**Background:** Celiac disease is associated with increased oxidative stress due to gliadin-induced disruption of the pro-oxidant–antioxidant balance in the small intestinal mucosa. A gluten-free (GF) diet rich in antioxidant compounds may aid mucosal healing, but GF bread (GFB) is often nutritionally inferior to wheat bread. This review examines plant-based antioxidants as a strategy to enhance GFB, covering sources, quantification methods, technological and sensory effects, and bioaccessibility.
**Methods:** A literature search was performed in Scopus, Web of Science, and Google Scholar for articles published from 2010 to 2023 using terms related to bioactive compounds, phenolic compounds, gluten-free bread, and antioxidant activity. The review includes 46 hits from Scopus and additional independent searches. It summarizes data from 34 research articles published between 2020 and 2023 and 23 articles from 2010 to 2020.
**Key Results:** The most frequently applied methods for antioxidant quantification in GFB are total phenolic content (TPC), DPPH, ABTS, FRAP, and total flavonoid content (TFC). Sample preparation typically involves extraction with methanol/water mixtures, often with ultrasound or stirring, followed by centrifugation. The review notes wide variability in methods, including differences in reaction times (e.g., TPC from 20 to 120 min), wavelengths (e.g., DPPH at 515 or 517 nm), and reference standards (e.g., gallic acid, ferulic acid, catechin).
Basic sources of antioxidants include gluten-free cereals (rice, maize, millet, sorghum), pseudocereals (buckwheat, quinoa, amaranth, chia), and legumes (chickpea, soybean, lentil, pea). For example, Tartary buckwheat has a TPC of 72.8 ± 0.5 mg GAE/g and FRAP of 40.5 ± 4.4 μmol TE/g, while common buckwheat has 29.3 ± 0.5 mg GAE/g and 9.1 ± 1.6 μmol TE/g. Pigmented varieties (e.g., violet rice, purple maize) show higher antioxidant activity. Plant-based additives (e.g., fruit by-products, vegetable powders, microalgae) at levels from 1% to 100% increase GFB antioxidant content. For instance, adding 5% red onion peel to GFB increased TPC to 5.28 ± 0.11 mg GAE/g and DPPH to 4.70 ± 0.02 μmol TE/g.
Bread-making can both increase and decrease antioxidant content. Losses of up to 60% in phenolic compounds occur during baking, but increases are attributed to release of bound phenolics, Maillard reaction products, and conversion of complex compounds. Specific volumes of enriched GFB range from 0.6 to 4.78 cm³/g, and crumb hardness from 0.2 to 3957 N, depending on the source and level of addition. Sensory evaluation using hedonic scales (5- to 9-point) shows that texture, taste, and appearance are most affected; bitterness and astringency from phenolic compounds can limit acceptability. Bioaccessibility studies (in vitro digestion) show variable results: TPC increased after digestion of GFB with carob fiber or coffee extracts but decreased with sorghum flour. In vivo studies (FORD/FORT assays) on GFB with red onion peel showed a double increase in FORD values but no significant changes in FORT.
**Clinical Implications:** Antioxidant-enriched GFB has potential as a therapeutic tool for celiac patients by reducing oxidative stress and supporting mucosal healing. However, the review highlights major gaps: lack of standardized quantification methods, limited studies on bioaccessibility and bioavailability, and insufficient exploration of changes during storage. Future research should focus on standardizing antioxidant assays, elucidating mechanisms of antioxidant changes during bread-making, and conducting in vivo studies to confirm health benefits. The use of food industry by-products aligns with sustainability goals but requires careful sensory optimization.