Rheology, Microstructure, and Storage Stability of Emulsion-Filled Gels Stabilized Solely by Maize Starch Modified with Octenyl Succinylation and Pregelatinization

Abstract

We prepared emulsion-filled gels stabilized using octenyl succinic anhydride-modified and pregelatinized maize starch (OSA-PGS). The effect of the oil volume fraction (Φ, 0.05-0.20) and OSA-PGS concentration (3-10% w/v) on the rheological and microstructural properties of the emulsion-filled gels was evaluated. Confocal fluorescence images showed that OSA-PGS stabilized the emulsion, indicated by the formation of a thick layer surrounding the oil droplets, and simultaneously gelled the aqueous phase. All of the emulsions exhibited shear-thinning flow behavior, but only those with 10% w/v OSA-PGS were categorized as Herschel-Bulkley fluids. The rheological behavior of the emulsion-filled gels was significantly affected by both the OSA-PGS concentration and Φ. The mean diameters (D1,0, D3,2, and D4,3) of oil droplets with 10% w/v OSA-PGS were stable during 30 days of storage under ambient conditions, indicating good stability. These results provide a basis for the design of systems with potential applications within the food industry.

Keywords: emulsion-filled gels; microstructure; octenyl succinic anhydride-modified and pregelatinized maize starch; rheological property; storage stability.

Figure 1

(a) Fourier transform infrared spectra, (b) X-ray diffractograms, and (c) heating calorigrams of maize starch, pregelatinized maize starch (PGS), and octenyl succinic anhydride-modified PGS (OSA-PGS). (d) Confocal laser scanning micrographs of emulsions stabilized by 3, 5, or 10% w/v OSA-PGS and oil volume fraction = 0.05 (Nile red, lipid-labeled; Concanavalin A conjugated with fluorescein isothiocyanate, OSA-PGS labeled).

Figure 2

Flow behavior plots (shear stress vs. shear rate) of the emulsions stabilized by pregelatinized maize starch modified with octenyl succinic anhydride (OSA-PGS). Oil volume fraction: (a) 0.05, (b) 0.10, and (c) 0.20. Lines indicate the fitted curves based on the Herschel–Bulkley model ($\tau ={\tau }_0+K{\dot{\gamma }}^n$; $\tau$, shear stress; $\dot{\gamma }$, shear rate; ${\tau }_0$, yield stress; $K$, consistency index; $n$, flow index). Loss tangent angles ($\tan \delta =G^{″}/G^{\prime }$; $G^{″}$, loss modulus; $G^{\prime }$, storage modulus) of the emulsions stabilized by OSA-PGS. Oil volume fraction: (d) 0.05, (e) 0.10, and (f) 0.20. Data were obtained by oscillation frequency sweep test. Lines indicate $\tan \delta$ = 1.

Figure 3

(a) Confocal laser scanning micrographs of emulsions stabilized by pregelatinized maize starch (PGS) or PGS modified with octenyl succinic anhydride (OSA-PGS) (Φ, oil volume fraction), before and after storage for 30 days. (b–j) Changes in the droplet diameter distribution of emulsions stabilized by OSA-PGS before and after storage for 30 days. OSA-PGS concentration: (b,e,g) 3, (c,f,i) 5, and (d,g,j) 10% w/v; oil volume fraction: (b–d) 0.05, (e–g) 0.10, and (h–j) 0.20. Data were obtained from confocal laser fluorescence micrographs of emulsions using image J image-processing software. Lines indicate the fitted curves based on the equation $\mathrm{Area} \left[\%\right]=a{e}^{-0.5{\left(\ln \left(D/D_0\right)/b\right)}^2}$; $a$ and $b$, constants; $D_0$, $D$ at the peak.