Dose-Dependent Preservation of Highland Barley Flour Storage Quality by Lycium barbarum Polysaccharide: Evidence from 240-Day Storage Monitoring and Untargeted Lipidomics

Highland barley (hulless barley, Hordeum vulgare L. var. nudum) flour is a nutritionally dense staple of the Qinghai–Tibet Plateau, but its high contents of unsaturated lipids and active endogenous enzymes render it highly susceptible to storage deterioration. Natural polysaccharides have been proposed as green preservatives, yet the dose-dependent effects of Lycium barbarum polysaccharide (LBP) on the storage quality of cereal flours and the underlying lipid-level mechanisms remain unclear. Here, highland barley flour (cv. Kunlun-15) was blended with LBP at 0.2%, 1.0% and 2.0% (w/w) stored in sealed bags at ambient temperature for 240 days, with three independently stored units per treatment; untreated flour served as the control. Storage was monitored for basic nutritional components, functional components, antioxidant activity, storage-stability indices and microbial counts, and untargeted lipidomics was performed by UPLC-MS/MS to resolve the lipid-level response. All LBP supplementations retarded the loss of nutritional and functional components, with dose-specific optima: 0.2% LBP best preserved protein, total starch, β-glucan and γ-aminobutyric acid, kept DPPH and hydroxyl radical scavenging stable, and most strongly suppressed microbial growth and the rise in peroxide value; 1.0% LBP most effectively limited moisture loss and malondialdehyde accumulation; and 2.0% LBP most strongly suppressed lipase activity, fatty acid value and the decline of polyphenols and flavonoids. Lipidomics identified 819 lipid species. Among the LBP-supplemented groups, the number of differential lipids decreased as the supplementation level increased (255, 216 and 174 for 0.2%, 1.0% and 2.0%, respectively; the control group contained 243), and LBP protected membrane phospholipids (PC, PE), storage lipids (TG) and galactolipids (MGDG) while suppressing the formation of lysophospholipids (LPC, LPE). KEGG enrichment showed that 0.2–1.0% LBP preserved glycerophospholipid and glycerolipid metabolism, whereas 2.0% LBP suppressed even the core lipid metabolic pathways. Considering the overall retention of nutritional and functional components, the stability of antioxidant activity, and the suppression of microbial growth and lipid oxidation, 0.2% LBP is recommended as the optimal supplementation level, while the lipidomic data reveal a dose-dependent, membrane-protective mechanism that supports the application of LBP as a natural preservative for whole-grain flours.