Acid hydrolysis of saponin-rich extracts of quinoa, lentil, fenugreek and soybean to yield sapogenin-rich extracts and other bioactive compounds

This is the peer reviewed version of the following article: Journal of the Science of Food and Agriculture 99. 6 (2019): 3157-3167, which has been published in final form at https://doi.org/10.1002/jsfa.9531 . This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Use of Self-Archived VersionsBACKGROUN: Typical hydrolysis times of saponins generally do not take into consideration the effect of time on the degradation of the target compounds, namely sapogenins. When producing natural extracts, it should be borne in mind that conducting hydrolysis to yield a target compound might also affect the final composition of the extracts in terms of other bioactive compounds. In our study, saponin-rich extracts from fenugreek, quinoa, lentil, and soybean were produced and their acid hydrolysis to give sapogenin-rich extracts was conducted over different periods (0–6 h). The disappearance of saponins and appearance of sapogenins was analyzed using high-performance liquid chromatography–diode array detection–mass spectrometry (HPLC-DAD-MS) and gas chromatography–mass spectrometry (GC-MS), respectively. The impact of hydrolysis on the phytosterols and tocopherol in the extracts was also evaluated. RESULTS: Fenugreek showed the highest saponin content (169 g kg −1 ), followed by lentil (20 g kg −1 ), quinoa (15 g kg −1 ), and soybean (13 g kg −1 ). Hydrolysis for 1 h caused the complete disappearance of saponins and the greatest release of sapogenins. Hydrolyzed fenugreek and quinoa extracts contained the highest amounts of sapogenins and minor fractions of phytosterols and tocopherol. Hydrolyzed extracts of lentil and soybean contained a major fraction of phytosterols and a low fraction of sapogenins. In all cases, sapogenins decreased after 1 h of hydrolysis, phytosterols slightly decreased, and tocopherol was unaffected. Standards of diosgenin and oleanolic acid also showed this decreasing pattern under acid hydrolysis conditions. CONCLUSION: Hydrolysis times of 1 h for saponin-rich extracts from the assayed seeds guarantee the maximum transformation to sapogenin-rich extracts, along with phytosterols and tocopherol. Fenugreek and quinoa seeds are preferred for thisThis work was supported by the Ministerio de Economía y Competitividad, Spain (AGL2016-76736-C3-1-R) and the Community of Madrid, Spain (ALIBIRD-CM S2013/ABI-2728). Teresa Herrera thanks the Community of Madrid for her contract (Fondo Social Europeo, Programa Operativo de Empleo Juvenil e Iniciativa de Empleo Juvenil YEI). Joaquín Navarro del Hierro thanks the Ministerio de Educación, Cultura y Deporte for funding his research with a Formación de Profesorado Universitario (FPU) predoctoralcontract (FPU 15/04236). The authors would like to acknowledgethe support of the chromatography laboratory from the Interde-partmental Investigation Service (SIdI-UAM) for the HPLC-MS anal-yse