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2.3. PHYSICOCHEMICAL CHARACTERIZATION OF TOMATO

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    Colour, soluble solids, pH and titratable acidity of tomato were determined at each
    

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    ripeness stage according to Soliva-Fortuny and others (2005). Tomato surface colour
    

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    was directly measured with a CR-400 Minolta colorimeter (Konica Minolta Sensing,
    

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    Inc., Osaka, Japan). Colour was measured using the CIE L*, a*, b*coordinates
    

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    (lightness, L*; green-red chromaticity, a*; and blue-yellow chromaticity, b*). The
    

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    equipment was set up for a D65 illuminant and 10º observer angle. A white standard
    

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    plate (Y = 94.00, x = 0.3158, y = 0.3322) was used for calibration. The a*/b* ratio on
    

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    the skin of tomato was calculated in order to observe the colour development during
    

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    tomato ripening. Each sample was homogenised with a blender (Solac Professional
    

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    Mixter BV5722, Spain). Afterwards, soluble solids content was determined by
    

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    refractometry (Atago RX-1000 refractometer; Atago Company Ltd., Tokyo, Japan) and
    

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    expressed as ºBrix. pH measurements were carried out on the homogenized tomatoes
    

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    using a Crison 2001 pH-meter (Crison Instruments S.A., Alella, Barcelona, Spain).
    

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    Titratable acidity was estimated after titration at pH 8.1 with 0.1 N NaOH and results
    

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    were expressed as grams of citric acid kg^-1.
    

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