Effect of heat processing of spices on the concentrations of their bioactive principles: Turmeric (Curcuma longa), red pepper (Capsicum annuum) and black pepper (Piper nigrum)

Studies were made to examine the loss of curcumin, capsaicin and piperine, the active principles of turmeric (Curcuma longa), red pepper (Capsicum annuum) and black pepper (Piper nigrum), respectively, as a result of subjecting the spices to domestic cooking processes. This involved heat treatment of each of these spices by: (i) boiling for 10 min, (ii) boiling for 20 min and (iii) pressure cooking for 10 min. Quantitation of the spice principles in the organic solvent extracts of the freeze-dried cooked spice samples was made with an appropriate HPLC method. Significant loss of spice active principles was observed when the spices were subjected to heat processing. Curcumin loss from heat processing of turmeric was 27–53%, with maximum loss in pressure cooking for 10 min. Curcumin loss from turmeric was similar even in the presence of red gram. In the presence of tamarind, the loss of Curcumin from turmeric was 12–30%. Capsaicin losses from red pepper ranged from 18% to 36%, with maximum loss observed in pressure cooking. Presence of either red gram or tamarind or both did not influence the loss of capsaicin. Piperine losses from black pepper ranged from 16% to 34%, with maximum loss observed in pressure cooking. The loss was somewhat lower in the presence of red gram. The results of this investigation indicated diminished availability of spice active principles from cooked foods when the food ingredients have been subjected to either boiling or pressure cooking for few minutes.