Compositional variability in roller-mill processed streams: distribution of macro- and micronutrients, phytochemicals, and contaminants (heavy metals and anti-nutrients)

Abstract

This study investigated the micro- and macronutrient compositions, phytochemicals, heavy metals, and antinutritional factors of industrial wheat milling streams, including straight run flour (SRF), breaks (B1–B4), reductions (C1–C5), and by-products (fine bran, coarse bran, and germ). Specific streams such as B2, C1, C2F1, and C2F2 exhibited higher brightness, while the proximate composition varied significantly (p <0.05) across streams. Endosperm-rich flours were dominated by proline (6.07–14.19%) and glutamic acid (22.97–41.40%), whereas germ was richer in lysine (6.28%), arginine (7.13%), and threonine (4.27%). Break flours contained significantly (p <0.05) lower mineral levels but higher gluten strength (10.07–15.47%), while by-products were abundant in phenolics (127.16–138.80 mg GAE/100 g), carotenoids (0.115–0.141 mg/100 g), and antioxidant capacity (FRAP: 36.08–69.19 µmol Fe²⁺ per g). The particle size distribution (PSD) (<50 µm: 0.86–38.38%) influenced the functionality, with finer fractions showing significantly reduced phytochemical content. Heavy metals and anti-nutrients (tannins: 0.59–1.397 mg g⁻¹; phytic acid: 0.157–0.167%) were concentrated in bran fractions. Principal component analysis (PCA) revealed substantial variability, with PC1 and PC2 explaining 53.5% and 12.52% of the variation, respectively. Overall, these findings emphasize the potential of precision milling and strategic stream recombination to develop tailored ingredients, refined flours optimized for functionality, and by-products enriched for nutritional fortification. Additionally, understanding the distribution of acrylamide formation precursors (amino acids and reducing sugars) provides opportunities to minimize acrylamide formation in end products.