Valorization of tomato waste with subcritical water extraction

• Autor(a) principal: Soares, Daniela Pereira
• Data de Publicação: 2021
• Tipo de documento: Dissertação
• Idioma: eng
• Título da fonte: Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
• Texto Completo: http://hdl.handle.net/10362/129171
• topic: Agro-industrial residues; antioxidant activity; biomass; carbohydrates; phenolic compounds; subcritical water; Domínio/Área Científica::Engenharia e Tecnologia::Engenharia Química

World energy demand is increasing rapidly, and the search for new renewable and clean technologies has been a priority for the agro-industrial sector. Greenhouse gases emission and pollution has had great concern all over the globe. Biomass is the only renewable resource abundant enough to be used as an energy source. Tomato waste is a common agro-industrial residue, and it is abundantly produced by tomato processing industries. Biorefineries can use agro-industrial residues to produce added-value residues, increasing its value. The aim of this work is to evaluate the possibility of tomato waste valorization from the tomato processing industries, through the extraction/hydrolysis of carbohydrates and phenolic compounds with antioxidant activity, using a clean and efficient technology, subcritical water extraction. ScW extraction was performed at 100 bar, a constant water flow of 12 mL/min and a range of temperatures until 250 ºC, by extracting different compounds at the target temperatures of 140 ºC, 190 ºC and 250 ºC. Tomato waste (TW) was chemically characterized, having a high content in carbohydrates (around 38 wt.%), of which ca. 52% was non-structural carbohydrates. Main carbohydrate monomers identified by HPLC, were glucose and fructose. Tomato waste has also a high content in lignin (19.2 wt.%) and protein (15.2 wt.%). Phenolic content was about 0.6 wt.%. Ash, lipid, and water content were also determined. Tomato waste was initially submitted to supercritical CO2 extraction to remove most of its lipid and lycopene content. The residue that was left from the previous extraction, labelled as defatted TW (DTW), was subjected to subcritical water (ScW) extraction, with a high yield of 67% and a mass conversion of 86%. ScW residue and ScW extracts were chemically characterized. 73% of the total amount of carbohydrates were recovered in the ScW extracts, and 11% in the ScW residue, making a total of 84% of carbohydrate recovery in the process. A higher amount of phenolic compounds was recovered in the ScW extracts than quantified in the original material, indicating that the subcritical water treatment allowed access to compounds not recovered in the hydro-alcoholic extraction. The antioxidant activity of each extract was evaluated, where the extract with a higher antioxidant activity, obtained at 250 ºC, had an inhibition percentage of 54%. The main goals of this work were achieved successfully. Carbohydrate and phenolic compounds were extracted with subcritical water with high biomass recovery, and antioxidant activity was confirmed in ScW extracts, demonstrating the possibility of tomato waste valorization.