EFFECTS OF DRYING METHODS ON THE ANTIOXIDANT PROPERTIES AND ANGIOTENSIN-I CONVERTING ENZYME INHIBITORY ACTIVITY OF AFRICAN MISTLETOE (LORANTHUS BENGWENSIS L.) LEAVES.

Abstract

African mistletoe (Loranthus bengwensis L.) has been employed in sub-Sahara African folklore for the treatment of many degenerative diseases such as hypertension. It has been reported that drying methods play an important role in herbs production. This study sought to investigate the most appropriate drying method for mistletoe leaves by assessing the influence of drying methods of these leaves on their antioxidant properties and inhibition of Angiotensin I-converting enzyme (ACE); a key enzyme linked to hypertension. Fresh leaves obtained from almond and kolanut host trees were subjected to oven drying, sun drying and air drying respectively. The aqueous extract of the samples were prepared (1:20 w/v) and then used for subsequent analysis. The extracts were characterized using HPLC-DAD, thereafter, the vitamin C, total phenol and flavonoid contents as well as the antioxidant properties were evaluated. Then, the inhibitory effect of the aqueous extracts of the leaves on ACE was determined in vitro. The vitamin C content ranged from 17.33mg.AAE/100g (almond-oven dried) to 8.09mg.AAE/100g (almond-air dried). Also the total phenol ranged from 10.26mg.GAE/100g (almond-oven dried) to 6.19mg.GAE/100g (Kolanut-air dried), while the flavonoid content ranged from 4.05mg.QUE/100g (almond-oven dried) to 2.09mg.GAE/100g (almond-air dried). In addition, all extracts scavenged DPPH, ABTS, NO, OH radicals in dose-dependent manner as well as reduced Fe3+ to Fe2+ and chelate Fe2+. Also, the extracts dose-dependently inhibited Fe2+ and sodium nitropruside induced lipid peroxidation in rat’s heart and kidney. Furthermore, oven dried mistletoe extract from almond host [kidney (276.09μg/mL), lungs (303.41μg/mL)] plant had the highest inhibitory effect on angiotensin І converting enzyme while air dried mistletoe extract from kolanut [kidney (324.09μg/mL), lungs (458.21μg/mL)] had the least. This study revealed that oven drying is the best method for mistletoe obtained from almond host tree while sun drying is the best for mistletoe obtained from Kolanut host tree confirming that diversity in drying methods leads to different loss of phenolic compounds and antioxidant property, suggesting that each plant family needs a special drying method.