Application of FTIR spectroscopy for the quantification of sugars in mango juice as a function of ripening

FTIR-ATR spectroscopy and multivariate analysis were used for quantification of sugars in mango juices as a function of ripening. Calibration was based on sucrose/glucose/fructose mixtures, with six concentration levels and following a triangular experimental design. PLS1 regression of the spectra first derivatives gave the best results, enabling quantification of fructose, sucrose, and glucose with 1.4, 1.4, and 4.9% prediction errors, respectively. Throughout ripening, sucrose and fructose were accurately quantified by PLS-FTIR, whereas the accuracy of glucose determination decreased at later stages, when concentrations fell to 0.6-1.5 g/L. These results enabled a correlation with fruit ripening stage to be established. This may be particularly useful to detect over-ripening in fresh fruits, a period when other indicators (pH and % soluble solids (SS)) do not change significantly; this knowledge may help in predicting fruit stability to transport and storage. Similar information obtained for nonfresh juices (in which pH and %SS may be masked by additives), may help determine whether the source fruits had suitable ripening stages.