Quince (Cydonia oblonga Miller) Fruit Characterization Using Principal Component Analysis BRANCA M. SILVA, ² PAULA B. ANDRADE, ² RUI C. MARTINS, § PATRI ÄCIA VALENTA ˜ O, ² FEDERICO FERRERES, # ROSA M. SEABRA,* ,² AND MARGARIDA A. FERREIRA ⊥ REQUIMTE, Servic ¸ o de Farmacognosia and Servic ¸ o de Bromatologia, Faculdade de Farma ´cia, Universidade do Porto, R. Anı ´bal Cunha, 4050-047 Porto, Portugal; Centre for Biological and Chemical Engineering, IST, Technical University of Lisbon, Av. Rovisco Pais, P-1049-001 Lisbon, Portugal; and Research Group on Quality, Safety and Bioactivity of Plant Foods, Department of Science and Technology, CEBAS-CSIC, P.O. Box 164, E-30100 Espinardo (Murcia), Spain This paper presents a large amount of data on the composition of quince fruit with regard to phenolic compounds, organic acids, and free amino acids. Subsequently, principal component analysis (PCA) is carried out to characterize this fruit. The main purposes of this study were (i) the clarification of the interactions among three factorssquince fruit part, geographical origin of the fruits, and harvesting yearsand the phenolic, organic acid, and free amino acid profiles; (ii) the classification of the possible differences; and (iii) the possible correlation among the contents of phenolics, organic acids, and free amino acids in quince fruit. With these aims, quince pulp and peel from nine geographical origins of Portugal, harvested in three consecutive years, for a total of 48 samples, were studied. PCA was performed to assess the relationship among the different components of quince fruit phenolics, organic acids, and free amino acids. Phenolics determination was the most interesting. The difference between pulp and peel phenolic profiles was more apparent during PCA. Two PCs accounted for 81.29% of the total variability, PC1 (74.14%) and PC2 (7.15%). PC1 described the difference between the contents of caffeoylquinic acids (3-O-, 4-O-, and 5-O-caffeoylquinic acids and 3,5-O-dicaffeoylquinic acid) and flavonoids (quercetin 3-galactoside, rutin, kaempferol glycoside, kaempferol 3-glucoside, kaempferol 3-rutinoside, quercetin glycosides acylated with p-coumaric acid, and kaempferol glycosides acylated with p-coumaric acid). PC2 related the content of 4-O-caffeoylquinic acid with the contents of 5-O-caffeoylquinic and 3,5-O-dicaffeoylquinic acids. PCA of phenolic compounds enables a clear distinction between the two parts of the fruit. The data presented herein may serve as a database for the detection of adulteration in quince derivatives. KEYWORDS: Cydonia oblonga Miller; quince fruit; pulp; peel; phenolic compounds; organic acids; free amino acids; principal component analysis INTRODUCTION Quince is the fruit of a deciduous tree of the Rosaceae family, Cydonia oblonga Miller. Although quince fruit is not edible raw because of its hardness, bitterness, and astringency, it is very appreciated in Portugal for its jam, called “marmelada”. According to Portuguese legislation (1), quince jam is the food product of a homogeneous and consistent mixture obtained exclusively by boiling quince mesocarp with sugars. Before 1998, only a few chemical studies have been developed in this matrix. These works concerned mainly the volatile constituents of quince fruit (2-7) and the glucosides of procyanidin polymers (8). For the past few years, quince fruit and its derivatives have been studied by our research group to examine their chemical constituents (9-19) and to evaluate their antioxidant potential (20). Among the various studied chemical parameters, the phenolic profile seemed to be the most useful in the discrimina- tion of the different parts of quince fruit (pulp, peel, and seed) (10, 14, 15). This procedure also allowed the detection of adulterations in quince jams by the addition of quince peel (10). As the published literature was based on results from only one year of quince harvest (2000), and considering the pos- * Corresponding author (e-mail rseabra@ff.up.pt; telephone 351 222078934; fax 351 222003977). ² REQUIMTE, Servic ¸ o de Farmacognosia. § Technical University of Lisbon. # CEBAS-CSIC. ⊥ REQUIMTE, Servic ¸ o de Bromatologia. J. Agric. Food Chem. 2005, 53, 111-122 111 10.1021/jf040321k CCC: $30.25 © 2005 American Chemical Society Published on Web 12/09/2004