Pyropia yezoensis exhibited the characteristic of multiple harvests, and its quality was closely associated with the harvest period. Odor served as a crucial criterion for evaluating the quality of Pyropia yezoensis. To investigate the mechanism by which harvest period affected the odor of Pyropia yezoensis, headspace-solid phase microextraction-gas chromatography-mass spectrometry (HS-SPME-GC-MS) was utilized, with cyclohexane used as the internal standard, to determine the volatile organic compounds (VOCs) that contributed to the odor of Pyropia yezoensis from the first to the fifth harvest period. Simultaneously, an electronic nose was employed to detect the odor profiles of Pyropia yezoensis at different harvest periods. The obtained data were then subjected to principal component analysis (PCA) and orthogonal partial least squares discrimination analysis (OPLS-DA) for in-depth exploration. The results indicated that 49, 42, 40, 52 and 47 kinds of VOCs were respectively detected in the first to the fifth harvest Pyropia yezoensis. In total, 71 kinds of VOCs were identified. These VOCs mainly consisted of hydrocarbons (18 kinds), aldehydes (24 kinds), and ketones (10 kinds). Benzaldehyde, safranal, β-cyclocitral, β-ionone, epoxy-β-ionone, α-ionone, 3,5-octadien-2-one, 1-octen-3-ol, dihydroactinidiolide, 8-heptadecene, eicosane, and 1-bromo-5-heptadecene were the common and relatively high-proportion VOCs in Pyropia yezoensis at various harvest periods. The variations in the relative contents of VOCs among different harvest periods of Pyropia yezoensis mainly stemmed from 8-heptadecene, eicosane, dimethyl sulfide, 1-bromo-5-heptadecene, β-ionone, nonanal, (E)-cyclododecene, α-ionone, pentadecanal, 3,5-octadien-2-one, epoxy-β-ionone, dihydroactinidiolide, hexanal, and octanal. The odor characteristics of Pyropia yezoensis encompassed floral, fruity, woody, grassy, and fishy notes. Specifically, the odor of first-harvest Pyropia yezoensis was more intense, the fishy odor of third-harvest Pyropia yezoensis was milder, while fourth-harvest and fifth-harvest Pyropia yezoensis exhibited more unpleasant odors, such as the pungent odor associated with lipid oxidation, as well as the characteristic sulfurous and fishy odors imparted by dimethyl sulfide. The electronic nose was basically capable of discerning the odor differences among first-harvest to fifth-harvest Pyropia yezoensis. This study indicates that the VOCs profile—including both qualitative composition and quantitative abundance—in Pyropia yezoensis exhibits significant temporal variation across successive harvests. Specifically, samples from the first to the third harvest period are characterized by favorable olfactory attributes, whereas those from the fourth and fifth harvest period to develop off-odors and demonstrate a marked decline in overall quality.

Pyropia yezoensis  /  head space-solid phase microextraction (HS-SPME)  /  gas chromatography-mass spectra (GC-MS)  /  odor activity value (OAV)  /  electronic nose  /  principal component analysis (PCA)  /  orthogonal partial least squares discrimination analysis (OPLS-DA)