ELSEVIER Food Confro/, Vol. 9, No. 4, pp. 187-194, 1998 0 199X Elsevier Science Ltd PII: SO956-7135(97)00073-X All rights reserved. Printed in Great Britain 0956-7135/9R $lY.oO+O.00 PAPER Influence of milk source and ripening time on free amino acid profile of Picmte cheese A. Cristina Freitas,” J. Maria Fresno,+ Bernard0 Prieto,+ Inmaculada France,+ F. Xavier Malcata*” and Javier Carballo’ The evolution of concentration of j?ee amino acids in Picante cheese throughout ripening was studied for several volumetric ratios of ewe’s and goat’s milks. The concentrations of all free amino acids, except asparagine, y-aminobutytic acid, and cysteine, generally increased as ripening time elapsed. Analyses of variance have indicated that ripening time and, to a lesser extent, milk composition have significant effects on the overall concentration of free amino acids. The major free amino acids present in the various cheeses along the ripening period were valine, leucine, and phenylalanine; these three amino acids accounted for 50, 49, 57, 46 and 42% of total free amino acids at 0 days and 42, 42, 43, 39 and 36% of total free amino acids at 180 days for cheeses manufactured with 0, 25, 50, 7.5 and 100% goat’s milk, respectively. Significant differences could be detected in terms of amino acid profile when the relative proportions of ewe’s and goat’s milks were altered (eg valine changed from 251.79 &- 0.99 to 352.20 + 16.49 mgllO0 g of dy matte< leucine from 181.48k1.77 to 224.OO+11.6OmgJlOOg of dty matte< and phenylalanine from 120.39f1.44 to 155.36 +8.39 mgl1OOg of dry matter in 140-day ripened cheeses when plain eweS milk was replaced by plain goat S milk). The correlation coefJicients between the concentrations of valine, isoleucine, leucine and phenylalanine, on the one hand, and ripening time, on the other; were greater than 0.93. 0 1998 Elsevier Science Ltd. All rights reserved INTRODUCTION Picante is a Portuguese traditional cheese produced on the farm level only from blends of raw ewe’s and goat’s milks, and possesses a few distinctive charac- teristics: it is hard, salty and spicy. Picante cheese- making milk is coagulated with animal liquid rennet *Escola Superior de Biotecnologia, Universidade Cat6lica Portuguesa, Rua Dr Ant6nio Bernardino de Almeida, P-4200 Porto, Portugal, +Departamento de Higiene y Tecnologia de 10s Alimentos, Universidad de Lion, 24071 Le6n, Spain and *Area de Tecnologia de 10s Alimentos, Facultad de Ciencias de Orense, Universidad de Vigo, 32004 Orense, Spain. “To whom correspondence should be addressed. extracted from calf’s stomach without addition of a starter culture; fresh cheeses are rubbed with dry salt after manufacture and ripened via appropriate piling up on straw and sand in maturation rooms. Studies on this cheese, which must be ripened for at least 120 days to meet the legal specification, are relatively scarce (Freitas and Malcata, 1996; Freitas et al., 1995, 1996, 1997), and most of those available are virtually outdated (eg Cruz et al., 1945). Proteolysis is one of the most important pheno- mena that takes place during cheese ripening, and studies pertaining to the evolution of the free amino acid profile in several cheeses during ripening have been published (Marcos and Mora, 1982; Polo et al., 1985; Ramos et al., 1987; Gonzalez de Llano et al., Food Control 1998 Volume 9 Number 4 187