# Extraction of Lycopene from Tomato Peels Using Supercritical Carbon Dioxide and Conjugation of the Extracted Lycopene with TiO2 Nanoparticles

## TL;DR

This paper introduces a new method to extract lycopene from tomato peels using supercritical CO2 and then attach it to TiO2 nanoparticles, offering a green alternative to traditional solvent-based methods.

## Contribution

The first report of conjugating supercritical CO2-extracted lycopene with TiO2 nanoparticles, eliminating the need for organic solvents.

## Key findings

- Supercritical CO2 extraction at 50 °C and 30 MPa for 2 h yielded the highest lycopene recovery.
- Lycopene was successfully conjugated to TiO2 nanoparticles with 95.0 ± 2.1% loading efficiency.
- The TiO2NPs-lycopene conjugate showed potential for antimicrobial applications due to a synergistic effect.

## Abstract

The tomato processing industry is one of the most widespread
food
manufacturing sectors globally, generating substantial amounts of
residue, including tomato skins, peels, seeds, and vascular tissues.
These residues still retain valuable bioactive compounds (e.g., carotenoids
like lycopene), essential for food, pharmaceutical, and nutraceutical
applications. Currently, traditional solvent extraction is the most
common method for retrieving these compounds from tomato residue.
However, this approach has notable disadvantages, including high solvent
consumption and difficulties in utilizing leftover biomass. To address
these issues, innovative technologies have introduced modifications
to process configurations and techniques that alter or break down
plant cells, significantly improving compound recovery. Supercritical
fluid extraction offers an effective method for enhancing the value
of tomato residues before disposal, as it is an environmentally friendly
approach, particularly when carbon dioxide is used as the extraction
solvent. The novelty of the present work is the specific optimization
and integration of this green extraction technique with the subsequent
conjugation of the extracted lycopene to TiO2 nanoparticles
(TiO2NPs). This is the first report demonstrating the conjugation
of supercritical CO2-extracted lycopene with TiO2NPs, effectively eliminating the use of organic-solvent-derived carotenoids
traditionally used in such conjugates. The supercritical CO2-extraction (scCO2) was employed at various times (2,
3, and 4 h), temperatures (40–80 °C), and pressures (25,
30, and 35 MPa). Among the tested protocols, the treatment of tomato
at 50 °C and 30 MPa for 2 h showed the highest yield based on
the UV–vis and HPLC results. For the potential pharmaceutical
benefits of these extracts, lycopene was directly conjugated with
TiO2NPs, using a mild and green approach (TiO2NPs-lycopene) and characterized using different techniques, including
HPLC, UV–vis, FTIR-ATR, FESEM-EDS, and DLS to assess the successful
loading of 95.0 ± 2.1% of lycopene on the TiO2NPs.
The FESEM results exhibited the grain-like TiO2NPs-lycopene
particles with a 60–80 nm size distribution, indicating size-controlling
effect of the lycopene on the TiO2NPs during the conjugation
process and the presence of the organic molecule layer on the surface.
TiO2NPs-lycopene represents a promising candidate for antimicrobial
studies due to the potential synergic effect of TiO2NPs
and lycopene in a single nanoplatform. The results show the importance
of scCO2-based techniques, as valid alternatives to the
conventional methods that exploit organic solvents, to prepare the
TiO2NPs-carotenoids conjugates. To the best of our knowledge,
this is the first study to report the conjugation of TiO2NPs with lycopene, offering a novel approach to enhance their antioxidant
and photoprotective properties.