**1. Introduction**

Nowadays, residues are wrongfully disposed of and underutilized, becoming an increasingly alarming problem for the environment and the population's well-being. One of the primary sources of waste is the food industry. It is estimated that about 1600 Mton of food residues are produced annually, and about 500 Mton are entirely derived from fruits [1]. The consumption of natural fruit juices has been increasing recently, mainly due to health concerns in the population. A shift toward a healthier and more natural lifestyle implies a reduction in the intake of soft drinks that could contain a high concentration of sugars, artificial colorants, and artificial sweeteners with possible adverse effects on the human body [2]. Orange juice holds most of the market share due to its vitamin content and general health benefits. As with other citrus fruits, the majority of the fruit is discarded during the juice-making process.

The residues include peels, seeds, and remnant pulp, which represent almost 50% of the total weight of the fruit [3].

Over the years, research has been made to develop ways to use organic waste as a source of chemical substances and energy. There are many studies regarding the obtention of multiple products from citrus peels [1, 4–6]. Some of these addedvalue products include pectin, essential oils, bioethanol, biogas, and polyphenolic compounds. These products can serve as feedstocks for other industrial processes or as final products by themselves, so the possibilities for selling them are very extensive.

Nonetheless, pectin has been one of the main chemical substances retrieved from citrus residues with organoleptic characteristics that depend highly on the processing steps and conditions used for its production. Moreover, due to the multiple value-added products obtained from citrus residues, it is appealing to investigate the possibility of integrating all these processes under the biorefinery concept, which encompasses a series of steps aimed to transform, refine, purify, or separate different kinds of biological assets into other products [7].

This chapter intends to compile relevant information regarding the production of pectin from citrus residues and thus, determine the most efficient methods that result in the best quality and yields of the final product. Using information collected in the last ten years and reported in relevant scientific databases (Scopus, Springer Link, Wiley, Taylor & Francis, and ACS), a description of the processing alternatives for pectin production was made. Additionally, the gathered information was used to propose the most convenient alternatives and process conditions for its obtention. Finally, the possibility of integrating pectin production into a whole citrus residues biorefinery was discussed, including novel valorization pathways that could increase the process's economic, environmental, and social sustainability.
