Citrus limon peels: a valorisation approach

Citrus is the most abundant crop of fruit trees in the world, with an annual production of approximately 124.2 million tons. Among the different types of citrus fruits, lemons and limes account for 15.9 million tons [1]. Processing of citrus fruits results in a significant amount of waste (peels, pulps and seeds), which represent about 50% of the raw processed fruits. Industrialization of lemon processing creates large quantities of by-products, which can be of interest to the food industry. Lemon peels consist of the outer layer, called epicarp or flavedo, and the inner layer, called mesocarp or albedo [2]. The flavedo contains high amounts of phenolic compounds, such as hesperidin, diosmin, eriocitrin, and narirutin, whereas the albedo is rich in dietary fibers, particularly pectin, which grant them nutritional value with antioxidant properties. These lemon processing by-products, which are normally discarded as a waste in the environment, can be explored to produce new functional ingredients/additives/products, also desirable from a circular economy perspective [3] . In order to understand the potential valorisation of the lemon peels it is important to perform their nutritional characterization. The results show a high and main concentration of carbohydrates (89.23 g/100g DM) including a relevant content of total dietary fiber (41.16 g/100g DM). Phenolic compounds are the most important group of bioactive compounds, determining their biological activity. These compounds offer potential health benefits, including antimicrobial, anti-inflammatory, and antioxidant activities [4] . The total phenolic compounds (Folin-Ciocalteu assay) and the antioxidant activity (DPPH and ABTS assay) of the lemon peels were analysed. Lemon peels showed a polyphenol content of 2.30 mg GAE/g. Regarding antioxidant capacity, lemon peels showed 0.85 mg AAE/g for DPPH assay and 2.33 mg TE/g for ABTS assay. The different levels obtained from these assays may indicate a relative difference in the ability of antioxidant compounds in the extracts to quench aqueous peroxyl radicals. According to these results, it can be concluded that lemon peels by-products, contain interesting compounds (mainly dietary fiber and phenolic compounds), and their concentrations are significant and justify their valorisation in different food applications contributing for a circular economy and sustainable perspective.