Inhibition of some enzymes implicated in diabetes mellitus by raw and blanched extracts of African lettuce (Launaea taraxacifolia)

Abstract

This study evaluates the impacts of blanching on α-amylase, α-glucosidase and lipase activities, and Fe²⁺-induced lipid peroxidation (LPO) inhibitory potentials as well as phenolic constituents of African lettuce (AL) leaves. The results revealed that both raw and blanched of AL extracts inhibited all the enzymes dose-dependently, but extract from raw AL had the highest α-amylase (IC₅₀ = 0.20 mg/mL), α-glucosidase (IC₅₀ = 0.27 mg/mL) and lipase (IC₅₀ = 0.45 mg/mL) inhibitory potential compared to that of blanched AL (α-amylase, IC₅₀ = 0.33 mg/mL; α-glucosidase IC₅₀ = 0.52 mg/mL, lipase IC₅₀ = 0.71 mg/mL). Raw AL extract exhibited highest lipid peroxidation (IC₅₀ = 1.01mg/mL) inhibitory effect, scavenged DPPH (0.62 mg/mL) and OH (0.40 mg/mL) radicals than the blanched (LPO, IC₅₀ = 1.43 mg/mL; DPPH, 0.82 mg/mL; OH, 0.75 mg/mL). Furthermore, catechin, caffeic and ellagic acid, epigallocatechin, rutin, isoquercitrin and quercetin were identified in addition with gallic and chlorogenic acids and quercitrin in raw AL, while caffeic acid derivative (13.40 mg/g) was detected in blanched AL only. Conclusively, blanching reduced the antioxidant and antidiabetic potentials and phenolic contents of African lettuce leaves as evidence in the blanched AL.