Nutritional and metabolite composition characteristics of acid whey retentates obtained by membrane separation.

Multistage membrane separation fractionates acid whey by molecular size, yet systematic understanding of selective enrichment patterns of nutritional/bioactive components across stages and their high-value utilization basis remains limited. This study applied membrane separation, including microfiltration (MF), ultrafiltration (UF), nanofiltration (NF), and reverse osmosis (RO), to process acid whey and evaluated the nutritional and metabolic differences among the resulting retentates, aiming to identify fractions rich in oligopeptides and functional properties. Results showed selective enrichment of macromolecular proteins, oligopeptides, lactose, and salts in MF, UF, NF, and RO retentates, respectively. The UF retentate contained 16 amino acids and 6 fatty acids-significantly higher than others. Membrane treatments markedly altered metabolite profiles, with 1806 metabolites detected. Functional components like convalloside and dipeptides (Arg-Pro, Lys-Pro) were enriched in the UF retentate, which also exhibited strong DPPH/OH∙ scavenging activity, reducing power, and nitrite/cholesterol degradation rates. These findings highlight its potential for functional food and pharmaceutical applications.