Ozonation of Sago Starch (Metroxylon sagu Rottb.): Kinetic modeling and effects of the process on viscosity, structural, and morphological properties

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Abstract
Studies on the kinetics of starch ozonation under basic conditions remain limited, particularly the effect of the level of alkalinity during ozonation on the suitability of ozonated sago starch for noodle production. This study aims to investigate the kinetics of ozonation reactions at various basic pH levels and the impact of ozonation on the viscosity, structural, and morphological properties of sago starch and its potential use in noodle production. The presence of carbonyls and carboxyls are key parameters for starch ozonation. The reaction kinetics were successfully conducted by observing the formation of carboxyl in the ozonation time range of 5-20 min at a sago starch suspension pH of 7.5-9.5. Prolonged ozonation was found to cause significant increases in carbonyl and carboxyl content. In contrast, high alkalinity of sago starch suspension (9.0 and 9.5) caused significant increases in carbonyl and carboxyl content compared to low alkalinity suspension (7.5 and 8.0). Kinetic modeling of Sago starch ozonation showed that the reaction followed pseudo-first-order kinetics concerning starch concentration, with the reaction rate increasing with increasing pH. The reaction rate increased with increasing pH, with the highest k value at pH 9.0 of 3.3538 × 10-4 min-1 (R2 0.976). When applied as a raw noodle material, rapid visco analyzer (RVA) analysis was used to study the viscosity profile of ozonated starch, enhancing its suitability for noodle production. Peak viscosity decreases after ozonation, reaching 4474 cP at pH 8.5 but partially recovers at pH 9.5 (5139 cP), reflecting structural changes. Trough and setback viscosities peak at pH 9.5, indicating improved stability, gel strength, and retrogradation, essential for texture. Breakdown viscosity decreases, demonstrating enhanced granule resilience, while peak time and pasting temperature remain consistent. Scanning electron microscopic (SEM), Fourier transform infrared (FTIR), and X-ray diffraction (XRD) analyses confirmed structural changes in Sago starch after ozonation. Ozonation improved Sago starch noodles by increasing cooking stability, reducing cooking loss, and slightly enhancing water absorption compared to native starch. However, wheat flour noodles exhibited superior water absorption and minimal cooking loss, attributed to gluten’s strong water-binding and cohesive properties. Ozonated Sago starch shows promise as a partial wheat substitute in noodles, but further sensory and molecular studies are required.

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