The tomato processing industry generates vast quantities of pomace — the skins and seeds left after juice or paste extraction — from around 45 million tonnes of tomatoes processed worldwide in 2024 (European Commission, 2024). Italy, the world’s second-largest processor with 5.8 million tonnes in the 2025 campaign and the global leader in consumer-destined preserves, has every interest in valorising the by-products of this strategic supply chain (Dongo, 2026).
Rather than treating this material as waste, a recent Italian study published in Food Chemistry has demonstrated its potential as a fermentation substrate for the simultaneous production of γ-aminobutyric acid (GABA) and health-promoting phenolic bioactive compounds (Squillante et al., 2026). The work represents a meaningful step towards the upcycling of agri-food by-products through microbial biotechnology, consistent with the principles of the circular economy.
GABA: a non-proteinogenic amino acid of growing nutritional interest
GABA is a non-proteinogenic amino acid with an established role as the primary inhibitory neurotransmitter in the mature mammalian nervous system. Beyond neurophysiology, it has attracted increasing scientific interest for a broad spectrum of bioactivities, including anti-hypertensive, antioxidant, anti-inflammatory, hepatoprotective, and gut-modulating properties (Hou et al., 2024). Natural GABA concentrations in foods are generally insufficient to elicit significant physiological responses; accordingly, fermentation has emerged as an efficient and food-safe production strategy. The enzymatic mechanism relies on glutamate decarboxylase (GAD), which catalyses the irreversible decarboxylation of L-glutamic acid (L-Glu) to GABA, a reaction also serving as an intracellular acid-stress defence mechanism in lactic acid bacteria (LAB).
Strain selection and solid-state fermentation design
The authors first screened ten LAB strains across five genera for GABA-producing ability in MRS broth supplemented with L-Glu. Levilactobacillus brevis Y1 — a strain holding Qualified Presumption of Safety (QPS) status as recognised by the European Food Safety Authority (EFSA, 2023) — markedly outperformed all others, yielding 1.48 ± 0.069 mg/mL of GABA, a result attributed to its distinctive dual-GAD gene architecture (gadA and gadB) and the associated transcriptional regulator gadR (Gao et al., 2019). The strain was then applied to solid-state fermentation (SsF) of tomato pomace (TP), an approach offering lower water consumption and reduced waste compared with conventional submerged fermentation, while enabling the production of heterogeneous, multi-bioactive matrices.
Optimisation by response surface methodology
GABA production was optimised through Response Surface Methodology (RSM) employing a Central Composite Design (CCD), with three independent variables: L-Glu concentration, initial substrate pH, and fermentation temperature. A preliminary kinetic study established that GABA accumulation followed a time-dependent pattern, peaking on day 6 and declining thereafter — a decrease attributed to reconversion of GABA to L-Glu via the GABA shunt pathway and the tricarboxylic acid cycle (Squillante et al., 2026). The RSM model showed good predictive accuracy (R² = 0.91; R² adjusted = 0.86) and identified optimal conditions at 3.68% L-Glu, pH 4.47, and 30°C. Experimental validation under these conditions yielded 14.07 ± 0.58 mg/g of GABA — approximately 9% above the model prediction — confirming the robustness of the approach.
Modulation of the phenolic profile
A particularly noteworthy finding was the fermentation-induced remodelling of the TP phenolic profile, analysed by LC-ESI-QTOF-MS/MS. Unfermented TP contained neochlorogenic acid, quercetin, quercetin hexoside, naringin, rutin, rutin hexoside, and rutin pentoside — a profile consistent with published data on tomato by-products. Fermentation with L. brevis Y1 significantly increased the relative content of neochlorogenic acid, naringenin, quercetin hexoside, and rutin pentoside, while rutin decreased. These shifts are plausibly explained by the glycosidase activity (β-glucosidase, α-arabinosidase) of L. brevis, capable of hydrolysing the O-glycoside bonds of rutin to yield simpler glycosylated derivatives (Michlmayr et al., 2010). Notably, quercetin hexoside derivatives have been reported to exhibit superior bioavailability relative to rutin and quercetin aglycone, with potential implications for anti-diabetic and anti-inflammatory bioactivity (Liu et al., 2025).
Conclusions and outlook
This study establishes, for the first time, the feasibility of GABA biosynthesis from tomato pomace under solid-state fermentation conditions, while simultaneously demonstrating a favourable reshaping of the phenolic fraction. The resulting fermented product could serve as a multi-component functional ingredient combining the neurophysiological and cardioprotective properties of GABA with the antioxidant and anti-inflammatory bioactivities of enhanced phenolic compounds. The authors acknowledge that further work is needed, including investigation of pyridoxal-5′-phosphate (PLP) supplementation, substrate moisture, and inoculum size, alongside pilot-scale validation and in vitro or in vivo bioactivity assessments. Taken together, these findings position fermented tomato pomace as a scientifically credible candidate for nutraceutical and functional food formulations, contributing to the broader agenda of sustainable agri-food waste valorisation.
WIISE Benefit company, through its FARE — Food and Agriculture Requirements unit www.fareagrifood.com unit, supports research consortia and food business operators (FBOs) in translating R&D outcomes such as these into market-ready opportunities. Bringing a fermented by-product like tomato pomace to consumers as a functional ingredient entails a defined regulatory pathway — from novel food authorisation under Regulation (EU) 2015/2283, where applicable, to the substantiation of health claims under Regulation (EC) 1924/2006, alongside food safety, labelling, and intellectual-property considerations. FARE accompanies innovators across each of these steps, helping to convert scientific potential into compliant, commercially viable products.
#Wasteless
Dario Dongo
Credit cover Avin CP on Unsplash
References
Dongo, D. (2026, 22 June). Italian tomatoes: regulations, nutritional claims and health. GIFT (Great Italian Food Trade). https://www.greatitalianfoodtrade.it/verdure/%E2%81%A0pomodoro-italiano-proprieta-nutrizionali-benefici-salute%E2%81%A0/
EFSA Panel on Biological Hazards (BIOHAZ), Koutsoumanis, K., Allende, A., Álvarez-Ordóñez, A., Bolton, D., Bover-Cid, S., & Herman, L. (2023). Update of the list of qualified presumption of safety (QPS) recommended microorganisms intentionally added to food or feed as notified to EFSA. EFSA Journal, 21(1), e07747. https://doi.org/10.2903/j.efsa.2023.7747
European Commission. (2024). Short-term agricultural market outlook: Tomatoes. Agri-food portal. https://agridata.ec.europa.eu/extensions/DashboardSTO/STO_Tomatoes-m.html
Gao, D., Chang, K., Ding, G., Wu, H., Chen, Y., Jia, M., Liu, X., Wang, S., Jin, Y., Pan, H., & Li, H. (2019). Genomic insights into a robust gamma-aminobutyric acid-producer Lactobacillus brevis CD0817. AMB Express, 9(1), 72. https://doi.org/10.1186/s13568-019-0799-0
Hou, D., Tang, J., Feng, Q., Niu, Z., Shen, Q., Wang, L., & Zhou, S. (2024). Gamma-aminobutyric acid (GABA): a comprehensive review of dietary sources, enrichment technologies, processing effects, health benefits, and its applications. Critical reviews in food science and nutrition, 64(24), 8852–8874. https://doi.org/10.1080/10408398.2023.2204373
Liu, L., Barber, E., Kellow, N. J., & Williamson, G. (2025). Improving quercetin bioavailability: A systematic review and meta-analysis of human intervention studies. Food Chemistry, 143630. https://doi.org/10.1016/j.foodchem.2025.143630
Michlmayr, H., Schümann, C., da Silva, N. M., Kulbe, K. D., & del Hierro, A. M. (2010). Isolation and basic characterization of a beta-glucosidase from a strain of Lactobacillus brevis isolated from a malolactic starter culture. Journal of applied microbiology, 108(2), 550–559. https://doi.org/10.1111/j.1365-2672.2009.04461.x
Squillante, J., Giordano, I., De Simone, B., Mauriello, G., Ferranti, P., Picariello, G., Cirillo, T., & Esposito, F. (2026). Optimisation of γ-aminobutyric acid production and modulation of phenolic compounds through solid-state fermentation of tomato pomace by Levilactobacillus brevis Y1. Food Chemistry, Advance online publication, 150096. https://doi.org/10.1016/j.foodchem.2026.150096
Dario Dongo, lawyer and journalist, PhD in international food law, founder of WIISE (FARE - GIFT - Food Times) and Égalité.
