Abstract
Sweet potato (Ipomoea batatas L.) roots contain amylolytic enzymes, which hydrolyze starch thus having the potential to affect the viscosity of sweet potato porridges provided the appropriate working conditions for the enzymes are attained. In this study, the effect of sweet potato variety, postharvest handling conditions, freshly harvested and room/ambient stored roots (3 weeks), and slurry solids content on the viscoelastic properties of complementary porridges prepared using amylase enzyme activation technique were investigated. Five temperatures (55°C, 65°C, 70°C, 75°C, and 80°C) were used to activate sweet potato amylases and the optimum temperature was found to be 75°C. Stored sweet potato roots had higher soluble solids (⁰Brix) content in the pastes compared to fresh roots. In all samples, activation of amylases at 75°C caused changes in the viscoelastic parameters: phase angle (tan δ) and complex viscosity (η*). Postharvest handling conditions and slurry solids content significantly affected the viscoelastic properties of the porridges with flours from stored roots yielding viscous (liquid‐like) porridges and fresh roots producing elastic (solid‐like) porridges. Increase in slurry solids content caused reduction in the phase angle values and increase in the viscosity of the sweet potato porridges. The viscosity of the porridges decreased with storage of sweet potato roots. These results provide a possibility for exploiting sweet potato endogenous amylases in the preparation of complementary porridges with both drinkable viscosities and appropriate energy and nutrient densities for children with varying energy needs.
Highlights
Complementary foods in many developing countries are prepared from locally available sources, which are mainly starchy staples, especially cereals like maize, millet, sorghum, and rice (Kikafunda, Abenakyo, & Lukwago, 2006; Mosha, Loswai, & Tetens, 2000; Sanni, Onilude, & Ibidapo, 1999)
Results from this study revealed that weaning porridges with increased solids content, acceptable consistency (2,000–3,000 cP), and increased energy density can be obtained from sweet potato flour through saccharification of pastes at 75°C for 10–30 min
This study confirms that endogenous amylases in sweet potato flour can be manipulated by heating at 75°C for 10–30 min to cause reduction in the viscosity of sweet potato pastes and facilitate increase in paste solids content increasing the energy density of the resulting porridges
Summary
Complementary foods in many developing countries are prepared from locally available sources, which are mainly starchy staples, especially cereals like maize, millet, sorghum, and rice (Kikafunda, Abenakyo, & Lukwago, 2006; Mosha, Loswai, & Tetens, 2000; Sanni, Onilude, & Ibidapo, 1999). The energy density of the porridges can be enhanced through increase of porridge solids content, up to 20% (Nout & Ngoddy, 1997; Songré-Ouattara, 2010; Rombo et al, 2001). The resultant porridges are very thick due to enormous starch content making the porridge unsuitable for young children (Nout & Ngoddy, 1997). A number of methods have been employed in an attempt to modify the behavior of starch during the heating process in order to deal with the issue of paste bulkiness. These include precooking, extrusion, fermenting, malting, and use of enzymes. Some of these methods have registered some level of success (Amankwa, Barimah, Nnaji, & Addai, 2009; Kikafunda et al, 2006; Potter & Hotchloss, 1995)
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