Influence of ß-casein genotype on physicochemical properties and functionality of bovine milk.

Several studies have been focused on the effect of milk protein genetic variants on milk physicochemical properties and functionality in recent years. ß-casein, an important protein related to milk processibility, has been reported to have 2 main genetic variants A1 and A2, for which cows may be homozygous or heterozygous. In this study, several physicochemical properties of milk with ß-casein variants A1A1, A1A2, and A2A2 from 3 collection occasions were analyzed. Higher manganese content and lower pH were found to be associated with the A1A1 variant compared with the other 2 genotypes. Better rennet and acid coagulation were found in A1A1 milk compared with A1A2 and A2A2 milk (although P > 0.05), whereas A2A2 milk was more stable to creaming compared with the other 2 genotypes, which may be linked to its smaller fat globule size. Thus, milk from cows with A1A1 genotype could be preferable for cheese making, while that with A2A2 variant can be used in formulations requiring good stability against creaming, and for example, yogurt making, where the softer yogurt texture may be easier to digest.

A descriptive study of the multidisciplinary healthcare experiences of inpatient resuscitation events.

Background: In-hospital resuscitation events have complex and enduring effects on clinicians, with implications for job satisfaction, performance, and burnout. Ethically ambiguous cases are associated with increased moral distress. We aim to quantitatively describe the multidisciplinary resuscitation experience. Methods: Multidisciplinary in-hospital healthcare professionals at an adult academic health center in the Midwestern United States completed surveys one and six weeks after a resuscitation event. Surveys included demographic data, task load (NASA-TLX), overall and moral distress, anxiety, depression, and spiritual peace. Spearman's rank correlation was computed to assess task load and distress. Results: During the 5-month study period, the study included 12 resuscitation events across six inpatient units. Of 82 in-hospital healthcare professionals eligible for recruitment, 44 (53.7%) completed the one-week post-resuscitation event survey. Of those, 37 (84.1%) completed the six-week survey. Highest median task load burden at one week was seen for temporal demand, effort, and mental demand. Median moral distress scores were low, while "at peace" median scores tended to be high. There were no significant non-zero changes in task load or distress scores from weeks 1-6. Mental demand (r = 0.545, p < 0.001), physical demand (r = 0.464, p = 0.005), performance (r = -0.539, p < 0.001), and frustration (r = 0.545, p < 0.001) significantly correlated with overall distress. Performance (r = -0.371, p = 0.028) and frustration (r = 0.480, p = 0.004) also significantly correlated with moral distress. Conclusions: In-hospital healthcare professionals' experiences of resuscitation events are varied and complex. Aspects of task load burden including mental and physical demand, performance, and frustration contribute to overall and moral distress, deserving greater attention in clinical contexts.

In-process rheometry as a PAT tool for hot melt extrusion.

Real time measurement of melt rheology has been investigated as a Process Analytical Technology (PAT) to monitor hot melt extrusion of an Active Pharmaceutical Ingredient (API) in a polymer matrix. A developmental API was melt mixed with a commercial copolymer using a heated twin screw extruder at different API loadings and set temperatures. The extruder was equipped with an instrumented rheological slit die which incorporated three pressure transducers flush mounted to the die surface. Pressure drop measurements within the die at a range of extrusion throughputs were used to calculate rheological parameters, such as shear viscosity and exit pressure, related to shear and elastic melt flow properties, respectively. Results showed that the melt exhibited shear thinning behavior whereby viscosity decreased with increasing flow rate. Increase in drug loading and set extrusion temperature resulted in a reduction in melt viscosity. Shear viscosity and exit pressure measurements were found to be sensitive to API loading. These findings suggest that this technique could be used as a simple tool to measure material attributes in-line, to build better overall process understanding for hot melt extrusion.

Application of hot melt extrusion for improving bioavailability of artemisinin a thermolabile drug.

Hot melt extrusion has been used to produce a solid dispersion of the thermolabile drug artemisinin. Formulation and process conditions were optimized prior to evaluation of dissolution and biopharmaceutical performance. Soluplus®, a low Tg amphiphilic polymer especially designed for solid dispersions enabled melt extrusion at 110 °C although some drug-polymer incompatibility was observed. Addition of 5% citric acid as a pH modifier was found to suppress the degradation. The area under plasma concentration time curve (AUC0-24h) and peak plasma concentration (Cmax) were four times higher for the modified solid dispersion compared to that of pure artemisinin.

The effect of storage conditions on the composition and functional properties of blended bulk tank milk.

The objective of this study was to investigate the effects of storage temperature and duration on the composition and functional properties of bulk tank milk when fresh milk was added to the bulk tank twice daily. The bulk tank milk temperature was set at each of 3 temperatures (2, 4, and 6°C) in each of 3 tanks on 2 occasions during two 6-wk periods. Period 1 was undertaken in August and September when all cows were in mid lactation, and period 2 was undertaken in October and November when all cows were in late lactation. Bulk tank milk stored at the 3 temperatures was sampled at 24-h intervals during storage periods of 0 to 96 h. Compositional parameters were measured for all bulk tank milk samples, including gross composition and quantification of nitrogen compounds, casein fractions, free amino acids, and Ca and P contents. The somatic cell count, heat stability, titratable acidity, and rennetability of bulk tank milk samples were also assessed. Almost all parameters differed between mid and late lactation; however, the interaction between lactation, storage temperature, and storage duration was significant for only 3 parameters: protein content and concentrations of free cysteic acid and free glutamic acid. The interaction between storage temperature and storage time was not significant for any parameter measured, and temperature had no effect on any parameter except lysine: lysine content was higher at 6°C than at 2°C. During 96 h of storage, the concentrations of some free amino acids (glutamic acid, lysine, and arginine) increased, which may indicate proteolytic activity during storage. Between 0 and 96 h, minimal deterioration was observed in functional properties (rennet coagulation time, curd firmness, and heat stability), which was most likely due to the dissociation of ß-casein from the casein micelle, which can be reversed upon pasteurization. Thus, this study suggests that blended milk can be stored for up to 96 h at temperatures between 2°C and 6°C with little effect on its composition or functional properties.

Activities of indigenous proteolytic enzymes in caprine milk of different somatic cell counts.

Individual caprine milk with different somatic cell counts (SCC) were studied with the aim of investigating the percentage distribution of leukocyte cell types and the activities of indigenous proteolytic enzymes; proteolysis of casein was also studied in relation to cell type following recovery from milk. The experiment was conducted on 5 intensively managed dairy flocks of Garganica goats; on the basis of SCC, the experimental groups were denoted low (L-SCC; <700,000 cells/mL), medium (M-SCC; from 701,000 to 1,500,000 cells/mL), and high (H-SCC; >1,501,000 cells/mL) SCC. Leukocyte distribution differed between groups; polymorphonuclear neutrophilic leukocytes were higher in M-SCC and H-SCC milk samples, the percentage macrophages was the highest in H-SCC, and levels of nonviable cells significantly decreased with increasing SCC. Activities of all the main proteolytic enzymes were affected by SCC; plasmin activity was the highest in H-SCC milk and the lowest in L-SCC, and elastase and cathepsin D activities were the highest in M-SCC. Somatic cell count influenced casein hydrolysis patterns, with less intact α- and ß-casein in H-SCC milk. Higher levels of low electrophoretic mobility peptides were detected in sodium caseinate incubated with leukocytes isolated from L-SCC milk, independent of cell type, whereas among cells recovered from M-SCC milk, macrophages yielded the highest levels of low electrophoretic mobility peptides from sodium caseinate. The level of high electrophoretic mobility peptides was higher in sodium caseinate incubated with polymorphonuclear neutrophilic leukocytes and macrophages isolated from M-SCC, whereas the same fraction of peptides was always the highest, independent of leukocyte type, for cells recovered from H-SCC milk. In caprine milk, a level of 700,000 cells/mL represented the threshold for changes in leukocyte distribution, which is presumably related to the immune status of the mammary gland. Differences in the profile of indigenous lysosomal proteolytic enzymes in caprine milk may influence the integrity of casein based on proteolysis patterns of sodium caseinate incubated with isolated and lysed leukocyte types.

A novel transflectance near infrared spectroscopy technique for monitoring hot melt extrusion.

A transflectance near infra red (NIR) spectroscopy approach has been used to simultaneously measure drug and plasticiser content of polymer melts with varying opacity during hot melt extrusion. A high temperature reflectance NIR probe was mounted in the extruder die directly opposed to a highly reflective surface. Carbamazepine (CBZ) was used as a model drug, with polyvinyl pyrollidone-vinyl acetate co-polymer (PVP-VA) as a matrix and polyethylene glycol (PEG) as a plasticiser. The opacity of the molten extrudate varied from transparent at low CBZ loading to opaque at high CBZ loading. Particulate amorphous API and voids formed around these particles were found to cause the opacity. The extrusion process was monitored in real time using transflectance NIR; calibration and validation runs were performed using a wide range of drug and plasticiser loadings. Once calibrated, the technique was used to simultaneously track drug and plasticiser content during applied step changes in feedstock material. Rheological and thermal characterisations were used to help understand the morphology of extruded material. The study has shown that it is possible to use a single NIR spectroscopy technique to monitor opaque and transparent melts during HME, and to simultaneously monitor two distinct components within a formulation.

Effect of fat content and homogenization under conventional or ultra-high-pressure conditions on interactions between proteins in rennet curds.

The objective of this study was to investigate the influence of conventional and ultra-high-pressure homogenization on interactions between proteins within drained rennet curds. The effect of fat content of milk (0.0, 1.8, or 3.6%) and homogenization treatment on dissociation of proteins by different chemical agents was thus studied. Increasing the fat content of raw milk increased levels of unbound whey proteins and calcium-bonded caseins in curds; in contrast, hydrophobic interactions and hydrogen bonds were inhibited. Both homogenization treatments triggered the incorporation of unbound whey proteins in the curd, and of caseins through ionic bonds involving calcium salts. Conventional homogenization-pasteurization enhanced interactions between caseins through hydrogen bonds and hydrophobic interactions. In contrast, ultra-high-pressure homogenization impaired hydrogen bonding, led to the incorporation of both whey proteins and caseins through hydrophobic interactions and increased the amount of unbound caseins. Thus, both homogenization treatments provoked changes in the protein interactions within rennet curds; however, the nature of the changes depended on the homogenization conditions.

Proteolytic and proteomic changes in milk at quarter level following infusion with Escherichia coli lipopolysaccharide.

Mastitis is a major disease in dairy cattle, which causes significant economic losses due to decreased milk production, veterinary costs, and discarded milk. Escherichia coli is one of the most prevalent species of gram-negative bacteria that induce clinical mastitis. The objective of the present study was to characterize the proteolytic and proteomic changes in milk in response to infusion with lipopolysaccharide (LPS) at quarter level in a model mastitis system. One quarter of each of 2 cows was infused with 0.1 or 5 µg of LPS. The somatic cell count of the infused quarters reached a peak 6 h after infusion to a greater extent in the cow infused with 5 µg of LPS and changes in plasmin activity in milk differed between the 2 animals. Urea-polyacrylamide gel electrophoretograms of milk samples of the cow infused with 5 µg of LPS obtained at different time points after infusion and incubated for up to 7 d showed almost full hydrolysis of ß- and α(s1)-casein during incubation of milk samples due to indigenous proteolytic activity. Two-dimensional gel electrophoretograms of milk at 0, 6, or 12 h after infusion with LPS showed hydrolysis of α(s)-casein and ß-casein as well as the appearance of lower molecular weight products. Eleven fragments from proteolysis of the caseins were identified by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry and, in addition, proteolysis patterns of casein by the indigenous bovine milk proteases plasmin and cathepsin D were studied in model studies using 2-dimensional gel electrophoretograms. Twelve hours after infusion, lower abundance markers of inflammation were identified, including serotransferrin, fibrinogen ß chain, protein S100 A12, and the antimicrobial polypeptide cathelicidin.

Monitoring ibuprofen-nicotinamide cocrystal formation during solvent free continuous cocrystallization (SFCC) using near infrared spectroscopy as a PAT tool.

The purpose of this work was to explore NIR spectroscopy as a PAT tool to monitor the formation of ibuprofen and nicotinamide cocrystals during extrusion based solvent free continuous cocrystallization (SFCC). Drug and co-former were gravimetrically fed into a heated co-rotating twin screw extruder to form cocrystals. Real-time process monitoring was performed using a high temperature NIR probe in the extruder die to assess cocrystal content and subsequently compared to off-line powder X-ray diffraction measurements. The effect of processing variables, such as temperature and mixing intensity, on the extent of cocrystal formation was investigated. NIR spectroscopy was sensitive to cocrystal formation with the appearance of new peaks and peak shifts, particularly in the 4800-5200 cm(-1) wave-number region. PXRD confirmed an increased conversion of the mixture into cocrystal with increase in barrel temperature and screw mixing intensity. A decrease in screw rotation speed also provided improved cocrystal yield due to the material experiencing longer residence times within the process. A partial least squares analysis in this region of NIR spectrum correlated well with PXRD data, providing a best fit with cocrystal conversion when a limited range of process conditions were considered, for example a single set temperature. The study suggests that NIR spectroscopy could be used to monitor cocrystal purity on an industrial scale using this continuous, solvent-free process.

A role for proline synthesis and transport in Listeria monocytogenes barotolerance.

AIMS: To assess the contribution of proline biosynthesis to listerial barotolerance. METHODS AND RESULTS: Using a Listeria monocytogenes proBA deletion mutant, incapable of synthesizing proline, together with a proline-overproducing strain, the contribution of proline synthesis to listerial barotolerance was determined. The ΔproBA strain does not survive as well as the wild type when subjected to treatment of 500 MPa in rich media and 400 MPa in minimal media (c. 1 log lower survival in both conditions). Betaine and carnitine decrease the ability of the wild type to survive at low pressures (300 MPa), but confer normal or slightly increased levels of protection at higher pressures (350 and 400 MPa). CONCLUSIONS: A functional proline synthesis system is required for optimal survival of Listeria following treatment at high-pressure (HP) levels (500 MPa in brain heart infusion and 400 MPa in defined medium), particularly where other compatible solutes are absent or limiting. SIGNIFICANCE AND IMPACT OF THE STUDY: Given the potential of HP processing as an effective food processing/safety strategy, understanding how pathogens such as Listeria have evolved to cope with such stresses is an important food safety consideration. In this context, the work presented here may help to develop safer and more effective processing regimens.

Novel listerial genetic loci conferring enhanced barotolerance in Escherichia coli.

AIMS: To identify Listeria monocytogenes genes with a role in high-pressure (HP) resistance. METHODS AND RESULTS: A L. monocytogenes genomic library constructed in an Escherichia coli background was screened for loci conferring increased HP resistance. Pressure treatments at 400 megapascals for 5 min in Luria-Bertani (LB) agar were used to screen for increased resistance to pressure. Colonies arising on the treated agar plates were isolated, the plasmid extracted and the inserts sequenced to identify the genetic loci conferring HP resistance. Seven different genetic regions were identified, which encoded proteins similar to an inorganic polyphosphate/ATP-NAD kinase, the septation ring formation regulator EzrA, flagellar motor proteins MotA and MotB, proteins similar to the quorum sensing Agr system from Staphylococcus (AgrA, AgrC and AgrD), proteins similar to a transcription regulator (RpiR family) and a fructose phosphotransferase system, proteins of unknown function, and a Fur regulator. Of the seven loci confirmed, three (EzrA, MotA/B and the Agr system) maintained significantly reproducible HP tolerance when expressed in a different E. coli background. CONCLUSIONS: Novel genetic loci from the L. monocytogenes genome confer increased HP resistance when heterologously expressed in an E. coli background. SIGNIFICANCE AND IMPACT OF THE STUDY: Molecular and functional approaches to the screening of genetic elements linked to HP resistance provide greater insights into microbial inactivation and/or survival mechanisms when using HP as a means of controlling/eliminating bacterial growth. This information will ultimately have significant implications for the use of HP processing in the food industry, in terms of both food quality and safety.

Proteomic and peptidomic study of proteolysis in quarter milk after infusion with lipoteichoic acid from Staphylococcus aureus.

Mastitic milk is associated with increased bovine protease activity, such as that from plasmin and somatic cell enzymes, which cause proteolysis of the caseins and may reduce cheese yield and quality. The aim of this work was to characterize the peptide profile resulting from proteolysis in a model mastitis system and to identify the proteases responsible. One quarter of each of 2 cows (A and B) was infused with lipoteichoic acid from Staphylococcus aureus. The somatic cell counts of the infused quarters reached a peak 6h after infusion, whereas plasmin activity of those quarters also increased, reaching a peak after 48 and 12h for cow A and B, respectively. Urea-polyacrylamide gel electrophoretograms of milk samples of cow A and B obtained at different time points after infusion and incubated for up to 7 d showed almost full hydrolysis of ß- and α(S1)-casein during incubation of milk samples at peak somatic cell counts, with that of ß-casein being faster than that of α(S1)-casein. Two-dimensional gel electrophoretograms of milk 6h after infusion with the toxin confirmed hydrolysis of ß- and α(S1)-casein and the appearance of lower-molecular-weight products. Peptides were subsequently separated by reversed-phase HPLC and handmade nanoscale C(18) columns, and identified by matrix-assisted laser desorption/ionization time-of-flight tandem mass spectrometry. Twenty different peptides were identified and shown to originate from α(s1)- and ß-casein. Plasmin, cathepsin B and D, elastase, and amino- and carboxypeptidases were suggested as possible responsible proteases based on the peptide cleavage sites. The presumptive activity of amino- and carboxypeptidases is surprising and may indicate the activity of cathepsin H, which has not been reported in milk previously.

The combined effects of high pressure and nisin on germination and inactivation of Bacillus spores in milk.

AIMS: The aim of this work was to investigate the germination and inactivation of spores of Bacillus species in buffer and milk subjected to high pressure (HP) and nisin. METHODS AND RESULTS: Spores of Bacillus subtilis and Bacillus cereus suspended in milk or buffer were treated at 100 or 500 MPa at 40 degrees C with or without 500 IU ml(-1) of nisin. Treatment at 500 MPa resulted in high levels of germination (4 log units) of B. subtilis spores in both milk and buffer; this increased to >6 logs by applying a second cycle of pressure. Viability of B. subtilis spores in milk and buffer was reduced by 2.5 logs by cycled HP, while the addition of nisin (500 IU ml(-1)) prior to HP treatment resulted in log reductions of 5.7 and 5.9 in phosphate buffered saline and milk, respectively. Physical damage of spores of B. subtilis following HP was apparent using scanning electron microscopy. Treating four strains of B. cereus at 500 MPa for 5 min twice at 40 degrees C in the presence of 500 IU ml(-1) nisin proved less effective at inactivating the spores of these isolates compared with B. subtilis and some strain-to-strain variability was observed. CONCLUSIONS: Although high levels of germination of Bacillus spores could be achieved by combining HP and nisin, complete inactivation was not achieved using the aforementioned treatments. SIGNIFICANCE AND IMPACT OF THE STUDY: Combinations of HP treatment and nisin may be an appealing alternative to heat pasteurization of milk.

Stability of casein micelles cross-linked by transglutaminase.

In this study, caseins micelles were internally cross-linked using the enzyme transglutaminase (TGase). The integrity of the micelles was examined on solubilization of micellar calcium phosphate (MCP) or on disruption of hydrophobic interactions and breakage of hydrogen bonds. The level of monomeric caseins, determined electrophoretically, decreased with increasing time of incubation with TGase at 30 degrees C; after incubation for 24 h, no monomeric beta- or kappa-caseins were detected, whereas only a small level of monomeric alphaS1-casein remained, suggesting near complete intramicellar cross-linking. The ability of casein micelles to maintain structural integrity on disruption of hydrophobic interactions (using urea, sodium dodecyl sulfate, or heating in the presence of ethanol), solubilization of MCP (using the calcium-chelating agent trisodium citrate) or high-pressure treatment was estimated by measurement of the L*-value of milk; i.e., the amount of back-scattered light. The amount of light scattered by casein micelles in noncross-linked milk was reduced by >95% on complete disruption of hydrophobic interactions or complete solubilization of MCP; treatment of milk with TGase increased the stability of casein micelles against disruption by all methods studied and stability increased progressively with incubation time. After 24 h of cross-linking, reductions in the extent of light scattering were still apparent in the presence of high levels of dissociating agents, possibly through citrate-induced removal of MCP nanoclusters from the micelles, or urea- or sodium dodecyl sulfate-induced increases in solvent refractive index, which reduce the extent of light-scattering.

Influence of starter culture on flavor and headspace volatile profiles of fermented whey and whey produced from fermented milk.

Rennet whey and skim milk were compared as media for fermentation by commercial cheese, yogurt, and probiotic starter cultures. Effect of culture, medium, and their interaction on flavor was assessed and compared by sensory descriptive analysis and headspace volatile analysis by proton transfer reaction-mass spectrometry. In general, the aroma of fermented whey was similar to that of whey separated from fermented milk, indicating a favorable possibility of substituting milk with whey in the manufacture of fermented milk-like beverages. Starter culture significantly affected most sensory characteristics of the products. Key volatile compounds for the characteristic flavor of yogurt, such as acetaldehyde and diacetyl, were not significantly affected by medium when fermented with the yogurt culture, and reached similar levels in both systems. Volatile analysis results were consistent with the results of the sensory evaluation, indicating the high reliability of proton transfer reaction-mass spectrometry in detecting important volatile compounds for aroma. Integration of this sensory and chemical information allows a better understanding of how flavor and related compounds are affected by ingredients or processing, which may be useful for the development of value-added whey products.

Sensory characteristics and related volatile flavor compound profiles of different types of whey.

To characterize the flavor of liquid whey, 11 samples of whey representing a wide range of types were sourced from cheese and casein-making procedures, either industrial or from pilot-plant facilities. Whey samples were assessed for flavor by descriptive sensory evaluation and analyzed for headspace volatile composition by proton transfer reaction-mass spectrometry (PTR-MS). The sensory data clearly distinguished between the samples in relation to the processes of manufacture; that is, significant differences were apparent between cheese, rennet, and acid wheys. For Mozzarella and Quarg wheys, in which fermentation progressed to low pH values, the starter cultures used for cheese making had a significant influence on flavor. In comparison, Cheddar and Gouda wheys were described by milk-like flavors, and rennet casein wheys were described by "sweet" (oat-like and "sweet") and thermally induced flavors. The volatile compound data obtained by PTR-MS differentiated the samples as distinctive and reproducible "chemical fingerprints". On applying partial least squares regression to determine relationships between sensory and volatile composition data, sensory characteristics such as "rancid" and cheese-like odors and "caramelized milk," yogurt-like, "sweet," and oat-like flavors were found to be related to the presence and absence of specific volatile compounds.

Randomised, double-blind, placebo-controlled parallel group study of P54FP for the treatment of dogs with osteoarthritis.

P54FP is an extract of Indian and Javanese turmeric, Curcuma domestica and Curcuma xanthorrhiza respectively, which contains a mixture of active ingredients including curcuminoids and essential oils. A randomised, double-blind, placebo-controlled, parallel group clinical trial of P54FP as a treatment for osteoarthritis of the canine elbow or hip was conducted to assess its efficacy and safety. Sixty-one client-owned dogs with osteoarthritis were recruited through first-opinion practices and examined at a single centre. After a two-week wash-out period, they were randomly allocated to receive P54FP or a placebo orally twice daily for eight weeks, and were re-examined after four, six and eight weeks of treatment. The effectiveness of the treatment was assessed in terms of the peak vertical force (PVz) and vertical impulse of the affected limbs, as measured with a force platform, by clinical assessments of lameness and joint pain by the investigators, and overall assessments of the response to treatment by the investigators and the owners. The results from 25 P54FP-treated dogs and 29 placebo-treated dogs showed that there was no statistically significant difference between the groups in terms of the PVz of the affected limb. The investigators' overall assessment showed a statistically significant treatment effect in favour of P54FP (P=0.012), but the owners' assessment just failed to reach statistical significance (P=0.063). No serious adverse effects were recorded, but two P54FP-treated dogs and four placebo-treated dogs were withdrawn from the study because their condition deteriorated.

Influence of transglutaminase treatment on some physico-chemical properties of milk.

Transglutaminase (TGase) is an enzyme that cross-links many proteins, including milk proteins. In this study, the effects of TGase on some physico-chemical properties of milk were studied. TGase-treated milk was not coagulable by rennet, which was due to failure of the primary (enzymic) stage of rennet action rather than the non-enzymic secondary phase. Dissociation of TGase-treated casein micelles by urea or sodium citrate or removal of colloidal calcium phosphate by acidification and dialysis was reduced, presumably due to the formation of cross-links between the caseins. Casein micelles in TGase-treated milks were also resistant to high pressure treatment and to hydrolysis by plasmin. Results of the present study show that milk proteins are fundamentally modified by the action of TGase, which may have applications in the manufacture of functional proteins for use as novel food ingredients.

Effect of transglutaminase on the heat stability of milk: a possible mechanism.

Treatment of milk with transglutaminase (TGase) affects its heat stability, but the manner in which it does so depends on whether or not the milk had been preheated before incubation and on the temperature of preheating. In raw milk, it appears that cross-link formation between the individual caseins is responsible for preventing the dissociation of kappa-casein from the micelles at pH values in the region of minimum stability. In milks preheated before incubation with TGase, denaturation of whey protein may have allowed the formation of cross-links by TGase between denatured whey proteins and the individual caseins which, in combination with cross-linking of the caseins, contributed to greatly improved heat stability at pH > 6.5. It appears from the results of this study that TGase has potential commercial applications as a food-grade additive capable of improving the heat stability of milk.