Impact of cooking, drying and grinding operations on chemical content, functional and sensorial qualities of Curcuma longa L.

The impact of cooking, drying and grinding on essential oil content, curcuminoid contents and their bioaccessibility and sensorial quality of Curcuma longa L. was assessed. Sliced fresh turmeric rhizomes (5 mm thick) were air-dried at 60 degrees C, 40% RH directly or pre-cooked (95 degrees C/3 min) before drying at different conditions (50, 60 or 80 degrees C; 40% RH). Dried slices, at 0.11 kg kg(-1) db water content, were ground to obtain two powders of different particle sizes (i.e. fine < 500 mu m and coarse < 750 mu m). Cooking had no impact on essential oil content, curcuminoid contents and their bioaccessibility but reduced drying time. Drying decreased essential oil content (- 22.5%), curcuminoid contents (- 11.0%) and their bioaccessibility (- 28.6%). Surprisingly, grinding had no impact on curcuminoid contents and their bioaccessibility. The combination of the tested unit operations produced final products with the same quality in terms of total curcuminoid contents (12.1 g/100 g db) and bioaccessible curcuminoids (1.0 g/100 g db). However, consumers detected significant differences in colour, texture and overall liking between processed turmeric powders (dried and cooked-dried). Our results demonstrate that smooth cooking (95 degrees C/3 min) followed by drying (60 degrees C, 40% RH) is the most appropriate process to produce a curcuminoid-rich powder and improve consumer acceptance.