Abstract: Objective: The effect of cryogenic treatment on the structure of grape skin cells was investigated to reveal the mechanism of wine quality improvement. Methods: Grapes of the cultivars Hutai No. 8 and Cabernet Sauvignon were treated at 4, −8, −20 and −32 ℃ and with liquid nitrogen, respectively, and then examined with an electron microscope. The contents of tannins, total phenols, total anthocyanins and aroma compounds were also determined. Results: Grape skin cells had no significant change after treatment at 4 ℃, but cell plasmolysis and crystals of tannin and starch were observed after treatment at −8 ℃. Serious deformation of cells, clutter of intracellular contents, cracking of the cell membrane and organelles, and exosmosis of cell inclusion were observed in parallel with the increase of ergastic substances and crystals after treatment at −20 ℃. The structures of the cell wall and membrane were destroyed completely after treatments at −32 ℃ and with liquid nitrogen. These data showed that cryogenic treatment especially at −8, −20 and −32 ℃ allowed the extraction of more tannins, total phenols, total anthocyanins and aroma compounds from grape skins, and the contents of these substances were significantly different at different treatment temperatures. However, aroma substances could not be extracted at 4 ℃ and liquid nitrogen. Conclusion: Cryogenic treatment results in cell damage of grape skins and improved exosmosis of phenolics and aromatic compounds, thereby being beneficial to wine quality.

Key words: grape, cryogenic treatment, grape skin cells, electron microscope, wine quality