Seasonal variation in yield, nutritive value, and antioxidant capacity of leaves of alfalfa plants grown in arid climate of Saudi Arabia

Abstract

In addition to its high nutritional value, alfalfa (Medicago sativa L.) has several health benefits including antioxidant, neuroprotective, antimicrobial, antiulcer, hypocholesterolemic, hypolipidemic, and estrogenic effects. We aimed to assess the nutritional value and antioxidant capacity of alfalfa leaves at different times of the year in arid regions. Alfalfa was harvested in autumn, winter, spring, and summer and fresh yield and leaf:stem ratio were measured. Leaves were collected to determine their nutritional value and antioxidant capacity using two different extracts viz.: absolute ethanol or distilled water. Fresh yield and leaf:stem ratio were highest in spring (20 t ha-1 and 57.6%, respectively), followed equally by winter and autumn, and were lowest in summer (10.75 t ha-1 and 51.6%, respectively). The autumn cut had the highest crude protein (33.52%) and crude fat content (3.79%) and the lowest content of crude fiber (13.95%) and acid detergent fiber (16.55%), which are good indicators of suitability for human nourishment. However, leaves collected in autumn were characterized by lower digestibility values (86.2%) compared to the other cuts. Antioxidant capacity of leaves harvested in autumns and extracted with either ethanol or distilled water was examined in terms of total polyphenols, total flavonoids, DPPH scavenging capacity, and reducing power. Ethanol extract showed higher antioxidant capacity in terms of total phenol and total flavonoid contents (6.41 and 4.88 mg gallic acid equivalents g-1 DW, respectively). These results suggest that autumn is the most appropriate season to cut alfalfa leaves for human nutritional purposes.