Production of dihydrochalcone-rich green rooibos (Aspalathus linearis) extract taking into account seasonal and batch-to-batch variation in phenolic composition of plant material

Abstract

a b s t r a c t a r t i c l e i n f o Available online xxxx Edited by: J. van StadenRandomly selected rooibos plants from three plantations were harvested (a few branches per plant) at intervals from early summer to late spring. The aspalathin and nothofagin content of the plant material was highest at the first harvest date (3.76% and 0.54%, respectively) in summer whereafter their content decreased gradually to the lowest levels in winter and increased to 3.31% and 0.36%, respectively in mid-spring. Commercial green rooibos production batches (n = 47), produced over a period of 49 days (end of January until mid-March) from plant material harvested from one plantation were analysed to provide further insight into expected batch-to-batch variation in aspalathin, nothofagin, orientin and iso-orientin content. The aspalathin content of green rooibos varied between 2.50% and 4.49%, even though the plant material was harvested from the same plantation. The other compounds were present in the plant material in much lower quantities (b0.5%). The iso-orientin and orientin contents of the green rooibos samples did not vary substantially. The variation observed in the plant material was subsequently also observed in the freeze-dried hot water extracts prepared from the commercial green rooibos production batches, with the theoretical dried extract yield varying between 15.07% and 22.89%. The aspalathin content and total polyphenol content of the dried extract varied between 8.11% and 12.33% and between 29.7 and 43.5 g gallic acid equivalents/100 g, respectively. The mean content values for the other compounds were less than 1.2%. Combined these major dihydrochalcones and flavones comprised between 10.22% and 14.88% of the freeze-dried extract. Aspalathin contributed between 13.1% and 22.8% of the total antioxidant capacity (2873-4286 μmol Trolox equivalents/g) of the dried extract as determined by the DPPH radical scavenging assay.

Aspalathin from Rooibos (Aspalathus linearis): A Bioactive C-glucosyl Dihydrochalcone with Potential to Target the Metabolic Syndrome

“…tional manner that includes the "fermentation" (oxidation) step for development of the characteristic red-brown leaf colour and "woody", "fynbos-floral", and "honey" flavour [23,24], and contains very little aspalathin (0.02-1.2 %) [20], while the "unfermented product", green rooibos, has an aspalathin content between 2.5 and 4.5 % [25]. Hot water extracts prepared from fermented and green rooibos are used as food and/or cosmetic ingredients.…”

“…Hot water extracts prepared from fermented and green rooibos are used as food and/or cosmetic ingredients. If a high aspalathin content is required, a hot water extract (aspalathin content > 8 %) of green rooibos [25] is preferable. On the other hand, a hot water extract (aspalathin content < 2 %) of fermented rooibos [26] is more economical to produce and it is preferred in food products, such as rooibos iced tea, when the flavour is important [27].…”

Rooibos (Aspalathus linearis) Genome Size Estimation Using Flow Cytometry and K-Mer Analyses

“…Analyses with different plant species [37] showed that plant tissues richer in polyphenols yielded higher flow cytometry genome size estimates than plant tissues with low polyphenol contents. In rooibos, aspalathin concentrations have been shown to be higher in leaves than in stems [38], but comparative analyses for seedling tissues are outstanding.…”

Minimising variation in aspalathin content of aqueous green rooibos extract: optimising extraction and identifying critical material attributes

“…Subchronic feeding of type 2 diabetic model (KK‐A y ) mice with a cold‐water based green rooibos extract containing 66 g kg −1 aspalathin suppressed the increase in their fasting blood glucose levels . Previously, we demonstrated that green rooibos extract containing at least 80 g kg −1 aspalathin was achievable when green rooibos was subjected to a hot water extraction process, similar to that used industrially for the production of food grade extracts of fermented rooibos …”

“…This is manifested as a large variation in the AC of their hot water extracts. Only a moderate correlation ( r = 0.695) between the dihydrochalcone (sum of aspalathin and nothofagin) content of the plant material batches and their extracts was obtained, suggesting that other factors play a role that have not been taken into account. Extracts containing a higher than required level of a target bioactive compound could be diluted to meet the specification using an excipient.…”