Spectroscopic evaluation of the surface quality of apple.

Different spectroscopic techniques based on infrared and Raman were used to evaluate the natural wax and related surface quality of apple fruit. Transmission near-infrared (NIR) spectroscopy was applied to solutions of single wax components and extracted apple wax. Fourier transform infrared (FTIR) spectroscopy was used for transmission measurements of wax films on NaCl crystals, diffuse reflectance spectroscopy (DRIFTS) was used to analyze wax powders, and FT-Raman spectroscopy was explored to examine intact wax layers on whole fruit. The natural wax layers of apple fruit from a maximum of three different cultivars (Jonagold, Jonagored, and Elshof) from three picking dates (early, commercial, and late), three controlled atmosphere storage durations (0, 4, and 8 months), and three shelf life periods (0, 1, and 2 weeks) within each storage duration were examined. Canonical discriminant analysis was carried out on the first derivative NIR and FTIR spectra to describe the information contained in the spectra. Discrimination between cultivars and between storage duration based on wax layer properties was achieved with reasonable accuracy from both of the techniques. Information contained in the spectra of apples from different picking dates and shelf life periods was not significant. Differences between cultivars and storage periods in this analysis mostly related to differences in the number of aliphatic chains (e.g., alkanes and esters) and the presence of alpha-farnesene. No satisfactory results were obtained by means of Raman spectroscopy and DRIFTS.

Activation and inactivation of Talaromyces macrosporus ascospores by high hydrostatic pressure.

The effect of high hydrostatic pressure treatment (with pressures of up to 700 MPa) on Talaromyces macrosporus ascospores was investigated. At 20 degrees C, pressures of > or = 200 MPa induced the activation and germination of dormant ascospores, as indicated by increased colony counts for ascospore suspensions after pressure treatment and the appearance of germination vesicles and tubes. Pressures of > 400 MPa additionally sensitized the ascospores to subsequent heat treatment. At pressures of > 500 MPa, activation occurred in a few minutes but was followed by inactivation with longer exposure. However, even with the most extreme pressure treatment, a fraction of the ascospore population appeared to resist both activation and inactivation, and the maximal achievable reduction of ascospores was on the order of 3.0 log10 units. Pressure-induced ascospore activation at 400 MPa was temperature dependent, with minimum activation at 30 to 50 degrees C and > or = 10-fold higher activation levels at 10 to 20 degrees C and at 60 degrees C, but it was not particularly pH dependent over a pH range of 3.0 to 6.0. Pressure inactivation at 600 MPa, in contrast, was pH dependent, with the inactivation level being 10-fold higher at pH 6.0 than at pH 3.0. Observation of pressure-treated and subsequently dried spores with the use of light and scanning electron microscopy revealed a collapse of the spore structure, indicating a loss of the spore wall barrier properties. Finally, pressure treatment sensitized T. macrosporus ascospores to cell wall lytic enzymes.

Non destructive analysis of the wax layer of apple (Malus domestica Borkh.) by means of confocal laser scanning microscopy.

Confocal laser scanning microscopy (CLSM) was used to non-destructively analyse the changes in the structure and thickness of the cuticle during storage of apples (Malus domestica Borkh.). Interpretation of the confocal images was performed by comparison with scanning electron microscopy and environmental scanning electron microscopy images. The natural reflectance of the wax and the auto-fluorescence of the underlying cells made it possible with CLSM to distinguish the wax from the underlying layers without any pretreatment of the fruit. The thickness of the consecutive layers (wax, cutin, cells) could be estimated from measurements of the reflection and fluorescence intensities as a function of the number of pixels. The mean wax-layer thickness measured in this way amounted to 2.58 microm, 3.41 microm or 4.14 microm for the cultivars Jonagold, Jonagored and Elstar, respectively. Changes in the wax structure and cells of the same important Belgian apple cultivars as mentioned above were monitored during nine months of storage in ultra low oxygen and after exposure to ambient conditions. The changes in the wax ultrastructure and cell morphology are likely related to water losses and specific protection of the apple cultivars against water losses during storage and shelf life.