Sweet potato (
Ipomoea batatas
L.) is the sixth most important food crop in the world. The industry discarded huge amount of sweet potato stems, rich of peroxidases and phenolics. A simple procedure was developed to make peroxidases and phenolics from sweet potato old stems. Dried stem powder was loaded into columns with water and eluted sequentially with water and 50% ethanol. Peroxidases (91%) were extracted in 5.5-fold water extracts and 87% phenolics were extracted in 4.4-fold ethanol extracts. Purified peroxidases powder was yielded at 3.1 g (8.6 unit/mg) per kilogram stems by PEG6000/Na
2
SO
4
aqueous two-phase purification from the water extracts (93.2% recovery), followed by ethanol precipitation and vacuum freeze-drying. The purified peroxidase had high activity in transforming tea catechins into theaflavins. Phenolics powder containing 43% phenolics and 27% flavonoids was yielded at 76.9 g per kilogram stems after vacuum-concentrating the ethanol extracts. This method can make valuable functional products using the sweet potato waste.
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