Multidimensional investigation of the effect of pre-treatment solutions on drying characteristics and raisin quality

This study aims to evaluate the relationships between pre-treatment solution, variety, drying characteristics, and raisin quality in raisin production, using multivariate analysis methods. This study was conducted on raisins obtained by dipping Bineteti and Zeyti local seed grape varieties in 13 different pre-treatment solutions and drying in the sun on a concrete drying platform. In the study, data of 15 numerical variables related to drying characteristics and raisin quality were reduced to four principal components (PC1, PC2, PC3 and PC4) by principal component analysis (PCA), and their score values were numerically obtained. Then, two grape varieties, 13 pre-treatment solutions, and the four principal components were analyzed by non-linear principal component analysis (NLPCA). In addition, cluster analysis was performed to determine the prominent pre-treatment solutions in terms of drying characteristics and raisin quality. It was determined that the pre-treatment solutions were effective on L*, a*, b*, chroma (C*), hue (h°), a/b values, antioxidant activity, total phenolic content, and drying time constituting PC1. It was remarkable that the colour parameters in prominent clusters in cluster analysis also form PC1 in PCA analysis. The best pre-treatment solutions were found to be the "5% K2CO3 + 1% olive oil" solution for the Bineteti variety and the "5% K2CO3 + 2% hazelnut oil" solution for the Zeyti variety. It was determined that the pre-treatment solutions recommended for the varieties caused to be obtained brighter, more vibrant, and yellow-coloured raisins and shortened the drying time, and had positive effects on the total phenolic content and antioxidant activity.