Abstract
Moringa oleifera leaf is a popular green leafy vegetable which has found its usefulness in the preparation of traditional stews and soups. Like most green leafy vegetable which are not around year‐round, the leaf is usually dried and pulverized for storage and easier handling, and despite the popularity of this processing technique, there is dearth of information on how drying affects the health‐promoting properties of the leaves. Hence, this study sought to investigate the effect of some drying methods (freeze‐drying, sun, air and oven drying) on the phytoconstituents, antioxidant properties, and biological activities of moringa leaf. This study revealed that drying methods significantly altered the phytoconstituents (phenolics, flavonoids, vitamin C, tannin, saponin, phytate, oxalate, alkaloid, cardenolides, and cardiac glycosides), antioxidant capacities (reducing power, Fe2+chelating, ABTS •+, DPPH, and • OH scavenging abilities), and enzyme inhibitory (α‐amylase and α‐glucosidase) effects of the leaf, with freeze‐drying being the most promising method for preserving the nutraceutical properties of moringa leaf. However, for practical application, the order of preference of the drying methods which ensures adequate retention of phytoconstituents and possibly biological activities of the leaf as observed in this study is freeze‐drying > air drying > sun drying > oven drying, in the order of decreasing magnitude.
Highlights
Moringa oleifera is a pan-tropical plant having small-or medium- sized perennial softwood tree with timber of low quality
Sun drying and air drying at room temperature are the most common practices used in many parts of the world to preserve vegetables for dry season consumption while freeze-drying and oven drying are rarely used (Lyimo, Nyagwegwe, & Mukeni, 1991)
The phytochemical analysis of the moringa leaf showed the presence of phenolics, flavonoids, vitamin C, tannin, saponin, phytate, oxalate, alkaloid, cardenolides and cardiac glycosides and revealed a variation in their concentration after being subjected to different drying processes
Summary
Moringa oleifera is a pan-tropical plant having small-or medium- sized perennial softwood tree with timber of low quality. Moringa have found usefulness in the folk medicine where the infusions, decoctions, and concoctions of various parts of this plant are used in the treatment of several ailments such as cardiac and circulatory stimulants; possesses antitumor, antipyretic, antiepileptic, anti-inflammatory, antiulcer, antispasmodic, diuretic, antihypertensive, cholesterol lowering, antioxidant, antidiabetic, hepatoprotective, antibacterial, and antifungal activities (Anwar et al, 2007) These health-promoting effects have been attributed to its constituent phytochemicals such as zeatin, quercetin, β-sitosterol, caffeoylquinic acid, and kaempferol Like most green leafy vegetables in Nigeria, is not around year-round; they are usually processed dry using several local means such as sun drying, drying under shade, and oven drying These dried leaves are pulverized and applied directly to soups as thickener and to several other food preparations. This study sought to investigate the effect of some drying methods (air-, oven-, sun-, and freeze-drying) on some phytoconstituents of moringa leaf and to ascertain how this affects its antioxidant properties and inhibitory effects on α-amylase and α-glucosidase activities in vitro
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