New starches: Physicochemical properties of sweetsop (Annona squamosa) and soursop (Anonna muricata) starches

Starch from the fruits of sweetsop (Anonna squamosa) and soursop (Anonna muricata) were isolated and purified and the fat, ash, phosphorus and protein contents measured. The amount of amylose present was determined spectrophotometrically and found to be very similar(similar to 19%) for both starches. Scanning electron microscopy showed very small indented and spherical granules from both with an average granule size of 4.84 mu m and 4.72 mu m, respectively. The physicochemical properties, namely the swelling power, solubility, pasting characteristics, paste clarity and freeze-thaw stability were studied to assess the functionality of the starch pastes as hydrocolloids. The sweetsop starch showed higher swelling power and solubility compared to soursop starch and had a lower gelatinization temperature indicating a weaker granular structure. Sweetsop starch exhibited a lower pasting temperature, higher viscosity peak, higher viscosity breakdown and lower setback, higher paste clarity and freeze-thaw stability compared to soursop starch. The low gelatinization temperature and high freeze thaw stability of sweetsop starch are comparable to that of waxy corn. The properties of sweetsop indicate that it has potential for application as a thickener in frozen foods. (C) 2009 Elsevier Ltd. All rights reserved.