2.1. Bitter melon preparation
Bitter melon was grown at, Phitsanulok. The voucher specimens were kept at the PBM Herbarium, Mahidol University, Thailand. Unripe bitter melon fruits 3–5 in. long were collected and the seeds were removed. Fruit pulps were dried by hot air oven at 60 °C for 24 h. Dried fruit pulps were tested for microbial contamination by Faculty of Medical Sciences, Naresuan University, and heavy metal and insecticide contamination by Regional Medical Sciences Center, Phitsanulok. Dried fruit pulps which passed all tests were powdered. Each capsule contained 500 mg of dried powder of the fruit pulp, containing 0.04–0.05% (w/w) of charantin. The charantin level was determined by Faculty of Pharmaceutical Sciences, Mahidol University, Thailand, using HPLC method (Pitipanapong et al., 2007).