Optimisation of γ-aminobutyric acid production and modulation of phenolic compounds through solid-state fermentation of tomato pomace by Levilactobacillus brevis Y1

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γ-Aminobutyric acid (GABA) is a non-proteinogenic amino acid with health-promoting effects, which can be synthesized by several organisms, including bacteria. In this study Levilactobacillus brevis Y1 was used to produce GABA via Solid-state Fermentation (SsF) of tomato pomace (TP). GABA production was optimised by Response Surface Methodology (RSM) with Central Composite Design (CCD). GABA and L-glutamic acid (L-Glu) were quantified by DAD-HPLC, while the phenolic profile of fermented and unfermented TP was analyzed by LC-ESI-QTOF-MS/MS. Maximum GABA production (14.07 ± 0.58 mg/g) was achieved after 6 fermentation days at 30 °C, pH 4.47, and 3.68% L-Glu, reporting a model accuracy of 108.96%. Fermentation modified the TP phenolic profile, increasing the neochlorogenic acid, quercetin hexoside, rutin hexoside, and naringenin, while decreasing rutin. These findings demonstrate the potential of SsF of TP with L. brevis Y1 to produce GABA and create sustainable value-added, health-promoting ingredients from tomato industry by-products.