L3A Milk Chemistry and Processing Flashcards
What is food preservation?
Food preservation is the process of producing food in such a way as to stop or greatly slow down spoilage to prevent foodborne illness and extend its shelf-life.
What are some food preservation methods?
Refrigeration and freezing Canning Irradiation Dehydration Freeze-drying Pickling Pasteurizing Fermentation
How does food preservation work and what are the 3 Factors?
All of the food preservation processes work by slowing down the activity and growth of disease causing bacteria, or by killing the bacteria all together. They also slow down or stop the action of enzymes which can degrade the quality of the food.
Food preservation also includes processes which inhibit natural discoloration that can occur during food preparation, such as the enzymatic browning reaction in apples after they are cut.
Factors that can be utilized:
Temperature: It can be too low (freezing) or too high (ultra high temperature treatment)/ Try to find more on the danger zone
pH: Recall Dr. Forday’s sides. Most bacteria cannot withstand acidic pH
Water activity: You should be able to comfortably relate the concept of water activity with microbial spoilage in foods after gong through lecture 1
What are milk fats?
Milk fat: fat globules, interactions with milk proteins; saturated and conjugated unsaturated;
Define Plasma,Serum, SNF and Total Milk Solids.
Plasma: milk - fat (skim milk)
Serum: plasma - casein micelles (whey)
solids-not-fat (SNF): proteins, lactose, minerals, acids, enzymes, vitamins. It is the total solids content minus the fat content.
Total Milk Solids: fat + SNF
List the main compounds and their percentages in milk.
Fat Globules
(Long Chain) C14 - myristic 11% C16 - palmitic 26% C18 - stearic 10% C18:1 - oleic 20%
Short chain (11%) C4 - butyric* C6 - caproic C8 - caprylic C10 - capric
Proteins
Soluble Proteins (Whey) Lactalbumin Lactoglobulin Immunogloubulin Etc.
Globular
When heated will form a gel
Insoluble proteins (caseins)
Alpha Casein
Beta Casein
Kappa Casein
etc.
No fixed tertiary structure
How does fat exist in milk?
Triglycerides in milk are in the form of globules. Globules are surrounded by a protein and phospholipid membrane that stabilizes the globule in serum. Globules range from 1 µm to over 10 µm.
Why is milk homogenized?
The uneven size distribution allows the larger globules to float in a process called creaming, thus resulting in a “cream line” at the top of the container. Milk is homogenized to reduce the size of the large globules to less than 1 µm, create a uniform distribution of globules throughout the serum phase, and minimize creaming.
Explain the structure of a casein micelle and submicelle.
Casein submicelle is made of a hydrophobic core with some submicelles having a kappa casein peptide chain enriched surface. All the submicelles are held together by calcium phosphate Ca9(PO4)6. Submicelles that are rich in the kappa casein peptides chains occupy the surface of the micelle and surrounds the submicelles which are not rich in kappa casein peptide chains.
Explain the characteristics of proteins that milk contains.
Milk contains 3.3% total protein. Milk proteins contain all 9 essential amino acids required by humans. There are 2 major categories of milk protein that are broadly defined by their chemical composition and physical properties. The casein family contains phosphorus and will coagulate or precipitate at pH 4.6. The serum (whey) proteins do not contain phosphorus, and these proteins remain in solution in milk at pH 4.6. The serum (whey) protein family consists of approximately 50% ß-lactoglobulin, 20% α-lactalbumin.
Explain the characteristics of the fats in the milk.
Milk contains approximately 3.4% total fat. Milk fat has the most complex fatty acid composition of the edible fats. Over 400 individual fatty acids have been identified in milk fat.
Explain the characteristics of sugar in milk.
Milk contains approximately 4.9% carbohydrate that is predominately lactose with trace amounts of monosaccharides and oligosaccharides. Lactose is a disaccharide of glucose and galactose. Lactose is dissolved in the serum (whey) phase of fluid milk
How does different type of pasteurisation affect milk?
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
What are the causes of changes in milk in storage?
lipolysis
Hydrolysis of fats
Denaturation of proteins
Enzymes that degrade fat are called lipases, and the process is called lipolysis. Milk lipases come from several sources: the native milk, airborne bacterial contamination, bacteria that are added intentionally for fermentation in milk. Lipases remove fatty acids from the glycerol backbone of the triglyceride. Usually the action of lipase causes undesirable rancid flavors in milk. Pasteurization inactivates lipases and increases the shelf life of milk. However, in some cheeses, such as blue cheese and provolone, a small amount of lipolysis is needed to achieve the characteristic flavor.
Protein denaturation happens at temperatures higher than 65°C. It is a vital process in cheese manufacturing.
