EFFECT OF DRYING TEMPERATURE AND RHIZOME SIZE ON BIOACTIVE COMPONENTS OF TURMERIC (Curcuma Longa L.)

Abstract

The aim of this study was to optimize the rhizome size and drying temperature to produce high quality turmeric powder. The turmeric rhizomes were collected from local farm of Dharan. The rhizomes were cleaned and sorted into primary, secondary and tertiary rhizomes. Secondary rhizomes were taken for the study and cross section area of 2.434 ± 0.023 cm2 was maintained. Response surface methodology (randomized, design type D optimal with quadratic model) was applied using Design Expert version 13 taking factors as rhizome size from 1 to 4 cm and drying temperature from 40 to 70°C which generated sixteen samples. The samples were cut and dried as per the parameters obtained from design expert till the moisture content reached to 10%. The optimum value of rhizome size and drying temperature was obtained by the analysis of five response factors i.e. curcumin, oleoresin, essential oil content, total phenolic content and antioxidant activity. The optimized turmeric powder was compared with the market sun-dried sample. The optimum value of rhizome size and drying temperature was obtained to be 2.6 cm and 55°C with the value of curcumin, essential oil, oleoresin, TPC and antioxidant activity to be 5.8%, 7.04%, 20.85%, 38.12 mg GAE/ g dry matter and 49.68 %RSA respectively. The optimized turmeric powder was found to be superior in quality than sun-dried market sample in terms of all measured bioactive parameters and antioxidant activity. Thicker rhizome size and lower drying temperature led to the longer drying time which caused the oxidative degradation of bioactive components. Similarly, very high drying temperature and thinner rhizome size led to thermal degradation of bioactive components