Impact of millet and agro-industrial by-products on the technological quality and shelf life of gluten-free breads

Gluten-free breads (GFBs) are usually formulated with refined flours, starches, or premixes that are low in fibre, micronutrients, and have a high glycaemic index. In addition, these formulations often stale rapidly, leading to crumb hardness, reducing shelf life, and decreasing consumer acceptance. This study aimed to evaluate the effect of gluten-free raw materials such as rice bran (RB), millet, and extruded soybean expeller (SEE) on the staling kinetics and physico-chemical quality of GFBs. Millet and SEE were milled using a HC-1000Y mill (Arcano, China) and then sieved together with RB through an 840 µm mesh (Zonytest, Argentina). Two GFB formulations were prepared: optimal (GFB-O) and control (GFB-C). Both contained xanthan gum (0.5%), sunflower oil (6%), salt (2%), sugar (5%), and dry yeast (3%). GFB-O included 15% each of RB, millet, and SEE and rice flour (22.5%), corn starch (32.5%), and water (115%), while GFB-C was made with 100% corn starch and 90% water. Moisture content (AACC, 2000), water activity, and crumb hardness (peak force during the first compression cycle of the texture profile analysis) were evaluated during storage (0–168 h, 25 °C, 70% RH, LDPE bags). Hardness data were fitted to the Avrami equation to model staling kinetics. ANOVA with Fisher’s LSD test (95% confidence) revealed significant effects of formulation and storage time on crumb water activity, moisture, and hardness (p<0.0001). GFB-O exhibited lower crumb hardness and improved moisture retention throughout the storage period. Avrami modelling supported this, showing that GFB-O had a lower final hardness (Finf = 23.4 N), lower rate constant (k = 0.035 h⁻ⁿ), and exponent (n = 0.24), indicating a slower staling process and prolonged freshness. In contrast, GFB-C showed Finf ≈ 120 N, k = 0.05 h⁻ⁿ, and n = 1, consistent with faster staling. These results demonstrate that the addition of RB, millet, and SEE could modify the bread matrix, improving the technological properties and shelf life of FGFs.