Design of experiments for screening and optimizing factors influencing extraction of bioactive compounds from saffron

The quality of saffron is evaluated by the amount of the three main secondary metabolites which are picrocrocin, safranal, and crocin that are responsible for the bitterness, the characteristic aroma, and the red yellowish color of the most expensive spice of the world, respectively. These components should be first extracted before their quantification using different analytical platforms like chromatography and spectrometry. Currently, there are many processes for extracting these components. The efficiency of the extraction method depends on many factors such as the solvent concentration, the extraction pressure, time and temperature, the solvent ratio, etc. Consequently, the first step in the extraction process, called screening, consists of identifying the most influencing factors by checking their preliminary significance on the efficiency of the extraction process. There are many experimental designs used at this step like the full factorial design, the fractional factorial design, and the Plackett-Burman design. These designs allow a multivariate screening, taking into account any likely interactions between the different factors, and a considerable reduction in the size of the experiment. The second step in the extraction process consists in the optimization of the most influencing factors selected at the screening step. The largely used experimental designs at this second step are the Box-Behnken design, and the Box-Wilson or central composite design. In this research work, a short presentation of the main extraction methods of the most important saffron components will be done. This will be followed by the presentation of the most common experimental designs used at the screening step. Then, the frequently used experimental designs for optimizing the extraction process will be discussed. For both kinds of experimental designs, their general principles will be reviewed and the manner to choose the most adapted among them will be stressed.