Processing & Evaluation of Milk Quality Flashcards
Introduction to milk
❑ Milk is a type of emulsion that consists of 3.9% fat, 8.8% Non-Fat-Solids, and 87.3% of water.
❑ Cow milk contains low fat content (3.66%).
❑ Buffalo milk contains high fat content (7.44%).
❑ Milk is highly perishable commodity and likely to be
spoiled during transportation due to it is an excellent medium for the growth of microorganisms, particularly bacterial pathogens that can cause spoilage and disease in consumers
Classification of milk
1) Solution
2) Dispersion
3) Emulsion
Solution (milk):
Contains the sugar lactose, the water-soluble vitamins thiamin and riboflavin, and many mineral salts such as calcium, phosphate, citrates, and the minerals chloride, magnesium, potassium, and sodium
Colloidal dispersion (Milk):
A colloid is any material in which tiny particles of one substance are spread through a larger volume of another substance. E.g., casein and whey proteins and milkfat globules dispersed in watery liquid
Emulsion (Milk):
Fat globules suspended in the aqueous phase (serum) of
milk.
The fat globules are surrounded by a complex membrane, the milk fat globule membrane, which contains mainly protein and phospholipids (and a few carbohydrate side chains at the outer surface).
This membrane prevents coalescence of the fat droplets.
MILK,RAW MILK OR FRESH MILK (FOOD ACT 1983 & REGULATIONS 1985)
(1) In these Regulations,“milk”,“raw milk” or “fresh milk” means the normal, clean,fresh mammary secretion of healthy cow,buffalo, goat, or sheep that is properly fed and kept,excluding that obtained during the four days immediately following calving.
(2) Milk
(a)Shall contain not less than -
(i) 3.25 per cent of milk fat;and
(ii) 8.5 per cent of non-fat milk solids; and
(b) Shall not contain any –
(i) added water;
(ii) permitted food additive;
(iii) other added substance;or
(iv) trace of antibiotic substance
Milk Processing - Pasteurization
• Pasteurization minimizes the likelihood of disease and extends the storage life of milk.
• Pasteurization temperatures do not change milk components.
• Vitamin destruction and protein denaturation are minimal, and the result is that milk is made safe for consumption.
• The shelf-life of pasteurized milk held under 7 ℃ - 12 to 21 days (if unopened)
• Actually, Coxiella burnetii, which causes Q fever requires an even higher temperature for destruction; thus, the required 63 ℃ for pasteurization.
• The high pasteurization temperature, followed by rapid cooling, controls nonpathogenic growth.
LTLT
63 ℃ for 30 or more minutes; the batch or holding method and is considered low-temperature longer time (LTLT) pasteurization.
HTST
72 ℃ for 15 seconds; the flash method and is the High-Temperature Short-Time (HTST) method of pasteurization.
Milk Processing – Sterilization (Ultra-pasteurization)
• Sterilization is pasteurization that occurs at higher temperatures with a different time:
i. 138–150 ℃ for 2–6 seconds
ii. “Ultrapasteurized when used to describe a dairy ingredient means that such ingredient shall have been thermally processed at or above 138 ℃ for at least 2 seconds.”
• Ultra high temperatures (UHT) processing - It does not allow spoilage or pathogenic bacteria to enter the milk.
• If packaging too is sterilized, the package is referred to as being “aseptically packaged” and hermitically sealed.
• Milk treated in this manner may be safely stored up to 3 months or longer (if unopened)
• UHT milk will often have cooked flavor.
• Can keep at room temperature
Homogenization
• The primary function of homogenization is to prevent
creaming, or the rising of fat to the top of the container of milk (whole or some low-fat milk).
• The result is that milk maintains a more uniform composition with improved body and texture, a whiter appearance, richer flavor, and more digestible curd.
• The homogenization reduces fat globule size from an average of 3.5 µm in diameter to below 1 µm
• Preventing globules from reuniting or coalescing, and the fat remains homogeneously distributed throughout milk.
Fortification
• The addition of fat-soluble vitamins A and D to whole milk.
• Low-fat milk, nonfat milk, and low-fat chocolate milk must be fortified (usually before pasteurization) to carry 2000 international units (IU) vitamin A.
• Vitamin D to reach levels of 400 IU’s is optional but routinely practiced.
• Nonfat milk solids (MSNF) may be added to milk to low-fat milk - and it will state “protein fortified” or “fortified with protein” on the label
Evaporated and Concentrated Milks
• Evaporated milk (unsweetened condensed milk) is
concentrated through the process of evaporation (at 50–55 ℃) in a vacuum chamber.
• Either whole or nonfat milk with 60% of the water removed is then homogenized, fortified with vitamins A and D, canned, and sterilized in the can (115–118 ℃) in a pressure canner.
• Whole evaporated milk must contain not less than 25% total milk solids and not less than 7.5% milkfat.
• Evaporated nonfat milk must contain not less than 20% milk solids and no more than 0.5% milkfat.
• It must be fortified with 125 and 25 IU of vitamins A and D, respectively.
Sweetened Condensed Milk
• Sweetened condensed milk is concentrated whole or nonfat milk with approximately 60% of the water removed and sugar levels of 40–45% in the finished product.
• There is a calorie difference in this milk processing, as whole sweetened condensed milk contains no less than 8% milkfat and 28% total milk solids and nonfat contains no
more than 0.5% milkfat and 24% total milk solids.
Dried Milk
• Dried milk powder may be processed from either pasteurized whole or more commonly from nonfat milk.
• One method of drying involves spray drying.
• Milk is first condensed by removing two-thirds of the water and to dry to less than 5% moisture levels.
• Most nonfat dried milk is fortified with vitamins A and D.
Cultured milk/fermentation
• Cultured products are fermented by the addition of bacterial cultures, such as lactobacilli and streptococci, to fluid dairy products.
• Lactose is fermented to lactic acid, creating a low pH in the process, which
(1) controls both spoilage and pathogenic bacterial growth,
(2) causes the casein to coagulate.
• Because cultured and acidified products contain different amounts of lactic acid, they differ in flavor.
Buttermilk
• Traditionally, buttermilk was the liquid that remained
when cream was churned to form butter.
• It is more correctly named “cultured low-fat milk” or
“cultured nonfat milk.”
Process of Buttermilk
• The starting ingredient for buttermilk is skim or low-fat
milk. The milk is pasteurized at 82 to 88 °C for 30 minutes, or at 90 °C for two to three minutes.
• The milk is then cooled to 22 °C , and starter cultures
of desirable bacteria, such as Streptococcus lactis, S. cremoris, Leuconostoc citrovorum, and L. dextranicum, are added to develop buttermilk’s acidity and unique flavor.
Sour cream
• Traditionally, sour cream was made from heavy (whipping) cream that was soured.
• Today, it is made from pasteurized, homogenized, fresh, light cream (approximately 18% fat).
• While inoculation and fermentation steps are similar to buttermilk production, fermentation is shortened.
• S. lactis and Leuconostoc bacteria may be added for
flavor, and stabilizers such as gelatin or gums may be
present.
• Nonfat milk solids may be added to thicken the cream.
• A bitter taste in sour cream that is stored more than 3–4 weeks may form due to proteolytic bacterial enzyme activity.
