Phenolic Powerhouses: The Health Benefits of Citrus Fruits and Sweet Lime

Citrus fruits are rich in bioactive compounds, particularly phenolics, which are responsible for their diverse health benefits. Phenolic substances, also known as polyphenols, are characterized by their aromatic ring structure with one or more hydroxy groups and functional derivatives. These compounds, found abundantly in citrus fruits, include phenolic acids and flavonoids such as flavones, flavanones, and flavonols. These phenolics exhibit a wide range of physiological properties, including anti-inflammatory, antiallergic, anticarcinogenic, antihypertensive, and antiarthritic activities.

Sweet lime (Citrus limetta), a popular type of citrus fruit, is often consumed fresh or as juice, which is highly regarded for its polyphenolic content. The phenolic acids present in sweet lime include caffeic, p-coumaric, sinapic, ferulic, and chlorogenic acids. These compounds, acting as secondary metabolites, possess potent antioxidant properties, contributing significantly to the fruit's health benefits.

Caffeic acid, widely present in plant-based foods, is known for its antioxidant and anti-inflammatory effects. Recent studies suggest that caffeic acid may also modulate the immune system, offering protective effects against various diseases. P-coumaric acid, a hydroxy derivative of cinnamic acid, exhibits antioxidant, antimicrobial, antimutagenic, and immunoregulatory activities. These properties make p-coumaric acid a valuable compound in enhancing human health and preventing diseases.

Ferulic acid (FA), or 4-hydroxy-3-methoxycinnamic acid, is another significant phenolic compound found in sweet lime. As a major constituent of plant cell walls, ferulic acid serves as a powerful antioxidant. It is extensively used in anti-aging skincare products due to its ability to neutralize free radicals and protect the skin from damage.

Chlorogenic acid, a member of the hydroxycinnamic acid family, contributes to the sour and bitter taste of sweet lime juice. This compound not only enhances the fruit's flavor profile but also offers health benefits through its antioxidant properties. Chlorogenic acid has been linked to reduced risk of cardiovascular diseases and improved metabolic health.

Recent research continues to highlight the importance of these phenolic compounds in citrus fruits. Studies have shown that regular consumption of citrus fruits can lead to improved cardiovascular health, reduced inflammation, and enhanced immune function. The bioactive compounds in citrus fruits, particularly sweet lime, play a crucial role in promoting health and preventing chronic diseases, making them an essential part of a balanced diet.
Phenolic Powerhouses: The Health Benefits of Citrus Fruits and Sweet Lime

Bioactive compounds in citrus fruit: Flavonoids

Citrus plants possess a diverse array of flavonoid components, with examples including hesperidin, naringin, and polymethoxylated flavones (PMFs), which are distinctive to citrus plants. Furthermore, rutin and quercetin are widely occurring flavonoids found throughout the plant kingdom.

The white pulp surrounding the fruit contains a concentrated amount of flavonoids. These bioflavonoids aid in the body's retention and utilization of vitamin C. When combined, these two nutrients enhance the permeability and strength of capillary walls. Consequently, the application of citrus juice to bruises can expedite the healing process.

Flavonoids are aromatic secondary metabolites in plants that have gained recognition for their physiological and pharmacological roles, as well as their associated health benefits.

Flavonoids can be categorized as flavanones, flavones, and flavonols. They exist in both free form and as glycosides in various parts of citrus fruits.

The primary flavanones prevalent in citrus fruits, particularly in higher quantities compared to other fruits, are hesperidin and narirutin. Rutin and vicenin-2 are the principal flavonols and flavones found in significant proportions.

Flavonoids play a role in enhancing fruit and juice quality through multiple mechanisms, influencing factors such as appearance, taste, and nutritional value of the plant-derived product.

For instance, in the case of lemon and orange juices, hesperidin can contribute to sediment formation, resulting in undesired cloudiness. On the other hand, naringin significantly affects the bitterness of grapefruit and bergamot juices.
Bioactive compounds in citrus fruit: Flavonoids

Furanocoumarins in citrus fruit

The furocoumarins or furanocoumarins, more commonly known as psoralens, are secondary metabolites commonly found in citrus plants. They are pharmacologic agents and these molecules are allelochemical compounds in plants that have controversial effects on humans, such as phototoxicity and the commonly described interactions with drugs, referred to as the “grapefruit juice effect”.

Citrus plants are able to produce defense compounds such furanocoumarins to cope with herbivorous insects and pathogens. In humans, these chemical compounds are strong photosensitizers and can interact with medications, leading to the “grapefruit juice effect”.

Furanocoumarins can block an enzyme produced by the liver and intestines to break down certain medications in the body. Without this enzymatic activity, levels of these medications can grow to harmful, even toxic, levels.

Citrus peel contains larger diversity and higher concentrations of furanocoumarin than the pulp of the same fruits. Grapefruit is not the only rich in furanocoumarins here. Pomelos (a hybrid between an orange and an Asian fruit called Citrus maxima) also contain furanocoumarins, as do Seville oranges (used in marmalades) and limes. Sweet oranges, such as navel and Valencia, do not contain furanocoumarins.

The major furanocoumarins found in grapefruits include bergamottin, epoxybergamottin, and 6′,7′-dihydroxybergamottin.

Furanocoumarins represent a class of photosensitizers whose use level is likely to be restricted to 1 ppm in cosmetic products by the EU. Furanocoumarins are a therapeutically important subtype and have various clinical applications. They have been used in folk medicine for a long time. The first furanocoumarin, 5-methoxypsoralen, was isolated in 1838 by Kalbrunner from bergamot oil.
Furanocoumarins in citrus fruit

Vitamin C (ascorbic acid) in orange juice

Vitamin C, also known as ascorbic acid, is water soluble, meaning it will dissolve in water and is not stored in the body. The recommended amount of vitamin C is 60 to 90 mg per day.

Orange juice is the most nutrient dense fruit juice commonly consumed in the United States. An 8 oz serving provides 110 cal and contains 72 mg of vitamin C.

Variability in the vitamin C (ascorbic acid) content of citrus fruit and their products is influenced by variety, cultural practice, maturity, climate, fruit quality, fresh fruit handling, processing factors, packaging, and storage conditions.

Vitamin C is known for its potent antioxidant properties and is lost during handling, processing and storage. Therefore, vitamin C content is widely considered as an appropriate marker for monitoring quality changes during processing and storage.

Citrus fruit juices provide an important source of vitamin C for human nutrition, even though only about one-fourth of the vitamin C content of citrus fruit is found in the juice. Vitamin C is usually considered the major antioxidant in citrus.

Vitamin C is important for the human body because it is needed in the production of collagen to make connective tissue. Vitamin C also helps the body to absorb iron, helps wounds to heal, helps red blood cell formation and helps to fight infections. Some studies say that vitamin C prevents cancer.

Vitamin C helps to enhance availability and absorption of iron from non-heme sources. Vitamin C also has antioxidant properties since it can easily lose the electron to neutralize and inhibit free radicals from being oxidized in preventing cell damage.
Vitamin C (ascorbic acid) in orange juice

Fruit preserve – Marmalade

Marmalade is a product made from citrus fruit (usually) which slices of the fruit (or) its peel are suspended. It is the jelly-like product made from properly prepared juice and peel, with sugar.

Commonly used fruits include lime, orange, grapefruit, lemon and orange. Ginger may also be used alone or in combination with these citrus fruits. The fruit content should not be less than 20% citrus fruit and the sugar content is similar to jams.

It is concentrated to achieve its gel structure, similar to jelly, with approximately the same standards, except for the use of sliced peel. The principles of jelly making, therefore, apply also to the preparation of marmalade.

It may be made from one or more of the following ingredients: whole fruit or fruit pieces, which may have all or part of the peel removed, fruit pulp, puree, juice, aqueous extracts and peel and is mixed with foodstuffs with sweetening properties, with or without the addition of water.

Manufacture consists of blending the ingredients, raising the temperature, and evaporating to the correct soluble solids content either at 100 °C at atmospheric pressure or at temperatures down to 60 °C under vacuum. Vacuum boiling avoids heat damage, caramelization, and loss of fruit volatiles, but an additional pasteurization step is required.
Fruit preserve – Marmalade

Citrus fruit of lime

There are historical reports that consider that lime originated in the Asian continent, in Malaysia, from where it was introduced to North Africa and Europe (mainly to Spain) by the Arabs. The three main types of lime largely cultivated worldwide are Persian lime, Key lime (Mexican lime) and Makrut lime.

The external part of the rind, which consists of several morphologically different tissues, is called the flavedo because of the presence of flavonoid compounds. The flavedo of fruit contains pigments like chlorophyll and carotenoids. Albedo is rich in content of cellulose, hemicellulose, lignin and pectin.

Flavedo also contains oil glands from which essential oils are extracted to use in cosmetics and perfume industry.

The outermost layer of the fruit is the epidermis which is formed by a layer of isodiametric, polygonal cells that cover the entire surface of the fruit.

The outer cell walls of this layer are heavily cutinized and partly covered with a waxy substance. These cutinized walls and the wax prevent excess loss of water from the fruit.

Acid lime fruits are high in acid. Citrus aurantifolia grow throughout tropical and warm subtropical regions of the world and the world's leading producers are Mexico, Florida, the West Indies, and Egypt. The most common acid lime is the small-fruited acid lime or Citrus aurantifolia Swingle.

‘Mexican’ lime (Citrus aurantifolia Swingle) has a smooth, thin skin, is greenish-yellow in color, and has a very small neck, a flat base, and a small nipple at the apex. The highly acidic flesh is juicy with a distinct aroma and flavor.

On the other hand, Persian lime (Citrus latifolia Tanaka) has bigger; oval, obovate, oblong or short-elliptical fruits; with rare or lacking seeds. They present a thin rind, smooth surface; and a pale lemon-yellow color at maturity.

Acid lime can be used as fresh fruit or as juice to increase the flavor of drinks. The acid lime fruit is rich source of vitamin C, which helps in increasing the resistance to diseases. Toothache, dental caries and swollen gums are reduced by using the fruit. Lime improves the digestion and helps in reducing acidity problem, constipation and peptic ulcers. It will also help in curing obesity.
Citrus fruit of lime

Naringin: Flavonoid of citrus fruit

Citrus plants are a good source of flavonoids. Naringin, naringenin, nobelitin, narirutin, and hesperidin are the most important flavonoids thus far isolated from citrus fruits.

Naringin, the bitter principle of grapefruit, is found in the juice, flower, and rind of the fruit and constitutes up to 10% of the dry weight.

The flavonoid naringin occurs naturally in citrus fruits, especially in grapefruit. Naringin and its aglycone naringenin belong to this series of flavonoids and were found to possess strong antioxidant and anti-inflammatory activities both in vitro and in vivo. Several lines of investigation suggest that naringin supplementation is beneficial for the treatment of obesity, diabetes, hypertension, and metabolic syndrome.

Naringin (with the molecular formula C27H32O14 and a molecular weight of 580.4 g/mol) is a flavanone glycoside found in grapes and citrus fruits. It possesses the distinct bitter taste of grapefruit juice. Two rhamnose units are attached to its aglycon portion, naringenin, at the 7-carbon position.

Naringin showed a range of properties that help protect the cardiovascular system, including antihypertensive, lipid lowering, insulin-sensitizing, anti-oxidative and anti-inflammatory properties.

Naringin has been shown to inhibit cell proliferation and to promote cell apoptosis in tumour cells, including triple-negative breast cancer (TNBC) cells, human cervical cancer (SiHa) cells and bladder cancer cells. In TNBC cells, the pro-apoptotic activity of naringin results from G1-phase cell cycle arrest. Suppression of the growth of breast cancer cells by naringin is mediated by inhibition of the β-catenin pathway, leading to a significantly increased p21 level and decreased cell survival.

It has antioxidant potential and plays an important role in the development of leaves, flowers, buds and fruits of plants. It has further induced bitterness to the fruits as in grape fruit. However, the bitterness can be reduced upon reduction by the enzyme naringinase.

Both naringin and naringenin are strong antioxidants; however, naringin is less potent compared with naringenin because the sugar moiety in the former causes steric hindrance of the scavenging group. Naringin is moderately soluble in water. The gut microflora breaks down naringin to its aglycon naringenin in the intestine; it is then absorbed from the gut.

The skin of pummelo contained a higher amount of naringin (3910 μg/g fresh weight) than the juice (220·0 μg/g fresh weight) whereas the amounts of naringin obtained from the skin, juice and seed of rough lime were 517·2 μg/g, 98·4 μg/g and 29·2 μg/g fresh weight, respectively.

Three steps are needed to isolate naringin from fruits: extraction, separation and purification. The naringin content in fruit depends on a number of factors the time of fruit collection, the part of the fruit used and if the peel is the source of naringin, the drying time.
Naringin: Flavonoid of citrus fruit

Health Benefits of Mandarin Oranges

Mandarin oranges are rich in vitamins, minerals and antioxidants. High mandarin oranges consumption has been linked to reduced risk for heart disease and cancer. The pectin in mandarin oranges also possesses properties in lowering the cholesterol levels.

The combination of high vitamin C content and flavonoids make mandarin oranges important whenever vitamin C is required to function, especially within the immune system, lens of the eye, adrenal glands, and reproductive organs and in the connective tissues of human body, such as the joints, gums and ground substance and in promoting overall good health.

Japanese researchers found that mandarin orange reduced risk for liver disease, atherosclerosis, and insulin resistance among people regularly eating mandarin orange. The dried peels of mandarin oranges have long been used to aid digestion.
Health Benefits of Mandarin Oranges

Kaffir lime (Citrus hystrix)

Scientific name: Cirrus hysteric.   Family: Rutaceae (citrus family).

Kaffir lime is a very popular spice used in Southeast Asia foods, especially in Thai, Malaysia, Cambodia, and Balinese. Limes vary in size depending on variety and growing condition, begin anywhere from the size of a large cumquat with some Southeast variety, to the size of a lemon in the case of tropically grown Tahitian limes.

Among citrus, kaffir lime had medium sensitivity to cold and will grow in coastal areas and protected location in central Florida.

Kaffir lime fruits

The leaves and the rind of the fruit are similar in taste except the leaves are more intense with the zesty pungent citrusy notes which Southeast Asian cultures enjoy.

Kaffir limes are used for treatments with the belief that these herbs and plant parts carry some medicinal properties that would be able to heal, rejuvenate and cure the recipients of these treatments from ailments.

Kaffir lime leaves

The leaves are used to enhance flavour. Typically kaffir lime leaves are added to liquid based dishes, such as curries, stews or soups, the leaves are tough and fibrous and can be unpleasant to eat. This is why they are usually used whole but brushed or torn to release their fragrance.

Kaffir lime also has antibacterial activity. The volatile oil obtained from leaf, fruit peel and juice inhibited bacterial growth, which could be ascribed to the presence of citronellal.
Kaffir lime (Citrus hystrix)

Mandarin orange (Citrus reticulata)

The mandarin orange (Citrus reticulata) does not appear to have reach Europe until the nineteenth century.

They were grown in China for about 3,000 years as evidenced by their description in the list of tribute articles sent to the Chinese ruler around 2200 BC.

In Tang times, the fruiting of mandarin trees in the imperial gardens, apparently indoors, led to ‘formal congratulation to the monarch on his divine charisma’.

The first mandarins grown in the Mediterranean region appear to have been those planted by the Arabs in various parts of North Africa.

Mandarin is a very interesting citrus fruit. The fruit is small, flattened fruit with a thin rind separating very easily form the pulp, frequently parting from it of itself, and leaving a partially hollow space.

The flesh is dark orange colored, juicy and very rich.

Mandarin trees are adaptable to a wider range of climatic conditions that other types of cultivated trees. They are better able to stand heat than most other types.

They also tend to be more cold resistant than other citrus trees of commercial importance, though the fruit, mainly because it is small and thin skinned, is more readily damaged by cold than are other oranges.

The flavor of the mandarin is somewhat sweeter and less turpenoid than orange owing to a greater amount of trace esters.

Most of the United States mandarin crop comes from Arizona which produces tangelos, Temple oranges and tangerines.
Mandarin orange (Citrus reticulata)

Citrus

Citrus
Botanically, citrus varieties are forms of berry fruits n which the hairs inside the ovary walls form juice sacs.

Epicarp is the familiar highly colored, oil bearing outer layer. Both juice and oils are now valuable commodities in all citrus varieties and the recovery of both material is important to the economics of processing.

Many different processes are used world-wide for citrus types with a two stage operation being widely employed. In a typical process, the fruit passes over an abrasive surface or roller where the sacs in the epicarp are pierced and oil washed away by water spray.

The resulting oil-in-water emulsion is screened to remove vegetable debris and oil is separated by centrifugation and then dried and packed.

The rasped fruit then moved onto an extractor where the juice is removed leaving albedo (pith) and peel (flavedo).

Various juice extractors have been used with fruit being encompassed in a roll mill or screw press, or the juice bearing material reamered out.

Expressed juice is subjected to screening (sometimes referred to as finishing) before being further processed.

Limes are normally processed in a slightly different manner. Washed fruit is compressed in a screw press to yield a pulpy juice that typically also contains the oil emulsion.

Larger pieces of pulp are screened out and in the classical process, juice and oil emulsion are fed to large tanks where a natural separation process occurs.

Naturally occurring enzymes, which may be enhanced by the addition of commercially available synthetic pectolytic enzymes, clarify the juice while the oil bearing emulsion and pulp settle to the top of the tank. At the same time other debris settles below the clarified layer.

Clarified juice is then typically filtered and concentrated while oil bearing emulsion is steam distilled. The process often requires a period of some hours of heating before actual distillation starts and it is in this way that the oil is brought to the specification required by the consumer.

Stream distillation of lime oils usually brings about a number of changes to the components present in the undistilled oil.

The fate of citrus juices both during and after processing will vary with their subsequent use. Whereas lime juice us normally available only as a clarified juice, lemon and orange juices are available both clear and cloudy.

Because of the very high natural acidity (up to 8% s citric acid) of lime and lemon juices, clarification can take place using unpasteurised juices which will not normally ferment.

Orange juice must be treated differently. Clarification is carried out by addition of pectolytic enzymes after pasteurization to destroy microbiological activity.

As with soft drinks fruit juices, the bulk of citrus are subjected to concentration to facilitate shipping and during the process, volatile component are usually collected separately from the juice concentrate.

Both oil an water phase volatile fractions are collected from processes and these are widely used in flavorings.
Citrus