What is in a kiwifruit, and how do green and gold differ?

Kiwifruit is the fruit of plants in the genus Actinidia. Green kiwifruit usually comes from Actinidia deliciosa and gold kiwifruit from Actinidia chinensis. In the US Department of Agriculture's FoodData Central, 100 g of raw green kiwifruit has 92.7 mg of vitamin C, 3.0 g of dietary fibre and 312 mg of potassium; a gold cultivar has 161.3 mg of vitamin C, 1.4 g of fibre and 315 mg of potassium. The Thai Reference Daily Intake (Thai RDI) for vitamin C is 100 mg a day. Kiwifruit also contains actinidin, an enzyme that breaks down protein, which is why it can soften meat, and which is also one of the proteins behind kiwifruit allergy.

In short:

• What it is: the fruit of Actinidia plants; green mostly A. deliciosa, gold A. chinensis
• Green vs gold: in USDA data for one gold cultivar, gold has more vitamin C and sugar; green has more fibre, vitamin K and calcium
• Vitamin C varies: 29 to 80 mg per 100 g across green cultivars in a Japanese study
• Actinidin: a protein-splitting enzyme, similar in specificity to papain from papaya
• Allergy: actinidin is one of several kiwifruit allergens; severe reactions are reported more often in children

This article explains what kiwifruit is, how green and gold kiwifruit differ in nutrients, what actinidin is and what it does to food, and what is known about kiwifruit allergy.

What is kiwifruit?

Kiwifruit is the fruit of plants in the genus Actinidia. NCBI Taxonomy, the US National Library of Medicine's species database, lists Actinidia deliciosa with the common names kiwifruit and Chinese gooseberry, and Actinidia chinensis as golden kiwifruit. Both are in the family Actinidiaceae, in the order Ericales. The genus Vaccinium, to which blueberries and cranberries belong, is in the same order.

Green and gold kiwifruit

A 2004 study from Japan describes Hayward, a green cultivar of A. deliciosa, as the most common commercially available kiwifruit. The 2013 New Zealand study described below compared varieties from the four most widely cultivated Actinidia species, including A. arguta.

What nutrients are in green and gold kiwifruit?

Both are mostly water and contain similar amounts of energy and potassium. They differ in vitamin C, sugar, fibre, vitamin K and calcium. The gold figures below are for one gold cultivar in the USDA database, not for all gold kiwifruit.

Nutrients per 100 g (green, and one gold cultivar)

Sources: USDA FoodData Central (SR Legacy) for raw green kiwifruit and a gold cultivar; Thai RDIs. USDA lists one green kiwifruit as 69 g and one gold kiwifruit as 81 g. Each column comes from one set of US samples.

Vitamin C differs between cultivars

The USDA figures are single values. The 2004 Japanese study measured vitamin C in many cultivars. Hayward had 65.5 mg per 100 g, below the USDA figure for green kiwifruit, and green A. deliciosa cultivars ranged from 29 to 80 mg. Most A. chinensis cultivars had more vitamin C than Hayward, and one of them, Sanuki Gold, had more than three times as much. In A. arguta, vitamin C ranged from 37 to 185 mg per 100 g.

Source: Nishiyama and colleagues (2004). The study was done in Japan, so fruit sold in Thailand may differ. For how kiwifruit compares with fruits grown in Thailand, see Which fruits are high in vitamin C, and how much is in each?

What is actinidin?

Actinidin, also called actinidain, is an enzyme that breaks down protein. UniProt, the international protein database, classifies it as a cysteine protease with enzyme number EC 3.4.22.14 and says its specificity is close to that of papain, which UniProt lists as an enzyme from papaya (Carica papaya). UniProt lists it as found in the fruit and made as a precursor protein of 380 amino acids.

Amounts differ between varieties

A 2013 study from The New Zealand Institute for Plant and Food Research compared 15 kiwifruit varieties from the four most widely grown Actinidia species and found wide variation in actinidin levels. The green cultivar Hayward had both an acidic and a basic form of actinidin, while the gold cultivar Hort16A had only a basic form. The enzyme's activity rose with the amount of actinidin protein in all species except A. arguta.

Kiwifruit and meat

Because actinidin breaks down protein, kiwifruit can soften meat. A 2023 review from Universiti Putra Malaysia and partner universities says papain, bromelain and ficin are the plant enzymes most often used to tenderise meat, and that actinidin is among the others being explored. It also notes that uncontrolled enzyme action can over-tenderise meat, giving a mushy texture.

A 2018 study from Massey University in New Zealand measured how heat stops actinidin. Kiwifruit enzyme extracts on their own lost their activity in under 5 minutes at 60 °C and 65 °C, but when mixed with homogenised meat the same temperatures took up to 24 hours.

Can people be allergic to kiwifruit?

Yes. Kiwifruit is one of the fruits that can cause allergic reactions, and actinidin is one of the proteins involved. UniProt notes that actinidain causes an allergic reaction in humans.

What reviews and studies report

A 2023 review from Sapienza University of Rome describes kiwifruit allergy as increasingly reported in both the general population and children. It notes that thirteen kiwifruit allergens have been described, that reactions can be linked to latex, pollen and other fruit, and that severe reactions have been reported more often in children than in adults. The New Zealand study above names actinidin, kiwellin and a thaumatin-like protein as the three major allergenic proteins, and found that their levels differ between varieties, so results from one variety cannot simply be applied to another.

Does heating remove the allergen?

Not necessarily. A 2012 study from the University of Belgrade found that actinidin made inactive by heat still reacted with antibodies from people allergic to kiwifruit, both in tests on people and in the laboratory. The researchers concluded that heat-processed kiwifruit products may also cause reactions.

Is there a recommended daily amount of kiwifruit?

No. Kiwifruit is a fruit, so it has no value of its own in the Thai Reference Daily Intakes (Thai RDIs), and actinidin is an enzyme, not a nutrient. The Thai RDIs do cover nutrients that kiwifruit contains, such as vitamin C at 100 mg a day, dietary fibre at 25 g, potassium at 3,500 mg and vitamin K at 60 µg. For the full list, see What are the Thai daily reference amounts for each nutrient?

Who should talk to a doctor or pharmacist?

People who have reacted to kiwifruit

If you have had a reaction after eating kiwifruit, or react to latex or pollen, ask a doctor before eating kiwifruit or using products made from it, including extracts.

People who take regular medication

If you take medication regularly and are thinking about a kiwifruit 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.