Discrimination of 'Isabella', 'Concord', 'Ives' and 'White Niagara' grape juices by their free amino acid composition.

In 2006 Brazil commercialized 15.64 million L of natural grape juice and 23,328 t of the concentrated type, which means that over 130 thousand t of grapes were crushed for this purpose. In this way, the country is one of the most important grape juice producers of the world. The main cultivars used by the grape juice industry are primarily 'Isabella' and 'Concord', and secondly 'Ives', but there is a small market for the 'White Niagara' grape juice. Aiming to characterize and to discriminate these grape juices, analyses of 16 free amino acids were performed using an amino acid autoanalyser. Data were submitted to the principal component analysis. Results show that most variables had strong correlation with the factors 1, 2 and 3. Indeed, they represented, respectively, 46.37, 36.39 and 17.24% of the total variation. Projection of the variables on the factor-plane 1 × 2 shows that 'Isabella' grape juice was better characterized by lysine, arginine, aspartate, histidine and glutamate; 'Concord', by α-alanine, α-alanine/arginine and α-alanine/proline ratios; 'White Niagara', by phenylalanine, tyrosine, isoleucine, leucine, proline, valine, glycine and proline/arginine ratio. Projection of the variables on the factor-plane 1 x 3 shows that 'Ives' is characterized by methionine and threonine. However, serine was not well represented in any grape juice and factor-plane. This work is an important contribution to the characterization of the Brazilian grape juice made from American/hybrid cultivars, which can be discriminated by its free amino acid composition.