International Journal of Biological Macromolecules 37 (2005) 268–277 Studies on the hydrothermal modifications of new cocoyam (Xanthosoma sagittifolium) starch Olayide S. Lawal ∗ Department of Chemical Sciences, Olabisi Onabanjo University, P.M.B 2002, Ago–Iwoye, Ogun State, Nigeria Received 30 May 2005; received in revised form 3 December 2005; accepted 8 December 2005 Abstract Native new cocoyam starch (nNCS) was subjected to annealing (aNCS) and heat moisture treatment at 18% moisture level (h 18 NCS), 21% moisture level (h 21 NCS), 24% moisture level (h 24 NCS) and 27% moisture level (h 27 NCS) as hydrothermal treatments. Scanning electron and light microscopy revealed round and polygonal shapes with sizes ranging from 15 to 40 m for native and modified starches. nNCS showed “A” pattern X-ray diffraction and no significant differences were observed in the X-ray pattern of the modified starches. Swelling power and solubility reduced following heat moisture treatment. At all pH studied (2–12), unmodified new cocoyam starch exhibited higher swelling capacity and solubility than the modified derivatives. Hydrothermal modifications improved water absorption capacity but reduced oil absorption capacity. Pasting temperature of native starch shifted to higher values following annealing and heat moisture treatment. Hot paste viscosity (Hv), viscosity after 30 min holding at 95 ◦ C (Hv 30 ) and cold paste viscosity (Cv) reduced after annealing and heat moisture treatment. The result also indicates that hydrothermal treatments reduced the tendency for setback. As the number of days of storage of starch paste increased from 1 to 10, light transmittance of all the starches reduced but marked reduction of light transmittance was observed in native starch. DSC studies revealed increase in gelatinization temperature following annealing and heat moisture treatment. Starch hydrothermal modifications reduced retrogradation as enthalpies of regelatinization reduced following modifications. The regelatinization peak in the second day scanning shifted to lower temperature than the gelatinization peak in first run heating DSC curve for all samples. The regelatinization peak also became larger and shifted to higher temperature range when the storage days increased from 2 to 7. © 2005 Published by Elsevier B.V. Keywords: New cocoyam starch; Annealing; Heat moisture treatment 1. Introduction New cocoyam (Xanthosoma sagittifolium) is a tuber crop that grows widely in tropical Africa. However, it is a potential source of food and industrial starch that have not been exploited in Nigeria [1]. The largest percentage of food and other industrial starches used in Nigeria and the rest of Africa are mainly from cassava, potato and maize [1–5], unfortunately these crops also serve as sources of staple foods and these often make them less available for starch production. In view of this, it is reason- able to search for alternative crops [6,7], at least lesser known crops to meet the increasing demand for starch as biomateri- als in a developing country like Nigeria and the rest of African countries. ∗ Tel.: +234 802829 3036 E-mail address: laidelawal2@yahoo.com. In food and non-food applications, modified starches have been used as improvements over native starches in various capac- ities. Different modifications are tailored towards the end use of the starches in various products. However, there is considerable interest in physical modifications, as it is considered to be natural and safe as compared to chemical modifications. Hydrother- mal treatments at various temperatures and amount of water can be used to improve some of the functional properties of starches. Heat moisture treatment as a form of physical modifi- cation entails treatment of starch at low water content (18–27%), temperature above the gelatinization temperature (100 ◦ C) and for a long period (>16 h) [8]. The physical properties of heat moisture treated starches depend on the starch origin and treatment conditions used [9]. Differential scanning calorimetry was used to study the effect of heat moisture treatment on thermal properties of wheat and potato starches and the broadening of the gelatinization tem- perature range and the shift of the gelatinization endothermic 0141-8130/$ – see front matter © 2005 Published by Elsevier B.V. doi:10.1016/j.ijbiomac.2005.12.016