Raw data used for the manuscript entitled Cold tomato soup industry by-products as functional ingredients for ruminants: Nutritional composition, bioactive potential, and modulation of in vitro ruminal fermentation and methanogenesis [Dataset]

1. Acronyms Introductory sheet defining the abbreviations used throughout the file for the studied by‑products: TP (tomato peel), TS (tomato seed), SBP (salmorejo by‑products) and GBP (gazpacho by‑product). 2. Chemical composition Contains the proximate and fibre composition of the by‑products (TP, TS, SBP and GBP) under different processing conditions. Variables include drying temperature, particle size, dry matter, organic matter, crude protein, neutral detergent fibre (NDF), acid detergent fibre (ADF) and acid detergent lignin (ADL). Data are presented with analytical replicates for each factor combination. 3. Mineral composition Reports the mineral and trace‑element composition (ppm or mg/kg) of each by‑product, including major elements and trace elements (e.g. Ca, P, K, Mg, Fe, Zn), organised by matrix. 4. Amino acid composition Provides the amino‑acid profile (g/kg dry matter) of each by‑product, including both essential and non‑essential amino acids, with replicate measurements to characterise protein quality. 5. Bioactive potential Dedicated to the bioactive and antioxidant potential, including total polyphenol content, total carotenoids, β‑carotene, lycopene, and antioxidant activity assays (ABTS and DPPH). Data are classified by by‑product, drying temperature and particle size. 6. Oxidative stability Includes measurements of lipid oxidative stability (TBARS, mg MDA/kg DM) at different storage times (0, 7 and 60 days), allowing assessment of oxidative evolution as affected by matrix and processing conditions. 7. In vitro – CTSIB Contains results from ruminal in vitro fermentation assays of individual by‑products and the control diet, including gas production, metabolizable energy, organic matter digestibility, methane production (6 and 24 h), volatile fatty acid profiles, acetate/propionate ratio, ruminal ammonia (N‑NH₃) and lactic acid concentration. Multiple technical replicates are reported per treatment. 8. In vitro – GBP 25%