Abstract
Sweetpotato varieties (five) were investigated for changes in α- and β-amylase activities during root development and on subjection of harvested roots to different postharvest handling and storage conditions. Changes in α- and β-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 α- and β-amylase activities increased during development with NASPOT 9 and 10 consistently registering the highest activities and NASPOT 1 the lowest activity. Generally, maximum α-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 β-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 α- and β-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.
Highlights
Sweetpotato (Ipomoea batatas) is an important food crop, ranks fourth among the world’s most important food crops and is seventh in production worldwide [1]
Increase in α-amylase activity has been attributed to de novo synthesis of α-amylase [3] and its diffusion into the starchy endosperm [24] during storage. These results revealed that the different storage conditions (23 ̊C - 26 ̊C, 70% - 80% RH and 19 ̊C - 21 ̊C, 90% - 95% RH) did not significantly affect the activities of the sweetpotato α- and β-amylases (p ≥ 0.05) the activities were generally higher in room stored roots (23 ̊C - 26 ̊C, 70% - 80% RH)
This study has shown that the activities of both αand β-amylases of sweetpotato depend on the storage conditions especially the temperature and relative humidity
Summary
Sweetpotato (Ipomoea batatas) is an important food crop, ranks fourth among the world’s most important food crops and is seventh in production worldwide [1]. The endogenous amylases have a substantial influence on sweetpotato roots in storage and during processing because they facilitate the breakdown of starch [5,6,7]. Despite its reported low quantity in the sweetpotato root, αamylase has been demonstrated to be the major enzyme controlling viscosity in model starch systems. This is attributed to the fact that α-amylase has the capacity to bind and attack raw starch producing maltose and limit dextrins [11]. Beta-amylases on the other hand are unable to hydrolyze raw sweetpotato starch but rather facilitate the breakdown of chemically solubilized or boiled starch [14,15]
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