Simultaneous detection of total antioxidant capacity and total soluble solids content by Fourier transform near-infrared (FT-NIR) spectroscopy: A quick and sensitive method for on-site analyses of apples

• Antioxidant capacity and total soluble solids content (total sugar) of apples were determined with a handheld instrument.
• We compared different FT-NIR devices and methods for this purposes.
• Instruments for laboratory, industrial and on-site (handheld) analyses were used.
• Principal component analysis were utilized.
• “Green science”, modern, quick and non-destructive measurements were developed.

Antioxidant capacity and total soluble solids content (SSC) of seven cultivars of apples (Braeburn, Evelina, Gala, Golden Delicious, Granny Smith, Jonagold, Pink Lady) were successfully determined applying a FT-NIR handheld spectrometer. On-site prediction of SSC of 92 apples was possible applying partial least squares (PLS) analyses with a standard error of prediction (SEP) of 0.55 °Bx (RPD = 2.5, R2 = 0.76). Polyphenolic compounds of the peels, which are responsible for the antioxidant capacity, were predicted with an SEP of 0.13% gallic acid equivalents of peels dry matter (RPD = 2.8, R2 = 0.85). Results were compared with a standard method (point measurements) using a desktop spectrometer of the latest generation in combination with a fiber optic probe and with a recently developed enhancement (surface scanning) of the latter. Applying surface scanning, SEP values decreased significantly by 39% and 10% compared to on-site analyses for the prediction of SSC and polyphenolic compounds respectively.