Quantitative analysis of minerals and electric conductivity of red grape homogenates by near infrared reflectance spectroscopy

The use of near infrared (NIR) reflectance spectroscopy to measure the concentration of minerals and electric conductivity (EC) in red grape homogenates was investigated. Wine grape samples (n = 209) from two vintages, representing a wide range of varieties and regions were analysed by Inductively Coupled Plasma Optical Emission Spectrometry (ICPOES) for the concentrations of calcium (Ca), potassium (K), magnesium (Mg), phosphorus (P), sulphur (S), iron (Fe), and manganese (Mn) and scanned in reflectance in a NIR instrument (400–2500 nm). The spectra were pre-processed using multiple scatter correction (MSC) before developing the calibration models using partial least squares (PLS) regression and cross validation. Coefficients of determination in cross validation (R2) and the standard errors of cross validation (SECV) obtained were for Fe (0.60 and 1.49 mg kg−1), Mn (0.71 and 0.41 mg kg−1), Ca (0.75 and 60.89 mg kg−1), Mg (0.84 and 12.93 mg kg−1), K (0.78 and 285.34 mg kg−1), P (0.70 and 40.19 mg kg−1), S (0.88 and 14.45 mg kg−1) and EC (0.87 and 7.66 mS). The results showed that Mg, S and EC in grape berries might be measured by NIR reflectance spectroscopy.

► Grape viticultural regions in Australia yield different grape compositional parameters due to differences in soil characteristics.
► The use of near infrared spectroscopy was explored to predict electric conductivity and elements in grapes as a rapid method to monitor such compositional parameters.
► First time that fresh materials is being analysed by NIR to predict elements.