Ultrasound-assisted Co-extraction and characterization of saponin-rich Co-extracts from fenugreek seeds (Trigonella foenum-graecum L.) and quinoa husk (Chenopodium quinoa Willd.) and their hydrolysates

The co-extraction of steroidal and triterpenoid saponins, followed by hydrolysis to produce sapogenin-rich extracts, offers an efficient strategy to enhance the multi-bioactive potential of extracts. The resulting chemical composition modifications, including the presence of other co-extracted or co-hydrolyzed compounds, must also be considered. In this study, ultrasound-assisted co-extraction of fenugreek seeds and quinoa husk using methanol and 50% aqueous methanol was conducted to obtain extracts and co-extracts with varying proportions of steroidal and triterpenoid saponins, in ratios of 0:100, 25:75, 50:50, 75:25, and 100:0, respectively. Aqueous methanol produced the highest extraction yields (15-25%) and saponin contents (40-70%) in the extracts and co-extracts. The conversion by microwave-assisted acid hydrolysis of saponins to sapogenins was more efficient for triterpenoid saponins, leading to a higher triterpenoid sapogenin content in all co-extracts, accounting for over 70% of the total sapogenins. The co-extracts also contained other bioactive compounds, such as phenolic compounds (3-4 g/100 g), with their content being favored by the presence of fenugreek. Hydrolysis altered the overall composition of the saponin-rich co-extracts, enriching the resulting hydrolyzed products in both types of sapogenins, along with fatty acids, carbonyls, non-protein nitrogen compounds and organic acids, while reducing monoglycerides, removing carbohydrates and significantly modifying the phenolic profile by eliminating many original phenolic compounds and generating new ones. Therefore, co-extraction and post-extraction hydrolysis of fenugreek and quinoa allowed the combination of triterpenoid and steroidal saponins or sapogenins into single products, along with other specific compounds from both sources. • Fenugreek and quinoa were simultaneously co-extracted by UAE to obtain saponins • Microwave-assisted acid hydrolysis allows to obtain sapogenin-rich co-extracts • The conversion of saponins to sapogenins is more efficient for triterpenoid type • Co-extracts contain other bioactive compounds such as phenolic compounds • Acid hydrolysis process leads to changes in the overall composition of co-extracts