Method for studying surface topography and roughness of onion and garlic skins for coating purposes

Surface topography and roughness of garlic and onion skins were studied by atomic force microscopy in order to estimate the surface area. Image-processing and Arc/Info software were used to interpret the data. The calculated ratio between apparent and measured surfaces (roughness factor) deviated from 1.11 to 1.15 for untreated and chloroform-treated onion skin, respectively. For garlic, higher values were detected for the untreated skin. The higher the roughness factor, when the coating solutions are easily spread on the fruit or vegetable surfaces, the better the adhesion between coating and skin. A knowledge of true surface areas can help to better estimate required coating-solution volumes.