Steam treatment of green Cyclopia longifolia - Delivering herbal tea infusions with a high bioactive content and improved aroma

Steam treatment of fresh, shredded plant material (0, 30, 60, 90 and 120 s) and dried, shredded green plant material (0, 1, 2, 3 and 4 min) of Cyclopia longifolia was investigated to reduce negative aroma notes, such as “green grass” and “hay/dried grass”, but without compromising the green leaf colour and phenolic content. Steam treatment not only decreased the vegetal aroma intensities, but also increased sweet, fruity intensities. The dried plant material was less susceptible to the impact of steam than the fresh plant material, and steam duration had little effect. Steam treatment had little impact on leaf colour, although the total chlorophyll content was decreased. The content of only two polyphenols, namely tetrahydroxyxanthone-di-O,C-hexoside isomer A and scolymoside, were slightly but significantly (P < 0.05) reduced by steam treatment of the fresh plant material. Infusions prepared from a large number of batches of green C. longifolia (n = 50) confirmed high levels of polyphenols at “cup-of-tea” strength, in particular the xanthones, mangiferin and isomangiferin, and the benzophenones, 3-β-d-glucopyranosyliriflophenone and 3-β-d-glucopyranosyl-4-β-d-glucopyranosyloxyiriflophenone. It could thus make a substantial contribution to the dietary intake of these types of polyphenols.