400 MPa and for microproteolysis after pressure treatment at 200 MPa. Storage (48 h/5°C) of the pressurized preparations had an insignificant effect on their coagulating and proteolytic activities.