Influence of postharvest processing and storage conditions on key antioxidants in pūhā (Sonchus oleraceus L.).
OBJECTIVE
To investigate effects of different postharvest drying processes and storage conditions on key antioxidants in Sonchus oleraceus L. leaves.


METHODS
Fresh leaves were oven-dried (60°C), freeze-dried or air-dried (∼25°C) for 6 h, 24 h and 3 days, respectively. Design of experiments (DOE) was applied to study the stability of antioxidants (caftaric, chlorogenic and chicoric acids) in S. oleraceus leaves and leaf extracts stored at different temperatures (4, 25 and 50°C) and relative humidities (15%, 43% and 75%) for 180 days. The concentration of antioxidants was quantified by a HPLC-2,2'-diphenylpicrylhydrazyl post-column derivatisation method. Antioxidant activity was assessed by a cellular antioxidant activity assay.


RESULTS
The three antioxidants degraded to unquantifiable levels after oven-drying. More than 90% of the antioxidants were retained by freeze-drying and air-drying. Both leaf and extract samples retained >90% of antioxidants, except those stored at 75% relative humidity. Leaf material had higher antioxidant concentrations and greater cellular antioxidant activity than corresponding extract samples.


CONCLUSIONS
Freeze-drying and air-drying preserved more antioxidants in S. oleraceus than oven-drying. From DOE analysis, humidity plays an important role in degradation of antioxidants during storage. To preserve antioxidant activity, it is preferable to store S. oleraceus as dried leaf material.
School of Pharmacy, University of Otago, Dunedin, New Zealand.
Zong-Quan
ZQ
Ou
David M
DM
Schmierer
Clare J
CJ
Strachan
Thomas
T
Rades
Arlene
A
McDowell
D000975:Antioxidants / Q000032:analysis*; D002109:Caffeic Acids / Q000032:analysis; D002726:Chlorogenic Acid / Q000032:analysis; D003890:Desiccation; D004355:Drug Stability; D004356:Drug Storage; D005612:Freeze Drying; D006801:Humans; D006813:Humidity; D010636:Phenols / Q000032:analysis; D010936:Plant Extracts / Q000737:chemistry*; D018515:Plant Leaves / Q000737:chemistry*; D031184:Sonchus / Q000737:chemistry*; D013386:Succinates / Q000032:analysis; D013696:Temperature
D000975:Antioxidants; D002109:Caffeic Acids; D010636:Phenols; D010936:Plant Extracts; D013386:Succinates; D002726:Chlorogenic Acid; C100435:chicoric acid; C515101:caftaric acid
Sonchus oleraceus; antioxidants; design of experiments; leaf extracts; postharvest storage