Stress Relaxation of Acid-induced Milk Gels

Abstract

The effects of the addition of sugar (sucrose) or salt (KCl/NaCl mixture) on the rheological properties of acid milk gels formed under different process and composition conditions were studied using an experimental design and surface response analysis. The variables evaluated were: sodium caseinate, whey protein concentrate, carrageenan, sucrose or KCl/NaCl concentration, and the mixing temperature of the components. The stress relaxation measurements were made within the linear viscoelasticity domain, and the data obtained were fitted to the generalized Maxwell model. Five parameters were obtained from the fitting: three elastic elements and two viscous elements. In addition, the denaturation process of whey protein with different solute concentrations was evaluated using differential scanning calorimetry. Denaturation temperature increased with increases in the solute concentrations, but enthalpy values did not change independent of solute type and concentration. The results showed that the elastic and viscous moduli increased with sucrose concentration, i.e., the gel network was reinforced, while the opposite occurred with the addition of the saline mixture. Increasing ionic strength of saline mixture and the process temperature were the more important effects with respect to the rheological properties of gels with added saline mixture. On the other hand, the biopolymer concentrations showed the most significant effects on the properties of gels with added sugar.

Steady and transient rheological properties of four polysaccharides with different chain conformations

“…Compared with lentinan, the stress values of curdlan and xanthan solution showed a slow decline after stress overshoot, but did not reach zero within the experimental time, indicating that curdlan and xanthan had more significant viscoelasticity 59 due to their higher molecular weight than lentinan in water. In pullulan solution, the stress dropped to zero after a very short time (< 0.1 s) after stress overshoot, showing the same rheological property of a linear viscous fluid 60 . The different attenuation time of the stress was mainly dominated by the chain stiffness and molecular weight.…”

“…In pullulan solution, the stress dropped to zero after a very short time (< 0.1 s) after stress overshoot, showing the same rheological property of a linear viscous fluid. 60 The different attenuation time…”

Stress relaxation behaviour of high acyl gellan gels

“…Stress relaxation is a transient test of viscoelasticity involving application of small strains, allowing determination of elastic and viscous moduli if appropriate models are fitted to data. The stress relaxation tests have been widely used in rheological studies of food products (Guo et al, 1999;Mao et al, 2000;Singh et al, 2006;Moghimi et al, 2011;Sabadni et al, 2012;Mar ıa et al, 2013). Stress relaxation of viscoelastic materials has been conducted using dynamic rheological techniques and also by uniaxial compression or extension of the materials under a fixed strain.…”

Produção de microgéis para encapsulação de compostos hidrofóbicos

“…κ-Carrageenan can also interact with other ingredients, especially with milk proteins . Even though it has long been known that κ-carrageenan can form complexes with casein micelles (DALGLEISH & MORRIS, 1988;BOURRIOT et al, 1999;ARLTOFT et al, 2007), few studies have evaluated the interaction between κcarrageenan and sodium caseinate (OAKENFULL et al, 1999;BELYAKOVA et al, 2003;SABADINI et al, 2010).…”