Effect of pH on the stability of W1/O/W2 double emulsion stabilized by combination of biosilica and Tween-20

Abstract

Indonesia is amongst agricultural countries whose majority of the population consume rice as their staple food. Rice rice production tends to increase year by year followed by the increasing of their byproducts such as rice husks. The majority of rice husk waste has been generally thrown away by burning on site which cause pollution and may negatively impact on the environmental sustainability. In fact, rice husk waste contains of about 20% silica which potentially be used as emulsion stabilizers. Biosilica could stabilize the interface between water and oil due to their hydrophilicity and hydrophobicity characteristics in nature. However, their wettability was greatly influenced by pH. In this experiment, the effect of pH of the outer continuous phase (W2) was investigated. The primary emulsion (W1/O) was prepared by mixing a 40% water phase containing gelatin 3% w/w relative to the aqueous phase and Tween-20 of 1.1% w/w relative to the primary emulsion with the remaining oil phase for 5 minutes. The primary emulsions were then dispersed into the aqueous phase (W2) of various pH (2; 3; and 5.7) by using a mixture of Tween-20 and biosilica as emulsifiers. The result showed that the most stable double emulsion was obtained upon the acidic pH of 2. There was no differences between the stability of double emulsion prepared at pH 2 and that of pH 3 after 7 days. However those prepared without pH adjustment (5.7) tended to be instable in the long-term. This implied that acidic pH would increase the packing density of biosilica in the interfaces thus enhancing the barrier properties of the droplets against coalescences. A stable food grade double emulsion would be very beneficial to develop low-fat emulsion products in various food applications. Furthermore, the inner aqueous phase could be used as a vehicle to encapsulate bio-active agents such as nutrients or antioxidants for the advancement of developments of functional food products.

Rice husk silica for the stabilization of food-grade oil-in-water (O/W) emulsions

“…Low pH of outer continuous phase proved to produce higher stability of W/O/W emulsion stabilized by rice husk silica according to our previous investigation (Sapei et al, 2018). The proposed mechanisms of rice husk silica stabilization upon basic and alkaline pH has also been described (Sapei et al, 2018). The pH of the system seemed to play a significant part in influencing the wettability of silica particles and in establishing a stable O/W emulsion.…”

“…If particles were either very hydrophilic (q << 90 ) or very hydrophobic (q >> 90 ), they were easily removed from the interface (Binks & Rodrigues, 2009). Low pH of outer continuous phase proved to produce higher stability of W/O/W emulsion stabilized by rice husk silica according to our previous investigation (Sapei et al, 2018). The proposed mechanisms of rice husk silica stabilization upon basic and alkaline pH has also been described (Sapei et al, 2018).…”

“…The instability of O/W emulsion process due to mainly oil droplet coalescences followed the first-order kinetic model. Recent study demonstrates the influence of pH on the stability of W/O/W emulsion stabilized with rice husk silica/Tween-20 on the outer emulsion (Sapei et al, 2018). The acidic environment of the outer aqueous phase (pH < 4) enhanced the stabilizing action of rice husk silica particles on the interfacial layer.…”

Enhancement of the Stability of W/O/W Double Emulsion by Chitosan Modified Rice Husk Silica

“…Several particles which have been used for Pickering emulsions were silica, clays, polymer latex, magnetic particles, graphene, and polymethylpolymethylmethacrylate particles (Lee & Choi, 2018;Bao et al, 2019). The use of silica for the stabilization of O/W emulsion has been widely investigated (Sapei et al, 2017a;Sapei et al, 2017b;Sapei et al, 2018;Sapei, 2020). However, the use of bare silica was not effective and had to be combined with the use of polymeric emulsifiers to help its adsorption onto the interfacial layers (Pichot et al, 2012;Sapei et al, 2017a;Sapei et al, 2017b).…”

“…Furthermore, the stability of W/O/W stabilized by silica-chitosan was dependent on pH since pH may have affected particle charge and rheological properties of the emulsion (Klinkesorn, 2013;Alison et al, 2016). At acidic pH, rice husk silica tended to be chargeless (Sapei et al, 2018) which may have limited its interaction with chitosan. On the other hand, the positive charges of chitosan tended to be decreased as pH was progressing towards neutral pH (Tiraferri et al, 2014;Mwangi et al, 2016;Alison et al, 2018).…”