Osvaldo H. Campanella

Electrophoretic characterization of the protein products formed during heat treatment of whey protein concentrate solutions

Whey protein concentrate (WPC) solutions containing 10, 30, 60 and 120 g dry powder/kg were heated at 75°C and whey protein aggregation was studied by following the changes in the distribution of β-lactoglobulin, α-lactalbumin and bovine serum albumin, using one dimensional and two dimensional PAGE. The one dimensional PAGE results showed that a minimal quantity of large aggregates was formed when 10 g WPC/kg solutions were heated at 75°C for up to 16 min whereas appreciable quantities were formed when 30, 60 and 120 g WPC/kg solutions were similarly treated. The two dimensional PAGE analysis showed that some disulphide-linked β-lactoglobulin dimers were present in heated 10 g WPC/kg solution, but very little was present in heated 120 g WPC/kg solution. By contrast, SDS was able to dissociate monomeric protein from high molecular mass aggregates in heated WPC solution of 120 g/kg but not in 10 g WPC/kg solution heated for 30 min. The rates of loss of native-like and SDS-monomeric β-lactoglobulin, α-lactalbumin and bovine serum albumin during heating increased as the WPC concentration was increased from 10 to 120 g/kg. In 120 g WPC/kg solution heated at 75°C, the amounts of SDS-monomeric β-lactoglobulin in each sample were greater than the quantities of native-like protein. However, in WPC solutions of 10, 30 and 60 g/kg, the differences between the amounts of native-like and SDS-monomeric proteins were slight. The loss of the native-like or SDS-monomeric proteins was consistent with a first or second order reaction. In each case, the apparent reaction rate constant appeared to be concentration-dependent, suggesting a change of aggregation mechanism in the more concentrated solutions. Overall, these results indicate that in addition to disulphide-linked aggregates, hydrophobic aggregates involving β-lactoglobulin, α-lactalbumin and bovine serum albumin were formed in heated WPC solution at high protein concentration, as suggested by model studies using binary mixtures of these proteins.

Thermal aggregation and gelation of bovine β-lactoglobulin

Abstract Heat-induced aggregation and gelation of β-lactoglobulin, dispersed in imidazole-HCl buffer containing 0.1 mol/dm3 NaCl at a concentration of 10% (w/v), was studied at different temperatures and pHs. Gel electrophoresis under non-dissociating (PAGE, in the absence of dissociating and reducing agents) and dissociating but not reducing conditions (SDS-PAGE) was used to determine the extents of aggregation. The rate of loss of β-lactoglobulin from non-dissociating-PAGE was faster than from SDS-PAGE and the rates could be described by second-order kinetics. The loss of protein on heat treatment at 75°C increased as the pH increased from 6.0 to 9.0, under both non-dissociating and dissociating conditions. Dynamic shear measurements were used to determine the development of gel structure by measuring the changes in storage modulus (G′) during heating. No detectable changes in G′ were observed during heating at 70°C. At 75 and 80°C, G′ increased with heating time, the rate of increase being greater at 80°C. The increase in G′ on heat treatment at 75°C was faster at pH 7.0 than at pH 6.0, 8.0 and 9.0. Comparison of the loss of native β-lactoglobulin structure due to the formation of non-covalently linked protein aggregates and covalently cross-linked aggregates with the changes in G′ showed that no measurable changes in G′ occurred until most of the protein had formed covalently cross-linked aggregates. This suggested that protein aggregates are formed as an intermediate prior to the formation of self-supporting macroscopic gel networks.

Thermal gelation and denaturation of bovine β -lactoglobulins A and B

Heat-induced gelation, an important functional property of β -lactoglobulin, was studied by measuring the rheological properties of both the A and B variants of the protein during and after heat treatment within a range of pH, temperature and concentration. Gel electrophoresis was used to determine the extent of denaturation and disulphide bond crosslinking of some samples. Both variants formed gel networks on heating at temperatures > 75 °C, and under most conditions the storage modulus ( G′ ) of β lactoglobulin A gels was higher than the G′ of β -lactoglobulin B gels, in particular after cooling to 25 °C. A minimum protein concentration of 50 g/1 was required for gel formation at pH 7·0 in 0·1 M-NaCl by both variants at 80 °C. Increasing the protein concentration above 50 g/1 increased G′ , the extent of increase being much greater for the A variant than the B variant. G′ of variant A gels was not much influenced by pH whereas G′ of variant B gels decreased slightly from pH 3 to pH 6 and increased between pH 6 and pH 9. When mixtures of the two variants were gelled G′ increased at the temperature of heating (80 °C) and after cooling (25 °C) as the relative quantity of variant A was increased. Comparisons of the loss of discrete protein bands from electrophoretic gels (native-PAGE, SDS-PAGE and SDS-PAGE of reduced samples) showed that heating β -lactoglobulin solutions of 100 g/1 at pH 7 in 0·1 M-NaCl and at 75, 80 and 85 °C caused a faster loss of both native and SDS-soluble β -lactoglobulin A than of β -lactoglobulin B. It was concluded that the loss of native β -lactoglobulin structure from these solutions during heating was faster than the formation of disulphidelinked aggregates, which was faster than gel formation for both β -lactoglobulin A and β -lactoglobulin B, and that each of these reactions was faster for β -lactoglobulin A than for β -lactoglobulin B. This contrasts with conclusions drawn from some previous studies and may arise from the differences in protein concentration between the present study (∼ 100 g/1) and the previous ones (

Streptococcus mutans-derived extracellular matrix in cariogenic oral biofilms

Biofilms are highly structured microbial communities that are enmeshed in a self-produced extracellular matrix. Within the complex oral microbiome, Streptococcus mutans is a major producer of extracellular polymeric substances including exopolysaccharides (EPS), eDNA, and lipoteichoic acid (LTA). EPS produced by S. mutans-derived exoenzymes promote local accumulation of microbes on the teeth, while forming a spatially heterogeneous and diffusion-limiting matrix that protects embedded bacteria. The EPS-rich matrix provides mechanical stability/cohesiveness and facilitates the creation of highly acidic microenvironments, which are critical for the pathogenesis of dental caries. In parallel, S. mutans also releases eDNA and LTA, which can contribute with matrix development. eDNA enhances EPS (glucan) synthesis locally, increasing the adhesion of S. mutans to saliva-coated apatitic surfaces and the assembly of highly cohesive biofilms. eDNA and other extracellular substances, acting in concert with EPS, may impact the functional properties of the matrix and the virulence of cariogenic biofilms. Enhanced understanding about the assembly principles of the matrix may lead to efficacious approaches to control biofilm-related diseases.

A study of the rheological properties of concentrated food emulsions

Abstract The rheological properties of oil-in-water emulsions stabilised by a variety of emulsifiers were investigated at oil phase volume concentrations ranging from 10 to 70%. Most emulsions exhibited Newtonian behaviour at lower oil concentrations and either pseudoplastic or plastic behaviour at higher concentrations. Oil concentrations for all emulsions were normalised using a normalisation factor which was dependent on shear rate. This resulted in shear-independent curves of relative viscosity of emulsion (μr) against normalised oil concentration. These experimental shear-independent curves could be fitted with a mathematical empirical model up to a normalised oil concentration of about 1.2. The model was successfully used to predict viscosities of other emulsion systems reported in the literature. It was also able to predict the rheological behaviour of an emulsion at a given oil concentration provided the flow curve of the same emulsion was known at another oil concentration. A theoretical model based on the increase of the volume of the emulsion globule due to the emulsifier adsorbed on the globule surface and a flocculation ⇆ deflocculation shear-dependent reaction was developed. This yielded an expression practically identical to the empirical model. Parameters of the theoretical model may be used to estimate the degree of aggregation and other microstructural characteristics of emulsions.

High moisture twin-screw extrusion of sago starch: 1. Influence on granule morphology and structure

Abstract Effects of barrel temperature (81–149°C) and screw speed (315–486rpm) on extrusion processing of sago starch in a co-rotating twin-screw extruder under a high moisture system (34–47%) were investigated using response surface methodology. Structural changes were characterised by measuring water solubility index (WSI), water absorption index (WAI), degree of gelatinisation (DG), dextrose equivalent (DE) and high performance size-exclusion chromatography (HPSEC) profiles of the extradates. Thermomechanical processing of sago starch in the twin-screw extruder at the high moisture (34–47%) system led to shearinduced limited degradation and starch phase transitions (a composite melting gelatinisation process). Strong positive correlations between WAI, WSI and DG showed that gelatinisation was the fundamental mechanism in this high moisture system rather than dextrinisation. Processing-induced solubility increased at the expense of water absorption. Low WSI (4.5–18.1%) is ascribed to the presence of structures of either granular crystallite remnants or rearrangement of bonds during extrusion.

Estimating microbial inactivation parameters from survival curves obtained under varying conditions—The linear case

When the isothermal semi-logarithmic survival curves of heat inactivated microbial cells or spores are known to be linear it is possible to calculate their survival parameters from curves obtained under nonisothermal conditions, provided that the temperature history (’profile’) satisfies certain simple mathematical requirements. These requirements have been identified. The concept was tested by retrieving the survival parameters of a Listeria-like organism from generated survival curves for linear and nonlinear heating profiles on which noise had been superimposed. The availability of such a procedure eliminates the need to determine the survival parameters under perfect isothermal conditions, which are difficult to create for technical reasons. It will also enable determination of the survival parameters in the actual medium of interest, which may contain particles or may be too viscous to be treated in a capillary or narrow tube as is currently done. The method can also be used to assess survival parameters in nonthermal inactivation. A treatment with a dissipating chemical agent or anti-microbial is an example. In principle, the concept can be extended to the more general situation where the isothermal or iso-concentration semi-logarithmic survival curves are clearly nonlinear, but this will require a modification of the model and a different numerical calculation procedure.

Improvement of sorghum-wheat composite dough rheological properties and breadmaking quality through zein addition

ABSTRACT Addition of sorghum flour to wheat flour produces marked negative effects on rheological properties of dough and loaf volume. Although there are notable differences in the chemical composition of sorghum proteins (kafirins) compared with wheat gluten that might imply poor functionality in breadmaking systems, a larger constraint may be the unavailability of kafirins due to encapsulation in protein bodies. In this study, zein, the analogous maize prolamin to kafirin, was used to determine the potential effects of protein-body-free prolamins on dough rheology and baking quality of wheat-sorghum composite flour. Mixograms run at 35°C (above the glass transition temperature of zein) were significantly (P < 0.01) improved with addition of zein. Mixogram peak heights increased while mixing time decreased uniformly with addition of zein. Dough extensibility studies showed an increase in maximum tensile stress, while baking studies showed an increase in loaf volume with increasing amounts of added zein. ...

Influence of maize starch granule-associated protein on the rheological properties of starch pastes. Part II. Dynamic measurements of viscoelastic properties of starch pastes

The influence of granule-bound starch synthase (GBSS) on viscoelastic properties of gelatinized starch pastes was studied using a normal, a waxy null, and two GBSS-containing waxy mutant maize starches (waxy protein was synthesized with no GBSS activity). The four starches were isolated using the toluene method (isolation procedure I) (IP I) and were then further purified using an extended period of washing (isolation procedure II) (IP II). Dynamic rheological measurements of IP I gelatinized starches showed that storage moduli (G′) were higher in the two GBSS-containing waxy starches than in the waxy null mutant starch not containing GBSS. The total non-GBSS granule-associated proteins of the three waxy starches were similar. Further removal of granule-associated proteins by purification decreased the G′, with decreases higher in the two GBSS-containing waxy mutants than in the waxy null mutant starch. This was interpreted to be due to the removal of GBSS during purification of the former. High shear broke gelatinized IP I waxy and normal maize starches starch granule or remnant structure, which caused a decrease in G′. Cox–Merz plots showed that the elastic properties of the starch pastes were reduced by removal of starch granule-associated proteins.

Using an In-Line Slit-Die Viscometer to Study the Effects of Extrusion Parameters on Corn Melt Rheology

ABSTRACT An in-line slit-die viscometer (SDV) was used to measure the viscosity of a melt extrudate independently of the extruder operating conditions. The melt produced by extrusion of the corn grits followed a power law rheological model. The viscosity of the melt and extrusion parameters such as specific mechanical energy (SME), torque, and die pressure decreased with increasing moisture content. The degree of starch gelatinization increased when barrel temperature increased from 90 to 130°C. At temperatures higher than 130°C, most of the starch had gelatinized. The increase in barrel temperature, however, resulted in small changes in the apparent viscosity of the melt, until a maximum of ≈130°C. At a constant feed rate, SME increased and torque decreased when screw speed increased due to the shear thinning behavior of the melt. At a constant screw speed, the torque increased and SME decreased with increasing feed rate. This was due to a decrease in apparent viscosity of the melt at higher feed rates. ...