Evaluation of advanced extraction techniques to obtain bioactive enriched extracts from garlic (Allium sativum L.) by-products

Garlic (Allium sativum L.) residues generated during its production are very abundant and their disposal can have a negative impact on the environment, in addition to entailing high management costs for producers. On the other hand, the numerous health benefits of garlic associated to its composition in organosulfur compounds (OSC), bioactive carbohydrates (BCH) and free amino acids (AA), among others, could be also attributed to these discarded residues. Therefore, there is great interest in the development of new, efficient, fast and environmentally friendly extraction methodologies of bioactive compounds for the revalorization of these by-products.Thus, in this work, new ultrasound-assisted extraction (UAE) and pressurized liquid extraction (PLE) methodologies were optimized using experimental designs to efficiently obtain multifunctional extracts from different garlic by-products. Stems were selected as the most promising bioactive source for their highest content of bioactive compounds. Concentration of bioactives extracted by these techniques were compared with those achieved by conventional solid liquid extraction (SLE). Among them, the optimized UAE methodology (40 °C, 60 min and 77 mg mL−1) was selected as optimal and applied to garlic stems of different ecotypes and stages of plant growth, obtaining high concentrations of OSC (e.g. S-allyl-L-cysteine, S-1-propenyl-L-cysteine and S-allyl-mercaptocysteine), BCH (myo-inositol, neokestose, 1-kestose, nystose and neonystose) and free AA (glutamine, lysine, phenylalanine, leucine, isoleucine, methionine, valine and threonine). Thus, UAE extracts of garlic stems are therefore proposed as a very interesting source of bioactive compounds to be used as food ingredients and as a way for revalorization of garlic by-products.