Week 2 (unit 4)

Classification of Crops and Their Role in Human Nutrition

Classification of crops
Types of food crops and their contribution to human nutrition
World food needs
Assignments
References

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Classification of Crops

There are hundreds of different crops grown for food around the world. Most belong to the Plant Division Angiospermae (also known as Anthophyta) which is commonly known as "the flowering plants". Here's a link that briefly describes some of the important features that can be used to distinguish members of this group:

http://biology.clc.uc.edu/courses/bio106/angio.htm

One important distinction within the Angiosperms are the classes commonly called monocots and dicots. A summary of the characteristics of these two classes can be found here:

http://www.csdl.tamu.edu/FLORA/201Manhart/mono.vs.di/monosvsdi.html

The table below shows the 33 crops that were grown on four million hectares or more in 2002. Clearly, the cereal crops (family Poaceae) dominate world food production. Pulse crops (Fabaceae) are also grown on a large scale. The top ten crops are all annuals.

Scientific names in the table are linked to a Crop Information Directory called the Purdue University Center for New Crops and Plant Products. We cannot provide in depth coverage of all food crops in a class such as this, so you are encouraged to pursue these links to find out more about crops of interest. The FAOSTAT databases are also a very useful resource for production and utilization statistics pertaining to world food crops.

Important World Food Crops

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Types of Food Crops and Their Contribution to Human Nutrition

Information for this section was obtained largely from a book by M.C. Latham (1997) entitled "Human nutrition in the developing world." This is a very comprehensive reference on a number of topics related to world food production and nutrition. Here are a few that may be of interest to you:

• Recommended intakes of nutrients
  
• Nutrient composition of foods
  
• International nutrition and world food problems
  
• Social and cultural factors in nutrition
  
• Basic nutrition (functions of foods in the body)
  
• Nutritional disorders

Another excellent resource on nutrition is the Food and Nutrition Information Center of the USDA.

Dietary requirements

Food is required to supply energy and as a raw material for body growth, maintenance and protection. Our basic requirements include water, carbohydrates, fats, proteins, minerals, vitamins, and fiber. Carbohydrates, proteins, and fats are required in relatively large quantities, and hence are called macronutrients. Minerals and vitamins are required in small quantities and are called micronutrients.

Water consitutes over 60% of our body weight, and can be considered to be the most important dietary requirement. A normal man or woman can live without food for 20 to 40 days, but humans will only survive for four to seven days without water. Metabolism of the minerals sodium and potassium, which are known as electrolytes, is linked with body water.

Human energy requirements vary according to age, sex and activity level, and may be as low as 1,200 Calories or as high as 3,200 Calories per day (a Calorie in dietary terms is equivalent to 1000 kilocalories of energy). Carbohydrates and proteins provide 4 Calories per gram, whereas as one gram of fat provides 9 Calories.

Proteins are generally used as raw materials for tissue growth and maintenance and for synthesis of important metabolites, but when insufficient Calories are provided in other forms, proteins may be used as a source of energy. During digestion proteins are broken down into their component amino acids, which are then transported through the bloodstream to body tissues where they are used to construct new proteins. Of the 20 naturally occuring amino acids, nine are considered essential in the diet because they cannot be synthesized by the body. Amino acids cannot be stored in the body, and thus it is important to consume all of the essential amino acids each day. Complete proteins contain all of the essential amino acids in the right proportions. Most animal proteins are complete, whereas plant proteins are generally deficient in one or more of the essential amino acids. The quantities of protein required in the diet are not great, provided that all of the essential amino acids are consumed. It is generally recommended that about 10% of our total Calorie intake be obtained from protein.

We will talk in more detail about types of carbohydrates and fats in later lectures.

Fiber is another important dietary component obtained from plants. Fiber is not digestible but is desirable because it helps food to transit through the digestive tract. Some studies have shown that a diet high in fiber can reduce the risk of colon cancer, but this benefit is still under investigation. Some types of fiber may also lower cholesterol.

Vitamins play a critical role as coenzymes in many metabolic pathways, or may be directly involved in synthesis of essential compounds. There are four fat-soluble enzymes (A, D, E, and K) and nine water-soluble vitamins (eight B-complex vitamins and C). The water-soluble vitamins are not stored in the body, and any excess that is consumed is excreted in the urine. The fat-soluble vitamins can be stored in fatty tissues in the body, so consumption of these vitamins in excess may lead to toxicity symptoms. Refer to the references at the beginning of this section for more information about dietary requirements.

Minerals are inorganic compounds that exist in the body as charged ions or as components of complex molecules. There are 17 minerals that are known to be essential in the diet, and further research may add to this list. The major minerals are needed in quantities greater than 100 mg per day, whereas the trace minerals are needed in smaller quantities.

Types of food crops

Cereals - cereals are edible seeds from the grass family (Poaceae or Graminae). They include wheat, rice, corn, barley, oats, sorghum, and millet, among others. The grain is a caryopsis, which is a dry, one-seeded fruit, with a hard outer pericarp fused to the seed coat. The grains of different cereal crops may differ in size and shape, but they all have a similar structure and composition.

The endosperm is predominantly starch. The aleurone layer and embryo (germ) are rich in protein, vitamins and minerals, but are often removed during processing. 100 µg of whole grain provides about 350 kcal, 8 to 12 µg of protein and useful amounts of calcium, iron (though phytic acid may hinder absorption) and the B vitamins. They lack Vitamin C, and with the exception of yellow maize, also lack carotene (provitamin A). For a healthy diet, they should be consumed with other foods rich in vitamins A and C and minerals. The protein of some cereals is deficient in the essential amino acids lysine and tryptophan, and should be supplemented with other sources of protein such as legumes or animal products.

Pulses - Pulses are the edible seeds of members of the Fabaceae (Leguminosae) family, which includes beans, peas, soybeans, groundnuts (peanuts) and lentils, among other crops. They provide an important source of protein and B vitamins in the diet, as well as carbohydrate. Protein quality is not quite as good as in meat, because legumes generally lack adequate levels of the essential amino acid methionine. However, this limitation can be overcome by consuming pulses and cereals together. Legumes also play an important role in the farming system, because they can fix atmospheric nitrogen, which helps to maintain soil fertility.

Roots and Tubers - edible tubers, roots and corms are widely consumed throughout the world. In the tropics, cassava, sweet potatoes, taro (cocoyam), yams (Dioscorea spp.) and arrowroot are staple food crops. Potato is widely grown in temperate and subtropical climates. The yield potential of these crops is very high. However, they are generally low in protein, minerals and vitamins in comparison to cereal crops. There is some variation among species in this regard - taro and yams have up to 6% good quality protein, and potatoes provide some minerals and vitamin C. It is expected that roots and tubers will play an increasingly important role as food security crops in the next 20 years.

Oil seed crops - important oil seed crops include soybeans, rapeseed, sunflower seeds, groundnuts, oil palm, sesame, and cottonseed. Some oil crops are important locally, such as Shea butter in West Africa.

Vegetable crops - The foods called vegetables are a diverse group that include some fruits (e.g., tomatoes), roots (e.g., carrots), and flowers (e.g., broccoli). Nonetheless, "vegetable" is a useful term that refers to crops that are generally eaten fresh or preserved in the fresh state. Vegetables are a very important part of the diet. They are nearly all rich in carotene and vitamin C and contain significant amounts of calcium, iron and other minerals. They are not usually good sources of B vitamins, energy, and protein. They often contain high amounts of dietary fiber. When looking at world food production figures it is easy to underestimate the importance of vegetables in the diet, because many species are grown and consumed locally, and so do not make the list of 30-40 most widely grown crops. Dark green vegetables such as amaranth and cassava leaves typically eaten in tropical countries are far superior nutritionally to cabbage and lettuce. An increase in consumption of these crops could help to ameliorate the problem of Vitamin A deficiency that is widespread in developing countries.

Fruits - A wide variety of fruits grow wild or are cultivated throughout the world. Fruits are often good sources of vitamin C, and many contain useful quantities of carotene. Fruits usually contain very little fat or protein and little or no starch. The carbohydrate is present in the form of various sugars. Fruits are high in cellulose, which contributes to dietary fiber. The citrus fruits, such as oranges, lemons, grapefruits, tangerines and limes, contain good quantities of vitamin C but little carotene. Papayas and mangoes contain both carotene and vitamin C.

Nuts - Important crops in this category include coconut, cashew nut, almond, and walnut, among others. These crops tend to be high in fat, but may also contain beneficial vitamins, minerals, and protein.

Spices - Aside from our need for salt, few of these flavorings have much nutritional importance, but all serve to make the food more pleasing to the taste.

Beverage crops - This group includes a diversity of drinks from plant sources, including fruit juices, tea, coffee, beer, wine, and spirits. The main contribution of this group to human nutrition is to supply water, essential for human life. Some also provide vitamins and minerals. Others provide stimulants (caffeine) or alcohol for relaxation.

Contribution to human nutrition

Direct contribution of selected food crops
to per capita consumption of calories, protein and fat in 2000

Some observations from the data in the table:

• Cereal crops provide by far the most calories in the diet. Wheat is the leading crop for direct human consumption in developed countries, whereas rice is the leading crop in developing countries.
  
• Although the pulse crops have a higher protein content than cereal crops, cereals are the most important source of protein, because they are consumed in much greater quantities.
  
• Soybean is the most important oil crop in developed countries, followed by rapeseed and sunflower oil. In developing countries, soybean and palm oil are the leading oil crops.
  
• Potato is the predominant starchy root and tuber crop in developed countries. Cassava is the lead crop in this category in developing countries, but potatoes and sweet potatoes are also important.
  
• People in developing countries obtain more calories from cereal crops than in the developed world. Calories obtained from oil crops are relatively high in developed countries.

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World Food Needs

Here are a few important facts about malnutrition from the World Health Organization:

• Malnutrition affects one in every three people worldwide, and plays a major role in half of the annual child deaths in the developing world.
  
• Iron deficiency and anaemia are the most prevalent problems.
  
• Protein-Energy Malnutrition has the most lethal consequences, affecting every fourth child worldwide.
  • marasmus - individuals with this disorder are deficient in both proteins and calories and appear emaciated and wasted
  • kwashiorkor - individuals with this disorder are deprived of calories. The stomach and extremities are swollen
• Iodine deficiency disorders cause goiter and brain damage. Great strides have been made in combatting this disorder through the use of iodized salt, but the problem is still widespread.
  
• Vitamin A deficiency is the leading cause of preventable blindness. The problem can be addressed through promotion of breastfeeding, Vitamin A supplementation, and increased consumption of fruits and vegetables.

The Food and Agricultural Organization of the United Nations publishes an annual report that describes the current status of food insecurity and malnutrition in the world. Different topics are featured each year. Here is the most recent report:

FAO. 2005. The state of food insecurity in the world. http://www.fao.org/sof/sofi/index_en.htm

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Assignments

Written Assignment

Due April 18th

Explore the internet resources available on world food crops and their production and utilization.

1. Pick a crop that is not one we have covered so far. Use the Purdue Crop Index to find out its scientific name, whether it is an annual or perennial and what botanical family it belongs to.
2. Go to the FAOSTAT core production data and find out how many tons were harvested of the crop in the United States in 2004.
3. Using the same FAOSTAT database, pick a country and select two foods you think would be important to that country. Determine the tons produced for 2004.
4. Now check how the two foods you selected rank in importance to the country you selected in 2005 at the FAO site for Major Food and Ag Commodities and Producers

Submit your findings using the assignments function on Blackboard.

Quiz

Take the quiz on this Unit on the Blackboard.

References

Center for New Crops & Plant Products, Purdue University. 2003. Crop Index. http://www.hort.purdue.edu/newcrop/Indices/index_ab.html

FAO. 2005. The state of food insecurity in the world. http://www.fao.org/documents/show_cdr.asp?url_file=/docrep/008/a0200e/a0200e00.htm

FAOSTAT. FAO Statistical Databases. http://faostat.fao.org/

Latham, M.C. 1997. Human nutrition in the developing world. Food and Nutrition Series - No. 29, FAO. http://www.fao.org/docrep/W0073E/w0073e00.htm

Levetin, E. and K. McMahon. 2005. Human Nutrition. Chapter 10 in Plants and Society, 4th edition. McGraw-Hill, New York, NY. Additional on-line notes and references:
http://highered.mcgraw-hill.com/sites/0072528427/student_view0/chapter10/chapter_outline.html

USDA. 2004. Food and Nutrition Center.
http://www.nal.usda.gov/fnic/index.html

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