Valorisation of Clementine, Mandarin, and Orange Peel By-Products as Value-Added Sources of Macronutrients, Fatty Acids, and Multiple Elements

Clementine, mandarin, and orange peels, which are usually discarded, can serve as promising, sustainable dietary supplements with beneficial compositions, as demonstrated in this study. Citrus peels are low in ash, fat, and protein, but high in moisture, fibre, sugar, and polyunsaturated fatty acids (PUFAs) (up to 60%). They contain high levels of omega-3 and omega-6 fatty acids, up to 30% each, making them a good health-promoting source, as shown by the values of nutritional indices as follows: PUFA/saturated fatty acid (SFA) (1.94 to 2.30), monounsaturated fatty acid (MUFA)/SFA (0.39 to 0.84), and PUFA/MUFA (2.37 to 5.82). Essential macro elements (K > Ca > Mg > S > P > Na) and trace elements (Fe > Zn > Mn > Cu > Cr > Mo > Co > Se) are unevenly distributed among the peels, along with non-essential elements, with Al (37 to 51 mg/kg) and Sr (17 to 30 mg/kg) predominating. Rare elements in food, such as V and W, are found up to 41 and 79 µg/kg respectively, followed by Nb > Ga > Y > Ge (5 to 11 µg/kg). Although citrus peels have a nutrient-dense composition, their monitoring must be ensured before inclusion in the common diet, particularly regarding non-essential elements, as for most of them the reference doses are not established and they could be harmful to human health.