Rennet Casein Research Articles

Influence of pre-gelatinised maize starch on the rheology, microstructure and processing of imitation cheese

Imitation cheeses were manufactured with increasing levels (0–9%, w/w) of pre-gelatinised maize starch in partial replacement of rennet casein. At increased starch levels, longer processing times (10 min at 78 °C using 9%, w/w starch) were necessary compared to the control (5 min) because of the reduced protein present to emulsify/stabilise the fat droplets. Scanning electron and confocal microscopy revealed that increased starch addition resulted in a less homogeneous protein matrix, with a honeycomb appearance although the fat globules remained small and uniformly sized. With increased levels of starch up to 9% (w/w), the storage modulus, peak stress and stress relaxation times significantly increased while hardness values remained unchanged. Results indicated that the inclusion of pre-gelatinised maize starch impaired the hydration of the casein as well as the thermoplastic properties of the imitation cheese and has most application in food products where flow resistance is required, particularly at increased temperatures.

Modification of imitation cheese structure and rheology using pre-gelatinised starches

The rheological properties and microstructure of imitation cheeses containing 3%, w/w, pre-gelatinised maize, waxy-maize, wheat, potato or rice starches were compared to a control (0%, w/w, starch). Dispersions of pre-gelatinised rice or waxy-maize starches with casein had the highest viscosities following heating at 80 °C compared to casein heated alone or in mixtures with the other starches. Imitation cheese products containing pre-gelatinised starches had larger fat globule size distributions (especially rice or waxy-maize starch) and less homogeneous background protein matrices than the control as evidenced by scanning electron microscopy, which indicated poorer fat emulsification. The resultant imitation cheeses were softer, less cohesive and had reduced melting properties compared to the control. During processing, the pre-gelatinised starch competed with the rennet casein for water and impaired the caseins hydration as evidenced visually by delayed emulsification of free oil. Differences in levels of amylose retrogradation may have been responsible for variances in functionality between starches of different origins.

Alteration of imitation cheese structure and melting behaviour with wheat starch

Imitation cheeses were manufactured with increasing levels (0–20%, w/w) of native wheat starch in partial or total replacement of rennet casein protein. With increased addition of native wheat starch up to 9% (w/w), irregular starch particles (sometimes horseshoe-shaped) became more numerous and disruptive of the protein structure. Differential scanning calorimetry showed the presence of a large endothermic peak at 42 °C, corresponding to the melting of the palm oil constituent, and a smaller second endotherm at 79–82 °C with the inclusion of starch at levels of up to 9% (w/w). This smaller endotherm was not present on heating imitation cheese containing 20% (w/w) starch, which had no meltability. Results indicated that the second smaller endotherm corresponded to a phase transition in the casein-continuous matrix facilitating flow behaviour in the imitation cheese network. At concentrations of 3–9% (w/w), wheat starch behaved like a filler material, with limited effects on the rheology of the casein matrix at temperatures below 50 °C, however its inclusion increased the processing time and reduced the meltability of the imitation cheese.

Physicochemical Variables Affecting the Rheology and Microstructure of Rennet Casein Gels

The rheology and microstructure of a rennet casein system were studied in the pH range from 5.8 to 12.0 during cooling from 80 to 5 degrees C at four cooling rates: 0.5, 0.1, 0.05, and 0.025 degrees C/min. A dramatic increase in storage modulus with pH was observed during cooling at a fixed cooling rate. Continuous networks were formed for gels at pH 7.2 and above, while a discontinuous network was observed for gels below pH 6.5. The monotonic increase in storage modulus with pH could be correlated to the number of net (negative) charges and the strength of the hydrophobic interactions. At a higher pH, the protein micelles were larger due to weaker hydrophobic interactions and stronger repulsive electrostatic interactions resulting from more charges. When these protein micelles aggregated into flocs during cooling, the flocs had similar sizes at different pH values but a smaller fractal dimension at a higher pH. Consequently, for systems of the same protein and salt concentrations, more flocs were present in the gels at a higher pH, which subsequently generated more cross-links and a higher storage modulus. The pH also determined how the cooling rate affected the gel properties. At pH 5.8 and 6.5, the gels were firmest at the fastest cooling schedule, and the cooling rate did not show a trend in affecting the gel strength at the other three rates. On the other hand, a slower cooling rate generated a firmer gel at pH 7.2 and 12.0. The analysis of casein interactions suggests that the cooling rate affected the casein floc size only when repulsive interactions enabled a slow flocculation (at higher pH values) comparable with temperature change rates during cooling. For rennet casein gels of pH within the range of processed cheese products (pH 5.8 and 6.5), particle or cluster rearrangements created more uniform networks for gels cooled at slower schedules and weakened the structure.

Influence of processing parameters on the texture and microstructure of imitation cheese

In this study the impact of cooker design and/or blade/auger speed on the functional properties of imitation cheese was investigated. Cheeses with similar compositions (48% moisture) were manufactured using water, rennet casein, rapeseed and hydrogenated palm oil and emulsifying salts in a twin-screw (Blentech) or a single-blade cooker (Stephan). The cookers were operated at auger speeds of 750, 1,125 or 1,500 (Stephan) or 100 or 200 rpm (Blentech). Increasing the blade speed of the Stephan increased (P < 0.001) the hardness and decreased the meltability of imitation cheese from 112 to 66 mm respectively. Hardness and meltability values of cheeses made in the Blentech cooker were only slightly affected by auger speed. The cheese made in the Stephan at 1,500 rpm had the highest G′ and G′′ values at 25 °C of all the cheeses. This study shows that imitation cheese with acceptable functional properties can be successfully manufactured in a single-blade cooker operated at moderate speeds.

Relationship between the glass transition temperature and the melt flow behavior for gluten, casein and soya

The effects of moisture content (25–45% wwb) and temperature (75–120 °C) on the viscosity of gluten, soya and rennet casein systems was studied using a capillary rheometer. An attempt was made to relate the viscosities to the glass transition temperature measured by differential scanning calorimetry, dynamic mechanical thermal analysis and the phase transition analyzer. The temperature where the material flowed was also determined by the latter technique. All three-protein systems showed shear and extension thinning. Over the shear rate range investigated (∼1–10 3 s −1), gluten had a substantially lower viscosity than the other two proteins, although the difference was less pronounced at the highest temperature studied. This low viscosity is reflected by lower values of the glass transition temperature, the melt flow temperature and the dynamic moduli E′ and E″ in the rubbery state. The results are discussed in terms of the structure and heat induced changes for the three proteins and their relevance to food processing considered.

Comparison of capillary electrophoresis and isoelectric focusing for analysis of casein/caseinate addition in processed cheeses

Capillary electrophoresis (CE) and immobilized pH gradient isoelectric focusing were applied for the determination of the addition of isoelectric casein, rennet casein and sodium caseinate to processed cheeses of known composition containing different dairy products. Both methods allowed the determination of these protein ingredients by analysing the intact κ-CN. The comparison of the quantitative determination by both techniques demonstrated that they presented similar recoveries for isoelectric casein, but for sodium caseinate, a considerably better recovery was obtained by using the isoelectric focusing method (85.6% versus 47.2%). However, CE showed higher precision. CE was applied for the determination of the addition of rennet casein by the use of a calibration curve calculated by plotting the peak area ratio ∑ β-CN A/para- κ-CN in the electropherograms versus the content of rennet casein of known composition cheeses from the same manufacture batch. This approach gave recoveries of added rennet casein between 94% and 102%.

A method for the large-scale isolation of β-casein

A method for the large-scale isolation of β-casein from renneted skim milk was developed. The curd from renneted skim milk was dispersed in hot (⩾70 °C) water to inactivate residual chymosin. The heated curd was subsequently recovered by centrifugation, resuspended in water and incubated at 5 °C, during which β-casein dissociated from the curd; the suspension was centrifuged and the aqueous phase lyophilised. The isolated protein consisted mainly of β-casein, containing a minor amount of γ-caseins and traces of other caseins. Unless chymosin was fully inactivated by heating, some β-casein was hydrolysed at the Leu 192–Tyr 193 bond. The yield of β-casein increased with incubation time, up to ∼20% of the β-casein present in the milk after 24 h at 5 °C. Reducing milk pH to 5.5 or 6.0, prior to renneting, caused a high level of contamination with α s-caseins. This isolation procedure can be easily scaled-up to an industrial process and the β-casein-depleted curd may be used for the manufacture of rennet casein or processed cheese.

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.

Cooling effects on a model rennet casein gel system: part I. Rheological characterization.

The gelation of a model rennet casein system was studied during cooling at different rates. During cooling, casein network structure development was proposed to evolve over a few steps at different length scales: molecules, particles, flocs, or network. Rennet casein flocs are fractal in nature, and fractal dimension and floc size are two variables affecting the rheology and microstructure of a rennet casein gel. Casein structure formation during cooling from 80 to 5 degrees C at four different rates (0.5, 0.1, 0.05, and 0.025 degrees C/min) was monitored by dynamic rheological tests, and a stronger gel developed at a slower cooling rate. During different cooling schedules, similar fractal dimensions were observed due to a lack of difference in the colloidal interactions. Differences among rheological data were possibly caused by variability in floc size, as observed in the second part of this paper. A larger number of smaller-sized flocs enabled gelation at a higher temperature and created a stronger network at a slower cooling rate. Controlling cooling schemes thus provides an approach for manipulating casein gelation and the microstructure for a system of fixed chemical compositions.

Cooling effects on a model rennet casein gel system: part II. Permeability and microscopy.

Microscopy and permeability studies were performed to further illustrate the cooling effects on rennet casein gel structure and help interpret the rheological observations in the first part of this paper. Samples of gels cooled from 80 to 5 degrees C at four rates (0.5, 0.1, 0.05, and 0.025 degrees C/min) were studied with a confocal laser scanning microscope. A larger number of smaller flocs were generated at slower cooling rates, creating more cross-links within a network and corresponding to a stronger gel. Formation of a larger number of smaller flocs was hypothesized to result from a greater degree of doublet formation because the system spent more time within the temperature region where doublet formation is favored when cooled at slower rates. The doublets represent sites available for floc growth, similar to nucleation sites for crystal growth. Microscopy results further substantiated that the cooling effects were different from the aging effects because cooling affected floc size, and aging enabled the addition of idle flocs into the casein network. The conclusions for the cooling effects on floc size were further supported by permeability tests. A smaller permeability coefficient resulted from smaller flocs obtained with a slower cooling schedule. This study showed the importance of controlling floc numbers to modulate the strength of a gel, and cooling rates provide an approach of modulating functional properties when the chemical composition of a system is fixed.

Kinetics of rennet casein gelation at different cooling rates.

A mathematical model was developed to quantitatively analyze the rheological data of rennet casein gelation at different cooling rates. Kinetic parameters were estimated and correlated with the microstructure development of the protein network. The kinetic model identified structure development upon cooling to be first order, and the network forming energies were estimated for four protein concentrations cooled at four rates. A lower energy for network formation was observed for a slower cooling rate and a higher protein concentration. This observation resulted from the availability of more flocs at a slower cooling rate and a higher casein concentration, simplifying floc cross-linking. By analyzing the kinetics during the aging process of casein gels, no difference in the reaction mechanism was observed. This study illustrated that structure formation resulted from the addition of flocs into the protein network: not all flocs were part of the network at a defined gel point. The incubation period following cooling integrated idle flocs into the network, thereby strengthening the gel. By understanding the gelation mechanism during cooling of rennet casein gels, the structure and thus quality of dairy products, such as processed cheese, may be better controlled.

The influence of moisture content on the rheological properties of processed cheese spreads

SummaryModel processed cheese spreads were prepared from rennet casein, sunflower oil, water and a trisodium citrate/citric acid chelating salt system. The samples were cooked using a laboratory‐scale processed cheese cooker. The moisture content of the samples varied from 49.1 to 55.6%. The samples were characterized by dynamic rheology, rotational viscometry and fat particle size analysis. With increasing moisture content, the rheological behaviour of the samples changed from solid‐like (concentrated solution) to liquid‐like (dilute solution). The moduli decreased and the frequencies at which G′‐G′′ crossed over increased with increasing moisture content. Increasing moisture content resulted in an increase in pH and increase in the volume‐to‐surface diameter of the fat droplets. Rotational viscometry indicated that all the samples were shear thinning. The flow curves fitted a power law relationship (r2 = 0.993). Thixotropic behaviour was displayed by all samples except those above 54% moisture. The shear stress at any particular shear rate increased with decreasing moisture content, indicating a stronger network structure in the low moisture samples.

Glass and polymeric membrane electrodes for the measurement of pH in milk and cheese

While there is a considerable interest in the food industry in determining various analytes using ion-selective electrodes (ISEs), only few reports describe their use for direct measurements in food. In this study, the suitability of glass electrodes and ionophore-based solvent polymeric ISEs for the determination of pH in Process cheese, Cheddar cheese and milk was investigated. The liquid junction potential between a 3 M KCl bridge electrolyte and diluted as well as undiluted Process cheese was found to be negligible. Reference electrodes with ceramic plug and sleeve-type junctions performed well, although precautions needed to be taken to prevent plugging at the junctions. While the protein rennet casein posed no problems in pH measurements, the extraction of neutral lipophilic compounds or hydrophobic peptides into solvent polymeric membranes was evident, resulting in some loss of selectivity for monovalent cations upon exposure to cheese. However, it was found that ISEs based on tridodecylamine (R 3N) as ionophore and o-nitrophenyl octyl ether (oNPOE) as plasticizer can be used to accurately measure the pH of milk and, after desensitization of the electrodes in a cheese emulsion, of diluted Process cheese. Since pH measurements with a glass electrode showed that emulsions of cheese moderately diluted to a cheese content of 70% have the same pH as undiluted cheeses, it is possible to determine the pH in cheese with ionophore-based ISEs. R 3N membranes also performed well in undiluted milk.

Characteristic aroma components of rennet casein.

Rennet casein, produced by enzymatic (rennet) precipitation of casein from pasteurized skim milk, is used in both industrial (technical) and food applications. The flavor of rennet casein powder is an important quality parameter; however, the product often contains an odor described as like that of animal/wet dog. Two commercial rennet casein powders were evaluated to determine the compounds responsible for the typical odor. Aroma extracts were prepared by high-vacuum distillation of direct solvent (ether) extracts and analyzed by gas chromatography-olfactometry (GCO), aroma extract dilution analysis (AEDA), and GC-mass spectrometry (MS). Odorants detected by GCO were typical of those previously reported in skim milk powders and consisted mainly of short-chain volatile acids, phenolic compounds, lactones, and furanones. Results of AEDA indicated o-aminoacetophenone to be a potent odorant; however, sensory descriptive sensory analysis of model aroma systems revealed that the typical odor of rennet casein was principally caused by hexanoic acid, indole, guaiacol, and p-cresol.

Biscoitos tipo "cookie" e "snack" enriquecidos, respectivamente com caseína obtida por coagulação enzimática e caseinato de sódio

The objective of the present work was the formulation and characterization, chemical, nutritional and sensorial, of two types of biscuits, cookie and snack, using rennet casein and sodium caseinate for cookies and snacks enrichment, respectively. The cookie type biscuit presented higher contents of moisture, protein, and total fiber than the snack type which was richer in fat and salt. As to essential minerals the cookies were richer than the snacks, except for sodium and phosphorous which were higher in the snacks. The amino acid profile was more adequate in the cookie than in the snack type. Except for true digestibility the protein value indexes were higher for the cookies. Acceptability of the two types of biscuits was tested for athlets of both sexes related to overall acceptability, surface color, odor, taste, crispness and hardness. Acceptability rated 98% for the snacks and 81% for the cookies. cookies and snacks had the same acceptability for both men and women but the snacks had higher acceptability by men (52.7%) against 37.8% by the women. Microbiological analysis revealed an acceptable profile for both types of biscuit.

Influence of drier inlet temperature during pilot‐scale manufacture of rennet casein on the hydration behaviour of the rennet casein in disodium orthophosphate solution

Rennet casein curds were dried in a pilot‐scale fluidized bed drier at air‐inlet temperatures of 80, 90, 110, 120 or 140°C. As the drier air‐inlet temperature was increased, there was a significant increase in hydration time and a significant decrease in hydrated viscosity and viscosity stability following hydration of the dried rennet caseins in 0.4% (w/w) disodium orthophosphate (DSP). The influence of air‐inlet temperature during drying on composition, the extent of Maillard reaction, the resolution of the proteins on urea–polyacrylamide gel electrophoresis (PAGE) and cation‐exchange fast protein liquid chromatography (FPLC), the dialysability of calcium and phosphorous from a 6 m urea dispersion at pH 4.6, and the particle‐size parameters of milled rennet caseins were determined. Relationships between all these latter parameters and the hydration behaviours of the rennet caseins in DSP solution were also studied. Results suggest that the increase in drier air‐inlet temperature resulted in a reduction in the mean particle size of milled casein, which was significantly correlated to the changes in hydration behaviour. Hydration times increased significantly and hydrated viscosities decreased significantly with increasing levels of fluorescent Maillard reaction products (MRPs) and with increasing levels of nondialysable calcium and phosphorous in the caseins. It appears that the increase in air‐inlet temperature during drying reduced the solubility of colloidal calcium phosphate (CCP), possibly through binding of CCP to the increased levels of MRPs. This change in CCP solubility led to increased difficulty in sequestering CCP from the curd when the pilot‐scale rennet caseins were dispersed in the DSP solution, leading to the changes in hydration behaviour.

The effect of cooking and washing temperature during pilot‐scale rennet casein manufacture on casein hydration characteristics in disodium orthophosphate solution

Variations were observed in the hydration behaviour of rennet caseins in a solution (0.4%, w/w) of disodium orthophosphate (DSP). These caseins were manufactured on a pilot scale from curds cooked at 45, 65 or 75°C and from curds washed at a hot‐wash temperature of 60, 70, 78 or 86°C. The influence of cooking temperature and hot‐wash temperature on various compositional characteristics, the electrophoretic resolution and particle size parameters of the milled rennet caseins were determined. Relationships between all of these parameters and hydration characteristics in DSP solution were also investigated. Cooking temperature or hot‐wash temperature did not influence electrophoretic resolution, the level of Maillard reaction compounds or the particle size parameters of the caseins. Increasing the cooking temperature increased whey protein levels and decreased calcium levels in the curd, leading to slower hydration rates. This suggested that increased whey protein denaturation and its precipitation onto the rennet casein curd retarded subsequent rennet casein hydration. Hot‐wash temperature influenced certain aspects of rennet casein hydration in 0.4% (w/w) DSP; however, the hydration characteristics of these caseins did not appear to be related to any of the other characteristics investigated.

The influence of high temperatures on milk proteins

High temperatures Induce certain changes in milk constituents, but the degree of these changes depends on both the temperature and time of heat treatment. The most pronounced changes take place in milk proteins. The forewarming of milk causes an increase in acidity, the precipitation of soluble Ca-phosphate, whey protein denaturation and coagulation, as well as the interaction with casein micelles, the Maillard browning reaction, the dephosphorylation of casein, the hydrolysis of casein micelles, changes in whey proteins, an extension of the rennet coagulation time and an exchange of the rheological properties of the acid and rennet casein gels, changes in the zeta-potential and casein micelle hydration, the interaction between the milk proteins and proteins of milk fat globule membrane.

Small Strain Oscillatory Shear and Microstructural Analyses of a Model Processed Cheese

The rheological and microstructural properties of a model processed cheese were investigated. The cheese contained 20% protein (rennet casein), 27% anhydrous milk fat, 1.5% NaCl and 1 to 3% Na2HPO4 (DSP). Processing time (10, 20, or 30min), DSP (1, 2, or 3%) and pH of the DSP-NaCl solution (5.4, 5.6, or 5.8) were adjusted to alter rheological properties.Small-strain oscillatory shear rheological parameters that correlated with transitions previously observed by large-strain (fracture) properties were moduli at 8°C and changes in moduli with cooling from 80 to 25°C. Mechanical spectra at 80°C indicated cheeses containing less than 2.0% DSP were entangled macromolecular dispersions, and those containing more than 2.0% DSP were gels. A compilation of small strain results suggested samples could be divided into three basic rheological states.A model describing the gel network is proposed based on the results of this investigation and large-strain (fracture) rheological properties. The model was based on increased breakdown of para-casein aggregates into amphiphilic molecules and rheological properties being related to the combination of para-casein aggregates and amphiphilic molecules.