Effects of acetylation, acid-thinning and oxidation on Chrysophyllum albidum (African star apple) kernel native starch

Abstract

Starch is a biological macromolecule with myriad of industrial uses. The growing need for starch and native starch deficiencies have necessitated researches into under-exploited starch sources and modifications, respectively. Chrysophyllum albidum (African star apple, ASA) seed is a waste consisting of 63.94% carbohydrate in its kernel. Its starch content can be fully utilised, industrially, if it is in a suitable form and its properties understood. That necessitated the isolation of ASA kernel starch, its modification and properties assessment. Acetylation, acid-thinning and oxidation were performed on the native Chrysophyllum albidum kernel starch, NACA, to produce the acetylated Chrysophyllum albidum kernel starch, ACCA, acid-thinned Chrysophyllum albidum kernel starch, ATCA, and oxidised Chrysophyllum albidum kernel starch, OXCA, respectively. The physicochemical properties of the native and modified starches were investigated with established methods. The yield of starch was 43.76%. The acetylated and oxidised starches had low degrees of substitution. FTIR results confirmed the introduction of carbonyl functionality into the acetylated and oxidised starches. Starch morphology revealed smooth, small rounded and truncated ellipsoid granules with diameter ranges of 7–20 μm. Swelling power of modified starches improved, except for the acid-thinned, and increased with temperature. Acetylated and oxidised starches had significantly (p < 0.05) higher water and oil absorption capacities, respectively. Acid-thinning significantly improved starch pasting properties and reduced retrogradation tendency. Modification improved the gelatinisation transition temperature of native starch.