Other limitations are due to the geometric characteristics of some fresh fruits and vegetables (e.g., bunches of fruit, folded leaves in vegetables, etc.) as again biological tissue is an effective barrier to UVC penetration. Finally, as UVC photons move in
straight-path
trajectories from their source, the round or oval geometry of many commodities provides effective shielding that force the need to expose a surface with different UV-path incident angles. The round surfaces, particularly when moving (rotating), enhance the natural shielding or shadowing effects and minimize the direct interaction of the straight-path incident UVC photons with the targeted pathogens. These natural and combined effects on fruit surfaces are illustrated schematically in Figure 10