Anatomical and morphological characteristics of laser etching depressions for fruit labeling

Abstract

Fruit etching is an alterative means to label produce. Laser beam-generated pinhole depressions form dot-matrix alphanumerical characters that etch in the required price-look-up information. Pinhole depressions can disrupt the cuticular and epidermal barriers, potentially weakening the natural protection against pathogens. In the present study we describe the anatomical and morphological characteristics of the pinhole depressions in the cuticle/epidermis, and the changes taking place during storage of two fruits: avocado (Persea americana) and tomato (Lycopersicon esculentum). These fruits represent the extremes from a thick, non-edible peel to a thin edible peel. On both tomato and avocado, etching depressions were fairly similar in diameter and depth, averaging 200 μm and 25 μm, respectively, for energy impact durations of 30 μs for tomato and 45 μs for avocado. Immediately after etching, the two- to five-cell-deep depressions contained cuticle/wax deposits. Additional cuticle/wax material was deposited in and around the depressions during storage as demonstrated by confocal, fluorescent, and light microscopy. In addition, the cells underlining the etch depression increased phenolic and lignin deposits in their walls, creating a potential barrier against pathogenic organisms.