Effect of Salt on the Rheological Properties of Low-in-Fat O/W Emulsions Stabilised with Polysaccharides

Abstract

The droplet size distribution, stability, flow and viscoelastic properties of 35% oil-in-water emulsions stabilised with 1% w/w Tween 60 and: (i) 5% potato starch (PS), (ii) 5% potato starch and 0.5% xanthan gum (PS + XG), or (iii) 1% xanthan gum (XG), with and without the addition of 0.5M NaCl were studied. Visual inspection of the emulsions that contained XG and PS + XG, with and without NaCl, showed that they remained stable after 6 months. Emulsions stabilised with PS (without salt) showed an incipient interface after four months storage, while those containing 0.5 M NaCl destabilised within a month. The presence of NaCl did not affect droplet size distribution. Microscopic observations showed that all the emulsions flocculated. The rheological properties of these emulsions were characterised on a controlled-stress rheometer. The linear viscoelasticity was determined by oscillatory measurements that revealed the systems that exhibited weak gel-like properties. The addition of NaCl to the systems caused a decrease of viscosity, storage modulus and of loss modulus for emulsions containing PS and PS + XG while it did not affect emulsions prepared with XG alone. The viscoelastic linear behaviour was described according to the Maxwell generalised model and the discrete relaxation time spectra of the emulsions by means of the BSW-CW model.

Microstructure and viscoelastic properties of low-fat yoghurt structured by monoglyceride gels

“…the energy used to deform the material will be viscously dissipated). In this way, the yoghurt variations behaved in a solid-like manner at frequencies lower than 40 Hz, even when the viscoelastic moduli were a function of frequency (Quintana, Califano, Zaritzky, & Partal, 2002). This overall behavior can be appreciated better by observing Fig.…”

Modeling rheological properties of low-in-fat o/w emulsions stabilized with xanthan/guar mixtures

“…Thus, the addition of xanthan and guar mixture stabilizes the emulsion against creaming either by increasing the viscosity of the continuous phase as a consequence of the formation of a gel network (Dickinson, Ma, & Povey, 1994;McClements, 2000;Quintana et al, 2002aQuintana et al, , 2002b or by promoting the formation of a three-dimensional network of aggregated droplets (Dickinson, 2003;Dickinson et al, 1994;Parker, Gunning, Ng, & Robins, 1995).…”

“…However, they are thermodynamically unstable systems, especially those with reduced oil content, usually splitting into two distinct phases. The presence of salts and an acidic medium, usually found in food emulsions used as salad dressing, enhances the instability of these systems (Kokini & Fischbach, 1988;Quintana, Califano, Zaritzky, & Partal, 2002a).…”

“…flocculated system where droplets form a structural network(Guerrero, Partal, & Gallegos, 1998;Partal, Guerrero, Berjano, & Gallegos, 1999;Quintana et al, 2002a;Quintana et al, 2002b).…”