The growth of the citrus industry, including the rapid development of frozen concentrated orange juice processing technology after World War II, has expanded with international trade and the continuous increase in citrus consumption and their products over the past few decades. Citrus fruits are known as an important food and have been integrated as part of our daily diet and have a key role in providing energy, nutrients, and health promotion. Citrus fruits with low protein and very small amounts of fat provide mainly carbohydrates such as sucrose, glucose, and fructose. Fresh citrus fruits are a good source of dietary fiber that help our health by preventing gastrointestinal diseases and reducing circulation cholesterol. Fruits, in addition to vitamin C, the most abundant nutrient, are the source of vitamins B (thiamine, pyridoxine, niacin, riboflavin, pantothenic acid, and folate) and phytochemicals such as carotenoids, flavonoids, and limonoids. These biological compounds are critical to improving human health because of their antioxidant properties, the ability to become vitamin A (for example, beta-cryptoxanthin), and protection against various chronic diseases.
What do we know about them?
Due to the uncertainty of the number of natural species and large areas for cultivation, the most well-known citrus specimens with high commercial importance are oranges, lemons, lemongrass, grapefruit, and tangerine. Although citrus fruits are cultivated in more than 140 countries worldwide, most of the crop is cultivated on both sides of the equator, which includes tropical and semi-tropical regions of the world. The annual production of the global citrus fruits over the past few decades has witnessed strong and rapid growth, from about 30 million tons in the late 1960s (FAO 1967) to an overall estimation of more than 105 million tons between 2000 and 2004, with more than half of the whole product is oranges. According to the UN, Food and Agriculture Organization (FAO) data in 2009, China, Brazil, the United States, India, Mexico, and Spain are the leading citrus-producing countries in the world, forming nearly two-thirds of global production. However, many citrus fruits such as orange, tangerine, and grapefruit can be eaten fresh. But about one-third of citrus fruits are used worldwide after processing, and orange juice production accounts for nearly 85 % of the total consumption of these processed products. The constant nutrient value of citrus is beyond the supply of vitamin C. These fruits are rich in nutrients such as simple sugars and dietary fiber and are the source of many micronutrients including folate, thiamine, niacin, vitamin B6, riboflavin, pantothenic acid. They also contain potassium, calcium, phosphorus, magnesium, and copper which are essential for maintaining natural health and growth. Citrus fruits also have a low energy density, free of sodium and cholesterol. Citrus consumption may also be very effective in preventing several chronic diseases such as cardiovascular disease, cancer, osteoporosis, and eye cataract.
Citrus origin is identified with a history full of controversy and interesting legends. Some researchers believe that citrus fruits are native to the semi-tropical and tropical regions of Asia and originate in certain parts of Southeast Asia, including China, India, and the Malay Assembly. Recent research shows that while some commercial species such as orange, mandarin, and lemons originally came from Southeast Asia, the real origin of Australian citrus, new Caldonia (outside East Australia), and New Guinea. Citrus expansion to other parts of the world, including North Africa and southern Europe, was slow. The first citrus arrival in the United States was carried out by Spanish and Portuguese explorers, and fruit gardens first appeared in Florida and California around 1655 and 1769. Commercial production, processing, and trade of citrus have increased significantly since then and have introduced citrus fruits as the most important fruit in the world. Some researchers believe that there may be only 25 real species of citrus fruits. Citrus plants are generally evergreen shrubs or small trees that contain flowers and give a strong aroma. Fruits can have different shapes (such as round, rectangular, or stretched) and different sizes from 3.8 to 14.5 cm in diameter.
Citrus coarseness includes carbohydrates, fiber, organic acids, protein, lipids, water-soluble vitamins, fat-soluble vitamins, flavonoids, and minerals, which will be briefly explained below.
Citrus compounds consist of two soluble and insoluble parts (in ethanol). The soluble part mainly contains single and disaccharides, non-frequent organic acids, amino acids, and other minor components. The insoluble part is mainly made up of cellular structure polysaccharides that determine the nature and profile of citrus carbohydrates. Succars, glucose, and fructose with a 2: 1: 1 ratio show the main components of citrus carbohydrates and are the key to the sweet taste of fruit juice. The insoluble solid segment in ethanol produces 80 % after extracting more polysaccharides. In the skin, dough, fruit juice, and citrus membrane, 45 to 75 percent of all solids are insoluble in ethanol and most solids are polysaccharides.
For citrus fruits, dietary fiber generally refers to insoluble alcohol compounds, which are usually made up of cellulose, lignin, and pectin. In addition to the capability of dietary fiber to reduce food transmission time through the gastrointestinal tract and thus prevent gastrointestinal disorders, pectin methoxyl content is associated with cholesterol-lowering. In general, citrus polysaccharides, especially in peel and pulp, are a source of dietary fiber.
Citrus acidity gives the sour taste, which plays a key role in the criteria for evaluating the commercial acceptance of citrus and provides a delectable taste with appropriate sugar levels. Carboxylic acids, especially citric acids, malic, and soxinics, form citrus organic acid content. Organic acids, in addition to the free form, also exist in the form of salts such as citrate and male. Although citric acid is prevalent in fruit juices, the malic, mortar, exalic, and quinik acids are the main organic acids in the citrus skin.
Total nitrogen content in oranges is between 0.08 % and 0.11 %, 0.08 % in grapefruit and 0.06 % in lemon. Free amino acids have the highest share in citrus nitrogen values, accounting for about 70 % of nitrogen compounds in all species. Therefore, citrus fruits are not the main source of protein.
Although citrus flesh is not a good source of lipids, it is mainly found in its seeds and peel. There is a small amount of non-polar and polar lipids in citrus juice.
In citrus fruits, vitamin A is the only fat-soluble vitamin A, which is sufficient in the form of provitamin A carotenoids, with carotins and beta-cryptoxanthin as the main precursors of vitamin A. Although alpha and beta-carotene are a small part of carotenoids in some oranges, beta-cryptoxanthin is the main precursor of vitamin A in tangerine, mandarin, and oranges. Citrus fruits also contain small amounts of vitamin E and vitamin K.
The high concentration of vitamin C (ascorbic acid) is probably the most important share of citrus in human health and nutrition. Previous findings show that consuming 5 mg of ascorbic acid daily is sufficient to prevent vitamin C deficiency and ascorbate symptoms in adults. A medium orange or grapefruit contains approximately 56 to 70 mg of ascorbic acid and a medium serving of 225 ml of orange juice usually contains 125 mg of ascorbic acid. The edible part contains about a quarter of the total vitamin C content in the whole fruit. The peels, although generally known as non-food parts, have a higher concentration than other components. The variety of vitamin C content in fresh citrus fruits and their commercial products is largely influenced by diversity, maturity, climate, displacement, processing, and storage conditions. In addition to ascorbic acid, citrus fruits also provide vitamin B complex, especially thiamine (vitamin B1) and pyridoxal phosphate (vitamin B6). Folic acid, a petroyl-glutamic acid, or folate as a natural form, is another water-soluble B vitamin found in citrus fruits.
Flavonoids have a polyphenolic structure and are responsible for the taste in many fruits and vegetables and may act as a defensive mechanism against fungal attacks. Flavonoids are considered as secondary plant metabolites and have many health effects if used. One of the most common flavonoid categories found in citrus fruits is flavons, especially Naringin, which gives grapefruit a bitter taste. Naringin is hydrolyzed before absorption by intestinal bacteria, which is a common precursor of many other flavonoids. The role of Narginnegen is its involvement in the prevention of bone analysis and osteoporosis.
Although sodium and potassium are the main cells of the cells, sodium fruits and crops have little sodium and less than 2 mg / 100 grams of fruit weight. In contrast, citrus fruits are good sources of potassium. Calcium, magnesium, and phosphorus have relatively small amounts in citrus fruits.
Other important ingredients in citrus
Stored ripe citrus fruits have a distinctive odor. The aroma-active volatile flavoring compounds contained in the peel oils characterize the aroma emanated by citrus fruits and are associated with their flavors. The release of volatile compounds increases with rising temperature, maturity, and ruptured peel and juice components. There are over 300 citrus volatiles and oils, and the chemical constituents include terpene hydrocarbons (such as monoterpenes and sesquiterpenes), esters, aldehydes, ketones, alcohols, and volatile organic acids. They are primarily found in the ductless oil sacs in the flavedo, as cold-pressed peel oil, and can be incorporated into the juice during extraction. Essence oil is a byproduct recovered from the concentration process in the preparation of frozen fruit juice concentrate. During juice evaporation, water in the juice is vaporized, and the vapor contains aqueous components, oils, and aromas. After the vapor mixture of water and oil is removed, condensed, and separated by decantation, the oil recovered is called essence oil and contains most of the flavoring components present in juice. The essence oil is characterized by a fresh-juice aroma and is used commercially as an important flavoring agent to add desirable bouquets to frozen concentrated juice.
For a more detailed study, refer to the article “History, Global Distribution, and Nutritional Importance of Citrus Fruits” by Liu et al.