title: Minimising variation in aspalathin content of aqueous green rooibos extract: optimising extraction and identifying critical material attributes.
abstract: BACKGROUND
  High levels of aspalathin, an antidiabetic dihydrochalcone, in green rooibos underpins interest in the production of a standardised extract. Elements of a quality-by-design approach were applied to optimise extraction conditions, aiming at the delivery of a dry matter yield (DMY) ≥ 160 g kg-1and an extract with an aspalathin content (AC) ≥ 80 g kg-1.
  
  
  RESULTS
  Hot water extraction parameters, namely extraction time, extraction temperature and water-to-plant material ratio, were optimised for DMY and aspalathin extraction efficiency (AEE) using Design of Experiments. Good polynomial prediction models were obtained and multiresponse desirability plots indicated 37 min, 93 °C and 23:1 as optimal conditions. Even when using 30 min and 10:1 instead for practical reasons, the target DMY and AC values could be achieved with the caveat that plant material with an AC ≥ 30 g kg-1is used. Particle size distribution and stem content were identified as contributing to variation in the AC of raw material.
  
  
  CONCLUSIONS
  By setting raw material specifications in terms of AC, as well as applying practical optimum extraction conditions, 160 g kg-1extract with an AC ≥ 80 g kg-1could be consistently achieved from green rooibos plant material. © 2017 Society of Chemical Industry.
authors.affiliation: Plant Bioactives Group, Post-Harvest and Wine Technology Division, Agricultural Research Council (ARC) Infruitec-Nietvoorbij, Stellenbosch, South Africa.|Department of Food Science, Stellenbosch University, Matieland, Stellenbosch, South Africa.
authors.forename: Neil
authors.initials: N
authors.lastname: Miller
authors.affiliation: Plant Bioactives Group, Post-Harvest and Wine Technology Division, Agricultural Research Council (ARC) Infruitec-Nietvoorbij, Stellenbosch, South Africa.|Department of Food Science, Stellenbosch University, Matieland, Stellenbosch, South Africa.
authors.forename: Dalene
authors.initials: D
authors.lastname: De Beer
authors.affiliation: Plant Bioactives Group, Post-Harvest and Wine Technology Division, Agricultural Research Council (ARC) Infruitec-Nietvoorbij, Stellenbosch, South Africa.|Department of Food Science, Stellenbosch University, Matieland, Stellenbosch, South Africa.
authors.forename: Elizabeth
authors.identifier: http://orcid.org/0000-0002-9717-9769
authors.initials: E
authors.lastname: Joubert
mesh_terms: D036903:Aspalathus / Q000737:chemistry*; D047188:Chalcones / Q000032:analysis / Q000302:isolation & purification*; D005591:Chemical Fractionation / Q000379:methods*; D010936:Plant Extracts / Q000032:analysis / Q000302:isolation & purification*; D018547:Plant Stems / Q000737:chemistry
chemical_list: D047188:Chalcones; D010936:Plant Extracts; C517016:aspalathin
keywords: Aspalathus linearis; aspalathin; green rooibos nutraceutical; hot water extraction; optimisation; quality-by-design