Effect of matrix pretreatment on microwave assisted extraction of curcumin as an alternative to conventional solid liquid extraction

The present work reports on an improved extraction method using microwaves based on solvent–sample duo-heating synergism, for the extraction of curcumin from Curcuma longa L rhizomes. The dual heating mechanism is based on simultaneous heating of sample matrix and extracting solvent simultaneously to different extent based on their differences in converting the absorbed microwave energy to heat energy [1]. The objective behind the work was to reduce the extraction time and solvent consumption for the extraction of botanicals with special care to thermolabile botanicals. Methanol was used as a modifier to soak the plant material to bring about selective and effective heating of the sample matrix under microwave. Acetone was used as the extracting solvent, which has excellent curcumin solubilizing capacity and heats up under microwave moderately owing to its good dissipation factor. Extraction conditions, namely microwave power, irradiation time, particle size and modifier volume were optimized using orthogonal array design approach and curcumin was quantified using high performance thin layer chromatography [2]. The optimum conditions as obtained from signal-to-noise ratio analysis and interaction studies between factors were as follows: 20% microwave power, 4min irradiation time, particles screened through sieve 20 and 8ml of modifier. Microwave assisted extraction (MAE) of 4min under the influence of dual heating mechanism showed a much greater yield with high degree of reproducibility than 24 hours of conventional solid-liquid extraction like Soxhlet, maceration and stirring extraction. Microwave energy absorbed by the plant material generates a sudden increase in temperature inside the cells. The higher temperature attained by the cell wall, during MAE, causes dehydration of cellulose and reduces its mechanical strength, which allows the solvent to gain an easy entry inside the oleoresin cells and solubilize out curcumin in a much shorter time.

References: 1. Luque de Castro, M.D., Garcia-Ayuso, L.E. (1998) Anal. Chim. Acta 369: 1–10.

2. Mandal, V. et al. (2007) Phcog. Rev. 1: 7–18.