Non-destructive analysis of α-farnesene and conjugated trienols in apples using near-infrared spectroscopy
D. Eisenstecken, A. Zanella, C.W. Huck, S. Stürz, P. Robatscher, M. Oberhuber
The accumulation of α-farnesene and formation of the corresponding oxidation products such as conjugated trienols (CTols) on apples is correlated with the occurrence of superficial scald, a physiological disorder affecting apples during storage. This study focuses on the potential of near-infrared spectroscopy (NIRS) to predict α-farnesene and CTols as a non-invasive and rapid method to monitor these compounds in stored apples. Destructive analysis of α-farnesene and CTols in 'Granny Smith' apple during 60 days cold storage under normal atmosphere showed a 38-fold increase in α-farnesene concentration to an average of 0.12 μmol cm-2, followed by a subsequent reduction with ongoing storage time, depending on the storage type. CTols, particularly CT258 and CT281, showed the same trend, but reached the maximum concentration after 90 days cool storage. NIR spectra were collected of intact apples before destructive analysis, with calibration models developed using partial least squares (PLS) regression using two thirds of the samples to form the calibration set, and the remaining third for the validation set. A very good correlation was found for both α-farnesene and CT258, with each of the correlation coefficient of calibration (r) above 0.90, and an RMSEC of 0.017 and 0.0042 μmol cm-2, respectively. These first results demonstrate the potential of near-infrared spectroscopy for rapid and non-destructive prediction of the scald-related compounds α-farnesene and CTols in apple fruit.