Comparison of different sample preparation techniques for NIR screening and their influence on the geographical origin determination of almonds (Prunus dulcis MILL.)

Abstract The aim of the present study was to conduct a systematic and in-depth comparison of four different sample preparation techniques for near-infrared (NIR) spectroscopy analysis of almonds and evaluation of their suitability for the geographical origin determination. Although it is generally known that the sample preparation has an impact on the NIR screening, there is no scientific consensus on a commonly accepted procedure. In this work, 64 almond samples from six countries were analyzed as whole and bisected nuts as well as in a ground and freeze-dried state (after grinding). In order to assess the suitability for future applications, both the labor effort for sample preparation and the classification accuracy were evaluated. Using support vector machine (SVM) classification we obtained a classification accuracy of 80.2% (±1.9%) on the validation set for the determination of origin of freeze-dried almonds. The other three sample preparations result in at least 8.3 percentage points lower classification accuracies. Nonetheless, the analysis of whole and bisected almonds is more suitable for an initial rapid screening due to a lower overall required work effort. The results confirm the influence of the sample preparation techniques in NIR screening and pave the way for future widespread analytical applications.