Hydrolysis activity of sweet potato flour (Ipomoea batatas L.) by bacterial isolates from the rhizosphere of cat’s whiskers (Orthosiphon stamineus)

Abstract

Introduction: Starch is a polysaccharide that can be hydrolyzed into simpler sugars by amylase-producing microorganisms.

Objective: This study evaluated the starch-hydrolyzing activity of six bacterial isolates from the rhizosphere of cat’s whiskers (Orthosiphon stamineus) using purple sweet potato (Ipomoea batatas L.) starch as the substrate.

Methods: The isolates, designated RKK-1 through RKK-6, were screened using a modified disc diffusion method on starch agar. Amylolytic activity was assessed by iodine staining and measuring the clear-zone diameter after 24, 48, and 72 hours of incubation at 37°C.

Results: Five isolates, RKK-1 through RKK-5, produced detectable clear zones, whereas RKK-6 showed no hydrolysis zone. Clear-zone diameters generally increased with incubation time. After 72 hours, RKK-3 demonstrated the highest activity, with a clear-zone diameter of 20.34 mm, followed by RKK-2 with 18.32 mm.

Conclusion: These findings indicate that most of the tested rhizosphere bacterial isolates can hydrolyze purple sweet potato starch and may serve as potential sources of amylase. However, quantitative enzyme assays, appropriate controls, molecular characterization, and safety evaluations are required before pharmaceutical or industrial applications can be considered.