Interactive Effects of Milk Fat Globule and Casein Micelle Size on the Renneting Properties of Milk (original) (raw)
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Gelation properties of partially renneted milk
International Journal of Food Properties, 2017
Acid-and rennet-induced gelation properties of milk with modified casein micelles, produced by partial renneting at 4 o C for 15 min, followed by inactivation of enzymes by heat at 60 o C/3 min (referred as low heat treatment milk) and 85 o C/30 min (high heat treatment milk), were investigated to provide a mechanistic understanding of gel formation from partially renneted milk. Acidification of low heat treatment milk gave firmer gel quality, this was reflected by its high elastic modulus (G′) and hardness. In addition, the high heating condition for enzyme inactivation of high heat treatment milk alone increased the elastic modulus of both the control and renneted milk samples. Gel development of the two milk types (low heat treatment and high heat treatment milks) was different. In contrast with acid gelation, rennet-induced gelation of partially pre-rennet treated milk had no impact on the elastic modulus of low heat treatment milk and the rennet gels were very weak. Similarly, the addition of rennet to pre-rennet treated high heat treatment milk did not produce "true gels," most likely due to the effect of the heat treatment on impairing the rennet coagulation. The findings in this study confirmed that pre-rennet treated milk had positive effects on the end-product acid gels of low heat treatment and high heat treatment milk.
Rheology and Microstructures of Rennet Gels From Differently Heated Goat Milk
Foods, 2020
Rennet coagulation of goat milk heated to 65 °C/30 min (Gc), 80 °C/5 min (G8) and 90 °C/5 min (G9) was studied. A rheometer equipped with a vane geometry tool was used to measure milk coagulation parameters and viscoelastic properties of rennet gels. Yield parameters: curd yield, laboratory curd yield and curd yield efficiency were measured and calculated. Scanning electron microscopy of rennet gels was conducted. Storage moduli (G’) of gels at the moment of cutting were 19.9 ± 1.71 Pa (Gc), 11.9 ± 1.96 Pa (G8) and 7.3 ± 1.46 Pa (G9). Aggregation rate and curd firmness decreased with the increase of milk heating temperature, while coagulation time did not change significantly. High heat treatment of goat milk had a significant effect on both laboratory curd yield and curd yield. However, laboratory curd yield (27.7 ± 1.84%) of the G9 treatment was unreasonably high compared to curd yield (15.4 ± 0.60%). The microstructure of G9 was notably different compared to Gc and G8, with a denser and more compact microstructure, smaller paracasein micelles and void spaces in a form of cracks indicating weaker cross links. The findings of this study might serve as the bases for the development of different cheese types produced from high-heat-treated goat milk.
Journal of Dairy Research, 2009
Rheological and microstructural properties of rennet-induced milk gels containing different fat globules were studied. Recombined milks were prepared by mixing reconstituted low-heat skim milk powder and anhydrous milk fat emulsified with reconstituted skim milk powder (SMP), sodium caseinate (NaCas), whey protein isolate (WPI) or Tween 20. Final elastic modulus of the rennet gels containing WPI- or Tween 20-stabilized fat globules showed significantly lower values compared with those prepared with SMP-emulsified fat globules. SMP-stabilized fat globules interacted with the continuous casein network reinforcing the gel structure. Confocal micrographs supported the rheological data revealing that gels containing SMP-stabilized fat globules formed a tighter network relative to other treatments. Microscopy images also showed some degree of droplet flocculation in the case of gels containing WPI- or Tween 20-stabilized fat globules, and this was most likely the cause of the increase of ...
Partial renneting of pasteurised bovine milk: Casein micelle size, heat and storage stability
Food Research International, 2016
The effects of partial renneting at low temperature on the casein micelle (CM) size and the storage stability of milk were investigated. Low chymosin concentrations (<0.03 IMCU mL-1) was applied to pasteurised skim milk at 4 o C and enzyme activity was terminated by thermal application at 60 o C/3 min and 85 o C/30 min, referred to as low heat (LHT) and high heat (HHT) treatment milk, respectively. The addition of rennet with concentrations of 0.01, 0.02 and 0.03 IMCU mL-1 for 15 minutes resulted in κ-casein hydrolysis of 10, 20 and 25%, respectively. Moreover, mean CM size of milk was reduced by up to 10 nm. For LHT milk, the renneted micelles appeared to be stable for up to 17 days, especially in response to the application of 0.01 IMCU mL-1 and at a storage temperature of 4 o C. Severe heating at 85 o C/30 min to inactivate the enzyme caused an increase in CM size.
Dairy Science & Technology, 2010
The present study investigated the renneting behaviour of casein micelles as influenced by the presence of fat globules. The gelation of skim milk, homogenized milk and homogenized milk with Tween 20 added was observed using diffusing wave spectroscopy and rheology. By adding Tween 20 to homogenized milk, it was possible to displace most of the milk protein from the oil/water interface and create a system with the same colloidal attributes as homogenized milk but with oil droplets with a very different interfacial composition, and relatively inert during rennetinduced aggregation. The primary phase of gelation was faster in homogenized milk compared to skim milk. Casein micelles were altered by the homogenization process which spreads them at the interface, making κ-casein more readily available. The addition of Tween 20 did not further affect the enzymatic activity on the micelles. However, the onset of gelation occurred earlier in homogenized milk with Tween 20 added, as the micelles aggregated at a lower level of proteolysis compared to homogenized milk. This work clearly showed that the gels formed in homogenized milk with and without Tween 20 have different physico-chemical properties, because of the different colloidal state of the filler particles.
Journal of Dairy Science, 2007
The effect of fortifying reconstituted skim milk with increasing levels of the β-lactoglobulin (β-LG) genetic variants A, B, and an A-B mixture on rennet-induced gelation was studied by small deformation-sensitive rheology. Free-zone capillary electrophoresis and highsensitivity oscillatory rheology were used to elucidate the role of potential heterotypic associative interactions between whey proteins and casein in a mixed colloidal system, subjected to moderate heating (65°C for 30 min) prior to renneting, on the gelling properties of the system. Increasing levels of added whey protein, in the concentration range of 0.225 to 1.35% of added protein, led to a concomitant progressive increase in the equilibrium shear storage modulus, G′ (recorded after ∼10,800 s), in the order β-LG B > β-LG A and β-LG A-B, as the general expected consequence of the setup of denser casein gel networks. The preferential effect of β-LG B over β-LG A on the mechanical strength of the gels may be due to the formation of cross-links and aggregates involving whey proteins and rennet hydrolysis products or an increase in the size of the casein micelle caused by the grafting of β-LG B to its surface, or both. The results of free-zone capillary electrophoresis were consistent with the notion that β-LG B (and not β-LG A) binds to the casein micelle under an optimal stoichiometry of 1:0.045 (mg/mg), even in the absence of heat treatment. The liquid-like character of the gel networks formed, tan δ, was a parameter sensitive to the level of addition of β-LG A in particular. At low concentrations (up to 0.45%) of β-LG A, tan δ increased by almost twice as much, which was interpreted as a result of the increase in the loss modulus, G″, of the sol fraction because of the presence of unbound β-LG A. At greater incremental concentrations of β-LG (>0.45%), the formation of smaller whey protein aggregates confined to 582 the sol fraction may have led to a progressive decrease in tan δ. The critical gel time, t gel , was also affected by the concentration of added whey protein and described 3 zones of behavior, irrespective of the type of whey protein variant. The critical gel time was slightly shorter for β-LG B than for β-LG A at 0.45% of added whey protein, but this difference became larger at 0.67%. Even when only β-LG B was found to associate with casein prior to renneting, both β-LG A and β-LG B, either alone or mixed, had a profound influence on the mechanical strength and coagulation kinetics of the rennet-induced casein gels. This knowledge is expected to be useful to exert better control and optimize processing conditions during the manufacturing of cheese and cheese analogs.
International Dairy Journal, 2010
Samples of raw skim milk, ultrafiltration/diafiltration retentate, concentrated retentate and milk protein concentrate powder (MPC80) from a single commercial production run were analysed using photon correlation spectroscopy. Measurements revealed insignificant differences in casein micelle size between the samples. In addition, there was no discernable difference between raw skim milk and MPC powder dissolved at 60 C in the amount of casein remaining in supernatants from centrifugation at either 25,000 Â g or 174,200 Â g. Casein micelles did not appear to be altered during manufacture of MPC. The rennet gelation behaviour of reconstituted MPC was compared with raw skim milk. Reconstituted MPC did not coagulate unless supplemented with approximately 2 mM calcium chloride, which was attributed to the mineral removal during ultrafiltration/diafiltration. Addition of sufficient calcium could restore rennet coagulation kinetics and gel strength of reconstituted MPC to approximately that of raw skim milk.
Gelation Properties of Milk Concentrated by Different Techniques
International Dairy Journal, 1998
The rheological properties of three different concentrated yoghurts (&23% total solids, pH 4.0) and a standard yoghurt (&16% total solids, pH 4.3) were determined during incubation and storage. The high solids yoghurts were manufactured from milks concentrated by ultrafiltration (UF) to 9% protein, by reverse osmosis (RO) to &6.8% protein and by direct reconstitution of full-fat milk powder to &6.4% protein; the standard product contained &4.3% protein. Development of the gel structures during incubation was monitored discontinuously using a stress-controlled oscillatory dynamic rheometer. The complex modulus (G*) and loss tangent (tan) were measured as functions of amplitude (torque range 10\-10\ mNm at 0.25 Hz). In the RO-and direct reconstitution yoghurts, a typical pattern of gelation was observed, with the initial viscous nature of the milk being modified by rapid development of a gel structure and, finally, a 'stationary phase' with respect to rheological changes. However, the complex modulus (G*) of the higher protein system (UF-milk) continued to increase with time, i.e., further development of the gel structure occurred during storage. The relative rates of gel development were dependent on protein content.
Effects of Mineral Salts and Calcium Chelating Agents on the Gelation of Renneted Skim Milk
Journal of Dairy Science, 2001
The effects of adding CaCl 2 , orthophosphate, citrate, EDTA, or a mixture of these, to reconstituted skim milk (90 g of solids/kg solution) on the gelation of renneted milk were mediated by changes in Ca 2+ activity and the casein micelle. At pH 6.65, the addition of citrate or EDTA, which removed more than 33% of the original colloidal calcium phosphate with the accompanying release of 20% casein from the micelle, completely inhibited gelation. Reformation of the depleted colloidal calcium phosphate and casein in the micelle, by the addition of CaCl 2 , removed this inhibition. When the minimum requirements for colloidal calcium phosphate and casein in the micelle were met, the coagulation time decreased with increasing Ca 2+ activity, leveling off at high Ca 2+ activity. The storage modulus of renneted gels, measured at 3 h, increased with increasing colloidal calcium phosphate content of micelles up to a level at which it was ∼130% of the original colloidal calcium phosphate in the micelles. Further increases in colloidal calcium phosphate by the addition of CaCl 2 , orthophosphate, or mixtures of these, which did not change the proportion of casein in the micelle, decreased the storage modulus. The gelation of the renneted milk was influenced by Ca 2+ activity, the amounts of colloidal calcium phosphate, and casein within the micelle, with the effects of colloidal calcium phosphate and casein within the micelle clearly dominating the storage modulus. These results are consistent with the model of Horne (Int. Dairy J. 8:171-177, 1998) which postulates that, following cleavage of the stabilizing κcasein hairs by rennet, the properties of the rennet gel are determined by the balance between the electrostatic and hydrophobic forces between casein micelles.
An original pH-reversible treatment of milk to improve rennet gelation
International Dairy Journal, 2004
The ability of an original pH-reversible treatment of milk to improve rennet gelation was evaluated by rheological measurements on reconstituted skim milk supplemented or not with casein. Samples were acidified at 4 C to pH 5.10 by injection of CO 2 in a laboratory pilot plant (pressure less than 2 MPa) and then depressurised under vacuum. Depressurisation induced the pH to return to its initial value (6.6570.02) and restored the mineral and protein partition of milk as well as the water solvation, the size diameter and the zeta potential of the casein micelles. After rennet addition, CO 2-treated milk showed a decrease of the rennet clotting time and an increase of the firming rate compared with a non-treated sample. Moreover, this treatment had a positive effect on the release of glycomacropeptide during enzymatic gelation, suggesting that the rennet accessibility of k-casein was greater in the CO 2-treated than in the non-treated sample. The pH-reversible CO 2 acidification greatly activated the rennet gelation of casein-supplemented milk. Indeed, without this treatment, no clotting was observed even 300 min after rennet addition. Therefore, this CO 2 treatment might involve modification of the micellar surface properties in favour of rennet gelation.