Comparative Insights into Enzymatic and High-Temperature Steam Treatment of Glycyrrhiza uralensis Fisch. Stems: Structural Remodeling, Flavonoid Transformation and Antioxidant Enhancement

Glycyrrhiza uralensis Fisch. (G. uralensis) stems are an underutilized agricultural by-product rich in polysaccharides, phenolics, and flavonoids. This study systematically compared enzymatic and high-temperature steam treatments for improving their functional value. Both treatments altered plant matrix architecture but exhibited distinct effects. Enzymatic processing largely preserved the original color and induced moderate cell wall loosening, whereas steam treatment caused more extensive tissue disruption, porous structure formation, and thermal browning. Enzymatic treatment increased extract solubility from 0.25% to 0.32%, soluble polysaccharide content from 266.06 ± 1.58 to 319.40 ± 4.19 mg/g, and total phenolic content from 49.69 ± 0.65 to 63.99 ± 0.81 mg/g. In contrast, steam treatment reduced solubility to 0.14% and total phenolic content to 38.39 ± 0.52 mg/g, despite increasing polysaccharide content to 300.50 ± 3.02 mg/g. Metabolomic analysis revealed divergent flavonoid remodeling between the two processing strategies, with enzymatic treatment associated with distinct changes in the relative abundance of several flavonoid subclasses and metabolites. Consistently, enzyme-treated extracts showed superior DPPH radical-scavenging activity (90.90% at 16 mg/mL) and markedly improved embryo survival and hatching rates (91.25%) in an AAPH-induced zebrafish model. Collectively, these findings highlight that controlled enzymatic remodeling, rather than excessive thermal disruption, is more effective for preserving functional molecules and enhancing the bioactive potential of G. uralensis stems.