Spicy kiwi? More weird flavors

Produced by: Science Popularization China

Produced by: Zhao Tingting, Zhang Fan (Wuhan Botanical Garden, Chinese Academy of Sciences)

Producer: Computer Network Information Center, Chinese Academy of Sciences

Autumn is here, and it’s time to eat kiwi fruit again.

Among the various types of kiwifruit, there is a kind of "soft kiwifruit" that has a smooth surface, is green all over, is small in size, and looks like a jujube. You may be surprised when you see it for the first time. It turns out that there is such a smooth kiwifruit!

That's right, in addition to the soft-fleshed kiwifruit, there are many "strange" varieties in the kiwifruit family. They are not only hairless, but also colorful and even have a spicy taste. Today, let's take a look at the eye-catching kiwifruit in the family group with the author.

Image source: Veer Gallery

Opening a new door to the world of kiwifruit

First, let us get to know the rich and large kiwi fruit family.

Under the genus Actinidia, 54 species, 21 variants and 75 taxa have been found so far. my country is the country with the richest wild kiwi resources, and most kiwi species are endemic to my country, with only the Nepalese kiwi and the white-backed kiwi being endemic to neighboring countries.

The famous commercial kiwifruit variety "Hayward" also originated from China. It was brought to New Zealand by a New Zealand female teacher who brought kiwifruit seeds from Yichang, Hubei, my country, and was then selected and bred by local gardening enthusiasts.

Different types of kiwifruit vary greatly in appearance and taste. There are at least 15 types of fruit shapes, including cylindrical, ovate, obovate, spherical, etc.; the flesh color varies widely from green, yellow, yellow-orange, pink to purple; the fruit skin hair varies widely from smooth and hairless to the long hard hairs of the prickly kiwifruit; the fruit flavor is sour, sweet, bitter, spicy, and numb.

It can be said that there is nothing you can’t eat, only things you can’t imagine.

Rich kiwifruit germplasm resources (Photo credit: David Li)

Kiwi fruit from the pure fruit group, the name sounds pure and white

Based on the characteristics of the fruit skin hair, taxonomists divide kiwifruit into three categories: clean fruit group (the fruit skin is smooth, hairless and spotless), spotted fruit group (the fruit skin is hairless and has spots) and hairy group (the fruit skin is covered with hair).

The clean fruit group is considered to be the ancestral group of kiwifruit, while the spotted fruit group is considered to be a parallel evolutionary group of the clean fruit group, representing the transition between the ancestral species of the clean fruit group and the hairy species.

The Jingguo Group is mainly distributed in northern my country, and is the only group distributed north of the Yellow River. It is more adapted to cold environments, but it is also distributed in high-altitude areas in eastern and southern my country. It is the group with the most consistent species morphology and the clearest within the genus.

Different types of kiwi fruit groups (Image source: David Li, Han Fei)

The presence of pure fruit kiwifruit makes the kiwifruit family particularly colorful. When reaching edible maturity, most species in the pure fruit group have green flesh, belonging to the "stay green" type of fruit, and some species will gradually change color as the fruit matures.

The color change of fruit flesh is mainly affected by chlorophyll, carotenoids and anthocyanins. Different combinations of the three can make the fruit color show a series of variations such as pink, brick red, yellow, orange, etc.

Below, we will introduce the more representative kiwifruit species in the pure fruit group based on color.

Green kiwi: full of chlorophyll

The emerald green color of kiwifruit flesh is mainly related to the fact that the chloroplasts in the mature fruit are not destroyed and the chlorophyll is not degraded. The greener the flesh is to the naked eye, the higher its chlorophyll content is. The soft-fleshed kiwifruit and "dog-fleshed kiwifruit" mentioned at the beginning are "staying green" species with high economic value in the clean fruit group.

Actinidia arvense (Photo credit: Han Fei)

The fruit of Actinidia chinensis is small, with an average single fruit weight of 2 to 3 grams. The fruit is cylindrical or nearly round in shape, and tastes very sweet with a pineapple flavor. Moreover, this variety is very cold-resistant and is only distributed in the northeast of my country. It can be planted in high-latitude areas where other fruit trees are difficult to survive. However, due to its small fruit size and poor storage resistance, it is difficult to promote it commercially on a large scale.

Actinidia chinensis kiwifruit (Photo credit: David Lee)

Spicy kiwi: carotenoids on top

As chlorophyll degrades and carotenoids develop color, the flesh of some kiwifruits changes from green to orange or yellow. These kiwifruits not only have bright colors, but also have unique flavors, showing spicy, numbing or pungent tastes.

For example, the flesh of the "big-seeded kiwifruit" is light green when immature and turns orange-yellow when ripe. It has a spicy flavor and cannot be eaten directly.

Large-seeded kiwifruit (Photo credit: David Lee)

The skin of the "Ge Zao Kiwifruit" is green, and the fruit is yellow or yellow-green when it is soft and ripe. The unripe fruit has a spicy or peppery taste, and is bland when ripe. The Ge Zao Kiwifruit cannot be eaten directly, but can be used to make wine.

Actinidia gezao kiwifruit (Photo credit: Hu Guangming)

There is also a kind of "opposite calyx kiwifruit", which is orange-yellow when ripe and has a spicy flavor. The root system of this kiwifruit is extremely resistant to flooding, and it can be called the "king of flood resistance" in the kiwifruit family.

Actinidia chinensis (Photo credit: David Lee)

Purple kiwi: rich in anthocyanins

Anthocyanin is the third most common pigment in fruit color and may be responsible for the deep purple color of some kiwifruit fruits when ripe.

For example, a variant of the soft-fleshed kiwifruit, the "purple fruit variant", has purple-red fruit when ripe and tastes sweet. It contains twice as much vitamin C as an orange.

Purple kiwifruit variant (Photo credit: provided by Li David, photographed by Zhao Tingting)

There is also a kind of "black-core kiwifruit", which has a light sweet taste. The fruit is green when harvested, but turns pink or dark red-purple when ripe.

Black-core kiwifruit (Photo credit: provided by Li David, photographed by Zhao Tingting)

After reading this, you may ask: Why are such beautiful kiwis rare in the market?

This is because the peel of pure fruit group kiwifruit, such as Actinidia arguta, is only composed of thick cuticle and hypodermal cells, which are more susceptible to mechanical damage and infection by pests and diseases during growth and development and post-harvest transportation. It is also more likely to lose water during storage, causing the peel to shrink, and has a short shelf life. These factors have seriously hindered its large-scale commercial development.

Currently, scientists are actively exploring the genetic basis of kiwifruit traits and using the pure fruit group kiwifruit as parents to carry out hybrid breeding, hoping to improve the fruit traits of the pure fruit group through genetic engineering and obtain kiwifruit varieties with a variety of excellent traits.

I hope that in the future, we can taste more kiwis with different colors, better taste, smoothness and no hair, which are more beautiful!

References:

(1) Huang Hongwen et al. Classification and domestication of Actinidia genus resources[M]. Beijing: Science Press, 2020.

(2) Huang Hongwen et al. Chinese kiwifruit germplasm resources[M]. Beijing: China Forestry Publishing House, 2020.

(3) Hallettt IC, Wegrzyn TF, MacRae E A. Starch degradation in kiwifruit: in vivo and in vitro ulstrastructural studies[J]. Int J Plants Sci, 1995, 156:471-480.

(4) McGhie TK, AIinge G D. Color in fruit of the genus actinicidia: carotenoid and chloropyll comositions[J]. Chem, 2002, 50: 117-121.

(5)Montefiori M, Costa G, McGhie T, et al.