## 1 Introduction  
The food industry is one of the sectors in Europe that generates great amounts of bio-waste. Annually, in Europe, food waste is around 1.3 billion tons, of which approximately 700 million tons are from agriculture. These residues result essentially from the processing of grains, fruits, and vegetables and have a high potential for reuse [1, 2]. These residues can be transformed into resources, using intensified conversion processes that can produce potentially sustainable bio-products, such as energy, fertilizers, materials, and molecules. In this sense, the valorization of residues and agri-food by-products is currently presented not only as a necessity, but also as an opportunity to obtain new products of high value and of great impact on the economy of the industrial sector [3].  
_Solanum melongena_ L. (Solanaceae), known by its fruit, eggplant, is a non-tuberous species of great agronomic and economic value [4]; however, mature eggplant fruits are considered unmarketable due to their unpleasant fruit color, texture, pith, and bitter taste as well as the large amount of mature seeds, thus becoming a bio-waste of the food industry [5].  
This matrix is considered a versatile food, as it is part of the gastronomy of many countries and different sorts of diets, namely Mediterranean and vegetarian [6]. In addition to their culinary interest, several authors describe the use of eggplants in traditional medicine, acting therapeutically on several health problems. This curative potential is manifested by its rich composition of ascorbic acid and phenolic compounds, both with high antioxidant potential [4; 7].  
Some of the main phenolic compounds found in eggplant are anthocyanins, responsible for the majority of red, purple, and blue colors of flowers and fruits [8; 9]. Anthocyanins are increasingly valued by the industrial sector, due to their application as natural colorant ingredients. However, in addition to their coloring potential, they also exhibit bioactive properties related to their high antioxidant activity [10]. The potential use of anthocyanins as food colorants has attracted the attention of the scientific community, for combining the pigmentation capacity with health benefits [11; 12]. In the case of eggplant, most of these anthocyanin compounds are concentrated in the epicarp [13].  
Considering the nutritional and bioactive potential of _Solanum melongena_ L. fruit pulp and the coloring compounds present in the epicarp, this study aims to optimize ultrasound-assisted extraction methodologies to obtain an anthocyanin-rich extract from _S. melongena_ epicarp, to be used as a natural coloring ingredient, and thus, contributing to the sector sustainability and improvement of environmental impact. It also targets the nutritional and chemical characterization of the fruit, as well as at its bioactive properties' assessment.  
In this sense, this work addresses a subject with high relevance for several sectors, such as industrial, environmental, scientific, economic, and social. This wide relevance is justified by the proposal to develop strategies that reduce food waste, improving the quality of some commercial products. Furthermore, it leads to the application of innovative extraction technologies, an increase in the quality of products available on the market, an expansion in consumers' preference for these products and, consequently, to an improvement in the environmental impact, economic growth, and the development of a sustainable economy.