Ultrasonic assisted synthesis of octenyl succinylated starch and its application as stabilizer of Pickering emulsions

HERRERA, MARÍA LIDIA; ALTUNA, LUZ; FORESTI, MARÍA LAURA

Mar del Plata

Simposio; XVI Simposio Latinoamericano de Polímeros (SLAP 2018)/ XIV Congreso Iberoamericano de Polímeros (CIP 2018).; 2018

INTEMA - UNMdP

INTRODUCTIONOctenyl succinylated starch (OS-starch) is synthesized by esterification in aqueous slurry under mild alkaline conditions and at room temperature yielding an additive with amphiphilic properties. Due to its amphiphilic character, OS-starch finds application as an emulsion stabilizer, and the stability of the emulsion depends on the degree of substitution (DS)1 and the distribution of the OS groups within the starch granules2. Characterization of OS-starches has shown that the reaction is mainly a surface phenomenon, due to the heterogeneous character of the system, the semicrystalline nature of the starch granules, and the low solubility of octenyl succinic anhydride (OSA) in the aqueous medium3. Therefore, increasing the granules surface could allow increasing the reaction efficiency (RE) and the DS during the synthesis of OS-starch. Ultrasonic (US) treatment of starch granules has been found to increase granules? surface due to particle size reduction4 and generation of cavities and fractures5. The objective of this work was to perform ultrasonic treatment to maize starch prior to esterification with OSA and evaluate its performance as an emulsion stabilizer. EXPERIMENTAL METHODSUltrasonic pre-treatment of starch: Native maize starch suspensions (13%) were subjected to ultrasonication (750 W, 20 kHz, amplitude 30%, 15 and 30 min).Synthesis and characterization of OS-starches: 30% maize starch suspensions were reacted with OSA (3 or 9%) during 4 h with constant stirring (35 °C, pH 8.5-9). The DS of OS-starches was determined by the saponification and back titration method. Fourier-transform infrared (FTIR) spectra of starch samples were acquired. Emulsion preparation and stability: Oil in water emulsions were prepared with 30% oil and 5% starch as stabilizer using an ULTRA-TURRAX T18 high-speed blender (3 min, 20,000 rpm). The stability of the emulsions was monitored by backscattering using a vertical scan analyzer Turbiscan MA 2000 after 0 min, 10 min, 20 min, 1 h and 72 h.RESULTS AND DISCUSSIONAs shown in Table 1, DS increased with the percentage of OSA and with the ultrasonic pre-treatment time used (Fig. 1 a). SEM images show granule damage in samples with high DS (Fig 1 b). Regarding emulsions, on the one hand the DS had a positive effect on the stability. On the other hand, ultrasonicated starches showed to be better emulsifiers than non pre-treated starches (Fig. 1 c and d). This could be attributed to: a) the higher DS attained for pretreated starches; b) a better distribution of OS groups within the ultrasonicated granules.