A new multivariate approach for the optimisation of the simultaneous distillation-extraction technique for free fatty acids using a face centred cubeexperimental design: application to Parmigiano-Reggiano cheese

A face centred cube (FCC) experimental design was used to investigate effec ts of extraction time, solvent temperature and sample temperature on the si multaneous distillation-extraction (SDE) extraction yields of 13 fatty acid s from Parmigiano-Reggiano cheese, and to find the best extraction conditio ns for these compounds. Each factor was tested at three levels; 20 experime nts were carried out, each producing 13 responses. In order to create a mat hematical model representing the relationships between factors and response s and to determine the best conditions for the SDE procedure, GC peak areas were processed by using the multiple regression analysis. The backward ste pwise selection of the regression coefficients led to the identification of seven groups of compounds having similar behaviour with respect to the thr ee variables investigated. The same set of models was found by performing p rincipal component analysis (PCA) on the t-values of the regression coeffic ients of the unrefined polynomials and cluster analysis on the scores of th e 13 acids obtained by PCA. The best experimental conditions were evaluated for each compound. The use of the FCC experimental design allowed to evalu ate not only the main effects of the variables analysed, but also curvature effects and interaction effects among them. (C) 1999 Elsevier Science B.V. All rights reserved.