Effect of storage and extraction on ratio of soyasaponin I to 2,3-dihydro-2,5-dihydroxy-6-methyl-4-pyrone-conjugated soyasaponin I in dehulled peas (Pisum sativumL)

The effects of solvent and time on extraction of 2,3-dihydro-2,5-dihydroxy-6-methyl-4-pyrone (DDMP)-conjugated soyasaponin I in dehulled peas (Pisum sativum L) were studied. Extraction in 80% ethanol gave a higher and more stable yield than 100% methanol over the time studied. Acetonitrile did not extract any detectable saponins. Both soyasaponin I and the DDMP-conjugated form were present in the extracts of dehulled, dried peas. The proportion of soyasaponin I to the DDMP-conjugate, calculated as the ratio of the molecular ions, increased with increasing extraction time, from an initial 0·24 after 0·5 h to 0·55 after 24 h of extraction in 80% ethanol, showing that the DDMP-conjugate was hydrolysed during the extraction. Storage of dried dehulled peas also increased the proportion of soyasaponin I, from 0·063 in newly harvested peas to 0·34 after 9 months of storage. Peas harvested in 1988 and stored for 7 years had a ratio of 0·78. These results clearly show that the DDMP-conjugate was converted to soyasaponin I both during storage and extraction of the peas.