Macro- and microscopic properties of milk proteins and k-carrageenan gels / Propriedades macro- e microscopicas de geis de proteinas do leite e k-carragena

AUTOR(ES)
DATA DE PUBLICAÇÃO

2008

RESUMO

Evaluation of acid-induced sodium caseinate (CS) gelation promoted by glucono-d- lactone (GDL) was performed at different acidification rates with several protein concentrations (2-6% w/w). The kinetics of acidification and gelation were followed from pH 6.7 to the isoelectric point of casein by evaluation of the pH and mechanical properties using uniaxial compression measurements (stress and strain at rupture). Gel network formation was more influenced by electrostatic interactions than different acidification rates, showing the contribution of rearrangements of bonds to strengthening the network, mainly at steady-state pH close to pI of caseins. Besides the hydrophobic interactions and hydrogen bonds were also important forces involved in structure stabilization, leading to stronger gels. Moreover, evaluation of gelation process of milk proteins at pH 6.7 in systems containing ?-carrageenan. In this study, the ?-carrageenan was added at concentration from 0.3 to 0.8% (w/w) into mixtures containing sodium caseinate (2 a 8% w/w), whey protein isolate (0.5 a 7% w/w) or sucrose (5 a 30% w/w). This systems was analysed using rheological measurements under oscillatory shear, mechanical properties and microstructure. The temperature at which structure development began or initial of gelation (Ts) augmented with increasing carrageenan concentration for pure systems, but sucrose or whey protein isolate addition promoted an increase of Ts and sodium caseinate did not affect this temperature, in relation to pure gel. After gel formation, increasing carrageenan concentration promoted more elastic, stronger, deformable and firmer, as well as sucrose addition showed a little effect to decrease elastic character of gel. Whey protein addition weakened gel network at lower concentrations (up to 3% w/w), but at higher concentration was observed a mixed gel network entanglement of carrageenan and whey protein, without sinergism between this biopolymers. Mixed gels of carrageenan and sodium caseinate showed synergism up to 5% (w/w/) of this protein and increasing concentration led to weaken the gel network, decreasing the rigidity and the firmness of gel, probably related to micro-phase separation, observed by confocal microscopy. Mechanical spectra showed that most of mixed systems presented weak gel behaviour, due to simultaneous effect of physical interactions and thermodynamic interactions. However, stronger gels were formed at higher and lower concentration of carrageenan and sodium caseinate, respectively, which indicate the relevance of electrostatic interactions between these biopolymers. Increasing carrageenan and proteins concentrations led to greater microstructure heterogeneity and increased repulsive interactions between biopolymers and thus gel formation, dominated by carrageenan, affected in a complex way the physical properties of these systems

ASSUNTO(S)

kappa-carrageenan leite - proteinas gelificação kappa-carragena interação de biopolimeros milk sucrose gelation sacarose biopolymer interactions

ACESSO AO ARTIGO

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