Effect of cultivars and deep freeze storage on saponin content of white asparagus spears (Asparagus officinalis L.)

A method was developed to prepare saponin samples of asparagus spears by Solid Phase Extraction (SPE) and to analyse these extracts by High Performance Thin Layer Chromatography (HPTLC). We chose six asparagus cultivars grown in Germany and measured total saponin contents of approximately 0.14–0.80 g kg−1 fresh weight (fw). Among these six cultivars grown under eaqual conditions ‘Grolim’ showed the highest levels of saponins while ‘Huchels Alpha’ had the lowest contents. The other four cultivars gave intermediate levels. Asparagus stored at −18°C subsequently resulted in maintenance of saponins during 20 weeks of storage. Up to six saponins were found in the extracted samples, but three of them were the main compounds with approximately 90% of the total saponin content. Two main saponins (AS 1 and AS 2) were characterised by mass spectrometry as protodioscin and methyl-protodioscin.