FROM SOIL ELEMENTS TO

FOOD NUTRIENTS:

Joyce Kinabo

Dept. of Food Science and Technology, Sokoine

University, Tanzania

All forms of life are directly dependent on

plants for food

Plant foods contain almost all of the inorganic

and organic nutrients (minerals, carbohydrate,

protein, fat and vitamins)

Organic phytochemicals that have been linked

to the promotion of good health

The human body requires

about 42 different essential

nutrients

Plants extract elements from

the soil to make the food

nutrients contained in grains,

tubers, roots,

vegetables, and fruits

Therefore, soil is the primary

source of all nutrients for

plants, humans and animals

• Nutrients contained in foods depend on the quantity and chemical forms of the elements present in the soil

• The extent to which plants are able to extract nutrients from the top soil

• Health of top soil is critical for people’s nutrition and health

• Good quality food depends on soil health and agricultural practices.

WHAT DETERMINES SOIL HEALTH?

Soil characteristics:

Texture: proportion of sand, silt and clay

Sandy: low cation exchange capacity (CEC)

Low nutrient holding capacity

High leaching

Low nutrient availability

Clay: High CEC

High nutrient holding capacity

Low nutrient leaching

WHAT DETERMINES SOIL HEALTH?...

Structure: arrangement of soil particles into

aggregates

Large particles:

Large spaces between particles, high water and nutrient

movement resulting into leaching

Very small particles:

Lead to soil compaction, hence enhanced water runoff

Medium size particles:

Allows good space between particles for water, nutrient

and roots movement; less leaching occurs

WHAT DETERMINES SOIL HEALTH?....

Acidity (pH): soil acidity or alkalinity for nutrient adsorption or desorption, precipitation,

mineralization, or immobilization

For example: when the soil is alkaline (pH > 7) solubility of iron and zinc decreases hence become unavailable to the plant

Many nutrients are more available in slightly acid soils (pH 6 – 6.5)

Moisture

Temperature

WHAT DETERMINES SOIL HEALTH?....

Low nutrient contents in plants are due to

inherently low content of such nutrients in soils

and/or low availability due to low solubility

caused by inherent physico-chemical properties

of soils as well as moisture levels

PLANT GROWTH AND DEVELOPMENT

Plants require 16 essential elements as well as

light, heat and water for:

growth and development

synthesis of nutrients

Each plant has an optimum range of

requirements (minimum and maximum)

Each essential element has a specific role to

play

FUNCTIONS OF ELEMENTS IN PLANTS Element Function Effect of Deficiency

Nitrogen Low protein content

Reduction in yield

Phosphorus Stunted growth & Delayed

maturity

Poor seed/grain & fruit

development

Potassium Reduces size & quantity of

fruits and seeds

Iron Chlorosis & reduced dry

matter production and yield

Calcium Poor cell membrane

formation

Zinc Reduced fruit formation in

citrus

Reduced pod filling

(legumes)

LOCATION OF NUTRIENTS IN PLANT FOODS

Roots extract elements from the soil to supply

to the leaves and later used to make the

nutrients, which are then located in various

parts of plants.

However, location of nutrients in the plant and

eventually in the grain, fruit or tuber is not the

same

LOCATION OF NUTRIENTS IN PLANT FOODS...

• A study by Wada & Lott, (1997) on nutrient storage in embryo and aleurone layer of rice showed that: – P, Mg, and K were located in all globoids

– Ca, Mn, Fe, and Zn were present in specific tissues and regions

• Calcium was mainly detected in globoids/granules of the aleurone layer.

• Iron was mostly found in globoids of radicle tissue.

• Zinc was commonly found in globoids of the scutellar epithelium and in provascular tissues of the mesocotyl, coleoptiles, and radicle.

• Manganese was distributed throughout most of the tissues, but was highest in globoids from the coleoptiles tip regions and the plumule.

STRUCTURE OF A RICE GRAIN

• Pericarp - protein, cellulose and hemicellulose

• Tegmen - fatty material

• Aleurone - protein and partially oil, cellulose and hemicellulose

• Endosperm - complex carbohydrates and some proteins

• Embryo - protein and fat

LOCATION OF NUTRIENTS IN PLANT FOODS....

Horvatić, Gačić, & Vedrina-Dragojević (2001)

showed that accumulation of iron, copper,

manganese and nickel in aleurone layer of

maize grain was positively and significantly

correlated with deposition of total dry matter,

total ash and crude proteins.

LOCATION OF NUTRIENTS IN PLANT FOODS

• Micronutrients and

phytochemicals are

located in the bran and

germ

• Starch is located in the

endosperm

Maize grain

ELEMENTS UPTAKE BY AMARANTHS

0

1

2

3

4

5

Mazimbu LITI Fungafunga

0.16 0.24 0.37

3

3.9

4.6

Pe

rce

nta

ge

Nitrogen content

Soil Amaranth

0

0.5

1

1.5

2

2.5

3

3.5

Mazimbu LITI Fungafunga

1.33

2.71

3.17

1 0.9

1.3

mg

/1

00

g

Calcium

Soil Amaranth

0

0.5

1

1.5

2

Mazimbu LITI Fungafunga

0.27

1.02

1.55

0.04 0.2 0.25

mg

/1

00

g

Zinc

Soil Amaranth

CALCIUM, ZINC AND IRON UPTAKE

0

2000

4000

6000

8000

10000

12000

14000

16000

Calcium Zinc Iron

g/k

g

Amaranth Chinese Cabbage Sweet potato Leaves

FOOD PROCESSING

• Food processing and preparation contribute to quality of foods (nutrient content)

• Peeling: most phytochemicals are located in the skin or outer layer of fruits and vegetables (non-leafy); removal of skin or outer layer reduces the amount of phytochemicals

• Milling: the aleurone layer and embryo contain most of the minerals, vitamins and proteins in cereals • Refining of maize and rice reduces micronutrients and phytochemicals levels

• If maize or rice is grown in poor soils, it means less nutrients in the final product after processing

Drying: Removal of water from foods reduces the amount of water soluble vitamins. The

extent of loss depends on the amount originally present in the food item.

How often do food industries analyse the nutrient content of foods before processing?!!!!

Does food processing really add value or reduce value??!!!

CONCLUSION

If the soil has adequate amounts of elements, and good agricultural practices are followed then there will be no need of fortification or supplementation. Plants are the best manufacturers of nutrients

However, it is important that food processing is done in such a way to protect the nutrients and not to remove them, not after the plants have laboured so much to put them in foods in the first place.

There is a need to reconceptualise food

processing so as to ensure that nutrients

originally present in foods are not removed but

conserved.

Agriculturalists, food scientists and nutritionists

should work together to ensure

wholesomeness of foods we consume.

CONCLUSION.....

WORK IN PROGRESS

From Soil Elements to Food Nutrients: Improving The Nutrient Content of Foods for Human Consumption Through Agriculture

link between soil elements, agriculture practices, nutrient content and nutrition

Maize

Rice

Round potato

Common beans

Amaranth

Sweet potatoes leaves

Package of recommendations for optimal soil elements uptake by crops and improved yield;

Data base of soil elements and nutrient composition of foods;

Information package of soil suitability for high nutrient crop production;

Package of information on conditions and practices for optimal soil elements uptake by plants;

Best practices of agricultural crop production for optimal nutrient content

WORK IN PROGRESS

3/3/2014

24