**2.2 Surfactant as stabilizing agent in formation of microbubbles**

SPAN-40 and TWEEN-40 are used as stabilizing agent in the preparation of microbubbles [15, 16]. For the formation of stable microbubbles, the SPAN/ TWEEN solution was sonicated in the presence of air. For maximum film stability, a Langmuir trough was used in the ratio of SPAN to TWEEN (roughly 1:1). By using sonicated microbubbles, modified surfactant was formed which was more stable film due to higher collapse pressure on the Langmuir trough [16]. Dressaire et al. recently reported stable microbubbles formed from a blending process at 70°C in 75 wt% glucose syrup, sucrose stearate (mono- and di-ester) formed [17].
