Physicochemical properties of cross-linked cassava starch prepared using a pilot-scale reactive twin-screw extrusion process (REX)

Abstract

Reactive extrusion (REX) was proposed as a means of modifying the functionalities of cassava starch through cross-linking using a pilot-scale, co-rotating twin screw extruder. Cassava starch was blended with sodium trimetaphosphate (STMP) and extruded at a constant feed rate of 5.3 kg/h, a reaction temperature of 40°C and a screw speed of 200 rpm. Response surface methodology was used to evaluate the effects of moisture content (50–85% of dry weight starch), NaOH concentration (0.05–0.1 M) and STMP level (0.5–2.0% of dry weight starch) on the degree of substitution (DS), degree of cross-linking, and pasting properties, as well as the water solubility index (WSI) and swelling power of cross-linked starch. Regression analysis showed that the DS of cross-linked cassava starch was affected significantly (p < 0.05) in linear terms, while the degree of cross-linking and pasting properties were affected significantly (p < 0.05) in linear, interaction, and quadratic terms. DS varied from 0.0038 to 0.0149 and increased as the moisture content decreased. Introduction of phosphate cross-links into the starch restricted the mobility of the molecular structure, leading to a reduction in WSI and viscosities of starch. Starch became slightly yellowish with an increase in NaOH concentration. Starches with a degree of cross-linking between 51 and 56% yielded the highest peak viscosity (2197–2448 cP), final viscosity (3185–3422 cP), and swelling power (8.03–8.45). Cross-linking reaction through REX altered the crystalline patterns of cassava starch. Cross-linked cassava starches with different degrees of cross-linking and functionalities were developed successfully using a pilot-scale REX, which could be utilized as food and non-food additives.