## 1 Introduction
In the pulp of the red variety, the monosaccharide composition of crude polysaccharide fractions was described. The aqueous fractions were constituted by pectin, having mainly galactans as side chains; the citric acid fraction mainly had galactose; and the hemicellulose fractions may be constituted by xyloglucans, xylans, and manmans [4]. When the fruits are processed fresh for seasonal consumption, the peel and seeds are important byproducts, and their antioxidant potential seems to be contributed by phenolic compounds [7]. Triterpenes, such as karoundiid dibenzoate and Cucurbitaceae,23-diene-3h,25-diol; flavones; taxifolin; and quercetin were isolated from the seeds [8], while several anthocyanins, such as cyanidin, peonidin, and pelargonidin glycosides, and quercetin and kaempfer glycosides were reported in the epicarp of this fruit [2; 5]. Low in vitro antioxidant activity has been reported for pulp extracts of Colombian varieties of red peel _S. odorifera_ relative to other fruits [7]. On the other hand, the flavonoids described in the seeds and epicarp are known for their high antioxidant activity and could be useful for novel food product development [2; 5; 8]. Recently, fruits and vegetables have been studied as sources of antioxidants due to the growing interest in natural additives for food application [9; 10; 11; 12]. In addition, most of them also present applications as a dye for the food industry, being an interesting source as a natural supplement. Among the most commonly employed extraction procedures, ultrasound-assisted extraction (UAE) is one of the most studied [9; 13], and it is considered to be one of the most efficient for the extraction of the compound of interest [14]. Power ultrasound has also been proposed for many other applications in chemical and food manufacturing processes [15], alone or in combination with other technologies: for example, for biomass pretreatment [16]. The extraction process has many variables that could influence the efficiency of the process. Consequently, an appropriate design of experiments is essential to determine the best operational conditions. In this sense, some designs aim to find some significant factors from many potential ones. One of them is the screening design. Usually, after some factors are discarded, the significant ones are analyzed again either to find the best operational conditions or even the optimal ones. For this application, designs such as the Box-Behnken are proposed. This allows the development of a response surface that might help to find the optimal operational condition [17]. Box-Behnken allows running fewer experiments than others, such as central composite design, which results in a less expensive optimization methodology. Furthermore, the method for response monitoring should be carefully selected to complement an adequate design and to accomplish the optimization. In this sense, spectrophotometric methods have been successfully employed for this purpose due to their speed and reliability [18; 19; 20]. Despite the popular use of this fruit as a repellent, perfume for clothing, or fresh food or the infusion of its seeds for therapeutic purposes, there is not much scientific knowledge about the use of inedible parts such as the peel. Recent studies on the composition of _S. odorifera_ epicarp showed that the hydroalcoholic extract has a high antimicrobial, antioxidant, antibacterial, and antifungal activity and a high concentration of anthocyanins and other phenolic compounds, organic acids, and tocopherols [5]. These reports contribute to the reduction of the knowledge gap for its integral use. This work's aim is to provide data on the extraction of a group of bioactive molecules of high added value with potential applications in the food and pharmaceutical industry, as new ingredients in functional foods to replace critical ingredients such as artificial colors, or in pharmaceutical preparations in the prevention or treatment of diseases as alternative therapies.