12_Nutritive value of proteins_DrGirija_FoodChemistry.pptx

Nutritive value of fish proteins Description

1. Nutritive value of proteins

2. I n t r od u ction The diet contains a variety of different animal and plant proteins. The nutritional quality or biological value of a given protein depends upon two factors: (i) its content of essential amino acids and (ii) its digestibility. On the basis of their nutritional quality the proteins has been classified into (1) complete protein (2) partially complete and (3) incomplete protein.

3. 1. Complete proteins: Complete proteins maintain life and provide for normal growth of the young when used as the only protein in the diet of experimental animals. Proteins of meat, poultry, fish, eggs and milk are complete proteins and are of high biological value because they contain all essential amino acids. Some proteins in legumes, cereals and nuts are also complete proteins e.g. glycinin of soybean, glutenin of wheat and glutelin of corn.

4. p r o t eins ma i n t a i n li f e but f a i l to 2 . P artia l ly c ompl e t e : P art i a l ly c o mpl e t e support normal growth. e.g. gliadin of wheat, hordein of barley. 3. Incomplete proteins : Incomplete proteins neither maintain life nor support growth. Most vegetable proteins are incomplete and are of low biological value (e.g. rice, wheat, corn, beans).

5. Amino Acids and Protein Structure Amino acids are the building blocks of proteins. There are 20 different amino acids that are commonly found in proteins. The sequence of amino acids in a protein determines its three-dimensional structure, which in turn determines its function. 1 Primary Structure The sequence of amino acids in a protein chain. 2 Secondary Structure The local folding of the polypeptide chain, including alpha-helices and beta-sheets. 3 Tertiary Structure The overall three-dimensional shape of a single polypeptide chain, formed through interactions between amino acid side chains. 4 Quaternary Structure The arrangement of multiple polypeptide chains into a functional protein complex.

6. Essential amino acids Essential amino acids: The 10 essential amino acids are methionine, tryptophan, threonine, valine, isoleucine, leucine, phenylalanine, lysine, arginine and histidine and are essential for growth in children. The remaining amino acids are called non-essential or dispensable as they can be synthesized in animals from other compounds. They are glycine, cysteine, alanine, serine, proline, tyrosine, aspartic acid, asparagine, glutamic acid and glutamine . Cereals contain lower value of lysine while pulses contain lower value of methionine. Combining plant proteins from different sources ensures a more complete complement of essential amino acids.

7. Digestibility Digestibility is defined as the proportion of food nitrogen that is absorbed after ingestion. The nutritive value of proteins depends upon its digestibility. Animal proteins are the most available for digestion and absorption and the proteins of legumes are the least available because of their incomplete digestibility. Digestibility depends upon the fibre content present in the food item and also in the remainder portion of diet.

8. Plant proteins, particularly those of wheat and ot h er g r a i ns , a r e no t c o mpl e t ely h y d r ol y z ed durin g d i g e s t ion be c ause t h e p r o t ei n - r ich portions of t h e g r a i n s a r e s u r r o unde d by p r o t e c ti v e hus k s o f c e ll u l os e a n d ot h er polysaccharides that are not hydrolyzed by intestinal enzymes. Since only free amino acids can be absorbed from the intestine, not all the amino acids of most plant foods are biologically available.

9. Nutritive Value of Proteins Proteins are essential nutrients for building and repairing tissues, producing enzymes and hormones, and transporting substances throughout the body. They also contribute to a feeling of fullness after meals. Essential Amino Acids These amino acids cannot be produced by the body and must be obtained from food. Non-Essential Amino Acids The body can synthesize these amino acids from other sources. Complete Proteins Proteins that contain all nine essential amino acids. Incomplete Proteins Proteins that lack one or more essential amino acids.

10. Protein Digestion and Absorption Protein digestion begins in the stomach with the enzyme pepsin. Further digestion occurs in the small intestine with the help of pancreatic enzymes. The resulting amino acids are absorbed into the bloodstream and transported to various tissues for use. 1 Mouth Mechanical breakdown of food. 2 Stomach Pepsin breaks down proteins into smaller peptides. 3 Small Intestine Pancreatic enzymes further digest proteins into amino acids. 4 Absorption Amino acids are absorbed into the bloodstream.

11. Food sources for the supply of proteins and amino acids Proteins are widely distributed in nature but only a few foods provide sufficiently higher quantity of proteins. Eggs, fish, meats, nuts and poultry have protein ranging from 12-29%. Cereal contributes 1-2% of proteins. Fruits and vegetables are low sources of protein foods. Syrups, oils and fat contain no protein. Animal foods have high protein values and also have good quality. Soya bean and some nuts contain protein of high quality.

12. The supplementary value of protein Foods differ in the nutritive value of the protein they contain. Each food, with the exception of gelatin, contains more than one kind of protein, each with a characteristic number and concentration of amino acids. The proteins of some foods contain limited amount of certain essential amino acids, generous amounts of others. Therefore a combination of foods in which the amino acid contained in the proteins supplement each other is of higher nutritive quality than either alone. There are possibilities of combining foods so that amino acids may supplement each other. For e.g. Lysine is a critical or limiting amino acid of cereals . Similarly methionine is limited in pulses and is the critical or limiting amino acid of their protein. They need to be supplemented by animal proteins.

13. Deficiency of Protein Protein- energy malnutrition results from inadequate intake of protein and/or calories. Two forms of child malnutrition, often occurring together, are Marasmus and Kwashiorkor. a. Marasmus: Marasmus (from Greek, “to waste”) is the term applied to chronic deficiency of calories in children. Marasmus is caused by a diet deficient in both protein and calories. (Total calorie deprivation). Marasmus is characterized by arrested growth, extreme muscle wasting, weakness and anemia. It is usually complicated by multiple deficiencies of vitamins and minerals. Calorie deficiency in early childhood, even if ultimately alleviated with an ample diet, leaves a permanent deficit in body growth.

14. b. Kwashiorkor: Chronic protein deficiency in children is called “Kwashiorkor”, an African word that means ‘weaning disease”. Kwashiorkor is caused by a diet inadequate in protein in the presence of an adequate calorie intake consisting primarily of carbohydrates. Since the protein content of plant foods is generally low and proteins are also low in quality, a serious shortage of “good” protein often occurs in areas where population growth is especially great.

15. Methods for the determination of nutritional quality of proteins T h e n u tr i ti o n al q u al i ty of p r o t e i n s c an be determines in the following methods 1 . P r o t ei n E ff iciency R a t io [ P E R ] : I t i s measu r e of weight gain/unit protein fed PER = weight gain (g)/Protein fed on dry on dry wt. basis(g)

16. Biological value It has been defined as the "percentage of absorbed nitrogen retained in the body" and a complete evaluation of the dietary protein includes measurement of the Biological Value and the Digestibility.  where I = Nitrogen intake of test protein F = Faecal nitrogen F o = Faecal nitrogen on nitrogen-free diet (Metabolic N) U = Urinary nitrogen U o = Urinary nitrogen on nitrogen-free diet (Endogenous N)

17. Protein Quality Evaluation The quality of a protein source is determined by its ability to provide essential amino acids in proportions that meet the body's needs. Biological Value (BV) Measures the amount of nitrogen retained by the body after consuming a protein source. Protein Digestibility Corrected Amino Acid Score (PDCAAS) Considers both the amino acid composition and the digestibility of a protein source. Net Protein Utilization (NPU) Measures the amount of protein retained by the body from a given protein source, taking into account both digestibility and utilization.

18. Biological Value of Proteins Biological Value (BV) is a measure of how efficiently a protein source can be used by the body to build and repair tissues. High BV Proteins Proteins with a BV of 70 or higher, such as eggs, milk, and soy. Medium BV Proteins Proteins with a BV of 50-70, such as beef, chicken, and beans. Low BV Proteins Proteins with a BV of less than 50, such as grains and vegetables.

19. Net Protein Utilization (NPU) or BV x Digestibility It is measure of the protein gain during an experimental period/ unit protein absorbed by the fish NPU = (Final body protein – Initial body protein/Total protein fed x 100

20. Chemical Score (CS) The quality of protein in a protein source is decided by the quantity of essential amino acid content present. The essential amino acid content of source is compared with that of a standard protein The usual standard protein used by the Nutritionists in hen’s egg white. Chemical score = Limiting amino acid in test protein (g)/Limiting amino acid in whole egg protein (g) x 100

21. Digestibility Coefficient Nutrients present in the food are not completely available to the human body. Large portions of the nutrients are excreted in the faeces because of being not digested in the alimentary tract. Hence, the digestibility of the food is defined as the portion of a food or nutrient which is not recovered in faeces, the portion which has been absorbed by the animal.

22. Pepsin digestibility Pepsin digestibility assesses the in vitro digestibility of the protein in fluids containing the proteolytic enzyme pepsin and the release of amino acids are measured. In one method, test proteins are first digested with pepsin and then with pancreatin. In another method proteins are digested c h y mo t ryps i n a n d p o r c i n e i n t e s t i n al p e pt i d ase with three enzymes namely pancreatic trypsin, under standard assay conditions.

23. Factors Affecting Nutritive Value of Fish Proteins Several factors can influence the nutritive value of fish proteins, including species, diet, and processing methods. 1 Species Different fish species have varying amino acid profiles and nutrient content. 2 Diet The diet of fish can affect the amount of omega-3 fatty acids and other nutrients in their flesh. 3 Processing Methods Methods like freezing, canning, and drying can affect the nutritional content of fish proteins.

24. Conclusion: Importance of Protein and Fish Proteins Protein is an essential nutrient for human health, and fish proteins are a high-quality source of essential amino acids and other nutrients. Including fish in your diet can contribute to overall well-being and reduce the risk of chronic diseases.