Integrated management of residues from tomato production: Recovery of value-added compounds and biogas production in the biorefinery context

The biorefinery approach must be boosted in the management of agro-residues in the future. The present study aims to investigate the valorization of tomato production residues, namely rotten tomato (unfit for consumption - RT), green tomato (GT), and tomato branches (TB). The assessment involves the recovery of value-added compounds through the extraction process followed by biogas production through anaerobic digestion. A thorough characterization of the three residues (RT, GT, and TB) was carried out, including the identification of volatile compounds by solid-phase microextraction (SPME) and gas chromatography/mass spectrometry (GC/MS). The volatiles analysis revealed the presence of flavor enhancer compounds and molecules with insecticidal properties. A solid-liquid extraction with ethanol allowed the recovery of value-added compounds in the extracts, in particular phenolic compounds, beta-carotene, and lycopene, which contributed to the antioxidant activity. RT and TB extracts were found to be richer in total phenolic compounds (similar to 27 mg GAE/g(db) dry basis) and exhibited higher antioxidant activity (IC50 = 0.911 and 0.745 mg/mL). The tomato branches extract had the highest concentration of carotenoids with 37.23 and 3.08 mg/kg(db) of beta-carotene and lycopene, respectively. The biochemical methane potential (BMP) was assessed in sealed reactors operating in anaerobic conditions for all the raw (RT, GT, and TB) and extracted substrates waste (RTe, GTe, and TBe). While the BMP of RT and GT was in the range of 232-285 mL CH4/g VS, a lower value of 141 mL CH4/g VS was obtained for TB. The methane production for each pair of raw and extracted substrates (RT/RTe, GT/GTe, and TB/TBe) was considered statistically similar at a 95 % confidence level. Overall, the value-added compounds recovery through ethanolic extraction did not compromise the methane production of the materials.

Automated summary

This study investigated the valorization of tomato production residues through extraction processes to recover value-added compounds and found that ethanolic extraction did not compromise methane production. The analysis identified flavor enhancer compounds and insecticidal molecules in the residues, and revealed that RT and TB extracts were richer in total phenolic compounds and exhibited higher antioxidant activity compared to GT extracts. The study also showed that the methane production from extracted substrates was statistically similar to that of raw substrates for all three types of residues.