Changes in the Volatile Composition of a Semihard Ewe Milk Cheese Induced by High-Pressure Treatment of 300 MPa BIBIANA JUAN, ² LUIS JAVIER R. BARRON,* ,‡ VICTORIA FERRAGUT, ² BUENAVENTURA GUAMIS, ² AND ANTONIO JOSE Ä TRUJILLO* ,² Centre Especial de Recerca Planta de Tecnologia dels Aliments (CERPTA), CeRTA, XiT, Departament de Cie `ncia Animal i dels Aliments, Facultat de Veterina `ria, Universitat Auto `noma de Barcelona, 08193 Bellaterra, Spain, Tecnologı ´a de Alimentos/Elikagaien Teknologia, Facultad de Farmacia/Farmazi Fakultatea, Universidad del Paı ´s Vasco/Euskal Herriko Unibertsitatea, 01006 Vitoria-Gasteiz, Spain The effect of high-pressure (HP) treatment (300 MPa, 10 min) on the volatile profile of semihard ewe milk cheeses was investigated. The HP treatment was applied at two different stages of ripening (1 and 15 days; 3P1 and 3P15) and microbiota, proteolysis indexes (soluble nitrogen and total free amino acid content), and volatile compounds were assayed at 15, 60, 90, and 150 days of ripening. The intensity of odor and aroma of cheeses was also assayed. 3P1 cheeses presented the highest content of free amino acids and were characterized by the lowest amounts of aldehydes, ketones, short-chain free fatty acids, and terpenes and higher levels of ethanol and ethyl esters. 3P15 cheeses were characterized by the highest content of short-chain free fatty acids and pyruvaldehyde and the lowest abundance of secondary alcohols and were more similar to control cheeses than those HP- treated on the first day. Intensities of odor and aroma were not significantly influenced by the HP treatment. However, the panellists found some differences in 3P1 as compared with control and 3P15 cheeses in what they perceived as lower odor and aroma quality. KEYWORDS: High-pressure; volatile compounds; ewe milk cheese INTRODUCTION The volatile profile of cheeses is characteristic of each cheese variety and was derived from the glycolysis, lipolysis, proteoly- sis, and secondary catabolic reactions that take place throughout the ripening of cheeses. The ripening of hard and semihard cheeses is a long and costly process, and consequently, there are many methods available to accelerate it (1). The possible application of high hydrostatic (high-pressure, HP) technology for ripening acceleration has been studied by different authors (2) and requires the study of treatment conditions in each variety of cheeses. In a previous study, working with a range of pressures from 200 to 500 MPa, we tested the possibility of accelerating the proteolysis of ewe milk cheeses by HP treatment, concluding that 300 MPa was the optimum treatment for accelerating cheese ripening in this variety of cheeses (3). Proteolysis involves the hydrolysis of caseins to peptides and free amino acids (FAAs), contributing directly to cheese flavor (4), and lipolysis releases short-chain free fatty acids (FFAs), which are important, or even predominant, components of the flavor of many types of ewe and goat milk cheeses (5). Subsequently, changes in the proteolysis and lipolysis rates due to HP treatment can affect the development of cheese flavor and therefore consumer acceptance. Few works have investigated the effect of HP treatment on the volatile profile of cheeses. Butz et al. (6) found lower concentrations of n-butanoic acid and 3-hydroxy-2-butanone in pressurized Gouda cheese, whereas Saldo et al. (7) described lower amounts of FFA in pressurized goat milk cheeses. According to Jin and Harper (8), a treatment of 550 MPa for 30 min delayed the fermentation process and ripening and reduced volatile compound formation in Swiss cheese slurries. A Ä vila et al. (9) assayed the effect of HP treatment (400 MPa for 10 min) applied to 15 day old Hispa ´nico cheeses and concluded that HP limited the formation of volatile compounds, decreasing the odor quality of cheeses. The aim of the present work was to establish the effect of an HP treatment at 300 MPa and the possible influence of the ripening stage at which the treatment is applied (1 and 15 days) on the headspace volatile profile of ewe milk cheeses. MATERIALS AND METHODS Cheese Making and HP Treatment. Two independent batches of cheeses were manufactured from pasteurized (75.5 °C, 1 min) ewe milk in a cheese factory (MontBru, Moia, Barcelona, Spain). Cheeses were produced by 1% of starter culture (Lactococcus lactis ssp. lactis and * To whom correspondence should be addressed. (L.J.R.B.) Tel: +34- 945013082. Fax: +34-945013014. E-mail: luisjavier.rbarron@ehu.es. (A.J.T.) Tel: + 34-935813292. Fax: +34-935812006. E-mail: toni.trujillo@uab.es. ² Universitat Auto `noma de Barcelona. ‡ Universidad del Paı ´s Vasco/Euskal Herriko Unibertsitatea. J. Agric. Food Chem. 2007, 55, 747-754 747 10.1021/jf062824r CCC: $37.00 © 2007 American Chemical Society Published on Web 01/17/2007