Extraction and purification of anthocyanins from purple-fleshed potato

Extraction and purification of anthocyanins from purple-fleshed potatoes was investigated. The effects of pretreatment method, time, and ethanol concentration on the extraction were studied. Boiling was the most efficient pretreatment method for the extraction. Extraction time and ethanol concentration were found to have only minor effect on the extraction yield. Six hour extraction time and 20 vol.% ethanol concentration were found to be sufficient. The resulting anthocyanin-rich extract contained glucose, proteins, amino acids, and unidentified compounds as impurities. Removal of these by adsorption was studied with six commercially available adsorbents, of which Amberlite XAD-7HP was the most efficient. Anthocyanin purification with XAD-7HP was studied in a column. The effects of flow rate on adsorption, and ethanol and acetic acid concentrations on desorption were investigated. In loading, a highly dispersed anthocyanins breakthrough curve was obtained. This most likely resulted from agglomeration of anthocyanins. Desorption of anthocyanins could be done efficiently with 75 vol.% acidic (7 vol.% acetic acid) aqueous ethanol. All glucose and unknown impurities, together with 87% of proteins and amino acids, could be separated from the anthocyanins. Process scale-up was demonstrated by processing 19 kg of purple-fleshed potatoes in a single batch.