Lec 1 & 2 Principles of Food and Dairy Sciences - PDF

Principles of Food and Dairy Sciences course (T 105) Biotechnology Program Students Level (1) BY Prof. Dr. OSAMA IBRAHIM ABDEL-SALAM EL BATAWY Prof. Dr., Food Science Department, Faculty of Agriculture, Ain Shams University,  Introd...

Principles of Food and Dairy Sciences course (T 105) Biotechnology Program Students Level (1) BY Prof. Dr. OSAMA IBRAHIM ABDEL-SALAM EL BATAWY Prof. Dr., Food Science Department, Faculty of Agriculture, Ain Shams University,  Introduction Dairy products are generally defined as food products that are produced from milk. They are rich sources of energy. Raw milk for processing generally comes from cows, but some time from other mammals such as goats, sheep, and buffalo. Water is the main constituent of milk (about 85-87%). Early-lactation milk contains colostrum  Milk Composition Carbohydrate (Lactose) Fat Protein Vitamins Minerals Enzymes In general, the gross composition of cow's milk is 87.7% water, 4.9% lactose (carbohydrate), 3.4% fat, 3.3% protein, and 0.7% minerals (referred to as ash).  Milk Carbohydrate (Lactose) ✓ Carbohydrates are made up of molecules called saccharides. ✓ Simple saccharides contain 1 or 2 molecules and are called monosaccharides or disaccharides, or, more commonly, sugars. ✓ Oligosaccharides and polysaccharides are chains that contain a few to many sugar molecules and may be referred to as starches. ✓ The monosaccharides important in food and health are glucose, fructose, and galactose.  The disaccharides such as (VI) sucrose (glucose + fructose), lactose (glucose + galactose), and maltose (glucose + glucose). The 2 sugar molecules in disaccharides are bonded together and this bond must be broken before the sugars can be used by the body for energy and other body functions. Starches are long chains of glucose that can be straight or have branches, o Milk contains approximately 4.9% carbohydrate that is predominately lactose with trace amounts of monosaccharides and oligosaccharides. (VI) o Lactose is a disaccharide of glucose and galactose. The structure of lactose is: (NI)  Effect of Heat Treatments on Lactose Properties The normal pasteurization conditions used for fluid milk have no significant effect on lactose. The higher temperatures used for ultra high temperature (UHT) pasteurization of extended shelf life products and spray drying can cause browning and isomerization reactions, which may affect product quality and nutritional properties. ❑The browning reaction, called the Maillard reaction, occurs between the lactose and protein in milk and produces undesirable flavors and color, and decreases the available content of the amino acid lysine in milk protein. (VI)  Milk Fat ❖Fats are made from individual fatty acid molecules attached to glycerol, a 3-carbon backbone. (VI) ❖The most common type of fat is called a triglyceride, ❑ Fat compounds can also be diglycerides that have 2 fatty acids or monoglycerides that have 1 fatty acid on the glycerol backbone. ❑ Mono- and diglycerides are used as emulsifiers, compounds that keep the fat and water from separating in foods such as ice cream. (VI)  Individual fatty acids can range in length from 4 to 22 carbons. (NI) Fatty acids may be saturated, which means that each carbon has a single bond to another carbon and 2 hydrogen atoms, or fatty acids may be unsaturated, which means that a carbon has two bonds to the adjacent carbon, called a double bond, and a single bond to another carbon and a hydrogen atom. ❖ Cow milk contains approximately 3.4% total fat. (VI) ❖ Over 400 individual fatty acids have been identified in milk fat. However, approximately 15 to 20 fatty acids make up 90% of the milk fat. (I) ❖ The major fatty acids in milk fat are straight chain fatty acids that are saturated and have 4 to 18 carbons (4:0, 6:0, 8:0, 10:0, 12:0, 14:0, 16:0, 18:0), monounsaturated fatty acids (16:1, 18:1), and polyunsaturated fatty acids (18:2, 18:3). (NI) ▪ The fatty acid composition of milk fat is not constant throughout the cow's lactation cycle. ▪ There are systematic changes in milk fat composition that are due to the stage of lactation and the energy needs of the animal. ▪ In early lactation, the animal's energy comes largely from body stores and there are limited fatty acids available for fat synthesis, so the fatty acids used for milk fat production are obtained from the diet and tend to be the longer chain 16:0, 18:0, 16:1 and 18:2 fatty acids. (NI) ▪ Later in lactation more of the fatty acids in milk are formed in the mammary gland so that the concentration of the short chain fatty acids such as 4:0 and 6:0 are higher than they are in early lactation. ▪ These changes in fatty acid composition do not have a great impact on milk's nutritional properties, but may have some effect on processing characteristics for products such as butter. (NI) ✓ Milk fat contains approximately 65% saturated, 30% monounsaturated, and 5% polyunsaturated fatty acids. (VI) ✓ Saturated fatty acids are associated with high blood cholesterol and heart disease. ✓ Conjugated linoleic acid is a trans fatty acid in milkfat that is beneficial to humans in many ways.  Deterioration of Milk Fat ❖ Enzymes that degrade fat are called lipases, and the process is called lipolysis. (VI) ❖ Milk lipases come from several sources: the native milk, airborne bacterial contamination ✓ Lipases remove fatty acids from the glycerol backbone of the triglyceride. (NI) ✓ Usually the action of lipase causes undesirable rancid flavors in milk. (I) ✓ Pasteurization inactivates lipases and increases the shelf life of milk. (I) Influence of Heat Treatments on Milk Fat ❖ Typical high temperature short time (HTST) pasteurization conditions do not affect the functional and nutritional properties of milk fat. (I) ❖Higher heat treatments may stimulate oxidation reactions and cause fat deterioration and off- flavors. (I)  Milk Protein Proteins are chains of amino acid molecules connected by peptide bonds. (VI)  There are many types of proteins and each has its own amino acid. There are 22 different amino acids that can be combined to form protein chains. (VI) There are 9 amino acids that the human body cannot make and must be obtained from the diet. These are called the essential amino acids. (VI)  Milk contains 3.3% total protein. (VI) Milk proteins contain all 9 essential amino acids required by humans. (I) There are 2 major categories of milk protein (VVI) 1- The casein family contains phosphorus and will coagulate or precipitate at pH 4.6. 2- The serum (whey) proteins do not contain phosphorus, and these proteins remain in solution in milk at pH 4.6.3  In cow's milk, approximately 82% of milk protein is casein and the remaining 18% is serum, or whey protein. (VI) The serum (whey) protein family consists of approximately 50% ß-lactoglobulin, 20% α-lactalbumin, blood serum albumin, immunoglobulins, lactoferrin, transferrin, and many minor proteins and enzymes (I)  Deterioration of Milk Protein Proteins can be degraded by enzyme action. Enzymes called proteases. (VI) Milk proteases come from several sources: the native milk, airborne bacterial contamination, bacteria that are added intentionally for fermentation, or somatic cells present in milk. (NI) Undesirable degradation (proteolysis) results in milk with off-flavors and poor quality (I)  Influence of Heat Treatment on Milk Proteins Caseins are stable to heat treatment. Typical high temperature short time (HTST) pasteurization conditions will not affect the functional and nutritional properties of the casein proteins. High temperature treatments can cause interactions between casein and whey proteins that affect the functional but not the nutritional properties. The whey proteins are more sensitive to heat than the caseins. HTST pasteurization will not affect the nutritional and functional properties of the whey proteins.  Vitamins & Minerals in Milk Vitamins in Milk o Vitamins have many roles in the body, including metabolism co-factors, oxygen transport and antioxidants. o They help the body use carbohydrates, protein, and fat. (I) ❑ Milk contains the water soluble vitamins (VI) ❑ thiamin (vitamin B1), ❑ riboflavin (vitamin B2), ❑ niacin (vitamin B3), ❑ pantothenic acid (vitamin B5), ❑ vitamin B6 (pyridoxine), ❑ vitamin B12 (cobalamin), ❑ vitamin C, ❑ and folate. ✓ Milk is a good source of (VVI) ✓ thiamin B1, ✓ riboflavin B2 and ✓ vitamin B12. Milk contains small amounts of niacin, pantothenic acid, vitamin B6, vitamin C, (VI) folate and is not considered a major source of these vitamins in the diet. ▪ Milk contains the fat soluble vitamins A, D, E, and K. (VVI) ▪ The content level of fat soluble vitamins in dairy products depends on the fat content of the product. Reduced fat (2% fat), low-fat (1% fat), and skim milk must be fortified with vitamin A to be nutritionally equivalent to whole milk. ▪ Fortification of all milk with vitamin D is voluntary. (NI) ▪ Milk contains small amounts of vitamins E and K and is not considered a major source of these vitamins in the diet. (VI)  Minerals in Milk Minerals have many roles in the body including enzyme functions, bone formation, water balance maintenance, and oxygen transport. ✓ Milk is a good source of calcium, magnesium, phosphorus, potassium, selenium, and zinc. (VI) ✓ Many minerals in milk are associated together in the form of salts, such as calcium phosphate. ✓ The fact that calcium and phosphate are associated as salts bound with the protein does not affect the nutritional availability of either calcium or phosphate. (NI) ✓ Milk contains small amounts of copper, iron, manganese, and sodium and is not considered a major source of these minerals in the diet. (VI) Effects of Heat Treatments on the Vitamin & Mineral Content in Milk ✓ The heat treatment used in pasteurization of fluid milk does not affect the vitamin content. (I) ✓ However, the higher heat treatment used for extended shelf combined with the increased storage life of these products does cause losses of some water-soluble vitamins. (I) ✓Riboflavin B2 is a heat stable vitamin and is not affected by severe heat treatments.  Milk Enzymes Each enzyme has a specific site of action on its target molecule, and optimal conditions (pH and temperature). There are a large number of enzymes in milk and the functions of many are not well-defined. It should be noted that the enzymes in milk do not make a major contribution to the digestion of milk in humans, which is accomplished by enzymes in the human stomach and small intestine. (NI)  Lipases are enzymes that degrade fats. Resulting in fat degradation and off-flavors. Pasteurization will inactivate the lipase in milk and increase shelf life. ❖ Proteases are enzymes that degrade proteins. (VI) ❖ Protein degradation can be undesirable and result in bitter off-flavors,  Alkaline phosphatase is a heat sensitive enzyme in milk that is used as indicator of pasteurization. (VVI) If milk is properly pasteurized, alkaline phosphatase is inactivated. ✓ Lactoperoxidase is one of the most heat-stable enzymes found in milk. (VVI) ✓ Lactoperoxidase, when combined with hydrogen peroxide and thiocyanate, has antibacterial properties. (I) ✓ It is suggested that the presence of lactoperoxidase in raw milk inhibits the disease causing microorganisms (pathogens) present in milk. (VI)