Milk Dr.Fatimah Yousef

Composition of milk Milk is a unique beverage that provides complete protein and many of vitamins & minerals. The basic composition of milk regardless of the source remains the same: Water 87.3% . Carbohydrate 4.8% . Protein 3.4%. Fat 3.7%. Vitamins (vitamin A,D, many of B-vitamins) Minerals 0.8%(especially calcium).

Composition of milk Water : The high concentration of water gives milk a near-neutral pH of 6.6. Carbohydrate: Lactose or milk sugar is primary carbohydrate found in milk. When bacteria in milk metabolize lactose, lactic acid is produced. Milk bacteria Milk products Lactose Lactic acid

Composition of Milk Protein: The protein in milk is a complete protein. Casein: The primary protein (80%) found in milk; it can be precipitated (solidified out of solution) with acid or certain enzymes. Whey: The liquid portion of milk, consisting primarily of 93% water, lactose, and whey proteins (primarily lactalbumin and lactoglobulin). Its concentrates are used as foaming and gelling agents. Add the milk protein to other food improves their texture, moisture retention, and flavor.

Composition of Milk

Composition of Milk Fat : It plays a major role in the flavor, mouth-feel and stability of milk products. Milk fat consists of triglycerides surrounded by phospholipid-protein membranes, which allow them to be dispersed in the fluid portion of milk, which is primarily water. The fat and caloric content are different in various milk products.

Composition of Milk Vitamins: Milk contains vitamins A and D, riboflavin (B), and tryptophan, and amino acid important in the formation of the vitamin niacin . It is low in vitamin C and E. MILK exposed to ultraviolet light loses riboflavin, so it is packaged in cardboard or opaque plastic containers to prevent the degradation of this vitamin by light vitamins A and D found in the the milk fat of whole milk because it is a fat soluble vitamin

Composition of Milk In reduced fat and fat free milk, however, the vitamin A has been diminished, so these milk are required to be fortified with that vitamin. Vitamin A fortification is also required in dry milk and evaporated skim milk 98 percent of milk processors add vitamin D in reduced fat and fat free milk also it is required in evaporated whole and fat free milk .

Composition of Milk Minerals: the major mineral in milk is calcium Other primary minerals found in milk and milk products include phosphorous, potassium, magnesium, sodium chloride, and sulfur. Although milk is rich in many minerals, it is low in iron.

Color compounds: Factors that contribute to the color of milk are: Fat, casein, calcium complexes, and water soluble riboflavin (B2). These compounds by interfering with light transmission contribute to milk's color. Carotenoid pigments dissolved in the milk fat influences the color of milk. Removing any fat eliminates a proportional amount of carotenoid pigments and solids, resulting in the color changing from a yellowish white to the bluish hue seen in fat-free (nonfat) milk.

Purchasing Milk Grades: Milk is graded according to its bacterial count Milk is an excellent growth medium for microorganisms such as bacteria, yeast, and molds pasteurization : is to heat milk for a short time to below its boiling point to kill microorganisms. pasteurization destroys 100 percent of pathogenic bacteria, yeasts, and molds and 95 to 99 percent of other of the enzyme that cause the off flavor. Pasteurization also inactivates many of the enzymes cause off flavors of rancidity Pasteurization temperatures and times vary but the on commonly used is heating milk at 63 centigrade for 30 minutes or 71c for 15 sec

Purchasing Milk Ultrahigh-Temperature milk (UHT): A process uses higher temperatures to destroy more bacteria than stander pasteurization and increases the milks shelf life. This milk is then packaged aseptically in sterile containers and sealed so that it can be stored unrefrigerated for up to 3 months.

Types of milk About half the milk produced in the market is sold as fluid milk and cream. Much of the rest comes to market as butter, cheese, and ice cream. The available market forms of milk include: Fresh fluid milk - whole, reduced fat, low fat, non fat (fat-free), flavored fluid milk ex. Eggnog, chocolate milk. Canned milk, evaporated, sweetend condensed, dry milk. and cultured milk such as buttermilk and yogurt.

Types of milk I- Fresh fluid milks: Whole milk: contain 3.25% fat and at least 8.25% milk solids-non-fat (MSNF), It is usually fortified with vitamin A&D. Reduced-fat and low-fat milk. These milks have had some of their fat removed, fat levels are decreased to 2 and 1 % respectively, the MSNF may exceeds to 10 % by protein fortified, thus improve the consistency, taste, and nutritive content. As well as fortified with V. A &D Fat-free or nonfat milk (Skim): Should contain no more than 0.5 %fat and 8.25% MSNF, fortification is required.

Purchasing Milk Reduced-lactose milk: any pasteurized milk Treated will enzyme lactase will have most of its lactose converted to its two mono sacharids glucose and galactose thus make it slightly sweeter flavor. This milk is more easily digested y people how have some d Goat, sheep an other animal milks: From various animals. Soy milk: A milk-like product made from soybean. Egree of lactose intolerance

Types of milk II- Canned fluid milks: Whole milk: some ultrahigh-temperature milk is canned. Evaporated milk: 60% of water evaporated. Then homogenized, canned, and sterilized. Sweetened condensed milk: 50% of water evaporated. 40-45% sugar by weight. Sterilization not needed.

Types of milk III- Dry milk: Milk is dried by either spray, foam-spray or roller drying processes. To long shelf life. In spray drying, concentrated milk is sprayed into hot air, while foam-spray drying sends a jet of hot air into the concentrated milk. Roller drying consists of moving pasteurized or condensed milk through two steam-heated rollers. Dried milks that originally contained some fat required to be fortified with vitamin A and D (fortified). The decreased in moist and fat gives milk a long shelf life. Increased the calcium and protein content. Jet تدفق

Types of milk IV- Cultured milk products: Cultured or fermented milk products have been used for centuries. Some cultured milk products commonly consumed in are: Buttermilk Yogurt Acidophilus milk. Sour milk.

Types of milk Yogurt: This smooth, semisolid fermented dairy product can be made from whole, reduced-fat or fat-free milks. It is produced by mixing two types of bacteria, Lactobacillus bulgaricus and Streptococcus thermophilous, and adding them to pasteurized, homogenized milk. The whole mixture is held at a warm temperature (42-46°C) to allow fermentation to develop the desired consistency, flavor and acidity. During fermentation, the bacteria convert lactose to lactic acid, increasing the acidity. In addition, folate levels increase as a natural by-product of bacterial growth.

Milk products in food preparation 1-Flavor changes: The bland, slightly sweet flavor of milk comes from its lactose, salts, sulfur compounds, and short-chain fatty acids. The percentage of fat determines the mouth-feel and body of a particular milk. Exposure to heat or sunlight, oxidation , the use of copper equipment or utensils, and the feed ingested by the source animal are just some of the other factors that can influence the flavor of milk.

Milk products in food preparation Off-flavor develops when the amino acid methionine reacts with the sunlight-sensitive riboflavin . The cooked flavor of heated milk develops in part because heating denatures whey proteins to release volatile sulfur compounds, which contribute to off- flavors. .

Milk Products in Food Preparation 2-Coagulation and precipitation Some milk proteins coagulate or precipitate to form a solid clot, or curd, under certain conditions. These conditions include: Application of heat Addition of: Acid Enzymes Polyphenolic compounds Salts التجلط والترسب

Milk Products in Food Preparation 1-Application of heat: When milk is heated to near the boiling point, the whey proteins lactalbumin and lactoglobulin become insoluble, mesh with the milk's calcium phosphate, and precipitate, forming a film on the bottom and sides the pan. Casein not coagulate with heat unless it is boiled for long periods of time. This film can scorch easily. Scorching can be prevented by constant stirring, slow temperature increases , or use of a double boiler. Mesh يشتبك film طبقة رقيقة جدا scorch يتحرق

Milk Products in Food Preparation Why dose a skim form on the surface of heated milk? This is caused by the evaporation of water, which is accompanied by an increased concentration of casein, fat, and mineral salts. This thin skim also scorches easily. To avoid this by continual stirring during heating. Skim القشدة

Milk Products in Food Preparation 2-Acid: Adding acid to milk causes the casein in the milk to coagulate. Casein precipitates when the normal 6.6 pH of fresh milk drops below 4.6. Sources of acids include those from foods such as lemon, tomato products and certain fruits, or from bacteria-produced acids in cultured milk products. To prevent this by add the acid to the milk base instead of the other way around, and avoiding high temperatures after milk has been mixed with acid. Or thickening fluid milk by adding starch or wheat flour.

Milk coagulates as pH drops The calcium in milk may be in one of two forms: either combined with the casein protein , or as free calcium ions (Ca++). At milk's near-neutral pH of 6.6, the casein combines with available calcium content, creating calcium caseinate. Coagulation of these casein proteins, occurs when the negative charges are neutralized by the hydrogen ions (H+) from acid. When the pH drops to 4.6 casein becomes very insoluble and precipitates readily into a curd. curd. خثارة اللبن

Milk coagulates as pH drops Milk products coagulated with acid are lower in calcium than those coagulated with an enzyme, because the acid releases calcium from the casein molecules, causing it to be lost in the whey.

Milk Products in Food Preparation 3-Enzymes: Milk coagulates when it is combined with certain enzymes originating from animal, plant, or microbial sources. The most commonly enzyme used to coagulate milk is rennin, which is used in the production of cheese and ice cream. One of the major differences between coagulation caused by enzymes and that initiated with acid is that rennin-coagulated clots are rich in calcium and have a tough, rubbery texture, unlike those created by acid, which are less elastic and more fragile in consistency. Tough ثقيل وثابت fragile ضعيف

Milk Products in Food Preparation 4-Polyphenolic compounds: Some fruits, vegetables, tea and coffee contain polyphenolic compounds, which when combined with milk result in the precipitation of proteins. 5-Salts: Salts may cause cured for milk. To prevent curdling, salt or salted foods should be added to the milk base, and high temperature must be avoided after the combination has been made .

Whipped Milk Products During whipping, the protein in these milk products is mechanically stretched into thin layers that trap air bubbles, fat particles, and liquid. Whipped cream: cream expands two to three times its volume when whipped. The stability of milk foams , especially whipped cream, is dependent on several factors: The fat content, the temperature, and the equipment used, the age of cream, the sugar content, and the length of whipping time. Whipped الخفق

Whipped Milk Products 1-Fat content: The higher the fat content, the more stable the whipped cream, because solid fat particles provide rigidity to the foam. Heavy whipping cream beats more easily than lower-fat whipping cream, but becomes lumpy and buttery with overbeating. 2-Temperature: Cooling cream increases its viscosity or firmness and its tendency to clump. Rigidity صلابة beats الخفق او الضرب lumpy متكتل buttery متصلب tendency to clump الميل للتكتل

Whipped Milk Products

Whipped Milk Products 3-The age of cream: The older the cream , the greater its viscosity and ability to foam. 4-Sugar: Sugar increases the stability of whipped cream, but it should be added gradually, toward the end of the whipping period. Added earlier, it increases the whipping time and reduces overall volume. For the best stability, powdered sugar instead of granulated sugar should be used, because it dissolves more readily in the cold cream

Whipped Milk Products 5-Whipping time: Physical agitation of the cream is necessary, because it disrupts the phospholipid membranes surrounding the fat globules, preventing them from aggregating. Overbeating, for even a few seconds over the peak point turns whipped cream into butter and whey. To make whipped cream with an electric beater, it is best to beat on medium high and then slow to a lower speed as soon as the cream starts to thicken. The formation of stiff , yet moist, peaks signals the completion of the whipping process. The cream should be under-beaten slightly if ingredients such as sugar are to be whipped into the cream. Agitation تهيج تحريك سريع او خض

Whipping evaporated milk: The high concentration of milk solids in evaporated milk makes it possible to whip it to three times its volume. But the flavor, texture, and stability are less acceptable than the whipped cream. Evaporated milk foams are less stable than whipped cream foams, because of former's lowest viscosity and lower fat content. Adding 1½ tablespoons of sugar per cup can further stabilize the protein and resulting foam. Lemon juice can also be used to stabilize the foam. former's المتكون

Whipping non-fat dry milk: This whipped milk product is very unstable, but it is much less expensive and lower in both calories and fat than whipped cream. Stability is increased by adding 1 tablespoon of lemon juice or 2-4 tablespoons of sugar during beating.

Storage of Milk Products Refrigerated All fluid milk except unopened, aseptic packs of ultrahigh-temperature pasteurized milk and certain canned milk products should be stored in the refrigerator. aseptic معقم

Storage of Milk Products Dry Storage Nonfat dry milk stored away from moisture and in tightly closed containers will keep for about one year. Unopened cans of evaporated and sweetened condensed milks will keep up to a year in dry, ventilated areas, double that if refrigerated. Ultrapasteurized milk can be stored unopened at room temperature for up to three months. They should all be stored at or slightly below room temperature (72°F/22°C). Once opened, all these milks must be refrigerated.