Wounding Citrus Peel By-Products as Abiotic Stress to Induce the Synthesis of Phenolic Compounds?

Wounding stress stimulates secondary metabolism and induces the phytochemical accumulation of fresh-cut fruit and vegetables. This research aims to study the biosynthesis of secondary metabolites in citrus peel by-products after different wounding intensities. Orange, grapefruit, and lemon peels were cut into rectangular shapes of 8.5 × 2 cm (CTRL), 1 × 1 cm dices (D), and 0.25 cm grates (G). Samples were stored at 15 °C and 65% relative humidity. Their total phenolic content (TPC), total antioxidant capacity (TAC), and individual organic and phenolic compounds were analyzed after 0, 4, 8, 24, 28, and 36 h. The results showed that the metabolite content decreased with the incubation time, so it is recommended to sample by-products between the first 8 h to achieve the maximum content. Grating, the most severe abiotic stress, was not a suitable technique to induce the synthesis of biocompounds because it allowed the full recovery of flavedo, but partial of albedo. However, it was different for CTRL and D, whose TPCs were ~170 and ~200%, ~98 and ~78%, and ~8 and ~36% higher for orange, grapefruit, and lemon, respectively, compared to G. A principal component analysis confirmed differences between the fruit species and cutting shapes combining all factors. Wounding citrus peels induces the accumulation of phytochemical compounds, but the layer of peel recovered in the cut is crucial in the concentration of phytochemicals extracted. It could be an innovative tool to revalorize these inedible parts of citrus, but further research is still needed.