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Subject: search.filters.subject.Calcium chloride

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    Influence of calcium chloride addition on the properties of emulsions formed with milk protein products : a thesis presented in partial fulfilment of the requirements for the degree of Master of Technology
    (Massey University, 1999) Ye, Aiqian
    The objective of this study was to investigate the effects of added CaCl2 on (i) the adsorption behaviour of caseinate and whey protein concentrate (WPC) at the oil-water interfaces and (ii) the stability of emulsions formed with caseinate or WPC. The relationship between aggregation state of protein, due to Ca2+ binding, and emulsifying properties is discussed. The effects of addition of NaCl to the emulsions containing various concentrations of CaCl2 were also explored. Protein solutions and 30% soya oil, at pH 7.0, were mixed and homogenized at 207/34 bar and 55°C to form emulsions. CaCl2 was added to protein solutions prior to emulsion formation or to the emulsions after they were made. The average particle size (d 32 or d43 ), the surface protein concentration, the composition of protein adsorbed layer at the interface and the creaming stability of emulsions were determined. The microstructure of emulsions was observed using the confocal laser microscopy. The droplet sizes of emulsions made with sodium caseinate or WPC were similar and were independent of the protein concentration at concentration above 0.5%. The surface protein concentration of emulsions made with sodium caseinate, WPC or calcium caseinate generally increased with increase in the protein concentration, although the trends were different. The emulsions made with calcium caseinate had higher (d32 and surface protein concentration than that of sodium caseinate or WPC. In emulsions made with sodium caseinate at low protein concentrations, the adsorption of β-casein occurred in preference to αs -casein, whereas αs- (αs1- + αs2 -)casein was found to adsorb in preference to β-casein at high protein concentrations. In calcium caseinate emulsions, the αs -casein was adsorbed in preference to β-casein at all concentrations. In emulsions made with WPC, β-lactoglobulin adsorbed slightly in preference to α-lactalbumin. In emulsions made with mixtures of sodium caseinate and WPC (1:1), the adsorption of whey proteins occurred in preference to caseins at low concentrations (< 3%), whereas caseins were adsorbed in preference to whey protein at high concentrations. In emulsions made with calcium caseinate or WPC, the creaming stability of emulsions followed mainly the changes in particle size of emulsions. However, the creaming stability of emulsions made with sodium caseinate decreased markedly as the caseinate concentrations were increased above 2.0%. This was attributed to depletion flocculation occurring in these emulsions. Whey proteins did not retard this instability, due to depletion flocculation, in emulsions made with mixtures of caseinate and WPC When CaCl2 was added prior to or after emulsion formation, the (d43 and surface protein concentration increased with increasing CaCl2 concentration in emulsions made with 0.5 and 3.0% sodium caseinate. The adsorption of αs -casein increased with increase in the concentration of CaCl2 , with a corresponding decrease in the adsorption of β-casein. The creaming stability of emulsions made with 0.5% caseinate decreased with increasing CaCl2 concentration. However, the creaming stability increased with CaCl2 concentration in 3.0% caseinate emulsion. The destabilising effects of CaCl2 in emulsions made with sodium caseinate were reduced by the addition of 200 mM NaCl. Addition of CaCl2 to protein solutions prior to emulsion formation increased the d43 and surface protein concentration in emulsions made with 0.5 or 3.0% WPC. In this case, the adsorption of β-lactoglobulin occurred slightly in preference to α-lactalbumin. The creaming stability of emulsions decreased with increase in the concentration of CaCl2 . The addition of CaCl2 to emulsions after emulsion formation also resulted in increases in and surface protein concentration of emulsions made with 0.5% WPC and formation of gel-like network structure at high CaCl2 concentrations. However, the stability of emulsion made with 3.0% WPC was not affected by the addition of CaCl2 . Different aggregation mechanisms are involved depending upon whether Ca2+ is added to protein solution before emulsification or to the emulsion after its formation. Addition of Ca2+ to protein solution may lead to decrease in emulsifying capacity and subsequently result in protein bridging flocculation between emulsion droplets. Ca2+ bridging flocculation between emulsion droplets may be formed in emulsions that have Ca2+ added. The change in aggregation state of caseinate due to Ca2+ binding could retard the instability of emulsion due to depletion flocculation. The protein unfolding at the surface of emulsions made with low whey protein concentrations may promote the protein-Ca-protein bridges forming between protein-coated emulsion droplets, consequently forming gel-like network structure in emulsions.
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    Comparative study of the effects of added calcium on the heat-induced changes in three complex whey protein systems : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Food Technology at Massey University, Riddet Institute, Palmerston North, New Zealand
    (Massey University, 2012) Riou, Emmanuelle
    Because of their superior functional properties and nutritional quality, whey proteins are widely used in the food industry. Some of the important functional properties of whey proteins include gelation, water-binding, emulsification and foaming. Heat-induced gelation of whey proteins is particularly important in many food applications, and it involves a series of complex changes to protein structures (denaturation, aggregation). However, recent clinical studies on health promoting properties of whey proteins (e.g. weight management, muscle mass retention) has prompted the food industry to develop foods with high levels of whey proteins, such as high protein beverages. In these products, the heat-induced aggregation and gelation functionality of whey proteins becomes a major limiting factor. The main objective of the present study was to determine the effects of added calcium on heat-induced denaturation, aggregation and gelation of whey proteins in three different whey protein products: whey protein isolate (WPI), acid whey protein concentrate (AWPC) and cheese whey protein concentrate (CWPC). The results were interpreted to assess the suitability of different whey protein systems as influenced by the effects of added calcium on their properties for making new denatured whey protein products. The effects of added calcium chloride on heat-induced changes in whey protein solutions prepared from WPI, AWPC and CWPC were investigated using polyacrylamide gel electrophoresis (PAGE), high-performance liquid chromatography (HPLC), differential scanning calorimetry (DSC), circular dichroism (CD), nuclear magnetic resonance (NMR), small deformation oscillatory rheometry, large deformation compression testing and transmission electron microscopy (TEM). The loss of native proteins in 4% (w/w) protein solutions increased with increase in added calcium levels up to an optimum level (varying between 20 – 110 mM depending on the whey protein product), but then decreased with further increase in added calcium levels. The firmness of gels was maximal at 4 mM added calcium for WPI solutions, 20 mM for AWPC, and 80 mM for CWPC. These results showed that a certain level of added calcium maximally enhanced the heat-induced aggregation and gelation of whey proteins, andthese levels were different for the different whey protein systems. The effects of added calcium appeared to be related to the initial calcium contents of the three systems (2.1, 8.4 and 11.2 mM for 4.8% w/w protein solutions of WPI, AWPC and CWPC). It was considered that the addition of calcium changed the types of protein interactions leading to the formation of protein aggregates during heating. Increasing levels of calcium caused dramatic decreases in the fracture stress of whey protein gels due to the formation of increasingly larger protein aggregates; the gels became softer and, to an extent, mushier depending on the whey protein system. The TEM micrographs showed that on addition of calcium, the gels became coarser. WPI (12%, w/w protein) gels without the addition of calcium had a very fine structure (< 0.1 µm). With 60 mM of added calcium, 0.5 µm bead-like aggregates formed, and with further increase in added calcium levels, the aggregate size increased to 2 µm. AWPC (12%, w/w protein) gels without addition of calcium also showed a relatively fine structure (< 0.2 µm), and with the addition of 60 mM of calcium, the aggregate size increased to 0.1 – 0.2 µm. In the case of CWPC (12%, w/w protein) gels, the aggregate size increased from 0.05 to 0.3 µm on the addition of 60 mM of calcium. The kinetics study showed that the mechanism of denaturation and aggregation of whey proteins in AWPC (but not in WPI or CWPC) was not affected by protein concentration in the range 4 – 28% (w/w). The orders of reaction were found to be 1.7 for ß-lactoglobulin and 1 for a-lactalbumin at all protein concentrations. Without addition of calcium, the transition temperature decreased from 85 to 80ºC with increasing total solids for both proteins, whereas with 20 mM added calcium the transition temperature remained constant (~ 80ºC) over the total solids range (5 – 35%, w/w) for ß-lactoglobulin and a-lactalbumin. The effects of added calcium on the aggregation kinetics appeared to be related to the calcium to protein ratio. The addition of 20 mM of calcium to low total solids solutions (5 – 10%, w/w) increased the rate constants, whereas addition of 20 mM of calcium to high total solids solutions (25 – 35%, w/w) decreased the rate constants. These findings contribute to knowledge of the effects of added calcium on changes in whey proteins during heat treatments, and the relevance of the initial mineral content of whey protein products. AWPC appeared to be potentially the most suitable of the three systems studied for use as a feed material for manufacturing denatured whey proteins with the aid of added calcium. The addition of calcium to AWPC solutions decreased the fracture stress and fracture strain of the gels formed, making them softer and mushier, and possibly more “processable”. Further, at high protein concentrations (20 – 28%, w/w), which correspond to desired feed material concentrations in a processing plant, the addition of 20 mM of calcium to AWPC solutions optimally slowed down the aggregation rate, which might help to decrease plant fouling during the manufacture of denatured whey protein products.