Analytical MethodsApplication of ATR-FTIR for a rapid and simultaneous determination of sugars and organic acids in apricot fruit
Introduction
Apricot fruit quality is a multicomponent concept, defined by physical, physiological and biochemical attributes such as firmness, skin and flesh colour, ethylene production, respiration rate, sugars, organic acids, pigments, phenolic compounds and volatiles (Audergon et al., 1989, Gurrieri et al., 2001, Marty et al., 2005, Ruiz et al., 2005, Guillot et al., 2006). Most instrumental techniques currently required for measuring these parameters are long, expensive and involve a considerable amount of manual work. Therefore, there is a demand for new and rapid analytical methods for assessing quality attributes. Recently, Fourier transform mid-infrared (FT-MIR) spectroscopy has become a well-accepted method for the determination of food constituents since it achieves high analysis speed and requires little or no sample preparation. FT-MIR spectroscopy often coupled with chemometrics has been used to study different quality attributes in many food samples including fruits, vegetables or beverages e.g. epicuticular wax of apple (Veraverbeke, Lammertyn, Nicolaï, & Irudayaraj, 2005), olive pulp cell-wall polysaccharides (Coimbra, Barros, Rutledge, & Delgadillo, 1999), polymethoxylated flavone of orange oil residues (Manthey, 2006), vitamin C in powdered mixture and liquid (Yang & Irudayaraj, 2002). FT-MIR spectroscopy has been widely used for must and wine analysis (Fernandez and Agosin, 2007, Patz et al., 2004, Urtubia et al., 2008). Moreover, it has become an alternative method for sugar analysis (Bellon-Maurel, Vallat, & Goffinet, 1995), in food such as mango juices (Duarte, Barros, Delgadillo, Almeida, & Gil, 2002), cane juices (Cadet & Offmann, 1997), soft drinks and fruit juices (Ramasami et al., 2004). More recently, this technique has been applied for the analysis of acids in fruits, and in particular apple and tomato (Beullens et al., 2006, Irudayaraj and Tewari, 2003). On the other hand, FT-MIR has been used for the authentication or for the detection of adulteration of many fruit-based products (Defernez, Kemsley, & Wilson, 1995) and for the discrimination or classification of foods such as wine and honey according to their origin (Bertelli et al., 2007, Edelmann et al., 2001).
A precedent paper presents the usefulness of ATR-FTIR reflectance spectroscopy to accurately predict the content of individual sugars and organic acids in apricot fruits using a small number of samples (50 samples) and the “leave-one-out” cross-validation test (Bureau, Reich, Marfisi, Audergon, & Albagnac, 2006). On a larger variability of apricot fruits and a larger number of samples, the prediction of soluble solids content and titratable acidity using the external cross-validation was shown in apricot fruit using the non-destructive near-infrared spectroscopy (Bureau et al., 2009). Here, the objective was to evaluate the potential of the ATR-FTIR as a fast technique to predict the main traits involved in organoleptic quality of apricot fruit. The prediction has been evaluated for individual sugars, organic acids and complementary quality traits such as fruit firmness, skin colour, ethylene production, soluble solids and titratable acidity through the comparison with standard techniques. A large diversity of fruits covering genetic factor and physiological stages was used in this work. The sample set was designed to be representative of the variability observed in the apricot species. Samples belonging to eight cultivars harvested at different stages of ripening were used as a calibration set. The prediction models for each quality parameters were developed with partial least square (PLS) technique using the external cross-validation.
Section snippets
Selection of apricot fruit samples
Eight apricot cultivars or hybrids, named ‘Moniqui’, ‘Goldrich’, ‘Bergeron’, ‘Iranien’, ‘Badami’, ‘Ravicille’, ‘Ravilong’ and ‘A4034’ were chosen for their contrasted fruit quality traits such as colour, taste, physiological behaviour. To obtain a wide range of fruit composition, apricot fruits were collected from June 22nd to August 2nd, during the maturation period, from the beginning of ethylene production to the full maturity. A total of 757 fruits were collected in 2005. Fruits came from
Diversity of apricot fruits
A synthetic view of the observed physical, physiological and biochemical traits is presented (Table 1). Chosen apricot fruits were contrasted for their colour (from white to red apricot skin), their firmness in relation with the ripening changes, their physiological activities (diversity in ethylene production in relation with ripening and genetic factor) and their biochemical characteristics (more or less sweet and acidic with particular composition in sugars and organic acids). According to
Conclusion
In this paper we have established the possibility of using ATR-FTIR technique for determining soluble solids content, titratable acidity, individual sugars (sucrose, glucose, fructose) and organic acids (malic and citric acids) in apricot slurry. The time of analysis was considerably reduced compared to the current method using enzymatic assays for individual sugars and organic acids. The method was calibrated and cross-validated on fruits representative of the variability observed in apricot
Acknowledgment
This study was supported by department for Science and Process Engineering of Agricultural Products (CEPIA) of INRA and by Region Provence-Alpes-Côte d’Azur (PACA).
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