Amylolytic Activity in Germinating Sweetpotato (Ipomoea batatas L.) Roots

Abstract

<jats:p>In vitro activity measurements indicate that storage sweetpotato roots contain high amounts of extractable amylolytic enzymes. These storage roots also have a very high starch content, a characteristic indicating that the in vitro measurements estimate potential amylolytic activity rather than actual physiological activity. We are interested in optimizing the use of endogenous amylases when processing sweetpotato roots and have undertaken a study to identify physiological parameters that control in vivo starch breakdown. Sweetpotato roots were allowed to germinate for 35 days in controlled conditions. Using a combination of in vitro activity measurements and immunochemical detection, the spatial distribution and changes in activity levels for the three major amylolytic enzymes in storage sweetpotato roots—α-amylase, β-amylase, and starch phosphorylase—have been followed. After 6 days, α-amylase protein increased in the outer starchy parenchymatous tissues surrounding the cambium layers, a result suggesting a <jats:italic>de novo</jats:italic> synthesis of the enzyme in cambium or laticifers layers. β-Amylase was abundant throughout the root at all times, and its high levels did not directly affect starch degradation rates. Starch phosphorylase protein level remained constant, while its extractable activity increased. Starch content decreased during sweetpotato seed root germination. However, the amount of starch that disappeared during germination was low compared with the calculated starch hydrolysis potential estimated by amylolytic activity measurements.</jats:p>

Amylolytic Activity in Selected Sweetpotato (&lt;i&gt;Ipomoea batatas&lt;/i&gt; Lam) Varieties during Development and in Storage

“…Results from a study conducted on potato had also reported low levels of α-amylase activity in potato at low temperature [26]. The trends of β-amylase activity in storage obtained in this study were in agreement with findings of similar studies [3,9,[16][17][18], despite the different storage conditions. These results were however not consistent with results obtained from tuberous-rooted chervil roots which indicated that β-amylase was high when stored at lower temperatures (4˚C) but, decreased at higher temperatures [25].…”

“…Whereas in the earlier studies the sweetpotato roots attained peak amylase activity after 8 and 12 weeks in storage [16,18], the roots used in this study attained peak amylase activity after 3 -4 weeks. The time taken to attain peak amylase activity in this study was similar to that observed during germination of sweetpotato roots [3]. The differences in results could be attributed to sweetpotato varieties used in the various studies and the ecological zones in which the sweetpotatoes were grown [23].…”

“…The differences in results could be attributed to sweetpotato varieties used in the various studies and the ecological zones in which the sweetpotatoes were grown [23]. 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.…”

“…The main constituents of sweetpotato dry matter are carbohydrates with starch forming 50% -70% [2]. Besides the high starch content, sweetpotato also contains endogenous amylases with the two major ones being α-and β-amylases [3,4].…”

Storage Quality and Composition of Sweetpotato Roots after Quarantine Treatment Using Low Doses of X-ray Irradiation

“…Starch analysis. Starch was determined by combining 30 mg of AIS with 10 mL distilled water, and heating at 100 °C in a water bath for 90 min (Hagenimana et al, 1994). A soluble starch standard was included also.…”