Our understanding of the foods we commonly eat is constantly changing -- and scientists at Plant and Food Research are gaining new insights all the time. The institute's general manager of science food innovation,
Dr Jocelyn Eason, shares 10 things we might not know about popular Kiwi foods
1 Pick a peck of Kiwi peppers
New Zealand has two native pepper trees: horopito and kawakawa.
Both have a long tradition of medicinal uses by Maori and are being developed by the New Zealand food industry for sale at home and overseas as indigenous spices.
Horopito has red blotchy leaves and is found in disturbed bush and margins throughout the North and South Islands. The leaves contain a pungent (spicy hot) compound called polygodial -- also found in the water pepper used as a spice in some Asian cooking. If you nibble (cautiously) some horopito leaf you will feel a slowly developing, then slowly fading, hot sensation in your mouth.
Horopito is grown commercially in Golden Bay and elsewhere, and sold for both flavouring and for its antifungal properties.
Kawakawa has dark-green, heart-shaped leaves and is found in shady bush on the North Island and warmer parts of the South Island.
Its leaves are less pungent than horopito, with myristicin (the main flavour of nutmeg) the most tasty component.
These leaves have been used as teas, and for flavouring beer (TaaKawa).
Surprisingly the fruits have not been used much, even though these contain pungent and medicinal compounds similar to those found in the black peppercorns used in European cuisine.
So next time you're out in the bush, keep your eyes open for these hot plants -- but mind your tongue.
2 Kiwifruit have relatively little effect on blood sugars
Common wisdom tells us that sweet sugary foods raise blood glucose and must be avoided by people with diabetes, or those who just want to stay healthy.
So why does a luscious, sweet kiwifruit have such a small effect on our blood sugar?
We know about 80 per cent of a kiwifruit is water, but there is a lot going on in the other 20 per cent.
A 100g kiwifruit contains about 10g of sugar.
However, half of the sugar in kiwifruit is fructose and, while we perceive fructose to be very sweet, it has little effect on our blood-glucose levels.
In addition, the cell walls of kiwifruit flesh are not digested but hang around in our intestine to further reduce glucose absorption.
To complicate the picture further, scientists now also believe there is another factor influencing our blood sugar response to kiwifruit -- scientists at Plant and Food Research are investigating whether compounds found in kiwifruit called phenolics reduce our blood-sugar response to the fruit.
Zespri kiwifruit have also been scientifically proven to contribute to normal bowel function and they are high in vitamin C, so if you put all this together you have a delicious, nutrient-rich, healthy fruit that doesn't put your blood sugars through the roof.
3 Your need for caffeine is due to your genetics
Some people can't consume caffeine post-lunch for fear of insomnia, whereas others can have a double shot as a night cap.
Research indicates that the reason is all down to our genetic make-up.
The genes we carry could also dictate how much we crave and consume caffeinated products, and therefore the market demand for these products.
That need for chocolate, for example, is all down to your DNA.
Scientists from the Harvard School of Public Health, the National Cancer Institute and other institutions say they have discovered two genetic variations that influence caffeine metabolism and are associated with how much caffeine people consume.
People with particular variations of two specific genes are more likely to consume caffeine, and to drink more of it when they do.
4 Eating vegetables is good for your bones
Most people think of dairy when they think of foods that are good for our bones and our teeth. While it's true that dairy is an excellent source of bone-building calcium, it is not the only or best source of important minerals to keep your bones healthy.
To build and maintain strong bones you need adequate amounts of calcium, vitamin D and vitamin K.
These three nutrients work in conjunction to build and repair bones, with vitamins D and K playing a central role in helping your body absorb calcium.
Certain vegetables provide calcium as well as vitamin K, a nutrient equally important to bone health.
Both vegetables and fruits promote bone health by neutralising blood, which helps to reduce the loss of calcium from your body and, in particular, your bones.
Green vegetables are the primary source of vitamin K and also provide calcium.
Kale, for example, can go toe to toe with many healthy dairy products when it comes to the amount of calcium per serving.
A single serve (75g) of kale provides 150mg of calcium -- 18 per cent of the recommended daily intake of calcium.
A cup of cottage cheese provides just 130mg and 1 cup of milk has 300mg.
Kale is also a good source of vitamin A, vitamin C, vitamin K and it contains copper, potassium, folate, vitamin B6, magnesium and manganese -- a truly super vegetable.
5 Berryfruit can help asthma patients to breathe more easily
Scientists at Plant and Food Research have analysed a range of different New Zealand blackcurrant varieties and found that in the lab, many reduced a key inflammatory step linked with allergy-induced asthma.
The consumption of some fruit types has been shown to reduce symptoms in allergy-induced asthma but this research has provided more insights into the likely bioactive compounds in fruit that are responsible for this health benefit.
The research shows compounds known as anthocyanins present in blackcurrant are important in controlling inflammation in the lung, but more importantly it is the ratio of specific anthocyanins rather than the presence or absence of them that makes blackcurrants a healthy fruit.
This new knowledge will enable New Zealand's food and drink companies to develop foods based on the correct balance of these compounds that can be consumed as safer, natural alternatives to assist conventional drug treatments for asthma and other allergic conditions.
6 Why chillis are hot and mint is cold
Taste is the sensation produced when a substance in the mouth reacts chemically with taste receptor cells located on our tastebuds. The heat sensation in chilli peppers is caused by capsaicin, a colourless, odourless, oily chemical found in peppers.
Capsaicin binds with sensory neurons which trick your body into thinking that it is experiencing excessive amounts of heat in the area that the capsaicin comes into contact with, even though no actual physical burning is taking place.
Conversely the chemical in mint, menthol, makes us think the area of skin touching the menthol is cold, by binding with cold-sensitive receptors, and tricks your brain into thinking you are feeling a cold sensation when in fact everything is more or less the same temperature as before.
7 All bananas are genetically identical
Have you ever noticed that while there are a plethora of varieties of nearly all common fruits such as apples, oranges and peaches, each banana seems identical to every other? When someone says "banana", you probably think of a large fruit with yellow skin and a soft, pale middle. That's because only bananas of the Cavendish variety are sold in our stores.
While there are many species in the banana genus Musa, those species are drastically different from the "banana" in taste and texture.
Fruit corporations long ago decided that it would train consumers to expect all bananas to be identical.
Until the 1950s, all bananas bought in shops were the Gros Michael variety but this was replaced by Cavendish when Gros Michael bananas -- another genetically identical cultivar -- were so devastated by disease they could no longer be supplied to the global market in any quantity. In order to preserve their distinctive properties, Cavendish bananas are never allowed to reproduce sexually.
That means they all have the exact same genetic code as the first Cavendish tree selected by UnitedFruit Corporation in the 1950s.
Now, the same disease that devastated the Gros Michael is targeting the Cavendish variety so plant scientists are looking for ways to stop the disease or breed new varieties with increased resistance.
8 A tropical tuber provides more of the world's carbohydrates than any crop beside rice or wheat
After rice and wheat, the most important human carbohydrate source is not what you might guess.
It's not the starchy potato, or any of the major sweetener-producing crops (sugar cane, sugar beet or corn).
It's a tropical tuber known by the names cassava, manioc and yuca (in Spanish), and it's the main ingredient in tapioca pudding.
Cassava was a staple food for the pre-Columbian cultures of tropical America and remains an important food in that region of the world today.
It has also acquired a central place in African cooking, and is a major calorie source for that continent.
That's because cassava is both versatile and highly nutritious -- it is a good source of fibre, vitamin C and contains dietary levels of other essential nutrients (biotin, folate, potassium, thiamine, zinc).
As well as being cooked and eaten like a potato, cassava can be ground into a flour.
The starch of the cassava is not called cassava starch (as you might expect based on corn starch or potato starch) but tapioca, and is most famously used in puddings and in the "boba" balls of certain Asian teas.
9 Enjoy your potato cold
Potatoes are often perceived as unhealthy because they have a reported high glycaemic index (or GI).
However, many nutritionists now believe the glycaemic index is not a very useful measure because it is a ratio that refers to the digestibility of carbohydrate relative to glucose, and does not reflect the density of carbohydrate in the food or the amount of food eaten to achieve a blood glucose response.
Glycaemic impact is a new way of measuring blood glucose response to food. The advantage of this measure is that it behaves like a nutrient -- it has gram units and can be expressed as g/100g of food or g/serving of food, just like other nutrients on a food label. Potatoes are in fact an excellent source of low-density energy.
This means that the energy we get from potato comes from carbohydrate (17kJ/g) rather than fat (34kJ/g) and is diluted about eight times with water. They are also a good source of vitamin C, a source of potassium and niacin, and if you keep the skin on a source of dietary fibre.
The glycaemic impact of potato is easy to manage in a healthy diet.
When potato is cooked the starch gelatinises and becomes digestible.
But when you cool cooked potato and let it stand for a while the starch chains partially join up, and this slows down the speed they are digested.
So starch in cold cooked potato is digested at a lower rate than in the hot potato, and correspondingly has a lower glycaemic impact per weight.
In addition, the acid in the vinaigrette you add to your potato salad (lemon juice, lime juice, or vinegar) will slow stomach emptying which means the starch does not reach digestion/absorption sites in the small intestine as quickly and the glycaemic impact is less acute.
So potato is not the villain it has been made out to be because it is not carbohydrate dense.
You should continue to enjoy your potatoes and by choosing a potato salad with vinaigrette keep your blood glucose under control.
10 The new "three minutes max" rule for cooking vegetables
We all know the effects of over-cooking on vegetables -- their flavour changes when components of fresh, green flavour are lost and bitter flavours become more dominant, and they become soft and mushy.
Boiling in water can also mean the water-soluble vitamins like vitamins B and C, as well as water-soluble phytonutrients like the purple colour in purple cabbage or beetroot, are lost.
However, the combination of heat and time makes vegetables softer and easier to eat and digest.
A new New Zealand-Australian study has undertaken research to separate the facts from the old wives' tales and provides a new "3min max" cooking guideline for steaming and stir-frying vegetables that optimises the taste and nutrition.
Steaming has very low water contact that leaves vegetables brightly coloured, crunchy and tasting great, and minimises loss of water-soluble vitamins like vitamin C.
Stir-frying includes the addition of a small amount of oil that makes fat-soluble vitamins and phytonutrients (like beta-carotene in carrots which makes Vitamin A) more available to our body.
Alternatively, a good cooking option for starchy root vegetables is oven-baking, which allows the release of energy and makes fibre available to our body.