3.2 Quantification of emulsion kinetic stability against phase separation
The emulsion layer height was measured from Figure 1 and presented as a fraction of the total emulsion height (Eq. 1) (Figure 2). A higher value of emulsion height fraction signifies emulsions with higher stability against phase separation. CO-emulsions height showed a significant increase from S0 (0.16 ± 0.01) to S0.125 (0.54 ± 0.02) (Figure 2A). Similarly, in MO emulsions, the height significantly increased from S0 to S0.125 (0.39 ± 0.01 to 0.72 ± 0.01). For both CO and MO emulsions, only AA and CA (both 0.125% and 0.5%) did not improve the emulsion height further than the S0.125, which indicates that the organic acids added to the aqueous phase were not as effective as salt in improving emulsion stability. Interestingly, when both salt and organic acids were present, the CO-emulsions height significantly increased compared to only salt-added emulsions. In contrast, for MO-emulsion, no significant difference was observed when both salt and organic acids were present compared to only salt (Figure 2A). For both the CO and MO emulsions, S0.125 with either AA or CA showed no significant difference in emulsion height fraction considering the same oil phase (Figure 2A).
With the addition of LMP (both 1.5 and 2%) (Figure 2B), a significant improvement in both CO and MO emulsion stability was observed. It is possible that the acidic aqueous phase (pH 3) induced structural opening in the pectin (Schmidt et al., 2015), which could have resulted in interfacial interaction with GMO polar head groups, thereby stabilizing GMO at the interface and increasing emulsion stability. The emulsion height reached the highest in MO-emulsions with LMP, although the values in CO-emulsions with LMP were not significantly different. However, as soon as Ca was added to the LMP-containing CO-emulsions, the height decreased to 0.67 ± 0.02 and 0.61 ± 0.02 for LMP1.5 and LMP2, respectively. It could be possible that Ca formed ionic linkages between the carboxylic groups from two LMP chains, which decreased LMP interaction with GMO at the interface leading to an increase in emulsion destabilization (Flutto, 2003). In MO-emulsions, 1.5 % LMP with Ca demonstrated reduced emulsions height (0.66 ± 0.02). Conversely, 2 % LMP with Ca did not significantly diminish emulsions height (0.75 ± 0.02) than only LMP-added MO-emulsions. It might suggest that for LMP2-Ca, excess unreacted LMP was available to stabilize the interfacial GMO leading to better emulsion stability. Between CO and MO emulsions, it can be said that the effectiveness of LMP in improving liquid W/O emulsion stability was hindered by Ca addition, more extensively in CO than MO.