Whey protein interactions in acidic cold-set gels at different pH values

Abstract

Cold-set whey protein isolate gels (7% w/w) were produced by the addition of different amounts of glucono-δ-lactone to thermally denatured protein solutions. After 48 h of incubation at 10 • C, different final pH values were obtained (5.2 to 3.9). The gels were analysed by uniaxial compression measurements, water-holding capacity and protein solubility. The water-holding capacity of the gels decreased at pH values near the pI, this being associated with the lower protein solubility at this pH value. Protein solubility in the presence or absence of denaturing and reducing agents indicated that electrostatic interactions were responsible for the maintenance of the acidified gel structure at pH values from 5.2 to 4.6, but at pH 4.2, more hydrophobic interactions were present in relation to other final gel pHs, in spite of β-lactoglobulin (β-Lg) and BSA being far from their pI values. Complementary PAGE assays showed that disulphide bonds were associated with internal stabilisation of the protein aggregates formed during heat treatment. The mechanical properties of the gels were influenced by the final system pH value, showing that the strongest network was observed at pH 5.2. The results allowed the conclusion that although the interactions amongst the aggregates in the network of cold-set whey protein gels were essentially the same at the pH values evaluated, β-Lg played an important role in gel stabilisation due to its high concentration in WPI, strengthening the structure at its pI and, at the same time, providing good water-retention capacity. whey proteins / glucono-delta-lactone / cold gelation / protein interactions

Whey Protein/Arabic Gum Gels Formed by Chemical or Physical Gelation Process

“…In such systems, the GDL addition caused a slow decrease of the system pH, leading to different rates of a gel structure formation depending on the GDL concentration. 8,9 The gels final pH corresponded to the pI region of the main whey protein fractions. In this process, protein aggregates were formed during the heating of the solution that did not gel due to the low protein concentration in the system and the prevalence of electrostatic repulsion among the formed aggregates at neutral pH.…”

“…In this process, protein aggregates were formed during the heating of the solution that did not gel due to the low protein concentration in the system and the prevalence of electrostatic repulsion among the formed aggregates at neutral pH. 2,7,9 However, the slow pH decrease reduced the electrostatic repulsion enhancing the aggregation and causing a rearrangement among the protein agglomerates near the pI, which induced hydrophobic sites association. The structure strength depended on the time of the system maintenance at the final pH value, especially at the higher acidification rates or higher GDL concentration added.…”

“…8 This can be achieved by the use of glucono-δ-lactone (GDL), which hydrolysis to gluconic acid in water medium with a resulting final pH depending only on GDL concentration. 9,10 A wide range of textural properties can be achieved as a function of system gelation process, and in general, heat-set gels tend to be harder and more elastic than cold-set gels. Moreover, depending on the chemical factor used to induce gelation (acids, salts, enzymes), the textural properties can be widely different.…”

Liquid Whey Protein Concentrates Produced by Ultrafiltration as Primary Raw Materials for Thermal Dairy Gels

“…The knowledge of the rheological or mechanical properties of the system is very important, since the physical attributes of food, including the lack of visual liquid separation and the perceived viscosity, are crucial aspects of quality and overall sensory acceptance by the consumers (22,23).…”

Viscosidade extensional e em cisalhamento de suspensões acidificadas de amido de amaranto e caseinato de sódio

“…Porém, nota-se que as amostras compostas por amido de amaranto gelatinizado previamente (acidificação lenta) possuíam maior valor de índice de consistência (k) e pseudoplasticidade que as amostras em que os componentes foram acidificados e gelatinizados simultaneamente (acidificação rápida). Diversos autores (CAVALLIERI; CUNHA, 2008;CAVALLIERI et al, 2007;BRAGA et al, 2006;JU et al, 1998) destacam a possibilidade de diferentes comportamentos dos géis em resposta aos processos de acidificação (lento ou rápido), dependendo dos diferentes tipos de biopolímeros envolvidos nos sistemas. De uma forma geral, géis acidificados lentamente tendem a formar géis mais fortes e mais elásticos do que sistemas acidificados rapidamente.…”