호화 옥테닐 호박산 전분의 유화 특성

Emulsifying Properties of Gelatinized Octenyl Succinic Anhydride Modified starch from Barley

Abstract

본 연구는 OSA 전분을 열처리 한 후, 이를 이용하여 제조한 OSA 전분 에멀션의 이화학적 특성 및 계면 흡착 구조 등을 조사하였다. 에멀션 중 지방구의 크기는 OSA 전분 농도의 증가와 더불어 지속적으로 감소하여 0.2 wt% 농도에서 최소값($0.31{\pm}0.01{\mu}m$)을 나타내었고, 그 이상의 농도에서는 변화가 없었다. 에멀션의 크리밍 안정도는 OSA 전분 농도가 높을수록 증가하였으며, 0.75 wt% 이상의 첨가 농도에서 크리밍 발생에 대하여 매우 안정하였다. 에멀션 중 OSA 전분의 계면 흡착량은 0.2 wt% 첨가 농도 이상에서 농도의 증가와 더불어 증가하였으며(0.2 wt% : $1.03mg/m^2$ ${\rightarrow}$ 1.25 wt% : $5.08mg/m^2$), 이는 계면에서 OSA 전분이 다층 구조를 이루는 것에 기인된 것으로 추정하였다. OSA 전분 에멀션의 pH를 조절하였을 때 산성 지역에서 지방구의 응집에 의해 크기가 증가하였으며, 이는 상대적으로 낮은 제타 전위에 기인된 것으로 사료되었다. 터비스캔에 의한 분산 안정도 또한 pH에 영향을 받아 산성 지역에서 낮았으며, pH 7 이상에서는 높은 분산 안정도 특성을 보였다. 공초점현미경을 이용하여 열처리된 OSA 전분이 흡착된 지방구 표면을 관찰한 결과, OSA 전분은 입자 형태가 아닌 두꺼운 계면막을 형성하는 것으로 나타났다. 따라서 에멀션 형성 전에 OSA 전분을 열처리할 경우, 전분의 호화과정에서 용출된 아밀로오스와 아밀로펙틴이 지방구 표면에 막의 형태로 흡착되므로, OSA 전분 에멀션에 있어서 중요한 유화 안정화 기작은 '입체장애 안정화(steric stabilization)'인 것으로 사료되었다.

The present study was carried out to investigate the emulsifying properties of heat-treated octenyl succinic anhydride(OSA) starch and the interfacial structure at oil droplet surface in emulsions stabilized by heat-treated OSA starch. First, the aqueous suspensions of OSA starch were heated at $80^{\circ}C$ for 30 min. Oil-in-water emulsions were then prepared with the heat-treated OSA starch suspension as sole emulsifier and their physicochemical properties such as fat globule size, surface load, zeta-potential, dispersion stability, confocal laser scanning microscopic image(CLSM) were determined. It was found that fat globule size decreased as the concentration of OSA starch in emulsions increased, showing a lower limit value ($d_{32}:0.31{\mu}m$) at ${\geq}0.2wt%$. Surface load increased steadily with increasing OSA starch concentration in emulsions, possibly forming multiple layers. In addition, fat globule sizes were also influenced by pH: they were increased in acidic conditions and these results were interpreted in view of the change in zeta potentials. The dispersion stability by Turbiscan showed that it was more unstable in emulsions at acidic condition. Heat-treated OSA starch found to adsorb at the oil droplet surface as some forms of membrane (not starch granules), which might be indicative of stabilizing mechanism of OSA starch emulsions to be steric forces.

Fig. 1. Fat globule sizes (d₃₂) in OSA-starch emulsions (10 wt% oil, pH 7) versus concentrations (0.1-1.25 wt% OSA-starch).

Fig. 2. Optical microscopic images of OSA-starch granules (a: raw OSA starch; b: Heat-treated at 80℃ for 30 min, before homogenization; c: Heattreated at 80℃ for 30 min, after homogenization).

Fig. 3. Changes in surface load (Γ) of OSAstarch emulsions versus concentrations (0.1-1.25 wt% OSA-starch).

Fig. 4. Changes in creaming index of emulsions stabilized with various concentration of OSA-starch (0.1-0.5 wt%) versus storage time.

Fig. 5. Changes in fat globule sizes (d₃₂) (a) and zeta-potential values (b) in 0.5% OSA-starch emulsions versus pH.

Fig. 6. Optical microscopic images of 0.5 wt% OSA-starch emulsions at pH 3 and 7.

Fig. 7. Changes in dispersion stability of OSA-starch emulsions (0.5 % OSA-starch, 10% oil) with pH (a: pH 3.0, b: pH 6.0, c: pH 7.0, d: pH 9.0).

Fig. 8. Mean migration velocity of fat globules in emulsions (0.5 wt% OSA-starch, 10 wt% oil) with pH.

Fig. 9. CLSM images of fat globules in emulsions (0.3 wt% OSA-starch, 10 wt% oil, pH 7) stabilized by heat-treated OSA-starch (a: Nile red, b: Con A-FITC, c: a and b were superimposed, d: magnified image).

Table 1. The particle size of 1% OSA-starch suspensions as affected by heat and high pressure treatments