Assessment of Phenotypic Characteristics, Polysaccharide Composition, and Hypoglycemic Potential in Different Commercial Grades of Lycium barbarum: A Comprehensive Study Using HPLC and NMR

<i>Lycium barbarum</i> L. (abbreviated to <i>L. barbarum</i>), a traditional dual-use plant as food and medicine, contains polysaccharides from <i>Lycium barbarum</i> L. (LBPs) as its key bioactive component. This study aimed to examine the phenotypic characteristics, polysaccharide content, and their correlation with activity across various commercial grades of <i>L. barbarum</i>. Five commercial grades of <i>L. barbarum</i> were selected for analysis to determine their phenotypic characteristics and polysaccharide content. High-performance liquid chromatogram-diode array detection (HPLC-DAD) and ¹H NMR were employed to analyze the monosaccharide composition of LBPs, of which their hypoglycemic activity was further valuated. Results revealed significant differences in fruit weight and diameter among different grades (<i>p</i> < 0.05), while floating rate and bulk density remained unaffected by grades. Variations were observed in the chromaticity coordinates, with the <i>c</i> values showing notable differences (<i>p</i> < 0.01). Polysaccharide content tended to increase with higher grades and smaller fruit sizes, ranging from 1.94% to 5.69%. The polysaccharides in different contained monosaccharides of Man, Rha, Ara, Gal, Glc, GalA, GlcA and Xyl, with Ara and Gal being predominant. Identified through ¹H NMR spectra, the peak intensity of Ara increased from lower to higher grades, and the arrangement of the chemical shifts reflected distinct commercial grade characteristics. The inhibitory concentration (IC₅₀) against <i>α</i>-amylase and <i>α</i>-glucosidase ranged from 0.418 to 1.345 mg/mL, and 0.474 to 1.052 mg/mL, respectively, indicating good hypoglycemic activity within this range. The main monosaccharide groups Ara, Gal, and GalA were identified as key contributors to enzyme inhibition. Collectively interpreting the phenotypic features, polysaccharide content, monosaccharide composition, NMR data and activity profiles, Ara, Gal and GalA emerge as signature monosaccharide components of LBPs. These results provide novel theoretical insights for <i>L. barbarum</i> quality assessment.