Chemical stratification across kimchi cabbage leaves links edible quality with burden-aware outer-leaf valorization

Kimchi cabbage exhibits within-head chemical heterogeneity, but the compositional basis linking edible inner tissues with outer-leaf utilization remains unclear. Unlike previous Brassica leaf-position studies focused mainly on selected metabolites or general positional variation, this study integrated multi-domain chemical profiles across four practically defined kimchi cabbage leaf fractions, including discarded outer leaves. Principal component analysis clearly separated the four leaf fractions. Nitrate, nitrite, total glucosinolates, and several mineral elements were enriched toward discarded outer leaves, whereas glucobrassicin showed an opposite inner-enriched pattern. In contrast, edible-quality-associated primary metabolites, including L-glutamic acid, L-proline, L-alanine, and total sugars, were preferentially concentrated in inner tissues. Discarded outer leaves also showed higher As, Pb, and Cd levels, indicating that outer-leaf utilization should consider potentially undesirable constituents. These findings demonstrate that leaf-position-dependent chemical stratification links edible quality with burden-aware outer-leaf valorization.