What is red orange (blood orange), and what is in it?

A red orange, more often called a blood orange, is a sweet orange whose flesh and juice turn red. The colour comes from anthocyanins, a group of red to purple plant pigments; the main one is cyanidin-3-glucoside. Blood oranges need cold weather to colour fully, so they are grown in relatively few regions, such as Sicily in Italy and parts of Spain. The best-known cultivars are Moro, Tarocco and Sanguinello. In a 2022 study of 11 cultivars, Moro juice had the most anthocyanins, at 133.10 mg per litre.

In short:

• What it is: a sweet orange (Citrus × sinensis) with red flesh, a group within the same species as ordinary oranges
• Colour: anthocyanins, mainly cyanidin-3-glucoside and cyanidin-3-(6''-malonyl)glucoside
• Why cold matters: a gene called Ruby switches the pigment on, and full colour needs cold
• Varieties: Moro, Tarocco and Sanguinello; the amount of pigment differs widely between them
• Vitamin C: 0.35 to 0.50 g per kg of juice in one study; the Thai RDI for vitamin C is 100 mg a day

This article explains what red orange is, where its colour comes from, how the cultivars differ, and what studies have measured in the fruit and juice during storage.

What is red orange?

Red orange is a sweet orange. The US Department of Agriculture's GRIN Taxonomy lists the sweet orange as Citrus × sinensis, in the family Rutaceae; blood oranges and ordinary oranges belong to this same species. NCBI Taxonomy, the US National Library of Medicine's species database, gives its common name as sweet orange and lists navel and Valencia orange among its other names.

Blonde oranges and blood oranges

A 2022 study by researchers in Spain and Italy (Legua and colleagues) describes sweet oranges as two main groups. Blonde oranges are grown in almost all citrus-producing countries. Blood oranges are grown in relatively few regions, where the climate favours the synthesis of the red pigment. The study says that switching on the pigment pathway in the rind and flesh is one of the main differences between the two groups.

Cultivars in a Spanish study

The 2022 study grew 11 cultivars on the same rootstock at a research institute in Valencia, Spain. The deepest red peel and juice were in Sanguinelli, Tarocco Rosso and Moro, and Moro's juice was the darkest red of all. Several cultivars, including Tarocco Comune, had pale red juice. The study notes that in Spain blood oranges make up only about 0.7% of sweet orange production, and that the most common one there, Sanguinelli, arose as a natural mutation of the cultivar Doble Fina. The cultivar makes a large difference to how red the fruit is.

What makes blood oranges red?

Anthocyanins. These are water-soluble plant pigments. Cyanidin-3-glucoside, the main one in blood oranges, is also one of the two main pigments in elderberries.

The main pigments

The two main anthocyanins in blood oranges are cyanidin-3-glucoside and cyanidin-3-(6''-malonyl)glucoside. Both are built on the same coloured core, cyanidin, with a sugar attached. In PubChem, cyanidin-3-glucoside has the formula C21H21O11+ and a molecular weight of 449.4. For another fruit coloured by the same pigment, see What is elderberry, and what is in the berries?

Why cold is needed

A 2012 study led by the John Innes Centre in the UK (Butelli and colleagues) traced the colour to a gene called Ruby, which switches on anthocyanin production. In Sicilian blood oranges, a mobile piece of DNA (a retrotransposon) inserted next to Ruby controls when the gene is active, and cold stress activates it. A blood orange of Chinese origin turned out to have a separate, similar insertion, and its colour also depends on cold. The researchers note that, because full colour needs cold, blood orange production is unreliable.

How much anthocyanin do blood oranges contain?

It depends a great deal on the cultivar and on how long the fruit has been stored.

Amounts in the juice of different cultivars

Source: Legua and colleagues (2022), Table 5 (CC BY). The study treats all 11 cultivars as blood oranges; in two of them, Entrefina and Maltaise Blonde, these two main anthocyanins were not detected. The same study measured total anthocyanins of 133.10 mg per litre in Moro and 45.59 mg per litre in Sanguinelli, and found no significant difference between the Tarocco cultivars. All trees grew in one orchard in Spain, so fruit from other places may differ.

Results differ between studies

A 2020 study by researchers in Iran and Spain stored Moro, Tarocco, Sanguinello and Sanguine oranges harvested in northern Iran. At the end of storage at 5 °C, Sanguinello juice had the most total anthocyanins (160.8 mg per litre) and Tarocco the least (53.6 mg per litre). The Spanish study did not include Sanguinello and the Iranian study did not include Sanguinelli, and the two used different regions and storage, so which cultivar has the most depends on the study. No single number describes "a blood orange".

How is a blood orange different from an ordinary orange?

The clearest difference is the red pigment. Other differences in the studies concern acidity and taste rather than one being better than the other.

The vitamin C figures come from different samples and units, so they are not directly comparable.

Nutrients in oranges

USDA FoodData Central has no separate entry for blood oranges. The figures below are for raw oranges in general.

Source: USDA FoodData Central (SR Legacy); Thai RDIs. USDA lists one fruit of this size as 131 g. For raw orange juice, the same database lists 50 mg of vitamin C and 0.2 g of dietary fibre per 100 g. For how oranges compare with other fruits, see Which fruits are high in vitamin C, and how much is in each?

Does storage change blood oranges and their juice?

Yes. Studies have measured both the fruit and pasteurised juice.

Whole fruit in cold storage

A 2001 study from the citrus research institute in Acireale, Italy stored Tarocco and Moro oranges at 8 °C and 22 °C for up to 85 and 106 days. Anthocyanins increased significantly in both cultivars kept at 8 °C. Vitamin C did not drop in Tarocco at either temperature, but fell sharply in Moro during the first 50 days. Acidity fell in both.

The 2020 Iranian and Spanish study stored four cultivars at 2 °C and 5 °C for up to 180 days. Total anthocyanins rose in every cultivar at both temperatures, and the increase was 65% higher at 5 °C. Sugars and organic acids fell, and ascorbic acid (vitamin C) fell significantly at both temperatures.

Pasteurised juice

A 2015 study by researchers in Algeria and France stored pasteurised blood orange juice for one month at 4 °C to 37 °C. Storage temperature and removing air from the juice had the most influence on how fast vitamin C and colour broke down. Adding extra vitamin C (100 or 200 mg per litre) made no significant difference to either.

Is there a recommended daily amount of red orange?

No. Red orange is a fruit, and anthocyanins are not nutrients, so they have no value in the Thai Reference Daily Intakes (Thai RDIs). The Thai RDIs do cover nutrients that oranges contain, such as vitamin C at 100 mg a day and dietary fibre at 25 g a day. For the full list, see What are the Thai daily reference amounts for each nutrient?

Who should talk to a doctor or pharmacist?

Blood oranges eaten as fruit are part of a normal diet. Extracts sold as supplements are a different matter.

People who take regular medication

If you take medication regularly and are thinking about a red orange extract or another supplement, tell your doctor or pharmacist what you plan to take.

Pregnant and breastfeeding women

If you are pregnant or breastfeeding, talk to a doctor or pharmacist before using supplements.

Dietary supplements are not intended to prevent, treat or cure any disease.