In Vitro Screening of α-Amylase Inhibition by Selected Terpenes from Essential Oils

Purpose: To assess some terpenes from herbal products for possible inhibitory effects on serum alpha-amylase in order to ascertain their potential usefulness in the prevention and/or treatment of diabetes Type 2. Methods: Solutions of terpenes (citral, eukalyptol, beta-pinene, myrcene, eugenol and terpineol) in deonized water were prepared by ultrasonic and manual mixing in four different concentrations ranging from 0.39 - 5.50 mu mol cm(-3). Commercial sera (with normal-N and high-H enzyme activity) were used as a source of alpha-amylase. alpha-Amylase activity was determined by standard methods using an automated analyzer. Results: All the selected terpenes at their maximal concentrations inhibited alpha-amylase in N-sera in the range 9.68 - 38.70 and 10.71 - 25.00 % for ultrasonic and manual mixing, respectively, while in H-sera, inhibition was in the range 17.10 - 21.05 and 13.58 - 25.92 % for ultrasonic and manual mixing, respectively. Regardless of the concentration of the inhibitor or the method of mixing, citral was the strongest inhibitor of alpha-amylase. Conclusion: The selected terpenes, in their appropriate concentrations, influence alpha-amylase activity to varying degrees. Principal component and agglomerative hierarchical analysis reveal that the most significant factor in alpha-amylase inhibition is the mode of mixing the samples, rather than their concentrations.