Differences in the composition of phenolic compounds, carotenoids, and volatiles between juice and pomace of four citrus fruits from Southern Italy

Abstract

Processing citrus fruits into juice generates large amounts of by-products, mainly pomaces. This study aimed to perform a comprehensive analysis of the composition in phenolic compounds, carotenoids, and volatile organic compounds (VOCs) of juices and pomaces of four citrus fruits from Southern Italy, i.e., mandarin, lemon, orange, and bergamot. Juices were produced by squeezing the fruits into an electrical juicer, whereas pomaces were obtained as by-products of the juice extraction. The phytochemical content of the samples was studied by targeted LC and GC approaches. Results indicated that lemon provided the juice with the greatest phenolic content. It was abundant in eriocitrin (90.9 ± 10.8 mg kg−1 FW), isorhamnetin 3-O-rutinoside (47.3 ± 8.03 mg kg−1 FW), and rutin (78.9 ± 14.5 mg kg−1 FW). Likewise, lemon pomace was the richest in phenolics, mostly narirutin (130 ± 14.7 mg kg−1 FW). As regards carotenoids, mandarin and orange pomaces were equally (p > 0.05) prominent sources of the compounds, providing primarily lutein and β-cryptoxanthin. The phytochemical profile of lemon and mandarin pomaces was unknown up to date. Bergamot accumulated great amounts of VOCs. In particular, bergamot juice was rich in monoterpenes, e.g., α-pinene (375 ± 62.7 mg kg−1 FW) and γ-terpinene (551 ± 67 mg kg−1 FW). The study investigated for the first time the carotenoid and VOCs profiles of bergamot products, and of mandarin and lemon pomaces. Since, citrus pomaces contained great amounts of phytochemicals, they should find new applications in the food and cosmetic industries.