## 3 Results and Discussion
### Maturity Index  
The intensities of the characteristic carotenoid bands at 1156 and 1515 cm\({}^{-1}\) were very similar in all measurement series, cf. Figure 1, while the intensities of the band at 1001 cm\({}^{-1}\) appeared with lower intensity but a proportional change referenced to the other two signals. Exemplarily, a fully ripe fruit would show a slightly higher ratio when the intensities of the two bands at higher wavenumbers were very large. Based on the proportional evolution of the signal at 1001 cm\({}^{-1}\), the peak intensity ratio was taken as a measure for ripeness. Hence, the level of ripeness could be assessed independent of the absolute value of the obtained intensities. The calculated value is referred to as the color-coded maturity index (MI), with the averaged intensities \(I_{x}\) of the signals at x = 1156 and 1515 cm\({}^{-1}\) and the intensity of the signal at 1001 cm\({}^{-1}\) as a reference (see Equation (1)). \[\text{MI }=\ \frac{I_{1156}+I_{1515}}{2*I_{1001}} \tag{1}\]  
The maturity index is hence dimensionless. As an advantage, the MI allows comparing studies from different Raman spectrometers, since the effect of different intensities due to different laser wavelengths and powers is compensated for. The maturity index can provide an estimate of the carotenoid level and hence the time of harvest. Previous work on tomatoes reported that harvesting too early might result in lower carotenoid contents, while within this study, no significant differences were observed for green peppers ripening on the plant and for those ripening post-harvest. The calculated maturity index for hot peppers was compared to the fruit color at the time of spectral recording. The values obtained could be assigned to four fruit color classes: green, orange, orange/red and red. During the extensive study, 1109 spectra were recorded from 130 fruits on plants, suggesting that a finer graduation would be possible. An MI between 1 and 2 corresponded to green hot peppers. Reddish green and orange fruits exhibited values with strong variation from 1 to 4. An MI between 3 and 4 indicated red fruits. Deep red fruits were associated with an index of 4. Dried nearly brown hot peppers gave rise to values above 4. It should be noted that a reference system for tomatoes may comprise five or six stages [26; 27]. For a feasibility study on hot peppers, an index comprising four levels was considered sufficient. The MI values and assignments to color, ripeness and possible harvest stadiums are listed in Table 3. The maturity states and possible harvest and storage recommendations were extracted and adopted from literature data mostly on tomatoes. Unripe peppers possess low amounts of carotenoids. They hence appear green due to the predominant color of chlorophylls. When the fruit turns to orange-red, the color becomes carotenoid-dominated. At this point, fruits may be picked and the evolution proceeds detached from the plant or fruits may proceed ripening on the plant (see above). Analysis of the Raman data revealed similar carotenoid levels for fruits that continued maturing post-harvest and for fruits that continued maturing on the plant. In Figure 6, the calculated maturity index was plotted versus the corresponding sample number of peppers and tomatoes of different maturing stages. The index range can be divided into unripe \begin{table}
\begin{tabular}{c c c} \hline \hline
**Maturity Index** & **Color** & **Maturity** \\ \hline \multirow{2}{*}{**<2**} & **green** & **Fully immature** \\  & & continued ripening proposed \\  & **momature** & **Immuture** \\  & & significantly lower carotenoid levels than full mature; further plant ripening recommended \\  & **Harvestable** \\
**3–4** & **orange/red** & might reach slightly lower carotenoid contents in the after-ripening than full ripening; harvest possible, post-maturity recommended \\  & & **Fully ripe/mature** \\ \multirow{2}{*}{**>4**} & **red** & suitable for immediate consumption; storage not recommended \\ \hline \hline \end{tabular}
\end{table}