Gas chromatographic patterns of some apple surface wax constituents

Differentiation of viable and dead Escherichia coli O157:H7 cells on and in apple structures and tissues following chlorine treatment

Confocal scanning laser microscopy (CSLM) was used to differentiate viable and nonviable cells of Escherichia coli O157:H7 on and in raw apple tissues following treatment with water and 200 or 2,000 ppm active chlorine solution. Whole unwaxed Red Delicious cultivar apples at 25 degrees C were inoculated by dipping in a suspension of E. coli O157:H7 (8.48 log10 CFU/ml) at 4 degrees C, followed by treatment in water or chlorine solution at 21 degrees C for 2 min. The dead cells on and in apples were distinguished from live cells by treating tissue samples with SYTOX green nucleic acid stain. Viable and dead cells were then labeled with an antibody conjugated with a fluorescent dye (Alexa Fluor 594). The percentage of viable cells on the apple surface, as well as at various depths in surface and internal structures, was determined. The mean percentages of viable cells located at the sites after treatment with water or chlorinated water were in the following order, which also reflects the order of protection against inactivation: floral tube wall (20.5%) > lenticels (15.0%) > damaged cuticle surrounding puncture wounds (13.0%) > intact cuticle (8.1%). The location of viable cells within tissues was dependent on the structure. Except for lenticels, the percentage of viable cells increased as depth into the CSLM stacks increased, indicating that cells attached to subsurface structures were better protected against inactivation with chlorine than were cells located on exposed surfaces. Further research is warranted to investigate the efficacy of other chemical sanitizers. as well as that of surfactants and solvents in combination with sanitizers, in removing or killing E. coli O157:H7 lodgedin protective structures on the surface and within tissues of apples.

Relationship Between Apple Fruit Epicuticular Wax and Growth of Peltaster fructicola and Leptodontidium elatius, Two Fungi that Cause Sooty Blotch Disease

Sooty blotch severity varied among apple cultivars or selections surveyed in 1989 and 1992. No mycelial growth was observed on russetted areas of the cuticle that are considered impermeable. Ursolic acid and n-alkanes were the most prominent components of the epicuticular waxes of the cultivars or selections evaluated. Although there were differences in the relative proportions of these compounds among the cultivars, the differences were not related to the severity of sooty blotch. Peltaster fructicola and Leptodontidium elatius were grown on compounds that comprise the epicuticular wax of the fruit to determine if one or more of these were needed for growth. The fungi did not grow on any of the five major components of the epicuticular wax unless dilute apple juice was included. Scanning electron microscopy studies showed that mycelia of P. fructicola grew on the surface of the wax and did not appear to degrade it. Our studies support the hypothesis that P. fructicola and L. elatius fungi are epiphytes and obtain their nutrients not from components of the cuticle, but more likely from fruit leachates.