Acid induced-gelation of whey proteins

• Autor(a) principal: Queirós, Ana Sofia Batista
• Data de Publicação: 2015
• Tipo de documento: Dissertação
• Idioma: eng
• Título da fonte: Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
• Texto Completo: http://hdl.handle.net/10773/15473
• topic: Bioquímica alimentar; Leite - Proteínas; Ácidos orgânicos; Gelificação

Traditionally, whey protein (WP) gelation requires the application of heat, hence limiting the use of whey protein ingredients as gelling agents in foods sensitive to high temperatures. Acid-induced gelation has been shown to promote whey protein gel formation at room temperature, using acidulants. However, it requires the application of heat in the initial stages of the process to achieve partial denaturation of the protein and the formation of soluble aggregates. Gelation in the presence of weak organic acids at room temperature has been reported for shark myofibrils. Nevertheless, according to the literature, these conditions have not yet been tested in whey proteins. Therefore, the aim of this study was to investigate whey protein gelation at ambient temperature upon addition of weak organic acids (formic, acetic and propionic). The effect of protein concentration, acid concentration, pH and acid type on the sol-gel protein phase behavior was investigated by macroscopic observation. Phase diagrams were established to define the physical state of the WP systems as a function of protein and acetic acid concentration, and pH. Small strain oscillatory rheological measurements were performed in order to characterize the gelation times and the viscoelastic properties of the obtained gels. Differential scanning calorimetry was applied to investigate the denaturation behavior of the WP, under the studied concentration and ionic conditions. Rheological measurements and visual assessment of the prepared samples indicated that all formic, acetic and propionic acids have induced whey protein gelation. However, this process was shown to be highly dependent on protein concentration, acid concentration, pH and acid type, which also seemed to influence the appearance of the final gels. Therefore, increasing protein and acid concentrations resulted in decreased gelation times and led to the formation of increasingly turbid and opaque gels. WPI gelation was also shown to occur more rapidly as the pH increased towards the isoelectric point, promoting the formation of translucent gels which became more turbid at higher values of pH. Lastly, propionic acid was the fastest to induce gel formation, yielding opaquer gels, followed by acetic acid and formic acid which formed clearer gels. DSC results showed a decrease in the denaturation temperature of WP in the presence of the highest acetic acid concentration studied (2.8 mol L-1, pH 3.2) in relation to the protein with no added acid, from 78 to about 58 ºC, indicating the lower thermal stability of the proteins in the presence of high acetic acid concentrations, probably related to changes in the intramolecular interactions stabilizing the proteins and to consequent conformational changes in the proteins upon acid addition.