The antioxidant properties and effect of essential oil of black pepper (Piper guineense) seeds on α-amylase, α-glucosidase (key enzymes linked to type-2 diabetes), and angiotensin-I converting enzyme (ACE) (key enzyme linked to hypertension) were assessed. The essential oil was obtained by hydrodistillation and dried with anhydrous Na2SO4, and the phenolic content, radical [1,1-diphenyl-2 picrylhydrazyl (DPPH), 2,2′-azino-bis(3-ethylbenzthiazoline-6-sulphonic acid) (ABTS) and nitric oxide (NO)] scavenging abilities as well as the ferric reducing antioxidant property (FRAP) and Fe2+-chelating ability of the essential oil were investigated. Furthermore, the effect on α-amylase, α-glucosidase, and ACE enzyme activities was also investigated. The characterization of the constituents was done using GC. The essential oil scavenged DPPH*, NO*, and ABTS* and chelated Fe2+. α-Pinene, β-pinene, cis-ocimene, myrcene, allo-ocimene, and 1,8-cineole were among the constituents identified by GC. The essential oil inhibited α-amylase, α-glucosidase, and ACE enzyme activities in concentration-dependent manners, though exhibiting a stronger inhibition of α-glucosidase than α-amylase activities. Conclusively, the phenolic content, antioxidant activity, and inhibition of α-amylase, α-glucosidase, and angiotensin-1 converting enzyme activities by the essential oil extract of black pepper could be part of the mechanism by which the essential oil could manage and/or prevent type-2 diabetes and hypertension. 1. Introduction Essential oils from aromatic spice plants have been shown to be good antioxidants using various antioxidant assay models [1–3] and the antioxidant activities have been linked to the phenolic contents in some of the oils [4, 5]. Furthermore, some medicinal properties of essential oils from aromatic spice plants have been established, especially essential oils from black pepper (Piper guineense) seeds which have been shown to have antimicrobial, antihypertensive, anticonvulsive, and sedative activities [5–7]. Black pepper (Piper guineense) is a spicy plant whose essential oils from the seed and leaves are being extracted and sold in commercial quantities in many countries [8]. Monoterpenes, benzoids, and sesquiterpenes have been identified among the volatile compounds of the black pepper [9]. In recent years, the management of type-2 diabetes and hypertension through natural sources has been done in two major ways: the scavenging of free radicals and inhibition of key enzymes involved in starch digestion (α-amylase and α-glucosidase) and high blood pressure
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