Some vegetables or fruits, such as potatoes, carrots or apples, need peeling. There are several peeling methods available, but on an industrial scale the peeling is
E33 Appearance (knife)
EH Appearance (carbo)
Fig. 14.1 Effect of peeling method and storage time on the odour and appearance of potato packed in a gas mixture of 20% CO2 and 80% N2 and stored at 5°C.
normally accomplished mechanically (e.g. rotating carborundum drums), chemically or in high-pressure steam peelers (Wiley, 1994). However, results have shown that peeling should be as gentle as possible. The ideal method would be hand peeling with a sharp knife. The relative effects of carborundum and knife peeling are shown in Fig. 14.1. Carborundum-peeled potatoes must be treated with a browning inhibitor, whereas water washing is enough for hand-peeled potatoes. If mechanical peeling is used, it should resemble knife peeling. Carborundum, steam peeling or caustic acid disturb the cell walls of a vegetable enhancing the possibility of microbial growth and enzymatic changes. Carborundum and knife peeling can be combined with a first stage of rough peeling and then a second stage of finer knife peeling. Enzymatic peeling can be successful, for example in the case of oranges (Pretel et al., 1998).
Many studies show that the cutting and shredding must be performed with knives or blades as sharp as possible and made from stainless steel. Carrots cut with a razor blade were more acceptable from a microbiological and sensory point of view than carrots cut with commercial slicing machines. It is clear that slicing with blunt knives impairs quality retention because of the increased breaking of cells and release of tissue fluid. A slicing machine must be installed solidly, because vibrating equipment may possibly impair the quality of sliced surfaces. Mats and blades used in slicing should also be disinfected, for example, with a 1% hypochlorite solution.
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