Mechanisms of KCl and κ-Carrageenan in alleviating browning in low-sodium suancai during aerobic storage

• Replaced NaCl with KCl and κ-carrageenan, reducing acidity and amino acid nitrogen • Revealed 70%–100% increases in browning degree and significant L* value declines • Detected reductions in ascorbic acid and polyphenols under low-sodium conditions • Identified negative correlations between browning and ABTS, DPPH antioxidant activity Excessive sodium intake is linked to various health issues, prompting the development of low-sodium foods like suancai. Low-sodium fermentation often leads to quality degradation, particularly color stability during aerobic packaging (AP) storage, though the precise mechanism remains unclear. To elucidate the causes of color changes, the browning phenomenon and its underlying mechanisms were investigated in four low-sodium suancai formulations, in which NaCl was partially replaced by KCl and κ-carrageenan, during AP storage at days 0, 4, 8, 12, and 16. Results indicated that low-salt treatments significantly reduced amino acid nitrogen (AAN) concentrations by 12%–18.95% and total acidity by 3.62%–9.74% during storage compared to pure NaCl-fermented suancai. Random forest analysis identified key biomarkers of suancai storage quality, including reducing sugars, salinity, and AAN. Besides, the surface of suancai progressively browned during AP storage, with the L* value decreasing and the browning degree (BD) increasing markedly by 70%–100%. Ascorbic acid and polyphenol levels exhibited declining trends. Correlation analysis revealed that the L∗ value was positively correlated with peroxidase (POD) activity, polyphenols, and ascorbic acid, while BD showed negative correlations with ascorbic acid, polyphenols, 2,2-diphenyl-1-picrylhydrazyl radical (DPPH) scavenging capacity, and 2,2′-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) antioxidant activity. UPLC-MS/MS analysis identified 1,477, 1,606, and 1,583 differentially abundant metabolites in low-salt and control (CK) groups on days 0, 8, and 16, respectively. Alterations in the abundance of metabolites, including caprylic acid, tyramine, and pyruvic acid, under low-sodium conditions may play a role in the browning of suancai. The low-salt treatment likely accelerated browning by modulating metabolic pathways, particularly cofactor biosynthesis, nucleotide metabolism, and purine metabolism. These findings advance understanding of quality stabilization and enhancement strategies for low-salt fermented vegetables during processing and storage.