# Prediction of Phytochemical Constituents in Cayenne Pepper Using MIR and NIR Spectroscopy
###### Abstract
In this study, we investigate the potential use of rapidly assessing quality parameters associated with chili fruit--specifically dry matter and total phenolic content--in the Australian Cayenne pepper crop. Dry matter (DM) content is often linked to maturity and eating quality across many crops [8,9] and has also been used as an index of fruit maturity in chiles [10]. Indeed, [PERSON] et al. [11] and [PERSON] et al. [12] found that the DM content of _C. annuum_ consistently increased during maturation, although the exact trends were dependent on the variety. Hence if calibrated for a specific chili variety, the rapid estimation of DM content could be used to inform optimum harvest times. As previously mentioned, the phenolic content and antioxidant capacity of chili are also of interest due to the potential health benefits associated with these compounds [13,14]. Rapid estimation of phenolic content in chiles could be used for grading fruit quality or finding applications in breeding programs attempting to develop high phenolic content chili varieties. Near-infrared (NIR) and mid-infrared (MIR) spectroscopy have been used for the assessment of a wide range of quality parameters in dried chili powder [15, 16, 17, 18, 19], principally the capsaicinoid content. The main difference between these two instrument types is the wavelength used: NIR operates between wavelengths of 750-2500 nm, while MIR spectroscopy uses wavelengths of 2500-25,000 nm (4000-400 cm\({}^{-1}\)). NIR spectroscopy has benefits, including cheaper cost, portability, and greater penetration depth into the sample--but at the expense of lower resolution and sensitivity for chemical moieties. A number of studies have used NIR spectroscopy for the prediction of dry matter and soluble solids [20,21], as well as vitamin C, total chlorophyll, and/or carotenoid contents in fresh fruit [10,12,20,22]. These studies have highlighted the benefits of rapid NIR spectroscopy as an in situ preliminary screening technique but noted that further work is required to develop robust models which can be applied to external populations. The prediction of antioxidant capacity appears to have only been considered by one previous author [23], and there are very few studies outside of our laboratory attempting the prediction of total phenolic content [6,12]. In addition, many of these studies have been performed on bell peppers rather than cyenne peppers, which are more widely grown in Australia. Hence the aim of this study was to compare the use of NIR and MIR spectroscopy for the analysis of cayenne pepper (_Capsicum annuum_ 'Cayenne') quality, including the prediction of DM content, total phenolic content, and antioxidant capacity. \begin{table}
\begin{tabular}{c c c c} \hline
**Parameter** & **Typical Content** & **\% RDI in 1 Serve (75 g)** & **Reference** \\ \hline Thiamin (Vit B1) & 0.057 mg/100 g & 4\% & [1] \\ Riboflavin (Vit B2) & 0.028 mg/100 g & 2\% & [1] \\ Vitamin A & 18 \(\mu\)g RAE/100 g & 2\% & [1] \\ Folate & 10 \(\mu\)g/100 g & 2\% & [1] \\ Vitamin K & 7.4 \(\mu\)g/100 g & 5\% & [1] \\ \hline \end{tabular}  
GAE = gallic acid equivalents; n/a = not applicable; RAE = retinoic acid equivalents; RDI = recommended dietary intake (calculated for an adult male).  
\end{table} 
Table 1: Cont.