Enrichment of polyamines across barley milling fractions and their correlation with markers of whole-grain content

Barley is increasingly recognized for its health-promoting constituents, including polyamines, phenolic compounds, and micronutrients concentrated in the germ and outer kernel layers. This study investigated the potential of dry fractionation, combining milling and size-based sieving, to enrich polyamines and whole-grain markers in barley milling products. Six barley cultivars representing malting, feed, and food types, including both hulled and hulless genotypes, were milled and separated into three particle-size fractions: fraction A (>500 µm), fraction B (200‒500 µm), and fraction C (<200 µm). Across all cultivars, the intermediate fraction B consistently exhibited polyamine enrichment, with total polyamine concentrations averaging 25% higher those in whole flour. Specifically, spermidine increased by 20‒70%, putrescine by 10‒68%, and spermine by 20‒36%, depending on genotype. In contrast, the fine fraction C and coarse fraction A showed reductions in total polyamines and a compositional shift toward the polyamine-poor starchy endosperm and hull materials, respectively. Hand dissection confirmed that polyamines are concentrated in the outer layers and germ tissues of the barley kernel, which were present in greater proportion in the intermediate fraction B, as indicated by physicochemical properties. Correlation analysis revealed positive associations between polyamines and markers of whole-grain status, including protein (r = 0.70‒0.84), ash (r = 0.44‒0.63), barley germ agglutinin (r = 0.67), and total phenolics (r = 0.44‒0.66). Overall, dry fractionation effectively concentrated polyamines and whole-grain constituents into a nutritionally superior milling fraction, underscoring its potential for producing functional barley ingredients with enhanced bioactive content.