Comparison of NIR and MIR spectroscopic methods for determination of individual sugars, organic acids and carotenoids in passion fruit

In this work, NIR and MIR spectroscopy was investigated and compared for predicting passion fruit ripening parameters as sugars, organic acids and carotenoids. Spectra of 56 samples of the lyophilized passion fruit were collected using an integrating sphere in NIR range and attenuated total reflectance accessory in MIR range. Individual sugars (sucrose, glucose and fructose), organic acids (malic and citric acids) and carotenoids (β-carotene) contents were determined by reference methods. Spectral and reference data were analyzed by principal component analysis. Partial least square regression (PLSR) was used to establish calibration models. MIR technique was better than the NIR technique for glucose (R2v = 0.942), fructose (R2v = 0.855), sucrose (R2v = 0.818), total sugar (R2v = 0.914) and citric acid (R2v = 0.913) content determination. On the other hand, NIR was superior for total acids (R2v = 0.903) content determination. For malic acid and β-carotene contents both methods were unsatisfactory due to low concentrations of these constituents in the passion fruits.