VIS-NIR spectroscopy, a tool that allows improving and guaranteeing the correct quality and food safety

VIS-NIR spectroscopy, a tool that allows improving and guaranteeing the correct quality and food safetyVIS-NIR spectroscopy, a tool that allows improving and guaranteeing the correct quality and food safety

Victoria Cortés López, Doctoral Thesis Universitat Politècnica de València

The food industry, concretely the post-harvest sector, needs to innovate in their production processes, optimizing them to make their activities profitable, guaranteeing quality products capable of satisfying the needs of consumers.

Nowadays, the improvement of post-harvest inspection processes is mainly focused on their optimization, applying new alternative techniques, which reduce processing times, minimize waste generation and achieve greater standardization of their products.

The present doctoral thesis focuses on evaluating the potential of visible and near infrared spectroscopy (VIS-NIR) for the characterization and inspection of fruit quality both off-line and in real time in automated processes.

Firstly, the viability of the technique was studied at the laboratory level in a static mode (off-line), in order to know and optimise the measurement conditions according to the characteristics of the raw material.

Subsequently, the internal and external quality of different types of fruits such as persimmon, nectarine and mango were evaluated.

Secondly, an automation of the inspection processes was carried out through the development of new in-line prototypes.

For this purpose, and with the aim of completing and corroborating the results obtained in a static mode, the integration of two VIS-NIR probes in a robotic gripper capable of manipulating mangoes was studied, fusionating non-destructive measurements of the firmness and the spectra in the VIS-NIR range obtained simultaneously.

Finally, the integration of a VIS-NIR probe to a conveyor belt was studied as an in-line monitoring tool on the inspection process of different apple varieties.

The results obtained in static mode have shown that VIS-NIR spectroscopy is a very promising non-destructive method to predict the astringency in persimmon.

Likewise, it has demonstrated to be an adequate tool to classify 100% between nectarine varieties such as 'Big Top' and 'Diamond Ray' with very similar external and internal appearance, but with different organoleptic properties. Similarly, it was possible to classify 100% varieties such as 'Big Top' and 'Magique' with external appearance and similar composition but different pulp colour.

An internal quality index (IQI) was developed to evaluate the  quality of nectarines, which can be predicted through VIS-NIR spectroscopy.

Regarding the off-line work carried out with mangoes of 'Osteen' variety, it was possible to predict its internal quality through the indexes of maturity (RPI) and quality (IQI) with a high performance using the whole spectral range.

Moreover, the experimental tests carried out with these same mangoes under the non-destructive manipulation of a robotic gripper, showed that the best models were able to predict both the mechanical firmness, the soluble solids content, the brightness of the pulp as well as the RPI index of the samples based on the information obtained by the accelerometers installed on the fingers of the robotic gripper.

Innovations in non-destructive techniques for fruit quality control applied to manipulation and inspection lines
Doctoral Thesis submitted by Victoria Cortés López
Supervisors: Full Prof. Pau Talens Oliag & Dr. Sergio Cubero García
Valencia, September 2018

1 - The electromagnetic spectrum with the location of the visible and infrared spectral regions
2 - Cover page of the Thesis