Impact of Drying Processes on Phenolics and In Vitro Health-Related Activities of Indigenous Plants in Thailand

Abstract

Thailand has vast areas of tropical forests with many indigenous plants, but limited information is available on their phytochemical profile and in vitro inhibitions of enzymatic and nonenzymatic reactions. This study investigated phenolic profiles using liquid chromatography-electrospray ionization tandem mass spectrometry (LC-ESI-MS/MS), antioxidant activities, and in vitro inhibitory activities of 10 indigenous plants on key enzymes related to obesity (lipase), diabetes (α-amylase and α-glucosidase), and Alzheimer's disease (cholinesterases and β-secretase). The nonenzymatic anti-glycation reaction was also investigated. The 10 indigenous plants were <i>Albizia lebbeck</i> (L.) Benth, <i>Alpinia malaccensis</i> (Burm.) Roscoe, <i>Careya arborea</i> Roxb., <i>Diplazium esculentum</i> (Retz.) Swartz, <i>Kaempferia roscoeana</i> Wall., <i>Millettia brandisiana</i> Kurz., <i>Momordica charantia</i>, <i>Phyllanthus</i><i>emblica</i> L., <i>Zingiber cassumunar</i> Roxb, and <i>Zingiber citriodorum</i> J. Mood & T. Theleide. Preparations were made by either freeze-drying or oven-drying processes. Results suggested that the drying processes had a minor impact on in vitro inhibitions of enzymatic and nonenzymatic reactions (<4-fold difference). <i>P. emblica</i> was the most potent antioxidant provider with high anti-glycation activity (>80% inhibition using the extract concentration of ≤6 mg/mL), while <i>D. esculentum</i> effectively inhibited β-secretase activity (>80% inhibition using the extract concentration of 10 mg/mL). <i>C. arborea</i> exhibited the highest inhibitory activities against lipase (47-51% inhibition using the extract concentration of 1 mg/mL) and cholinesterases (>60% inhibition using the extract concentration of 2 mg/mL), while <i>Mi. brandisiana</i> dominantly provided α-amylase and α-glucosidase inhibitors (>80% inhibition using the extract concentration of ≤2 mg/mL). Information obtained from this research may support usage of the oven-drying method due to its lower cost and easier preparation step for these studied plant species and plant parts. Furthermore, the information on in vitro inhibitions of enzymatic and nonenzymatic reactions could be used as fundamental knowledge for further investigations into other biological activities such as cell culture or in vivo experiments of these health-beneficial plants.