Twenty-one free amino acids present in several samples of quince fruit (pulp and peel) and quince jam (homemade and industrially manufactured) were analyzed by GC/FID. The analyses showed some differences between quince pulps and peels. Generally, the highest content in total free amino acids and in glycine was found in peels. As a general rule, the three major free amino acids detected in pulps were aspartic acid, asparagine, and hydroxyproline. For quince peels, usually, the three most abundant amino acids were glycine, aspartic acid, and asparagine. Similarly, for quince jams the most important free amino acids were aspartic acid, asparagine, and glycine or hydroxyproline. This study suggests that the free amino acid analysis can be useful for the evaluation of quince jam authenticity. It seems that glycine percentage can be used for the detection of quince peel addition while high alanine content can be related to pear addition.

Ion trap HPLC-PAD-ESI/MS/MS has been used to study C-glycosyl flavones in quince seeds. Comparative analysis of the ions [(M-H)-60]-, [(M-H)-90]- and [(M-H)-120]- from 6-C- and 8-C-glycosyl flavone isomers, together with their respective retention times, allowed deductions to be made about the nature of the sugar units and the positions of C-glycosylation. Vicenin-2 (6,8-di-C-glucosyl apigenin), lucenin-2 (6,8-di-C-glucosyl luteolin), stellarin-2 (6,8-di-C-glucosyl chrysoeriol), isoschaftoside (6-C-arabinosyl-8-C-glucosyl apigenin), schaftoside (6-C-glucosyl-8-C-arabinosyl apigenin), 6-C-pentosyl-8-C-glucosyl chrysoeriol and 6-C-glucosyl-8-C-pentosyl chrysoeriol were identified in quince seed.

Recebido em 21/11/97; aceito em 17/4/98 METHODS FOR THE EVALUATION OF THE DEGREE OF LIPID OXIDATION AND THEANTIOXIDANT ACTIVITY. In this work several methods for evaluation of the degree of lipid oxidation and antioxidant activity are reviewed. Some aspects related to the recent advances mentioned in the literature are also reported.Keywords: lipid oxidation; antioxidant activity; analytical methods. REVISÃO INTRODUÇÃOOs lipídios desempenham um importante papel no que respeita à qualidade de certos produtos alimentares, particularmente em relação às propriedades organolépticas que os tornam desejáveis (e.g. flavor, cor, textura). Por outro lado, conferem valor nutritivo aos alimentos, constituindo uma fonte de energia metabólica, de ácidos graxos essenciais (e.g. ácidos linoleíco, linolênico e araquidónico) e de vitaminas lipossolú-veis (e.g. A, D, E e K) 2 .A oxidação lipídica é um fenômeno espontâneo e inevitá-vel, com uma implicação direta no valor comercial quer dos corpos graxos, quer de todos os produtos que a partir deles são formulados (e.g. alimentos , cosméticos, medicamentos).A peroxidação lipídica constitui a principal causa de deterioração dos corpos graxos (lipídios e matérias graxas). Afastados do seu contexto de proteção natural, os corpos graxos sofrem, no decurso de processos de transformação e armazenamento, alterações do tipo oxidativo, as quais tem como principal conseqüência a modificação do flavor original e o aparecimento de odores e gostos característicos do ranço, o qual representa para o consumidor, ou para o transformador industrial, uma importante causa de depreciação ou rejeição 3 .Nos últimos anos, a preocupação constante de proporcionar aos consumidores produtos de alta qualidade levou à adoção de medidas que permitem limitar o fenômeno de oxidação durante as fases de processamento e armazenagem dos produtos (e.g. escolha de processos que limitem as operações de arejamento e o tratamento térmico; utilização de matérias-primas refinadas, com baixos teores de água e isentas de pró-oxidantes; armazenamento a baixas temperaturas e em atmosfera inerte; adição de compostos antioxidantes; utilização de embalagens estanques e opacas à radiação UV, etc.). Deste conjunto de ações, a adição de compostos antioxidantes é, sem dúvida, uma prática corrente, razão que justifica o atual interesse pela pesquisa de novos compostos com capacidade antioxidante. O baixo custo de obtenção, facilidade de emprego, eficácia, termo-resistência, "neutralidade" organoléptica e ausência reconhecida de toxicidade, são premissas para a sua seleção e utilização a nível industrial 3 . Neste contexto, torna-se necessário, por um lado controlar a qualidade dos corpos graxos, através da determinação do seu grau de oxidação e, por outro avaliar, a capacidade antioxidante de novos compostos. A grande diversidade de métodos analíticos (químicos, físicos e/ou físico-químicos) propostos na literatura para a avaliação do grau de oxidação lipídica e da capacidade antioxidante coloca, na prática, algumas dificuldades de sele...

Qualitative and quantitative analyses of phenolic compounds were carried out on quince fruit samples from seven different geographical origins in Portugal. For each origin, both pulp and peel were analyzed by reversed-phase HPLC-DAD and HPLC-DAD/MS. The results revealed differences between the phenolic profiles of pulps and peels in all studied cases. The pulps contained mainly caffeoylquinic acids (3-, 4-, and 5-O-caffeoylquinic acids and 3,5-dicaffeoylquinic acid) and one quercetin glycoside, rutin (in low amount). The peels presented the same caffeoylquinic acids and several flavonol glycosides: quercetin 3-galactoside, kaempferol 3-glucoside, kaempferol 3-rutinoside, and several unidentified compounds (probably kaempferol glycoside and quercetin and kaempferol glycosides acylated with p-coumaric acid). The highest content of phenolics was found in peels.

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 factors-quince fruit part, geographical origin of the fruits, and harvesting year-and 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.