Effect of Processing on Taste Quality and Health-Relevant Functionality of Sweet Potato Tips

The effects of fermenting, boiling, and steaming processes on the levels of free amino acids, organic acids, antioxidant properties (FRAP and DPPH), phenolic compounds, and angiotensine converting enzyme (ACE) inhibition of sweet potato tips were investigated. Seventeen free amino acids were found in the tips. Fermenting, boiling, and steaming processes significantly reduced total free amino acid contents and steaming processes caused smaller losses than fermenting and boiling processes. Five organic acids were investigated in the tips. In comparison with the total organic acid content of unprocessed sweet potato tips, steaming and boiling processes significantly reduced it, while fermenting process increased it. Chlorogenic acid, rutin, and quercetin were investigated in the tips. The total phenolic compounds contents of sweet potato tips significantly increased by steaming and boiling processes, but a substantial loss was caused by fermenting process. A similar result was shown in FRAP value. The result of ACE inhibitory activity indicated that boiling, steaming, and fermenting processes significantly increased ACE inhibitory activity.