Amylolytic Activity in Selected Sweetpotato (<i>Ipomoea batatas</i> Lam) Varieties during Development and in Storage

Abstract

Sweetpotato varieties (five) were investigated for changes in <i>α</i>- and <i>β</i>-amylase activities during root development and on subjection of harvested roots to different postharvest handling and storage conditions. Changes in <i>α</i>- and <i>β</i>-amylase activities in development were monitored from 10 weeks after planting. At physiological maturity, sweetpotato roots were harvested and subjected to various conditions: freshly harvested roots and cured roots (spread under the sun for four days at 29℃ - 31℃ and 63% - 65% relative humidity), stored at ambient conditions (23℃ - 26℃ and 70% - 80% relative humidity) and in a semi-underground pit (19℃ - 21℃ and 90% - 95% relative humidity). Generally <i>α</i>- and <i>β</i>-amylase activities increased during development with NASPOT 9 and 10 consistently registering the highest activities and NASPOT 1 the lowest activity. Generally, maximum <i>α</i>-amylase activities were achieved at week 3 in ambient stores for NASPOT 9 and NASPOT 10 at 0.930 and 0.897 CU/g, respectively. Maximum <i>β</i>-amylase activity was achieved in ambient stores at week 3 and 4 for fresh and cured NASPOT 9 at 806 and 782 BU/g, respectively. Generally, curing and storing sweetpotatoes in ambient conditions registered the highest amylase activity. Maximum <i>α</i>- and <i>β</i>-amylase activities were registered at 67℃ - 68℃ and 58℃ - 60℃, respectively. These findings provide information for controlled modification of amylase activities of these sweetpotato varieties for product development efforts and monitoring the shelf life of the roots during storage

Viscoelastic properties of sweet potato complementary porridges as influenced by endogenous amylases

“…The results from this study, showing very minimal changes in soluble solids at temperature ranges from 70 to 80°C, are in agreement with Nabubuya, Namuteb, Byaruhanga, Narvhus, Stenstrøm, et al. () who observed that the activity of amylases in sweet potato flours is highest at around 80°C, beyond which temperature the enzymes are denatured.…”

“…Nabubuya, Namuteb, Byaruhanga, Narvhus, Stenstrøm, et al. () in a study comparing fresh and stored sweet potato roots also observed that the activity of endogenous amylases was higher in stored than in fresh roots. This implies that pastes obtained by use of flours from fresh sweet potato roots are more firm and elastic in nature, unlike those prepared from flours obtained from stored roots, which are more viscous in nature.…”

“…Two sweet potato varieties (Kakamega and NASPOT 10) were used in this study and these were obtained from a farmer in Luwero district in central Uganda. The varieties were chosen based on their variations in amylase activity, both α and β amylases and starch content (Nabubuya, Namuteb, Byaruhanga, Narvhus, Stenstrøm, et al., ). Freshly harvested roots and stored roots (3 weeks at ambient conditions; 23–26°C and 75–80% relative humidity) were the sample Treatments.…”

“…), sweet potato roots also contains endogenous amylases. Sweet potato amylases can influence the roots' starch content especially in storage and during processing (Morrison, Pressey, & Kays, ; Nabubuya, Namuteb, Byaruhanga, Narvhus, Stenstrøm, et al., ; Prasanna ) due to their hydrolytic effect (Picha, ). The potential of sweet potato roots in complementary feeding has not been fully tapped into.…”

“…It has been reported that sweet potato amylase activity varies with variety and that it increases during storage (Morrison et al. ; Nabubuya, Namuteb, Byaruhanga, Narvhus, Stenstrøm, et al., ). The increase in amylase activity during storage leads to hydrolysis of starch, thereby reducing the quantity of native starch (Rocha, Carneiro, & Franco, ), given the right conditions (activated).…”