Fruits and Vegetables
The importance of fruit and vegetables – why learn about them?
"An apple a day keeps the doctor away" is an expression which goes back to before our great-grandparents’ day. The lesson from this phrase is still important today but we could also add "and 5-a-day is the best healthy way"! This refers to the campaign in the UK advising us to eat five or more servings of fruit and vegetables every day to keep ourselves in optimum health. Many countries now have such campaigns to try to inform and encourage people to eat more fruit and vegetables. In some countries, for example, in Australia, they actually say '7 serves a day'! Others specify five or more vegetable servings and two or more fruit servings. In all cases, the message is the same – eat more fruit and vegetables! Perhaps your school has tried to think of ways of encouraging students (and teachers) to eat more fruit and veg? Maybe you could think of ways of doing this yourself? In many infant schools, younger children now receive fruit from the school, supported by a Government initiative recognizing the importance of early childhood fruit consumption. But did you know that canned and frozen fruit also count towards your 5-a-day target? So do pulped fruit drinks (but only one portion). (Note that potatoes do not count in the 5-a-day scheme. They should be regarded more in the category shared with pasta and rice as carbohydrate sources).
How many fruits and vegetables can you think of? Here’s a fun activity to start the class off with:
Organize students into smaller groups and have each group brainstorm and compile a list of all the fruits and vegetable they can think of. Think also of all the tropical fruits we get in our supermarkets today. See which group can come up with the most.
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Different types of fruit and vegetables
The term "fruit and vegetables" encompasses a huge array of food products. From a botanical perspective we can sort these into eight categories: root vegetables (e.g. carrots), tubers (e.g. potatoes), leafy (e.g. spinach), inflouresence or flowerheads (e.g. broccoli), seed (e.g. green pea), bulbs (e.g. onions), stem or stalk (e.g. celery), and fruit vegetables (e.g. tomato, peppers). Fruits can be sorted into citrus fruits (e.g. orange), stone fruits (e.g. apricot), pomme fruits (e.g. apples), tropical/subtropical fruits (e.g. banana), and wild fruits (e.g. elderberry).
In addition to the essential nutrition that fruit and vegetables give us, they also lend a variety of sensory properties to the meals we eat. Can you think how?
Fruits and vegetables can decorate a meal. In addition to their unique nutritive properties, adding a variety of rich colours can make a meal look more attractive. Fruit and vegetables also add texture, such as the crispy lettuce leaves in a salad or crunchy carrots in a spaghetti bolognese sauce. When we cook vegetables, their texture changes as they soften. If we over-cook them, we lose the crisper texture and many of the good nutrients so it is better not to over-cook. In the 'Healthy Living' section, the page on 'Fruit Salad' considered the range of textures possible in a "texture medley fruit salad". Perhaps the class can come up with some of these textures. Fruit and vegetables also add or complement flavours - just think of onions and garlic for this. Fruit and vegetables can provide a contrast in taste to a meal, such as apple sauce with roast pork or cranberry sauce with the Christmas turkey.
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The good nutrition story
We cannot talk about fruit and vegetables without mentioning nutrition. It has long been known that fruits and vegetables are a valuable source of vitamins and minerals but now we know more about the true extent of the role that fruits and vegetables play in maintaining our health.
About 90% of the vitamin C in our diet comes from fruit and vegetables, particularly citrus fruits, green vegetables, peppers and tomatoes. Vitamin C is important for protecting our bodies from infections and allergies, it aids in absorption of calcium and iron from foods (it is advised to take iron supplements with a glass of orange juice), it assists in maintenance of blood vessel walls and helps to heal wounds.
In addition to vitamin C, certain fruit and vegetables also contain the Vitamin B group. This is particularly true for peas and pulses. This important vitamin group is responsible for many vital bodily functions such as enhancing nervous system function and aiding in the release of energy from carbohydrates. Fairly recently, it was discovered that folic acid, or folate, another member of the B group vitamins, is crucial in early pregnancy to prevent neural tube defects (like spina bifidia). Vitamin A, via beta-carotene, is another important contribution from carrots and other orange or yellow fruit and veg. Furthermore, calcium is found in green leafy vegetables and iron in dark green vegetables such as spinach.
The nutritional value of fruit and vegetables has been known for many years. For example, the discovery of vitamin C, in the last hundred years, followed on from the realization that scurvy-ridden sailors at sea could be treated with citrus fruits centuries ago. More recently, in the last 10-20 years, researchers have started to identify and understand the "super-nutrition" story behind fruit and vegetables too, increasingly supported by scientific research. We now accept without question that a diet rich in fruit and vegetables can protect against cancer, coronary heart disease and strokes. Furthermore, research also increasingly lends support for numerous other health benefits associated with eating lots of fruit and vegetables such as helping with high blood pressure, preventing cataracts and some chronic obstructive pulmonary disease like asthma and bronchitis (1). Of course, whilst including fruit and vegetables in our daily diets is important in itself, if those fruit and vegetables actually replace other things which are not so good for us then we gain a double benefit. For example, if we eat a piece of fresh fruit at snack time instead of a snack high in saturated fat and salt then our bodies will thank us twice! (That’s not to say we can’t still enjoy such less healthy snacks from time to time but they should constitute a much smaller part of our diet than they currently do for many people). You have probably seen a food pyramid diagram before – just think of where fruit and vegetables sit in that.
In addition to the food pyramid, there is the "colour wheel". This focuses specifically on nutritional benefits of including different colours of foods, the majority of these from fruit and vegetables. You may have been told before to "eat up your greens" but you could now respond that first you’re "eating your reds, yellows and oranges!". "Eating by colours" is another approach in fighting off disease and keeping our bodies working properly. So what are these colours?
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Red foods such as strawberries, tomatoes, red pepper, cherries, rhubarb, radishes and red grapes
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Purple/blue foods such as beetroot, aubergine, blackberries and blueberries, red cabbage and purple grapes
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Orange/yellow foods such as carrots, oranges (of course!), pineapples, lemons, mangoes, sweetcorn, pumpkin and sweet potato.
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Green foods such as broccoli, spinach, peas, avocadoes, green apples, green grapes, kiwi fruit, pears, asparagus
- White/brown foods such as onions, garlic and cauliflower.
We now know that there are a number of key chemical components, within these groups that are responsible for the health benefits. The extension section further on looks further at the food chemistry of fruit and vegetables and explores more fully the role of anti-oxidants and phyto-chemicals.
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Processing of fruit and vegetables
In addition to being enjoyed in their simple raw state, fruit and vegetables also come in many different processed states. This is usually driven by the need to increase the useable life of fruit and vegetables by drying, canning, freezing or other processes.
Fruit drying was one of the first procedures for food preservation and was originally performed by simply spreading the fruit in the warm air of a fireplace or hearth. Today solar drying is still a common practice in countries blessed with the sun to do it. Often pre-drying is carried out in the sun with additional artificial drying supplementing the drying process thereafter. Grapes are the most commonly dried berry fruits. Raisins are dark-coloured dried grapes which contain seeds whereas sultana raisins are seedless light-coloured dried grapes. Currants are darker in colour and much smaller than the raisins. Sometimes the surface of the dried berries are treated with oils or other agents to prevent caking or sticking. Tomatoes are another popular sun-dried product which find their way into many recipes and applications today. If you have tasted them you will know that the flavour they deliver to the food is quite different to that when fresh. For this process tomatoes are usually cut in half and left on raised drying trays in the sun for about 7-10 days. Sulphites are also often involved in the drying process. Organic products may use only natural oils.
Canning is also a method frequently associated with fruit and vegetables. Heat sterilization in cans and glass jars has been a very important method used for the last 150 years or so to preserve fruits and vegetables. Pears, pineapples and peaches are classic examples of fruits found in cans. Many people are not aware that canned fruits also count towards their 5-a-day target for fruit and veg intake. Often a blanching step (a short heat "shock" step) takes place prior to canning. This not only serves to inactivate enzymes (which could soften the vegetable for example) but can also remove unwanted flavour compounds and the air present in plant tissue.
Freezing - Many fruits and vegetables are now found frozen. Some are particularly suitable for freezing, others not so, due to textural changes. High quality fresh vegetables are usually treated with boiling water or steam for enzyme inactivation (steam is preferable). The blanching step is kept as short as possible to prevent leaching. Immediately after blanching the vegetable is cooled, frozen at -40C or lower then stored at -18C to -20C. Freezing is mainly conducted using conventional freezing techniques by indirect cold transfer in plate or air freezers.
Freezing preserves vegetable nutrient content to a great extent. Many vegetables are now frozen within a few hours of harvest ensuring the best quality of the resultant "fresh-frozen" product.
Fruits and vegetables can also be processed in many other ways. Pickled vegetables, marmalades, jams and gellies are just some examples.
In all cases the fruit and vegetables should be handled and processed with care to maintain nutrient content as well as possible. A few tips that can be applied in the domestic kitchen as well as the industrial process include the following. Cooking should be done as quickly as possible in a small amount of water. Steaming or microwaving are in fact best for preserving nutrients. Fruit and vegetables should be prepared just before they are needed as vitamin C in particular starts to be lost once cut or peeled. Likewise keeping pieces large reduces surface area and subsequent oxidation losses. Standing in water will leach out water-soluble vitamins B and C. Finally, storage should be in a cool, dark place for as short a time as practical.
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Production of fruit and vegetables and consumer issues
Today the wider societal impacts of our food production are important to many consumers, businesses and governments. Environmental considerations and sustainable practices are now increasing concerns. How our food is transported, how much energy is required to grow it and how it affects the land and our bodies are frequent questions asked of producers. Organically grown fruit and vegetables have become more popular and more available in recent times. The use of pesticides and other chemicals is being continually monitored and legislated over by authorative bodies. Genetically modified (GM) foods are still a big issue in many parts of the world, including Europe, and no one knows for sure if widespread acceptance will be a reality in the near future. Considering the carbon footprint of our food production, the "food miles" cost and provenance issues sometimes even feature on the packaging or at the point of sale. Packaging issues and water use concerns are other topics which today make food production – and particularly fruit and vegetable production - a truly multi-faceted subject!
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Research in the area of fruit and vegetables
Much research goes on in the world on fruit and vegetables, in production, processing and nutrition. Recent examples include:
A new apple which is red on the inside as well as the outside is being developed in New Zealand at Plant and Food Research(4). According to the researchers there the new apple owes its red colour to the healthy anthocyanins compounds also found in red and purple berries. Anthocyanin levels in the flesh are twice as high as that in the skin. The researchers claim that this should boost the antioxidant level to be similar to that in blueberries. They were also found to contain more beta-carotene (vitamin A). This is achieved through genetic engineering in the lab where DNA is transferred from "red-fleshed" apples grown naturally in Kazakhstan to the eating apple type Gala to bring about red colour expression. But the apples are unlikely to be in shops for quite a few years.
On apples again, but this time using classical breeding (i.e. non-GM) techniques, researchers at the University of Illinois in the US have developed an apple tree which is resistant to a fungus that can cause otherwise severe losses(5). These resistant trees could also cut chemical spraying requirements by 60-70%. By crossing a crab apple tree and a conventional tree over a period of 20 years the research team have produced a new apple called "Winecrisp". Reducing the amount of fungicide spraying required helps the environment and helps the farmer in terms of costs of production and meeting future fungicide legislation.
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Extension – some food chemistry behind fruit and vegetables
Last term in Food Bites we looked in more depth at some physical aspects around food rheology. This term we look further at some food chemistry, a very important and crucial element of food science. In particular we consider the chemistry behind the health benefits of many fruit and vegetables. If you study food science further then no doubt you will learn more about the wonderful colour chemistry, flavour chemistry and nutritional chemistry of fruit and vegetables.
The vibrant colours associated with fruit and vegetables are due to a number of chemical compounds. For example the carotenoid pigments are responsible for most of the orange and yellow colours of fruit and vegetables whilst the pink, red, violet and blue colours of many fruit and vegetables are caused by the presence of anthocyanins. As well as delivering colours these chemicals are also now attributed to many of the nutritional aspects of fruit and vegetables.
In yellow-orange fruit and vegetables the bright colour is attributed to the carotenoids (beta-carotene, lutein, zeaxanthin). These are examples of anti-oxidants, chemicals found naturally in fruit and vegetables, which can help protect our body cells from being damaged by ‘free radicals’. In this way, antioxidants can help protect against cancer and heart disease (2). Furthermore, lutein which is stored in the eye is important in preventing certain forms of blindness(3). Terpenes and flavonoids – other types of phytochemicals - also feature in this group. Researchers are continuously trying to better understand the role of antioxidants and application in treating other diseases. Like orange/yellow foods, green fruits and vegetables are particularly rich in antioxidants. They include varying amounts of many phytochemicals including flavonoids and carotenoids (lutein, beta-carotene and zeaxanthin). The brassica group (e.g. broccoli) also contains indoles, which can trigger enzymes to act against certain cancer causing substances (3). Indeed, broccoli is one of the vegetables repeatedly implicated for its anti-cancer potential. Saponins, another phytochemical found in green plant foods, also have anti-cancer properties. They interfere with the process whereby cancer cells multiply (2).
In red fruit and vegetables, the phytochemicals lycopene, ellagic acid and a flavonoid called kaempferol are important. These phytochemicals act as antioxidants, can be cancer protective and can also help reduce the risk of heart disease. Lycopene is a powerful antioxidant belonging to the group of carotenoids. A high intake of lycopene in particular has been linked with a reduced risk of prostate cancer (3). Cooking tomatoes, as in tinned tomato products, increases the natural lycopene content. The colour in purple/blue fruits and vegetables is mainly due to the flavonoids anthocyanins, which are powerful antioxidants and have a mild anti-bacterial effect (2). Another phytochemical discovered in this group of fruits and vegetables includes resveratrol, which is most commonly found in grapes and may have a cancer protective effect (3).
For completion on a discussion of colour, the role of the white-brown foods, such as garlic, onions and cauliflower should also be considered. Phytochemicals including allicin, indoles and isothiocyanates are associated with this group. Many of these phytochemicals have effects ranging from antibacterial, antiviral and anti-cancer, to the prevention of heart disease (3). This is partly why many people believe in taking garlic to prevent a cold from taking hold!
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