The vitamin C content, comprising l-ascorbic acid (AA) and l-dehydroascorbic acid (DHA), was determined according to Rybarczyk-Plonska et al. (2014) with the following minor modifications: approximately 5 g of frozen swede powder was weighed and placed into a polypropylene tube containing 10 ml ice-cold extraction solution (6% meta-phosphoric acid in 2 mM EDTA), before another 10 ml of the same ice-cold solution was added and the mixture was immediately stirred and homogenised. The homogenate was filtered through a folded cellulose filter paper without additional extraction solution. Further sample preparation and HPLC analysis was performed as previously described. Detection of AA was carried out at 264 nm and quantification was performed using external standard curves in the concentration range of 0.1–0.8 mM. Vitamin C was determined as total AA obtained after DHA reduction. The results are expressed as mg AA or vitamin C 100 g−1 fresh matter (FM).