Comparison of the Chemical Composition of Different Gluten-Free Brewer's Spent Grain Batches for Potential Applications in the Food Industry and Biorefineries

Brewer’s spent grain (BSG) is the main by-product generated during brewing. Information on the chemical composition of gluten-free BSG remains scarce. This study compared two millet-based gluten-free BSG batches and values reported in the literature to determine compositional differences affecting interchangeability and valorization potential. Samples were characterized using standardized (NREL-AOAC-AOCS) methods. Data were analyzed by ANOVA and Tukey’s test (p < 0.05). Results are reported on a dry basis, except moisture content.

Significant differences (p<0.05) were observed between batches for all parameters evaluated, except total solids content (p=0.16). For the 2022 batch, moisture, fat, protein, ash, fat acidity (expressed as linoleic acid equivalents), and extractives contents were 58.00 ± 0.54 % ; 3.19 ± 0.28 %; 12.67 ± 0.27 %; 4.53 ± 0.02 %; 14.00 ± 2.11 % and 16.37 %, respectively. The corresponding values for the 2025 batch were  71.00 ± 0.71 %;  6.35 ± 0.05 %; 18.41 ± 0.11 %; 6.78 ± 0.40 %; 4.20 ± 0.55 %  and 23.64 %, respectively. The lignocellulosic fraction of both batches consisted of cellulose (35.79 ± 0.07 % – 53.60 ± 1.43 %), hemicellulose (10.55 ± 0.17 % – 6.10 ± 0.03 %) and lignin (12.30 ± 0.30 % – 7.03 ± 0.04 %).

Differences in chemical composition were observed between the 2022 stored batch and the recently produced 2025 batch. Although the causes were not investigated, they may be associated with prolonged storage and batch-to-batch process variations. Comparison with conventional BSG and other lignocellulosic biomasses showed no consistent pattern, with some compositional parameters being comparable and others differing. These findings highlight the need for standardized characterization of gluten-free BSG to generate comparable datasets and support its valorization in food and biorefinery applications.