**1. Introduction**

Citrus is a genus of evergreen tree or shrub that belongs to the family of Rutaceae and a native to the subtropical and tropical region of Asia [1]. There are several species of the genus citrus which include sweet orange (*Citrus sinensis*), mandarins (*C. reticulata, C. clementina, C. deliciosa, C. unshiu* and others), lemon (*C. limon*), limes (*C. aurantifolia, C. latifolia, C. limettioides, C. limetta* and others), grapefruit (*C. paradisi*), sour orange (*C. aurantium*) and shaddocks (*C. grandis*) [2, 3]. Citrus fruit is a very popular and important fruit that is cherished all over the world in the form of fruit salad, mixed salad, fruit juice, drink, and condiment in several kinds of preparations [4]. One-third of total citrus fruit production comes from orange juice production and this account for 80% of citrus fruit processing. The world production of oranges was estimated to be 76 million metric tons in 2019–2020, the largest producers were led by Brazil, China, India, the USA, Mexico, Spain, and Egypt [5].

Global citrus production reaches to 144 million metric tons in 2020. China ranking as the biggest producer of citrus followed by Brazil, India, Mexico, Spain, Egypt, Iran, and South Africa [5].

Mineral nutrients are essential for plant growth and development. They are the major class of food components necessary for the maintenance of physiological conditions that are essential for life [6, 7]. These essential nutrients are found in many different types of plant and animal-based foods. Mineral nutrients are classified into macro-minerals and trace elements. Macro-mineral is required in greater amounts and include calcium, potassium, sodium, phosphorus, magnesium, chloride, and sulfur whereas trace minerals are needed in smaller amounts, which may include iron, zinc, selenium, manganese, copper, iodine, cobalt, and fluoride. Both types of minerals support building, and maintaining healthy bones and teeth and also help to keep the muscles, heart, and brain working properly [8, 9]. Plants are the major sources of mineral elements in our diets; these substances are not synthesized in plants but are absorbed from the soil and the atmosphere. Therefore, the amount of minerals absorbed by the plants depends largely on the nutrient content and compositions of the soil where they were grown among other environmental factors [7, 10]. Additionally, nutrients play a significant role in soil fertility and make it more productive for plant growth [11]. Mineral nutrients required by citrus trees are in large quantities in order to attain adequate growth and yield, and the requirements for some of the nutrients vary with soil fertility and type.

Trace elements in fruit may be influenced by the amount of mineral composition of the soil, irrigation water, weather conditions, and the types and amounts of fertilizers used. There is a significant impact of fruit variety on mineral content [12, 13]. Trace metals in fruits are selectively accumulated and pineapple, for example, accumulated a high level of manganese as compared to other fruits studied [14]. The citrus pulp is recognized as providing some mineral elements such as potassium, calcium, phosphorus, or magnesium for human nutrition but there are other parts of the fruit that also contain these elements. The peels of orange, lime, and mandarin are not recognized in nutrition because they are non-edible components. But these peels of the fruits (orange, lime, and mandarin) like in their pulps are promising sources of mineral elements which can be used for their health properties in food products [15]. These properties can also be applied to food as a source of functional compounds [15].
