Magesh Srinivasan - Academia.edu (original) (raw)

Papers by Magesh Srinivasan

The main objective of this study was to gain a better understanding of the formation, stability a... more The main objective of this study was to gain a better understanding of the formation, stability and microstructure of oil-in-water emulsions stabi l ized by commercial sodium (ALANATE 1 80) and calcium caseinates (ALANATE 380) . The study also determined the effects of heat treatment and NaCI addition on the formation and stability of these emulsions. Emulsions were prepared using various concentrations of sodium or calcium caseinate solutions (0.5 to 5.0%) and 30% soya oil . Surface protein coverage (mg/m2) in freshly prepared emulsions was determined from analysis of the aqueous phase after centrifugation of emulsions at 45,000 g for 40 minutes, using the Kjeldahl method. SOS-PAGE was used to identify the adsorbed protein components in the cream phase. Creaming stability was determined after storage of emulsions for 24 hours at 20°C by a low speed centrifugation method. The microstructure of these emulsions was determined using confocal laser scanning microscopy. The aggregation s...

The main objectives of this study were to determine the influence of compositional and processing... more The main objectives of this study were to determine the influence of compositional and processing parameters on: (i) the protein surface coverage and protein surface composition and (ii) the creaming stability, for emulsions stabilized by sodium caseinate. Emulsions were usually prepared from 2.5% (w /w) protein solution and 30% soya oil. In some cases, emulsions were made with varying concentrations of caseinate or soya oil. The mixture was usually homogenized at 102/34 bar at ssac and in some cases the mixture was homogenized at varying pressures. Surface coverage of protein in freshly prepared emulsions was determined from analysis of the aqueous phase, using Kjeldahl. SDS-PAGE was used to identify the unadsorbed protein components in the aqueous phase. As t.L~e concentration of caseinate was increased from 0.5 to 7.5% (w /w) the protein load increased; the protein load attained a plateau value of 1.3 mg/m 2 when the caseinate concentration was in the range 2-4% (w /w). Further increases in caseinate concentration markedly increased the protein load with a value of 3.55 mg/m 2 at 7.5% caseinate concentration. At low concentrations of caseinate (below 2%), [3-casein adsorbed at the surface of oil droplets in preference to other caseins while at higher concentrations of caseinate, no distinct preference of any caseins was observed. As the fat concentration was increased from 5 to 20% (w /w), the protein load decreased from-9.9 to 3.7 mg/m 2 , but further increases in fat concentration caused only slight decreases in the protein load. At high fat concentration (50%) ~-casein was adsorbed in preference to other caseins.

Journal of Food Science, 2001

Creaming stability of emulsions formed with calcium caseinate, determined after storage of emulsi... more Creaming stability of emulsions formed with calcium caseinate, determined after storage of emulsions at 20 °C for 24 h, increased gradually with an increase in protein concentration from 0.5% to 2.0%; further increases in caseinate concentration had much less effect. In contrast, the creaming stability of sodium caseinate emulsions showed a decreased with an increase in protein concentration from 0.5% to 3.0%. Confocal laser micrographs of emulsions formed with >2% sodium caseinate showed extensive flocculation of oil droplets with the appearance of a network structure. However, emulsions formed with calcium caseinate or emulsions formed with low concentrations of sodium caseinate (0.5% and 1.0%) were homogenous with no sign of flocculation.

Journal of Agricultural and Food Chemistry, 2000

A range of sodium caseinate samples were characterized by a multiangle laser light scattering (MA... more A range of sodium caseinate samples were characterized by a multiangle laser light scattering (MALLS) system or by the use of MALLS as an on-line detector with size-exclusion chromatography (SEC). Sodium caseinate solutions, analyzed using a MALLS system alone, gave weight-average molar mass (M w) values in the range 1200-4700 kDa and z-average root-mean-square radius (R g) values ranged from ∼50 to 120 nm. When these solutions were ultracentrifuged at 90000g for 1 h, a cloudy top layer was formed; the subnatant was carefully removed and analyzed by SEC-MALLS. The M w values were found to be in the range ∼30-575 kDa, and R g values ranged from ∼22 to 49 nm. During SEC, the MALLS system detected some very large-sized material that eluted close to the void volume; this material was hardly detected by the concentration detectors, i.e., ultraviolet (UV) and differential refractive index (DRI). The intensity of the light scattering (LS) signal from this very large sized material was greatly reduced in the subnatant. SEC of sodium caseinate samples revealed two main peaks with M w of ∼420-750 kDa and 39-69 kDa, respectively. The R g values were very large for a protein molecule, and initial calculations suggested that the shape of caseinate molecules was likely to be highly elongated.

Journal of Agricultural and Food Chemistry, 1996

International Dairy Journal, 1999

Adsorption behaviour of commercial sodium and calcium caseinates at the oil droplet surface in 30... more Adsorption behaviour of commercial sodium and calcium caseinates at the oil droplet surface in 30% (w/w) soya oil-in-water emulsions has been studied. The concentration of caseinate in the aqueous phase was varied from 0.5 to 5.0% (w/w). Size distribution of sodium caseinate emulsions appeared monomodal and showed no change with protein concentration. In contrast, a bimodal size distribution was obtained for calcium caseinate emulsions at low-caseinate concentrations, indicating #occulation of oil droplets. In sodium caseinate emulsions, the surface protein load increased as caseinate concentration in the aqueous phase was increased from 0.5 to 4.0%, but it levelled o! at higher concentrations. However, surface protein loads in calcium caseinate emulsion increased gradually with caseinate concentration in the aqueous phase. In general, surface protein loads were higher in calcium caseinate emulsions than in sodium caseinate emulsions. In sodium caseinate emulsions,-casein was adsorbed preferentially at caseinate concentrations below 1% but no distinct preference of any caseins was observed at higher concentrations. By contrast, in calcium caseinate emulsions-caseins appeared to be adsorbed preferentially at all caseinate concentrations used. These results are discussed in relation to the adsorption behaviour observed in emulsion systems.

Food Hydrocolloids, 2000

Studies have been made of changes in particle sizes, surface coverage and composition, and stabil... more Studies have been made of changes in particle sizes, surface coverage and composition, and stability of emulsions formed with soya oil and sodium caseinate. Different concentrations of NaCl (0-1000 mM) were added before and after homogenization. Addition of NaCl before and after homogenization had no significant effect on average size of emulsion droplets in all emulsion systems studied. In emulsions made with 1 or 3% (w/w) caseinate, addition of NaCl up to 40 mM resulted in an increase in surface protein concentration (mg/m 2) which appeared to be due largely to the enhanced adsorption of a s1-casein at the droplet surface, particularly in emulsions formed with 1% caseinate. Emulsion formed with 3% caseinate in the absence of NaCl showed extensive flocculation of emulsion droplets that resulted in very low creaming stability. Addition of NaCl up to 200 mM decreased the extent of flocculation and improved the creaming stability.

Food Hydrocolloids, 2002

Oil-in-water emulsions containing 30% soya oil and various concentrations of sodium caseinate wer... more Oil-in-water emulsions containing 30% soya oil and various concentrations of sodium caseinate were prepared in a two-stage valve homogenizer. The emulsions were sealed in glass bottles and then heated at 1218C for 15 min in an autoclave. In some experiments, the caseinate solutions were heated at 1218C for 15 min ®rst, mixed with soya oil (to give 30% oil in the ®nal emulsion) and then homogenized. Heat treatment (1218C for 15 min) of either sodium caseinate emulsions or sodium caseinate solutions prior to emulsion formation, at all caseinate concentrations used, resulted in an increase in surface coverage, an increase in creaming stability and a change in the proportions of individual caseins at the droplet surface. Heat treatment of sodium caseinate solutions resulted in the formation of several new peptides, due to protein degradation, as well as polymerization of casein molecules, as revealed by SDS±PAGE. Both the polymerized caseinate material and degradation products were adsorbed ef®ciently during emulsi®cation; the degradation products were more readily adsorbed than the parent protein. Experiments on heated emulsions indicated that the adsorbed caseinate molecules were more susceptible to degradation during heating than those in solution.

Food Chemistry, 2003

Oil-in-water emulsions, containing 30% soya oil and various concentrations of calcium caseinate, ... more Oil-in-water emulsions, containing 30% soya oil and various concentrations of calcium caseinate, were prepared in a two-stage valve homogenizer. The emulsions were sealed in glass bottles and then heated at 121 °C for 15 min in an autoclave. In some experiments, the caseinate solutions were heated at 121 °C for 15 min in an autoclave, and then mixed with soya oil (to

Food Chemistry, 2000

Oil-in-water emulsions containing 30% soya oil, calcium caseinate and various NaCl concentrations... more Oil-in-water emulsions containing 30% soya oil, calcium caseinate and various NaCl concentrations were prepared in a two-stage homogeniser. The average volume-surface diameter (d 32) of emulsion droplets decreased with increasing NaCl from 0 to 20 mM, but remained constant beyond 20 mM. The surface protein concentration (mg/m 2) decreased with NaCl addition up to 50 mM, but increased with increasing NaCl concentration above 50 mM. a s-(a s1-+a s2-)Casein adsorbed at the droplet surface in preference to b-casein in emulsions made both with and without NaCl. In emulsions made with <2% calcium caseinate, the droplet size distributions were broad and bimodal, but they became narrow when 50 or 150 mM NaCl was added prior to emulsion formation. The changes in creaming stability were consistent with the droplet sizes in emulsions. It appears that the aggregated protein in calcium caseinate dispersion was dissociated by NaCl, which consequently improved its emulsifying properties.

... Steve Glasgow, Mr. Hank van Til, Mr. Alistair Young, Mr. Garry Radford, Mr. Mike Sahayam, Mr.... more ... Steve Glasgow, Mr. Hank van Til, Mr. Alistair Young, Mr. Garry Radford, Mr. Mike Sahayam, Mr. Mark Dorsey, Mr. John Dawber and Mr. Cheng Tet Teo for ... Kui, Mrs. Katherine Limsowtin, Ms. Karen Ralph and Ms. Miria Busby. ...

Journal of Agricultural and Food Chemistry, 1995

... Douglas G. Dalgleish,",? Magesh Srinivasan,s and Harjinder Singht Department of Food Sci... more ... Douglas G. Dalgleish,",? Magesh Srinivasan,s and Harjinder Singht Department of Food Science, University of Guelph, Guelph, Ontario N1G 2W1, Canada, and Department of Food Technology, Massey University, Palmerston North, New Zealand ...

Journal of Dairy Science, 2002

Elevated plasmin enzyme activity has been suggested as a likely cause of impaired functional prop... more Elevated plasmin enzyme activity has been suggested as a likely cause of impaired functional properties that occur in milk from cows either in their latelactational period or that are experiencing mastitis. However, there are conflicting reports on the impact of plasmin on rennet coagulation properties of milk. The effects of added plasmin on the rheological properties, at small and large deformation, of rennet-induced gels were investigated. The microstructure of rennet-induced gels was studied, using confocal scanning laser microscopy. Porcine plasmin was added to reconstituted milk, and samples were incubated at 37°C for between 0.5 to 8 h. The hydrolysis reaction was terminated using soybean trypsin inhibitor. The extent of degradation of caseins was determined with SDS-PAGE. The extent of breakdown of α sand β-caseins increased with incubation time with plasmin. Storage modulus of rennet gels decreased linearly with increasing degradation of caseins. There was an increase in the loss tangent parameter of the gels with increasing casein degradation, indicating a more liquid-like gel character. Gelation time decreased until approximately 3 h of incubation with plasmin (when the amounts of intact α sand βcaseins were ∼ 46 and 50%, respectively); thereafter, gelation time increased considerably. Yield stress of rennet-induced gels decreased with increasing casein breakdown. When the level of casein hydrolysis was high (<40% of intact caseins), the microstructure of rennet-induced gels was drastically altered. Even when there were low levels of casein hydrolysis, the rheological properties of rennet gels were altered, which could have negative impacts on cheese yield and texture.