# Evaluation of the Influence of Bottle Type on the Acquisition of SORS Spectra of Extra Virgin and Virgin Olive Oils

## TL;DR

This study shows that SORS can reliably analyze olive oil in plastic and clear glass bottles without opening them, but not in green glass bottles.

## Contribution

A new similarity index (WSI) is introduced to assess spectral similarity in SORS measurements of olive oils in different containers.

## Key findings

- Plastic and colorless glass bottles showed high spectral similarity (WSI > 0.95) to reference measurements.
- Green glass bottles had lower similarity (WSI < 0.95), affecting spectral reliability.
- SORS spectra remained stable for 10–18 days under various storage conditions.

## Abstract

The objective of this study was to evaluate the impact of the material (plastic or glass) and color (green or colorless) of extra virgin olive oil (EVOO) and virgin olive oil (VOO) bottles on the acquisition of SORS spectra using portable equipment. Sixteen bottles of EVOO and three bottles of VOO were analyzed, including different volumes. A range of similarity indices was calculated between vial-reference (offline measurements) and bottles (online measurements), including R2, COS θ, NEAR, and a new index called WSI (Weighted Similarity Index). WSI is calculated from the pondered linear combination of the previous three, and a threshold of >0.95 is established as high similarity. The results showed that plastic bottles, regardless of color and volume, and colorless glass bottles had WSI values > 0.95. In contrast, green glass bottles demonstrated a lower degree of similarity (WSI < 0.95), which impacted the reliability of their spectral fingerprints. A hierarchical cluster analysis (HCA) was performed by locating EVOO bottles according to their material in two clusters. A study of storage under optimal, non-optimal, and commercial conditions showed that both EVOO and VOO maintain highly similar spectral profiles for 10–18 days (WSI > 0.965), even in bottles purchased in supermarkets. These results demonstrate that the SORS technique is suitable for the direct analysis of olive oils in plastic and colorless glass containers, without the need to open the bottles. The SORS technique is a fast, reliable, non-invasive, and non-destructive tool for quality control of olive oil.