Molecular Changes in Laver ( Porphyra haitanensis ) During Hot Air Drying: A Focus on Lipids and Volatile Flavors

Laver ( Porphyra haitanensis ) is a nutritious seaweed. Desiccation affects its quality and flavor, but the molecular changes during drying are unclear. Here, the effects of hot air drying temperatures (60°C, 70°C, 80°C, 90°C, and 100°C) on rehydration performance, drying kinetics, microstructure, and the biological activity of laver were evaluated. The laver dried at 60°C exhibited a rehydration ratio of 350%–450%, and its aqueous extract demonstrated substantially higher antioxidant activities than at other temperatures, with DPPH radical scavenging activity of 74.79%, hydroxyl radical scavenging activity of 86.42 U/mL, and ferric reducing antioxidant power of 0.53 μmol·TE/kg. The most suitable temperature was 60°C. Lipidomic profiling of laver during drying at 60°C for different durations (0–5 h) was conducted using liquid chromatography–mass spectrometry; 4092 lipids, including glycolipids, glycerophospholipids, and glycerides, were identified. Most lipids increased substantially with prolonged drying time, whereas five characteristic lipids, including cardiolipin (23:0/22:6/16:1/22:2), sulfoquinovosyldiacylglycerol (16:0/18:2 and 16:0/20:3), digalactosyldiacylglycerol (16:0/18:2), and monogalactosyldiacylglycerol (16:0/16:0), showed notable changes. Distinct patterns in five characteristic lipids during drying were identified: the contents of the sulfolipid, sulfoquinovosyl diacylglycerol (16:0/18:2 and 16:0/20:3) increased continuously, likely released from disintegrating photosynthetic membranes. The galactolipids, monogalactosyldiacylglycerol (16:0/16:0), and digalactosyldiacylglycerol (16:0/18:2), core constituents of thylakoids, decreased substantially after 3 h, directly reflecting photosynthetic membrane degradation. Changes in cardiolipin (23:0/22:6/16:1/22:2) were also noted, implicating alterations in mitochondrial membrane integrity. Additionally, 65 volatile compounds, including (E,Z)‐2,6‐nonadienal, decanal, (E)‐2‐octenal, (2E,4E)‐deca‐2,4‐dienal, butylated hydroxytoluene, and 2,4‐di‐tert‐butylphenol, were detected. These compounds, contributing to the aromatic properties of laver, decreased with increased drying time. Drying temperature and duration substantially influenced the physicochemical properties, lipid profiles, and volatile flavor compounds of laver. The molecular changes during drying were elucidated to improve the nutritional qualities of dried laver products.