Development of a Diffuse Reflectance FT-NIR Spectroscopy Method for the Shell Egg Quality Assessment

Egg industries are more and more interested in nondestructive and rapid methods for the assessment of freshness and quality of shell eggs. Some studies showed that NIR spectroscopy is a valid technique to determine shell egg freshness (Lin et al., 2011) and internal quality parameters (Abdanan Mehdizadeh et al., 2014). However, poor attention has been given to method development, and none of these papers demonstrated that the acquired spectra are really representative of the egg content rather than the eggshell. Thus, the aim of this work was the evaluation of beam penetration in a diffuse reflectance FT-NIR spectroscopy method intended for shell egg quality assessment. To that aim, twelve eggs of different sizes were emptied, and diffuse reflectance spectra were collected by using the fibre optic probe of an FT-NIR spectrometer. For each egg, four spectra were acquired in the equatorial region, in the 12,500–4,500 cm-1 range, with a resolution of 8 cm-1 and 16 scans for both sample and background. Afterwards, the eggs were filled first with ethanol and then with distilled water before collecting again spectra in the same conditions. Principal component analysis (PCA) was performed on the reduced spectra (7,300–4,200 cm1) pretreated with smoothing, SNV, and first derivative. The score plot of the first two PCs, which explained about 96% of the variance, showed a clear pattern for the different samples. In particular, empty eggs and those filled with water were well distinguished along PC1, whereas eggshells containing ethanol showed positive values of PC2, in contrast with the negative values of the other two groups of samples. This sample distribution confirmed beam penetration beyond the shell thickness and reliability of the developed method.