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- nein (51)
Ripeness and senescence of climacteric fruits are strongly related to the emission of ethylene gas. The ethylene emission of apples can be detected by a new developed ripeness indicator. This indicator is based on the reduction effect of ethylene causing colour changes in selected metal ions. The used molybdenum (Mo) chromophores change under the impact of ethylene in a colour spectrum from white/light yellow to blue because of a partial reduction of Mo(VI) to Mo(V). The sensitivity of molybdenum colour change reactions can be varied by composition and pH values (pH 1.4–pH 1.5) of used ammonium molybdate solution and thus adopted to different fruits and storage conditions. The indicator can be combined with a colour recognition sensor for quantitative measurements of colour change in the frame of the L*a*b* model. The b*-coordinate, reflecting changes from yellow to blue, and the luminance L* continuously vary with increasing ethylene emission. Results obtained with the indicator system were compared with direct determination of ethylene concentrations by gas chromatography (GC-FID). Furthermore, a descriptive sensory test was used to estimate the degree of ripeness. The indicator can be applied for ripeness gauge on single fruit or in paperboard crates.