88C-24 |
Microstructure and stability of oil-in water food emulsions |
M. QUINTANA1, A. Califano, and N. Zaritzky. (1) CIDCA, CONICET, Fac. Ciencias Exactas, Universidad Nac. La Plata, 47 7 116 (1900), La Plata, Argentina Sorbitan fatty acid esters and the corresponding polyoxyethylene (POE) adducts have applications as emulsifiers in the food industry. The objective was to analyze the influence of processing conditions such as emulsification time, energy input, hydrophilic-lipophilic balance (HLB), and ionic strength on the microstructure and stability of 40 % w/w sunflower oil-in water emulsions, stabilized with non-ionic emulsifiers SpanTM60 (S60, sorbitan monoestearate), TweenTM40 (T40, POE sorbitan monopalmitate) and TweenTM60 (T60, POE sorbitan monoestearate)). POE emulsifiers were added to the aqueous phase prior homogenization with an Ultra Turrax T25, at 20C; SpanTM 60 (S60) was dissolved in the oil phase. Droplet diameter distribution, average droplet size and Sauter average diameter (D[3,2]) were measured from micrographs. Stability was determined using a QuickScanTM equipment (Beckman-Coulter). As the creaming progressed, the back-scattered light at the bottom layer diminished with time because the emulsion became droplet-depleted; creaming rates were calculated from back-scattering data. The time required to unstabilize o/w emulsions increased when the rotor speed raised from 7,800 to 16,300 rpm due to the decrease in D[3,2]. The stability was independent of emulsifying time (between 2 and 6 min.). When the total content of surfactant was kept constant (1% w/oil weight), varying HLB from 5.8 to 14.9 (with combinations of T60 and S60), D[3,2] decreased and longer stability times were reached. Creaming rates showed that the relationship between stability and HLB was non-linear. Stability was also improved when the total amount of surfactant was increased. Addition of NaCl to the aqueous phase produced a clearly visible creaming interface; creaming rates increased resulting in shorter stability periods. Microscopic observations showed that emulsions with NaCl concentrations above 0.05M flocculated in minutes. The presence of NaCl might reduce the thickness of the double electric layer that surrounds the oil droplets reducing electrostatic repulsion between droplets and allowing flocculation.
Session 88C, Food Engineering: Physical and Chemical Properties
|