FROM SOIL ELEMENTS TO FOOD NUTRIENTS: Joyce Kinabo Dept. of Food Science and Technology, Sokoine University, Tanzania

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 Potassium Stunted growth & Delayed maturity Poor seed/grain & fruit development Reduces size & quantity of fruits and seeds Iron Calcium Zinc Chlorosis & reduced dry matter production and yield Poor cell membrane formation Reduced fruit formation in citrus Reduced pod filling

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

mg/100g Percentage mg/100g ELEMENTS UPTAKE BY AMARANTHS Nitrogen content Calcium 5 4.6 4 3.9 3 3 2 1 0.16 0.24 0.37 0 Mazimbu LITI Fungafunga Soil Amaranth Zinc 3.5 3 2.5 2 1.5 1 0.5 0 3.17 2.71 1.33 1.3 1 0.9 Mazimbu LITI Fungafunga Soil Amaranth 2 1.5 1 1.02 1.55 0.5 0 0.27 0.2 0.25 0.04 Mazimbu LITI Fungafunga Soil Amaranth

g/kg CALCIUM, ZINC AND IRON UPTAKE 16000 14000 12000 10000 8000 6000 4000 2000 0 Calcium Zinc Iron 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 Drying: after processing 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.

CONCLUSION... 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.

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

WORK IN PROGRESS 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

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