Optimizing the supercritical fluid extraction process of bioactive compounds from processed tomato skin by-products
Non-negligible amounts of various kinds of waste are generated in the vegetable processing industry. On particular, waste represents 2-3% of the raw material in the tomato processing industry, consisting mainly of peels (about 60%) and seeds (around 40%). Production companies generating this kind of waste due to disposal processes (Ćetković et al., 2012) are faced with the burden of additional costs. Several research studies have pointed out that tomato peels contain a high level of bioactive compounds including phenols, lycopene, ascorbic acid compared to their pulp and seeds (Vinha et al., 2014). Peels and seeds contribute particularly to 53% of the total amount of phenols, 52% of flavonoids, 48% of lycopene, 43% of ascorbic acid and 52% of the antioxidant activity occurring in tomatoes. These results demonstrate that the removal of peels and seeds during cooking or industrial processing leads to a significant loss of all the major antioxidants (Toor & Savage, 2005). Lycopene represents the most promising compound among tomato antioxidants (Story et al., 2010; Kaliora et al., 2006; Visioli et al., 2003). The request for lycopene as a functional ingredient for nutraceutical products or for functional food formulations has increased dramatically over the past decade due to its acknowledged healthy properties. Since there is still no favourable synthetic process allowing for its production, lycopene extraction from natural plant matrices continues to be necessary. Currently, the most common methods for extracting lycopene from tomatoes or tomato processing residues are based on the use of organic solvent solvents (Machmudah et al., 2012). After the extraction procedure, lycopene is subjected to a long and expensive purification process that does not lead, however, to a high degree of purity. To overcome these drawbacks, new solvent-free and environmental friendly compatible extractions support the use of supercritical fluids such as carbon dioxide (CD2) in order to obtain toxic-free solvent products (Amaral et al., 2018a, b). This technology is configured as an interesting alternative for the food industry due to the increased nutrient retention (Amaral et al., 2017).