Detecting Bruise Damage and Level of Severity in Apples Using a Contactless NIR Spectrometer

Highlights In the Emission Head (EH) configuration differences in apple bruise severity were well captured. A good representation of new samples variability, in calibration, ensured robust quantitative PLS-DA models. EH mode with PLS-DA is an attractive spectroscopic option for inline apple sorting based on bruise damage.  Abstract. Bruise damage in apples is very common and undesirable because it hinders consumer satisfaction and greatly contributes to food loss. Fast detection of bruise damage in fruit using spectroscopic systems is still problematic, especially in terms of quantitative and objective assessments of mechanical damage and standardization of bruise measurement method, among other issues. Non-destructive techniques among which is near infrared (NIR) spectroscopy are under development as a potential solution carrier for such issues. A study of bruise damage was conducted on three apple cultivars using Fourier transform (FT) near infrared spectroscopy in two configurations (‘emission head‘ of Bruker‘s Matrix-F and ‘integrating sphere‘ of Bruker‘s multipurpose analyzer, MPA). The emission head (EH) allows for contactless large sample (100 mm) exposure that simulates on-line applications, while the MPA (sample size: 22 mm) is commonly used for in-laboratory analysis of inhomogeneous material such as fruit. Bruise damages were mechanically induced in apples, bruise sizes measured physically and destructively. Partial least squares discriminant analysis (PLS-DA) was used to determine the differences captured by the scanning spectrometers in apple fruit tissues. Discriminant analysis revealed that in both sample acquisition modes, distinction between bruised and non-bruised apple fruit tissue was achieved with high (from 78% to 93%) accuracy of classification (ACcl) based solely on spectral data. The classification accuracy improved when individual cultivars were considered and ranged from 94% to 96%. Classification models were tested for robustness and showed that both cultivar and bruise severity had influence on classification models‘ performance. The results showed ability of the emission head configuration in detecting bruises and differentiating between severity of bruises in apple fruit, thus making it a good candidate for use in rapid detection and quantitative assessment of bruising in apple on sorting lines. Possibilities for improving the classification model performance and ensuring their robustness for the EH were suggested.