CHAPTER ONE
1.1 INTRODUCTION
Plants undergo photosynthesis and they constitute a primary resource of carbon, vitamins, minerals, protein, essential fatty acids, and utilizable energy for food production (Young and Pelett, 1994). Plants have played a significant role in maintaining the health and improving the quality of human life for thousands of years. (Mishra, 2010). They provide a major source of food and nourishment for man and animal.
Nutrition is a science of food and its relationship to health. Nutrition refers to nourishment that sustains life. The study of nutrient requirements and the diet providing these requirements is also known as ‘nutrition’ (Chutani, 2008). Pike and Brown, 1984 defined it as “the science that interprets the relationship of food to the functioning of living organism. It includes the uptake of food, liberation of energy, elimination of wastes and all the processes of synthesis essential for maintenance, growth and reproduction (Chutani, 2008). Apart from maintaining normal body functioning, nutrition is important in fighting infections and in the recuperation of an ill person. Nutrition interacts with infections in a synergistic manner, such that recurrent infections lead to a loss of body nitrogen and worsen nutritional status; theresulting malnutrition, in its turn, produces a greater susceptibility to infection (Kurpad, 2005). Aristotle (384-322 B.C.) was the first to suggest that the composition of foods in the normal diet might contribute to health.
In an 1897 literature on metabolic investigations, Atwater divided food composition into five classes; protein, fat carbohydrate, energy and water. However, today, proximate composition is the term usually used to describe six components of food namely; moisture, crude protein, crude ash,crude fibre, crude fat and carbohydrate (nitrogen free extract) which are all expressed in percentage (%) or gram per 100 grams (g/100g). The study of proximate analysis on foods was devised over a hundred years ago by two German scientists, Henneberg and Stohmann, and even though new techniques have been introduced, their system of proximate still forms the basis for the statutory declaration of the composition of foods. (Dublecz, 2011).
1.2 MOISTURE CONTENT
Water is essential for every living organism. In the human body, water content ranges from 50- 70% in different tissues. It is present in different fluid compartments of the human body- Intracellular (fluid inside the cells) and extra cellular. Plasma, interstitial fluid, cerebrospinal fluid, ocular fluid, lymph, peritoneal, pericardial, pleural and synovial fluids are part of the extra cellular fluid (Chutani, 2008). However, the moisture content of a feed is seldom of interest nutritionally as water is usually taken on its own.
The active ingredients from the view of feed nutrition are present in the part of dry matter (solid matter); therefore the level of moisture content is an important factor in both economy and storage (Famic). At high temperature and humidity the risk of putrefaction is predicted due to the proliferation of molds, etc., or self-digestion by enzymes in the feed when moisture in the feed is not less than about 15 %. As the assay for moisture in the feed measures loss on drying by heating at normal pressure as moisture, the result includes most of volatile substances other than H2O. Therefore, it may be more appropriate to be referred to as volatile matter rather than moisture for accuracy. Organic acids such as acetic acid and butyric acid in silage as well as ammonia and flavor components in feed materials are also vaporized and thus measured as moisture. Because the content of these in most feed is extremely low, there has hardly been a need to consider their influence on the measured value. (Famic)
1.3 CARBOHYDRATES
Photosynthesis is a process used by plants and other organisms to convert light energy from the sun, into chemical energy that can be later released to fuel the organisms' activities. The light energy harnessed from the sun drives the reduction of carbon from CO2 to produce O2 and fixed carbon in form of carbohydrate.
Early in the twentieth century, it was mistakenly thought that light absorbed by photosynthetic pigments directly reduced CO2 which then combined with water to form carbohydrate. In fact, photosynthesis in plants is a two stage process in which light energy is harnessed to oxidise H2O:
2H2O → O2 + 4 [H+][SO1]
The electrons thereby obtained subsequently reduce CO2:
4 [H2O] + CO2 → (CH2O) + H2O[SO2]
The two stages of photosynthesis are traditionally referred to as the light reactions and the dark reactions:
- In the light reactions, specialised pigment molecules capture light energy and are thereby oxidized. A series of electron- transfer reactions which culminate with the reduction of NADP+ to NADPH, generate ATP from ADP + Pi. The oxidised pigment molecules are reduced to H2O, thereby generating O2.
- The dark reactions use NADPH and ATP to reduce CO2 and incorporate it into the three-carbon precursors of carbohydrate.
The light reactions takes place in the thylakoid membrane of chloroplasts in leafs and green parts of plants. The inside of the thylakoid is referred to as the lumen. The light reactions are catalysed by enzymes located in the thylakoid membrane, whereas the dark reactions take place in the stroma. The principal photoreceptor of light is chlorophyll. These chlorophyll molecules do not participate directly in photochemical reactions but function to act as light harvesting antennas. The absorbed photons are transferred from molecule to molecule until it reaches the photosynthetic reaction centre.
In the respiratory chain, electrons flow from NADH+H+ to O2, with the production of water and energy. However in photosynthesis, electrons are taken up from water and transferred to NADP+, with an expenditure of energy. Photosynthetic electron transport is therefore energetically “uphill work.” To make this possible, the transport is stimulated at two points by the absorption of light energy. This occurs through two photo systems protein complexes that contain large numbers of chlorophyll molecules and other pigments Another component of the transport chain is the cytochrome bf complex, an aggregate of integral membrane proteins that includes two cytochromes (b563 and f). Plastoquinone, which is comparable to ubiquinone, and two soluble proteins, the copper containing plastocyanin and ferredoxin, function as mobile electron carriers. At the end of the chain, there is an enzyme that transfers the electrons to NADP+. Because photosystem II and the cytochrome b/f complex release protons from reduced plastoquinone into the lumen, photosynthetic electron transport establishes an electrochemical gradient across the thylakoid membrane, which is used for ATP synthesis by an ATP synthase.
ATP and NADPH+H+, which are both needed for the dark reactions, are formed in the stroma. (Voet et. al., 2013).
1.3aCalvin cycle
The actual CO2 fixation i.e., the incorporation of CO2 into an organic compound is catalysed by ribulosebisphosphate carboxylase/oxygenase (“rubisco”). Rubisco, the most abundant enzyme on Earth, converts ribulose 1,5-bis-phosphate, CO2 and water into two molecules of 3-phosphoglycerate. These are then converted, via 1,3-bisphosphoglycerate and 3-phosphoglycerate, into glyceraldehyde 3-phosphate. In this way, 1,2-glyceraldehyde 3-phosphates are synthesized from six CO2. Two molecules of this intermediate are used by gluconeogenesis reactions to synthesize glucose 6-phosphate. From the remaining 10 molecules, six molecules of ribulose-1,5-bisphosphate are regenerated, and the cycle then starts over again. In the Calvin cycle, ATP is required for phosphorylation of 3-phosphoglycerate and ribulose-5-phosphate. NADPH+H+, the second product of the light reaction, is consumed in the reduction of 1,3-bisphosphoglycerate to glyceraldehyde-3- phosphate.
Carbohydrates are the most abundant biomolecules produced on earth; photosynthetic plants and algae convert over 100 billion metric tons of Co2 and water into sugars, starches, and cellulose like substance. Carbohydrates supply energy for the human body to function. They are the most abundant bulk nutrients and form the major source of biological energy through their oxidation in the tissues. They also furnish organic precursors for the biosynthesis of many cell components. Carbohydrates are not essential in the human diet, but because carbohydrate rich foods are abundant and cheap, compared with fats and protein, they naturally form a major part of the diet in most of the world. (Voet et. al., 2013).
