Chromogenic assay is more efficient in identifying alpha-amylase inhibitory properties of anthocyanin-rich samples when compared to the 3,5-dinitrosalicylic acid (DNS) assay.

The inhibition of carbohydrate digestion by plant bioactive compounds is a potential dietary strategy to counteract type 2 diabetes. Indeed, inhibition of ?alpha-amylase, a key enzyme that carries out the bulk of starch digestion, has been demonstrated for a range of bioactive compounds including anthocyanins; however, sample pigmentation often interferes with measurements, affecting colorimetric assay outcomes. Therefore, the present study compared the performance of a direct chromogenic assay, using 2-chloro-4 nitrophenyl ?-D-maltotrioside (CNPG3) as a substrate, with the commonly used 3,5-dinitrosalicylic acid (DNS) assay. The direct chromogenic assay demonstrated a 5-10-fold higher sensitivity to determine ?-amylase inhibition in various samples, including acarbose as a reference, pure anthocyanins, and anthocyanin-rich samples. The IC50 values of acarbose presented as 37.6 ?g/mL and 3.72 ?g/mL for the DNS assay and the direct chromogenic assay, respectively, whereas purified anthocyanins from blackcurrant showed IC50 values of 227.4 ?g/mL and 35.0 ?g/mL. The direct chromogenic assay is easy to perform, fast, reproducible, and suitable for high-throughput screening of pigmented alpha-amylase inhibitors.