Comparative studies of acetylated and carboxymethylated starches obtained from red cocoyam (Colocasia esculenta) and white cocoyam (Colocasia antiquorum)

Abstract

Interest in biopolymer is on the rise due to the non-biodegradability of synthetic polymers. Starches obtained from red cocoyam and white cocoyam were subjected to chemical modifications through acetylation using acetic anhydride and carboxymethylation using monochloroacetic acid in the presence of sodium hydroxide followed by determination of their physicochemical and functional properties. The proximate analysis showed that moisture, protein and fat contents reduced following the modification. Moisture content falls within the permissible limit with white cocoyam starch (WCS) having the least in both native and modified starches. Carboxymethylated starches had higher fat and ash content than acetylated starches while acetylated starches had higher protein content. In addition, swelling power, solubility, oil and water absorption capacities increased following modification. Pasting temperature and peak time reduced following modifications, with carboxymethylation having slight reduction. There was a significant difference in the peak, rough, breakdown, final and setback viscosities of native and modified cocoyam starches. The viscosities increased following acetylation but decreased following carboxymethylation. Viscosities of the acetylated red cocoyam were higher than that of acetylated white cocoyam starches. FTIR studies revealed the introduction of new functional groups in the modified starches, with the bands of the - C=O shifting to a higher and -OH to a lower value. Chemical modification improved the physicochemical properties of the starches studied. The physicochemical properties of the native and modified red cocoyam starch make it a better binder than white cocoyam.