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

BACKGROUND 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 this. (c) 2018 Society of Chemical Industry