## 1 Introduction  
For the determination of the degree of fruit ripeness, no quantitative characteristics or parameters are listed in EU quality standards. However, qualitative characteristics are defined for the fruit-bearing cycle, e.g., the respiration increase or the development of ethylene [1]. To assess fruit development and growth, various parameters such as pulp color and pulp firmness are used [2, 3, 4, 5]. Other parameters comprise starch degradation, the Brix value, acidity and the sugar/acid ratio [4]. On a cell-size scale, the depolymerization and size of pectin and hemicellulose polysaccharides were associated with fruit maturation, particularly of tomatoes and hot peppers [6, 7, 8]. The determination of these parameters except fruit size and base color can only be achieved by destruction of the fruit, such as homogenization, extraction, staining or labeling, and at the expense of the producer. Fruit ripening is the last phase of fruit development and is associated with increased respiration, which is often accompanied by degradation of chlorophyll and increasing carotenoid content [9, 10]. A correlation between ethylene and abscisic acid levels at different stages of ripeness was investigated for hot peppers [11]. Raman spectroscopy has not been exploited to its full potential in food analysis, although its application is increasing [12]. Raman techniques do not require the laborious pre-treatment described above. Samples can be investigated at ambient temperature and pressure [13]. The technique is fast and non-invasive and portable handheld spectrometers allow spectral recording and testing the fruit on the plant or during sorting. Water has only little or no response, unlike in infrared spectroscopy, such that fresh and dried fruits can be analyzed. The Raman methodology also allows inspecting for food safety through a glass or polymer packaging [14; 15]. At the molecular level, one of the starting points of carotenoid synthesis is geranyl-geranyl pyrophosphate (GGPP; C\({}_{20}\)H\({}_{36}\)O\({}_{7}\)P\({}_{2}\)) [16; 17]. As a first step in this pathway, two GGPP molecules are condensed by phytoene synthase (PSY) into phytoene (C\({}_{40}\)H\({}_{64}\)) [18; 19]. Through desaturation reactions of the enzymes phytoene desaturase (PDS) and \(\zeta\)-carotene desaturase (ZDS), the characteristic double bonds are formed, which lend the carotenoids their intense color. Finally, the carotenoid cis-trans isomerase (CRTISO) forms the all-trans lycopene, where the synthetic pathway separates. At this point, various lycopene cyclases (LCY) start to produce either \(\alpha\)- or \(\beta\)-carotene [9; 20; 21; 22; 23]. The different carotenoids have been extensively studied in tomatoes and assigned to stages of ripeness using mobile Raman spectroscopy [24; 25]. Four to six classes of maturity were described, reflecting the color from green to red [26; 27; 28]. The spectroscopic results were interpreted with the help of advanced multivariate data analysis, such as soft independent modeling of class analogy (SIMCA), artificial neural networks (ANN) and partial least squares regression (PLSR), to achieve classification according to maturation. However, similar studies for hot peppers have not been described. The carotenoid pathway applies to all pepper species as can be recognized by the well-known color change during maturing. The molecular transformations and the color change do not only occur within the fruit on the plant, but also to already harvested fruit. Green or yellow harvested fruits also turn red when adequately stored and allowed to continue ripening. Since the degree of ripeness is related to the nutrients and to the carotenoid content, Raman spectroscopy is particularly suitable for monitoring of the process [29; 30; 31; 32; 33; 34]. It provides good sensitivity to carotenoids and is non-invasive, such that the fruit can continue to evolve after analysis. Handheld or portable spectrometers are suitable for on-site testing without sample preparation [35].