3.1. Emulsion gel characterization
3.1.1. Microscopy
Microscopic images showed that inulin concentration significantly influenced morphologies of emulsion gels prepared with 3% psyllium husk (Fig. 2).
(Place for figure 2)
Fig.2. microscopic observation (500X) of ultrasonic-treated and untreated 3% psyllium husk emulsion gel with different concentration of inulin. Dark arrow indicates length of 20 μm.
At 0% inulin concentration, emulsion droplets in close proximity to each other were large and polydispersed, which increased the flocculation rate. High flocculation of emulsion droplets indicates low emulsion stability (Yvonne and Victoria, 2018). The oil droplets in the emulsion gels became smaller and uniform with increased inulin concentration suggesting that the husk-emulsions were stable at higher inulin concentration. A similar result was reported previously (Xu et al., 2020), where the particle size of oil-in-water emulsion decreased with increasing inulin concentration. The droplet decrease may be due to high inulin concentration that forms a secondary interfacial layer enhancing surface coating of oil droplets to prevent against droplet aggregation and coalescence; and this result in smaller oil droplets and highly stable emulsion (Sarkar et al., 2018). These results were further confirmed by the particle analysis and SEM image.
The ultrasonic-treated emulsions showed higher stability with smaller particle size compared to untreated emulsion. Reduction of droplet size by ultrasound can be attributed to shear force generated by the cavitation of the ultrasonic wave breaking droplets into smaller sizes (Guo et al., 2014).