**7. Roles of mineral nutrients in human consumption of citrus fruits**

#### **7.1 Roles of potassium and sodium in citrus fruits**

Citrus fruits are good sources of potassium. An orange may provide 6% of the dietary reference intake (DRI) of potassium, while a glass of orange juice provides 10% of the DRI [59]. Potassium played an important role in regulating water, electrolyte balance, and acid–base balance in the body [59, 60]. In addition to potassium, sodium is also responsible for the regulation of water and electrolyte balance. A glass of chilled orange juice or a few fresh oranges/mandarins is very refreshing in summer and also provides the required electrolytes.

Citrus fruits contain much less amount of sodium than potassium, which is important to patients with high blood pressure regulation, a condition associated with hypertension [59]. Orange has been reported to contain more potassium than any other citrus fruit [61]. An important property of fresh citrus fruits is their low energy value, negligible sodium concentration, and their replacement by potassium, which may be important for low-fat and restricted diets. Potassium in citrus fruits enhances the normal functioning of muscles and the nervous system in the body. Without this essential mineral, the impulse to signal the body to move could not be possible. It helps in the contraction and flexing of the muscles in the heart and other organs [8].

Potassium is the most abundant mineral of citrus juices and accounts for 40 percent of the total ash content [62]. Citrus fruits are low in sodium with a value relatively low (3–4 mg/178 ml orange juice and 4.5 mg/178 ml tangerine juice) [63]. Potassium

content between 4 to 6 meq is available in 100 ml of orange juice [59]. Potassium contents in orange, grapefruit, and tangerine were reported to be 237, 350, and 132 mg, respectively [64]. Potassium intake can be increased by consuming citrus fruits and juices. One medium orange and one 225 ml of a glass of orange juice provide approximately 235 and 500 mg of potassium respectively [65]. These two elements are the main cations of the cell and persons with high blood pressure are usually placed on a lowsodium diet. Although potassium deficiency in normal adults is rare, people on diuretic medicine or on an improper diet have been known to need a supplemented intake of this element. The study of the researchers had confirmed that citrus fruits (oranges and pomelos) are not a rich source of sodium [66], therefore can be used in diets for people with cardiac or kidney problems or those susceptible to osteoporosis [67–69].

#### **7.2 Roles of calcium, magnesium, and phosphorus in citrus fruit**

Calcium and magnesium are the two major divalent cations of citrus fruit. These cations are found between 8 and 15 mg/100 ml in orange, tangerine, and grapefruit juices [63]. These two mineral nutrients contributed 2–3 percent U.S. RDA per serving of 177 ml in citrus juices. Phosphorus is a bivalent cation present in the blood cells as phosphates, in protein, lipids, and carbohydrates, and in adenosine triphosphate and adenosine diphosphate (ATP and ADP). The U.S. RDA for phosphorus is 1 g; orange juice and grapefruit juice contain between 14 to 20 mg per 100 ml of phosphorus [63]. Citrus fruits compared to other fruits, such as apples, pears, melons, peaches, plums, mangoes, and bananas, are a valuable source of calcium, which plays an important role in building hard, strong bones [59].

The citric acid in orange juice may act as a chelating agent and thus increase calcium absorption by preventing the formation of insoluble salts. They are also a valuable source of phosphorus, which together with calcium, participates in the formation of strong bones and teeth [70]. Pulp from one pomelo fruit (about 600 g) provides 9 to 16% of the DRI for phosphorus while the rind (about 320 g) also provides about 30–40% less of the DRI for phosphorus than the pulp [71]. Phosphorus is important in the diet of young people, pregnant and lactating women. Plant seeds (beans, peas, cereals, and nuts) and fruits contain phytic acid (also called phytate), that is not directly available to humans [71]. Phosphorus in citrus fruit is an essential element in the building blocks of life; the ribonucleic acids (RNA), which is required for many additional biochemical and physiological processes that include energy transfer, protein metabolism, and other functions [72]. Calcium is highly implicated in the maintenance of firmness of citrus fruits [73] and its requirements in fruits are related to cell wall stability and membrane integrity [74]. Magnesium is an important primary constituent of chlorophyll and as a structural component of ribosomes, which helps in their configuration for protein synthesis [75]. It is also required for the maximum activity of almost all phosphorylating enzymes in carbohydrate metabolism.

#### **7.3 The roles of copper, zinc, iron, and manganese in citrus fruits**

Trace metals (copper, zinc, iron, manganese, etc) are needed in the body in a small or minute quantity. These plant nutrients are supplied in citrus fruit during their cultivation. They are important in many metabolic activities of the body. Iron content in one orange (200 g) can provide about 2 mg of iron. Two oranges a day can give 4 mg, which would be more than 10% of the Recommended Dietary Allowance (RDA) in the USA. The RDA is set assuming a 10% rate of intestinal absorption [76, 77].

*Citrus Mineral Nutrition and Health Benefits: A Review DOI: http://dx.doi.org/10.5772/intechopen.107495*

Oranges and pomelos are the fruits richest in iron and copper, they could be recommended in cases such as hemoglobin production disorders resulting from a deficiency of these elements [61]. Pineapple contains copper, which regulates the heart rate and blood pressure [78]. Manganese in pineapple juice help to build strong bones, connecting tissues in the body and boosting the immune system [79]. A person can get rid of nausea, constipation, throat infections, and intestinal worms by consuming pineapple juice [79]. An equally important micronutrient is zinc, which protects the body against oxidative stress and stimulates immune mechanisms [80]. Its content in the peel of orange, lemon, and all grapefruit varieties was found to be significantly higher than in the pulp [61]. Cereals and vegetable diets contain phytates and these phytates inhibit zinc and calcium absorption supplied in citrus fruits therefore caution should be taken in consuming citrus fruits along with cereals and vegetables.
