935 Research Article Received: 26 February 2008 Revised: 16 December 2008 Accepted: 22 December 2008 Published online in Wiley Interscience: 2 March 2009 (www.interscience.wiley.com) DOI 10.1002/jsfa.3531 Effect of nitrogen fertilization on quality markers of strawberry (Fragaria × ananassa Duch. cv. Aromas) Laura A Ojeda-Real, a Philippe Lobit, b Ra ´ ul C ´ ardenas-Navarro, b Oscar Grageda-Cabrera, c Rodolfo Far´ ıas-Rodr´ ıguez, a Eduardo Valencia-Cantero a and Lourdes Mac´ ıas-Rodr´ ıguez a∗ Abstract BACKGROUND: Nitrogen is an indispensable element for fruit metabolism and low or excessive N levels can affect the accumulation of the most important components that contribute to the flavour and aroma of the fruit. Among them, sugars, acids and volatile compounds can be considered quality markers. The objective of this study was to evaluate the effect of N fertilization on these quality markers of the fruit at two harvest dates. RESULTS: Strawberry plants were grown in a hydroponic system and N was applied as Ca(NO 3 ) 2 at concentrations of 0.3, 3 and 6 mmol L −1 in the nutrient solution. Total soluble solids, soluble carbohydrates, amino acids and organic acids and volatile compounds of the fruit were analyzed. The fruits produced at 3 and 6 mmol L −1 N had higher contents of esters, soluble carbohydrates and amino acids. The hexanal content increased with the 6 mmol L −1 dose. The effect of fertilization was more marked at the second harvest date. CONCLUSION: The availability of N in strawberry plants affected the accumulation of quality markers. The fruits expected to have the best flavour and aroma, with both high levels of soluble carbohydrate and esters and low levels of hexanal, were obtained with 3 mmol L −1 nitrate in the solution. c  2009 Society of Chemical Industry Keywords: Fragaria × ananassa; strawberry; nitrogen fertilization; volatile compounds; amino acids; soluble carbohydrates INTRODUCTION Strawberry is one of the most popular fruits in the world. The strawberry flavour depends basically on the balance between acids and sugars expressed in the fruit; 1 while the aroma results of the combination of a very complex mixture of volatile compounds of different chemical classes and molecular weights. Zabetakis and Holden 2 reported around 281 different volatiles grouped in families such as acids, alcohols, aldehydes, ketones, esters, acetals, furanones, β -D-glucopyranosides, lactones, aromatics, sulfur-containing compounds and terpenes. During ripening, the metabolism of sugars, acids and volatile compounds determines the fruit quality and the level of acceptance of the consumer. As the maturity stage advances, the organic acid content decreases, the carbohydrate content increases and the flavour changes from acid to sweet. 3 Some quality components that contribute to the strawberry aroma are the concentrations of furaneol, methyl and ethyl butanoate, methyl and ethyl hexanoate, linalol, γ -decalactone, butanoic acid, and (Z)-3-hexenal. 4,5 They vary according to cultivar, climate and cultivation practices, among others. In Mexico, very high nitrogen (N) fertilization is often applied with the belief that it promotes vegetative development and fruit yield. 6,7 N is an indispensable element for the synthesis of proteins such as enzymes, which are responsible for the production of all the cellular components required for the development of the plant. 8 N deficiency in strawberry (foliar N content less than 1.9%) causes chlorosis of the leaves and a decrease in leaf area, root mass, fruit size and anthocyanin content. 9 However, an excess of N (foliar N content of 4%, approximately) promotes vegetative growth, delays maturation, and causes a loss of firmness in the fruit, which reduces its quality due to increased susceptibility to pathogen attacks and to mechanical damage caused by post-harvest handling. 5,6,10,11 Concerning fruit size, ∗ Correspondence to: Lourdes Mac´ ıas-Rodr´ ıguez, Instituto de Investigaciones Qu´ ımico-Biol´ ogicas, Universidad Michoacana de San Nicol´ as de Hidalgo, Edificio B3, Ciudad Universitaria, C.P. 58030 Morelia, Mich., M´ exico. E-mail: lmacias@umich.mx a Instituto de Investigaciones Qu´ ımico-Biol´ ogicas, Universidad Michoacana de San Nicol´ as de Hidalgo, Edificio B3, Ciudad Universitaria, Morelia, Mich., M´ exico b Instituto de Investigaciones Agropecuarias y Forestales, Universidad Michoa- cana de San Nicol´ as de Hidalgo, Km 9.5 Carr. Morelia-Zinap´ ecuaro, Tar´ ımbaro, Mich., M´ exico c Instituto Nacional de Investigaciones Forestales, Agr´ ıcolas y Pecuarias, Km 6.5 Carr. Celaya-San Miguel de Allende, Campo Experimental Baj´ ıo/Celaya, Celaya, Gto., M´ exico J Sci Food Agric 2009; 89: 935–939 www.soci.org c  2009 Society of Chemical Industry