Botanical composition and aroma compounds of semi-arid pastures in Algeria

This study aims to determine the botanical composition of different pastures in a semiarid region of Algeria and investigate the aromatic profile of the characteristic plant species grazed by goats and sheep. At three pastures (1: montane area with spontaneous vegetation 'never cultivated before', 2: previously cultivated but set at rest, 3: cultivated, under cereal production), plants were sampled twice during April-May to determine plant composition. Based on dominance of fresh aerial biomass of each plant per pasture and consumption by dairy goats, 10 species (Atractylis humilis, Calendula arvensis, Filago pygmaea, Globularia alypum, Hordeum vulgare, Malva sylvestris, Plantago sp., Scolymus hispanicus, Sonchus asper and Thymus algeriensis) were selected and sampled once at flowering stage to characterize their aromatic profile. The odour-active compounds (OACs) of the selected species were extracted using steam distillation, then detected and identified using gas chromatography/mass spectrometry/olfactometry (GC/MS/O). The analysis of botanical composition revealed the presence of 70 species (29 in mountain, 40 in set at rest, 11 in cultivated pasture) belonging to 62 genera and 22 families, with dominance of Asteraceae species. A total of 86 different OACs were identified, including mainly terpenes (21) and aldehydes (18). Among the OACs, 19 different compounds have various odour notes including herbaceous, floral, sweet spicy, fried, mint, cooked, fruity, sulphur, sweet and unpleasant notes. The number of OACs and individual chemical classes differed significantly between selected species. Atractylis humilis contained more OACs than Scolymus hispanicus and Plantago sp., whereas Globularia alypum had higher number of OACs compared to Plantago sp. This study gave a general overview on plant aroma profile of semiarid pastures in Algeria and suggests that the aromatic profile of grazed plants in the pasture is determinant of the aromatic quality of dairy-derived foods which depends also on animal feed selection.