Structure and nanostructure of the outer tangential epidermal cell wall in Vaccinium corymbosum L. (Blueberry) fruits by blanching, freezing-thawing and ultrasound

The design of minimal technologies for blueberries preservation requires, among others, the knowledge of structural and ultrastructural cell changes during the processing. This work examined the main structural alterations that occurred in the outer tangential epidermal cell wall of fruits of Vaccinium corymbosum L. (blueberries) due to blanching, freezing-thawing and ultrasound. Light microscope (LM), environmental scanning electron microscope (ESEM), transmission electron microscope (TEM) and atomic force microscope (AFM) observations were analysed and discussed. Each treatment produced specific effects on the outer tangential epidermal cell wall of the epicarp: swelling and rupture of the inner and outer tangential cell wall by blanching; and cell wall shrinkage and rupture by ultrasound; and folding and compression of the epicarp by freezing-thawing. After treatments, a delimited transition between the cuticle, the cutinised layer and the cellulosic layer on the outer tangential epidermal cell wall was observed in all treated fruits.