Microwave Assisted Extraction of Bioactive Carbohydrates from Different Morphological Parts of Alfalfa (<i>Medicago sativa</i> L.)

Abstract

Despite the nutritional properties of alfalfa, its production is mainly for animal feed and it is undervalued as a food source. In this study, the valorization of alfalfa as a potential source of bioactive carbohydrates [inositols, α-galactooligosaccharides (α-GOS)] is presented. A Box–Behnken experimental design was used to optimize the extraction of these carbohydrates from leaves, stems, and seeds of alfalfa by solid–liquid extraction (SLE) and microwave-assisted extraction (MAE). Optimal extraction temperatures were similar for both treatments (40 °C leaves, 80 °C seeds); however, SLE required longer times (32.5 and 60 min vs. 5 min). In general, under similar extraction conditions, MAE provided higher yields of inositols (up to twice) and α-GOS (up to 7 times); hence, MAE was selected for their extraction from 13 alfalfa samples. Pinitol was the most abundant inositol of leaves and stems (24.2–31.0 mg·g−1 and 15.5–22.5 mg·g−1, respectively) while seed extracts were rich in α-GOS, mainly in stachyose (48.8–84.7 mg·g−1). In addition, inositols and α-GOS concentrations of lyophilized MAE extracts were stable for up to 26 days at 50 °C. These findings demonstrate that alfalfa is a valuable source of bioactive carbohydrates and MAE a promising alternative technique to obtain functional extracts.

Keywords

• alfalfa (<i>Medicago sativa</i> L.)
• α-galactooligosaccharides (α-GOS)
• inositols
• sugars
• microwave assisted extraction (MAE)
• solid-liquid extraction (SLE)