Abstract
The study investigates the effect of acetylation on the physicochemical properties of composited starches from sweet potato and water yam. Starch was respectively isolated from both sources, dried and subjected to acetylation at different combination. The result shows that the modified starches were of low percentage of acetylation and low degree of substitution. Acetylation increased the water absorption capacity of the starch while compositing itself seemed to have a counteracting influence on the parameter. The oil absorption capacity generally got reduced with acetylation while synergistic role of acetylation and compositing was observed in the swelling capacity of a composited starch (SP/WY-20/80) and counteracting influence in others. The solubility indices of starches were greatly enhanced by acetylation and compositing at all temperatures of evaluation (50-90°C). Acetylation improved the colour lightness (L*-value) of the starches (93.05-94.02) while that of the native starches ranged between 92.18 and 92.31. Most pasting variables (peak, breakdown, final and setback viscosities) were lower in acetylated composite starches than that of the unmodified counterparts. Freeze-thaw stability of gels from composited starches was greatly enhanced as lower volume of exudate was generated from the acetylated starches in all the freeze-thaw cycles. The findings in this study have the potential of creating awareness among the food industry with respect to acetylated starch production from both sweet potato and water yam. Key words: Acetylation, starch, sweet potato, water yam, physicochemical properties.
Highlights
Starch is a commodity that serves as a food ingredient but with a uniqueness of having a greater versatility of application in the food industry than any other single food ingredient
Marginal differences were observed in the percentage of acetylation which implies that the level of acetylation reaction in the starch samples was almost the same
For food-grade acetylated starches, the maximum limit set for percentage of acetylation by the United States Food and Drug Administration (USFDA) is 2.5% acetyl content (Thomas and Atwell, 1997)
Summary
Starch is a commodity that serves as a food ingredient but with a uniqueness of having a greater versatility of application in the food industry than any other single food ingredient. Starch in its native form has limited usage in the food industry as it is prone to low shear resistance, minimal thermal resistance and greater tendency towards thermal decomposition and retrogradation (Singh et al, 2007). Starches from diverse biological origins do exhibit variations in their physicochemical properties and functional characteristics and their modifications are usually tailored towards meeting the requirements of specific food applications (Hermansson and Svegmark, 1996). The starch modification techniques are usually physical (e.g. pregelatinization), enzymatic (e.g. enzymatic hydrolysis) and chemical (e.g. oxidation, etherification, esterification and cross-linking) (Singh et al, 2007)
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