Determination of simple sugars,malic acid and total phenolic compounds in apple pomace by infrared spectroscopy and PLSR

The aim of this work was to develop a fast, versatile, inexpensive and environmentally safe analytical method to quantify simple sugars, malic acid and total phenolic compounds in apple pomace, considering its potential use as a raw material with value instead of as an industrial waste. Diffuse reflectance infrared spectroscopy (DRIFTS) measurements of twenty‐six samples of apple pomace were analysed by partial least squares regression (PLSR), using several signal pre‐processing methods. Multivariate models developed with four to five latent variables (LVs) and based in the MIR (mid‐infrared) region had good prediction for the determination of sucrose, fructose, malic acid and total phenolic compounds, with average errors between 3.9% and 6.6%. By contrast, glucose was better determined by models developed in the NIR (near‐infrared) region and using six LVs, yielding an average error lower than 7.4%. These results confirmed the feasibility of the multivariate spectroscopic approach as an alternative for expensive and time‐consuming conventional chemical methods.