Studies on quality of turmeric (Curcuma longa) in relation to curing methods

Abstract

Conventional and improved methods of primary processing of turmeric (Curcuma longa) were compared. Farm trials showed dried turmeric fingers produced by 3 treatments (water-cooking, alkaline water-cooking and traditional processing) were similar in appearance, drying characteristics, and curcumin, volatile oil and oleoresin contents. In laboratory trials, turmeric fingers were either (i) water-cooked, (ii) alkaline water-cooked, (iii) uncooked, (iv) uncooked and sliced, (v) water-cooked and sliced, (vi) water-cooked, pulped and shade dried, or (vii) uncooked, pulped and shade dried. Turmeric powder produced by treatments (vi) and (vii) was unacceptable in colour and odour. Drying times for treatments (i)-(v) were 11, 11, 30, 1 and 1 days, resp. for sun-drying, and 32, 32, 68, 7.5 and 5.5 h, resp. for mechanical drying, showing that slicing and cooking reduced drying time. Dry yield of approx. 20% was comparable for all treatments. Sun-dried samples had higher moisture contents (9.0-12.9%) than mechanically dried samples (6.3-10.8%). (ii) resulted in lower curcumin levels than (i) (2.91 and 3.16%, resp.), which differed from farm trial results due to a greater ratio of water:turmeric fingers. Recovery of curcumin using acetone solvent was reduced by pre-cooking from 92-94% (uncooked) to 76.7-84.7% (cooked). Volatile oil content (% v/w) of samples ranged from 2.97 to 3.91, non-volatile acetone extract (NVAE) from 5.22 to 7.50%, and oleoresin from 8.43 to 11.41%.