Effect of the timing of water deficit on the must amino acid profile of Tempranillo grapes grown under the semiarid conditions of SW Spain

Highlights

• The effect of regulated irrigation treatments (RDI) on the must amino acids was assessed.

• RDI modified must amino acid concentrations at harvest but not the amino acid profile.

• Late deficit irrigation increased the total concentration of nitrogen compounds.

• Pre-veraison water status of vines was a determining factor of must amino acidic concentration.

Abstract

Must nitrogen is very important for successful fermentation. Irrigation can influence vine nitrogen availability, and therefore must nitrogen content and wine quality. The aim of this work was to assess the effect of vine water status on the nitrogen concentration of cv. Tempranillo grown under semiarid conditions. A rainfed and two regulated deficit irrigation (RDI) strategies, late (LDI) and early deficit irrigation (EDI) were applied during pre- and post-veraison respectively periods over two seasons in Badajoz (Spain). Twenty-eight amino acids, amines and ammonia were determined by high performance liquid chromatography (HPLC) in the must. Results showed an effect of the pre-veraison vine water status on the must amino acid concentration. Higher values of nitrogenous indices were reached in musts from LDI treatments, mainly in the dry year. Significant correlations between pre-veraison stem water potential and 19 amino acid concentrations were observed. Therefore, LDI was a more suitable strategy for increasing the content of nitrogenous substances in the must.

Introduction

Nitrogen is the most abundant macronutrient in grapevines. Many of the fermentative functions of the microorganisms (such as yeasts and malolactic bacteria) involved in grape must fermentation, depend on the availability of nitrogenous compounds (Bell & Henschke, 2005). In grapes and musts, nitrogen is present in inorganic (ammonium and ammonium salts) and organic (proteins and amino acids) forms. Except for proline and hydroxyproline, all amino acids are metabolized by yeast under normal winemaking conditions (Bisson, 1991). The usable nitrogen fraction in must provided by free amino acids and ammonia is referred to as the yeast assimilable nitrogen (YAN). A deficiency in YAN slows yeast growth, causing sluggish fermentation sometimes even causing it to become stuck. It is a pervasive problem in the wine industry and has significant economic consequences (Jiranek, Langridge & Henschke, 1995).

The involvement of yeast in the development of wine aromas, flavors, mouth-feel and malodors is becoming better understood (Hernández-Orte et al., 2002, Vilanova et al., 2012), as is the effect of nitrogen availability on the compounds associated with these variables. Although controversy exists regarding the relationship between amino acids and the content of fermentative volatile compounds in wine (Garde-Cerdán & Ancín-Azpilicueta, 2008), links have been reported between must Asp, Ile, Leu, Phe, Thr, Tyr and Val concentrations and the wine content of important volatile compounds (Guitart et al., 1999, Hernández-Orte et al., 1998). Similarly, the amount of Cys and Met present in must appears to have a bearing on the appearance in wines of malodor-associated sulfur-containing compounds such as hydrogen sulfide, methylmercaptan (methanthiol), ethanethiol, methionol and dimethylsulfide (Mora, Eschenbruch, Knowles, & Spedding, 1986).

The amino acid content of grapes depends on the terroir (Garde-Cerdán et al., 2009, Lee and Schreiner, 2010, Oliva et al., 2011, Vilanova et al., 2015). Vine water status, but also both the timing and intensity of water stress are relevant for the amino acid concentrations in the grapes (Canoura et al., 2018, Niculcea et al., 2013, Ortega-Heras et al., 2014). Several researches focused on the effect of timing and intensity of vine water stress on the content of these substances in the grapes at harvest, yielding contrasting results. Water deficit is reported to increase the accumulation of amino acids in cv. Grenache noir berries (De Royer Dupré, Schneider, Payan, Salançon & Razungles, 2014). On the other hand, irrigation has been noted to increase the amino acid content (in relation to rainfed vines) in those of the white cultivar Verdejo (Ortega-Heras et al., 2014). Niculcea et al. (2013) reported similar findings for well-watered cv. Tempranillo grapevines compared to those under sustained irrigation deficit. In this regard, Deluc et al. (2009) showed that the metabolic responses of grapes to water deficit varied with the cultivar and fruit pigmentation. More recent research with the cv. Albariño two different geographic areas from NW Spain, reported that the concentration of several individual amino acids was modified by irrigation, especially in Ribeiro (a moderately-dry to sub-humid region), but only when low rainfall amounts occurred over the growing season (Bouzas-Cid, Díaz-Losada et al., 2018). Therefore, irrigation might offer a way for controlling grape and wine quality.

Regulated deficit irrigation (RDI) in vines has been used to improve berry and wine quality (Romero, Gil-Muñoz, del Amor, Valdés, Fernández & Martinez-Cutillas, 2013). This technique consist of applying water in smaller quantities than those required to fully satisfy crop evapotranspiration (ET_c) during certain periods of the growth cycle, and strategies have been designed to subject vines to greater or less severe water stress (depending on their phenological state) to achieve the desired balance between yield and quality (Kriedemann & Goodwin, 2003). For example, the pre- or post-veraison timing of RDI can lead to physiological alterations that affect the biosynthesis of grape compounds (Castellarin, Matthews, Di Gaspero, & Gambetta, 2007). In general, pre-veraison water stress tends to restrict berry size more strongly, leading to more negative effects on yield than post-veraison water stress. However, it increases the polyphenol content of grape skins (Intrigliolo, Pérez, Risco, Yeves, & Castel, 2012). The degree of pre-veraison stress that can be induced naturally depends on the soil water available at flowering, which in turn depends on winter and early spring rainfall amounts and on the water used during spring (Lopes, Santos, Monteiro, Rodrigues, Costa, & Chaves, 2011).

Recently, Canoura et al. (2018) showed significantly elevated proline levels in response to drought and that by regulating water supply to vines it is possible to control the relative concentration of key nitrogen compounds. In addition, Bouzas-Cid, Trigo-Córdoba, Falqué, Orriols, and Mirás-Avalos (2018) reported that it is necessary a level of stress enough to generate a response in the concentration of amino acids of Godello grapes. The effect of RDI on the amino acid and other N-containing compounds involved in berry and wine quality remains, however, insufficiently well known. Indeed, there are still few works on the impact on berry amino acid concentration of different levels of water stress during different phenological stages.

The aim of the present work was to determine, compared to rainfed conditions, the effect of RDI strategies inducing pre- and post-veraison water deficit on the ammonia, amino acid profile and nitrogen indices of the must (at harvest) of cv. Tempranillo grapes grown under semi-arid conditions. Knowing the relationship between vine water status in pre- and post-veraison and the amino acid composition of the must at harvest might allow for designing irrigation strategies that improve grape and wine quality.