Comparative study of stabilization of coffee bubbles at the air-water interface through different surfactants

This investigation reveals the influence of self-assembly of surface active components of surfactants in instant coffee in rendering a stable foam, thereby providing a visual delight. Three surfactants, sucrose stearate, quillaja saponin, and Tween 80, were administered to improve the foam quality of instant coffee. The influence of the addition of these surfactants showed a reduction in surface tension of the coffee solution. Sucrose stearate showed excellent foaming properties as well as foam stability for over 1200 s. For sucrose stearate, the maximum foam height of 168.2 +/- 0.1 mm was achieved at 75.98 +/- 1.87 s that sustained for 60.27 +/- 3.59 s with a minimum coalescence rate of 0.012 +/- 0.005 mu m/s, compared to other surfactants. FE-TEM results proved that closely packed patterned morphology of micelles at the air-water interface, specifically in sucrose stearate foam, could have aided in the development of the most stable foam. As deduced from the present findings, the preferred hierarchy of surfactant for a stable foam in instant coffee is sucrose stearate> quillaja saponin > Tween 80.