Characters of laser etching depressions of florida fruits and vegetables

Proc. Fla. State Hort. Soc. 119: 2006.353 Proc. Fla. State Hort. Soc . 119:353-357. 2006. CHARACTERISTICS OF LASER ETCHING DEPRESSIONSON FLORIDA FRUITS AND VEGETABLES

E D E TXEBERRIA *, W ILLIAM M. M ILLER AND D IANN A CHOR

University of Florida, IFASCitrus Research and Education Center700 Experiment Station RoadLake Alfred, FL 33850

Additional index words. Lycopersicum esculentum , Persea ameri-cana , Citrus aurantifolia , Solanum tuberosum , PLU, postharvest,produce labeling

Abstract. Fruit etching is rapidly becoming an alterative means

to label produce. The alphanumerical characters are formedby laser beam generated dot-matrix pin-holes which disruptthe cuticular and epidermal barriers. The present study de-scribes anatomical characteristics of the pin-hole depressionsin the cuticle/epidermis of several fruits and vegetables grownin Florida. Descriptions were made immediately after labelingand after 4 days in storage at 20°C and 95% relative humidity.Regardless of the energy impact durations, pin-holes werefairly homogeneous averaging 200 µm in diameter and 25 µmin depth. Immediately after etching, the two- to five-cell-deepdepressions contained cuticle/wax deposits. Additional cuti-cle/wax material was deposited in and around the depressionsduring storage as demonstrated by confocal, fluorescent, andlight microscopy. In addition, the cells underlining the etch de-pression increased phenolic and lignin deposits in their walls,creating a potential barrier against pathogenic organisms.

Used as an alterative means to label produce, laser beamgenerated dot-matrix characters can etch in the requiredprice look-up (PLU) information directly into the peel prod-uct (Drouilliard, 2006). The PLU coding index is based on afour-digit identification developed by the Produce ElectronicIdentification Board (PEI Board, 1995). Etched markings areformed in dot matrix style letters and numbers, each dot cre-ated by pin-hole depressions. However, some concerns ariseas the pin-hole depressions, applied after washing and wax-ing, disrupt the cuticular and epidermal barriers potentiallyweakening the natural protection against pathogens.Commercial implementation of this technique requires athorough understanding of the ramifications of the creationof pin holes on fruit surfaces, although preliminary observa-tions using tomato revealed that aqueous dyes were repelledfrom newly formed etch depressions, whereas work withpears (Robert Sugar, personal communication) did not showa detectable increase in postharvest decay, suggesting a possi-ble self-sealing mechanism. The present study was aimed atcharacterizing the laser generated pin-hole depressions inthe cuticles of fruits and vegetables in addition to describingthe changes that occur during storage. We included severalfruits and vegetables with edible and non-edible peel such astomato, avocado, potato, and citrus, which are produced inFlorida.

Materials and Methods Plant material. Tomato ( Lycopersicum esculentum Mill.), avo-cado ( Persea americana Mill.) acid lime ( Citrus aurantifolia Swingle), and potato ( Solanum tuberosum Linnaeus) were pur-chased at a local grocery store. Plant material was taken to theUniversity of Florida’s Citrus Research and Education Centerin Lake Alfred, Fla., where a Durand-Wayland etching ma-chine had been assembled. Fruit etching. A carbon dioxide laser unit (Model XYmark10, Durand-Wayland, LaGrange, Ga.) was assembled at thepackinghouse. Individual fruit were positioned on a 1-inchPVC (polyvinyl chloride) disk at approximately 10 cm fromthe laser’s output. The average laser energy level was 0.678watts per character at 35 µ s with a duty cycle range of 25%.Etching exposure times had been previously established bythe manufacturer in field trials. For tomato and potato, etch-ing time was of 30 µ s, whereas avocado and lime were etchedusing 40 µ s exposure times. After treatment, two fruit of eachkind were taken to the microscopy lab for immediate tissuepreparation and observation. A similar fruit sample wasstored for 4 d at 20°C and 95% relative humidity (RH). Tissue preparation. Tissue samples were prepared accord-ing to the type of microscopic observation intended (light,fluorescent, or confocal microscopy). The same preparationtechniques were used for tissue observed at time 0 and after 4d in storage. Confocal and fluorescent microscopy. A thin segment of fruitepidermis containing several etching depressions was slicedwith a razor blade and mounted on a microscope slide. Adrop of 0.01% solution of Auramine-O, a specific cuticle flu-orescent stain (Heslop-Harrison, 1977) in 0.05 M Tris buffer(pH 7.2) was applied over the etching depressions and al-lowed to penetrate the tissue for 1 h. After 1 h, the tissue wasthoroughly washed with water, covered with a drop of glyce-rol, and immediately observed. Microscopy. For light microscopy, small sections of fruitepidermis containing etching depressions were fixed in 3%glutaraldehyde in 0.1 M phosphate buffer (pH 7.2), and pre-pared as described by Etxeberria et al. (2006). Stained sec-tions fixed on glass microscope slides were observed under aLeitz Laborlux light microscope. Photographic images weretaken using a Sony Cybershot 505 digital camera mounted onthe microscope.Confocal microscope observations were made using aLeica TCS-SL (Leica, Heidelberg, Germany) as described byEtxeberria et al. (2006). A Nikon Eclipse TE 300 fluorescentmicroscope (Nikon Co., Tokyo, Japan) was used to observedlive fluorescence from treated fruit surfaces. The microscopewas equipped with a fluorescin H-2 filter and a Sony Cybershot505 digital camera (Sony Corp., Tokyo, Japan).