Effect of heat treatment on curcuminoid, colour value and total polyphenols of fresh turmeric rhizome

Abstract

Studies were undertaken to examine the effect of heat treatment on total phenolic content (TPC), colour value (yellowishness and brightness), polyphenol oxidase (PPO) activity and curcuminoid of fresh turmeric rhizome. Fresh turmeric rhizomes were subjected to heat treatment at different temperatures (60-100 degrees C) for different durations (10-60 min), causing a reduction in browning which was evident from the improved yellowishness and brightness. Activity of PPO was also decreased during heat treatment and PPO was almost inactivated when heated at 80 degrees C for 30 min. TPC of heat-treated turmeric after drying (powder) is significantly higher than that after the fresh process. TPC values increased gradually when samples were heated from 60 to 80 degrees C. At 90 and 100 degrees C, TPC values were almost identical. Maximum brightness and yellowishness were obtained when the turmeric was heated above 80 degrees C. Quantitation of curcuminoids in the turmeric sample was made with high performance thin layer chromatography (HPTLC). There was no significant change in the concentration of curcuminoids among the heat-treated samples. But in the sun-dried samples, a signi. cant reduction in curcuminoid concentration was observed.