INTRODUCTION TO DAIRY SCIENCE

Transcription

1 INTRODUCTION TO DAIRY SCIENCE PAUL EBNER, ASSOCIATE PROFESSOR, PURDUE ANIMAL SCIENCES PRODUCED FOR THE USWDP FOOD TECHNOLOGY BRIDGE PROGRAM AT HEART UNIVERSITY

2 Afghanistan Milk Statistics # of total cattle (cows): 3.7 million # of milking cows: 2.2 million Kilos of milk produced each year: 945,000 t Average yearly milk consumption: 66 kilos/person

3 Dairy Science Dairy: every product made primarily from milk from all species of mammal- including milk Milk Powdered or dry milk Separated cream Dried whey Butter Ice Cream Yogurt Solid yogurts Semi- solid yogurts Drinkable yogurts And much more!

4 Milk Production Basics Milk is highly nutritious Close to a perfect food Milk is easily converted to value- added products Examples: yogurt, cheese, butter, cream, etc. Can increase profit Can increase shelf- life

5 CHARACTERISTICS OF MILK

6 Solids in Milk Milk is approximately 87% water Milk solids: everything that makes up the remaining 13% Total solids: all solids together Solids, non- fat: all solids excluding the fat portion

7 Solids in Milk The solids of milk are what distinguishes milk from water. Protein: heavier than water Sugars: heavier than water Fat: lighter than water Result: Milk is always heavier than water Density of milk is determined by measuring its specific gravity

8 Solids in Milk Measuring the density of milk is easy Done with a lactometer Lactometer: hydrometer for milk Can quickly and easily tell if something is added to milk based on density We will do this in the lab

9 Solids in Milk Typical composition of raw milk: Water: 87% Fat: 4% Protein: 3.5% Sugars: 4.0% Vitamins/minerals: < 0.5% Total solids =?? Solids, non- fat =??

10 Solids in Milk The composition of milk can significantly affect production of dairy products Some yogurts require < 3.0% fat Some yogurts require higher protein The composition of raw milk is heavily dependent on: Animal genetics: for example, some species and breeds within species produce higher fat milk Animal feeding: high quality diets = high quality milk

11 Solids in Milk Fortunately, the composition of raw milk can be changed with some basic math Example: Have 3.8% fat milk Have skim milk (~0.1% fat) Need 3.0% fat milk

12 Solids in Milk Skim milk: ~0.1% fat So, to make 3.0% milk from 3.8% milk and 0.1% milk, you would add: 0.8 L of 0.1% milk to 2.9 L of 3.8% milk 0.1 Pearson s Square 0.8

13 ph ph of good quality, raw milk is ~ Knowing the proper ph of milk is very important for both quality and processing Low ph: Indication of spoilage and growth of bacteria (reduces shelf- life and profit) Interferes with yogurt, cheese production

14 Basic Science of Yogurt Chemically, when milk becomes yogurt it is changing from an emulsion to a colloid Emulsion: a mixture of two liquids, like oil and water. Emulsion comes from the latin word for milk. Milk is an emulsion of water and oil (milk fat) Colloid: a dispersion of solid particles in a liquid

15 Basic Science of Yogurt Heated to 85C and cooled to ~45C RAW MILK Emulsion of water and fat ph: 6.5 % acidity: 0.17 COOKED MILK Still an emulsion No change in acidity Bacterial culture added and incubated at 45C What exactly happened?? YOGURT Colloid of water and solid (protein) ph: 4.0 % acidity: 1.0

16 Basic Science of Yogurt The predominant protein in milk is casein In raw milk casein forms micelles Bacterial growth results in acid production Acid (low ph) breaks up micelles Casein then forms a net that traps water

17 Basic Science of Yogurt So, yogurt has approximately the same composition of water, fat, protein, and sugar as raw milk, but the proteins (casein) have formed a net that traps water The water that you sometimes see on top of yogurt is just water that has escaped the trap!

18 Microbial Component of Milk Raw milk is never sterile Bacteria (and other microorganisms) enter milk during collection: From the environment From animal itself From the milker Pasteurization is designed to control microbial populations

19 Microbial Component of Milk Pasteurization is designed to control microbial populations Pasteurization parameters: Batch: 63C for 30 min Continuous: 72C for 15 sec Destroys pathogens Many types of bacteria can survive pasteurization

20 Microbial Component of Milk UHT: Ultra- High Temperature Pasteurization > 135C for 1-2 seconds Designed to kill ALL bacteria including spores UHT milk has a shelf- life of about 6 9 months (if unopened)

21 Microbial Component of Milk Pasteurization System ksu.edu.sa

22 Microbial Component of Milk APC is used throughout the world to measure microorganisms in milk Also called, TPC, VPC, etc. Essentially the same thing TPC: Total Plate Count VPC: Viable Plate Some standards Raw Milk Pasteurized Milk APC <10 6 CFU/mL <200 CFU/mL Coliforms <200 CFU/mL undetectable

23 Microbial Component of Milk Because pasteurization does not kill all bacteria, very high initial bacteria counts in raw milk usually translate to unacceptably high bacteria counts even after pasteurization If initial counts are high (e.g., 10 7 ). Pasteurization may only reduce concentration to , then the remaining bacteria will grow to high concentrations very quickly High bacterial counts = quick spoilage = reduced shelf- life = loss of profit 7-10 days: shelf- life of high quality, pasteurized milk under refrigeration

24 Mastitis Mastitis: inflammation/infection of the udder

25 Mastitis Mastitis in milk producing animals is a world- wide problem: More contamination of milk (many mastitis causing organisms are also human pathogens) Reduced quality of milk Reduced profit Animal welfare Most of the time mastitis is controlled by proper sanitation and hygiene of the milking environment In severe cases, animals have to be treated with antibiotics

26 Mastitis Tests Somatic Cell Count (SCC): test of quality of milk Somatic cells are mostly leukocytes The number of leukocytes increases when there is an infection These cells are shed from the udder to milk High Somatic Cell Counts in milk indicate the cow may have mastitis SCC < 300,000 indicates mastitis Good, quality milk should be < 100,000

27 Milk Composition and Quality Tests Worldwide, the most common and standard milk tests are: 1. APC 2. SCC 2. Coliforms 3. ph/acidity % 4. Fat content 5. Protein content Knowing how and WHY you do these tests is critical in measuring and understanding milk quality

28 ADULTERATION OF MILK

29 Adulteration Adulteration: adding anything to milk, intentionally or unintentionally, that changes the composition, quality, or safety of milk Compounds used in adulteration are referred to as adulterants Milk is one of the most nutritious foods available, unfortunately it is also one of the easiest to adulterate

30 Adulteration Unintentional adulteration: antibiotic residues, detergents left in milk containers for washing Intentional adulteration is deliberate and done to make the milk appear that it is higher quality, more fresh, higher volume than it really is. It is done to cheat milk buyers and consumers Result can be reduced milk quality and nutrition. In severe cases, people have died from adulterated milk

31 Examples of Adulteraton Antibiotic residues Usually a case of unintended adulteration Antibiotics are used to treat a sick animal and are easily passed to the udder and to milk This is common if the milk producer does not understand antibiotic use Milk from cows receiving antibiotics should be discarded or used for animal feed, etc.

32 Examples of Adulteraton Problems caused by antibiotic residues: 1) Safety: at high concentrations it can be a health hazard 2)??

33 Examples of Adulteraton Water Adding water is done simply to increase volume Milk is sold to stores and to consumers based on weight or volume Milk that is >25% added water can have the same appearance as regular milk (higher in the case of skim milk)

34 Examples of Adulteraton Water Positive: adding water reduces the density of milk and is easily detected with a lactometer Negative: adding a second compound to milk adulterated with water can increase the density giving the appearance of normal milk We will see this in the lab

35 Examples of Adulteraton Preservatives Preservatives are regularly used in food production They should never be added to milk Adding preservatives: Reduces bacterial growth giving the milk the appearance that it is fresh when it could be very old Reduces the ability to make any fermented dairy product (e.g., yogurt, cheese, etc.) Some commonly used preservatives are somewhat harmless (citric acid) while others are very dangerous (formaldehyde)

36 Examples of Adulteraton ph buffers Buffer: a compound that prevents large changes in ph Example: sodium carbonate, used in food production, but should never be in milk When added, bacteria may grow, but there will be no change in ph (even though acid is being produced) Result: Old milk looks like new milk Milk cannot be used for fermented products

37 Examples of Adulteraton Unfortunately, there is a long list of adulterants that can be used in milk to make it appear more nutritious, fresher, etc. Other examples include: Adulterants that make milk appear to have more cream (soap) Adulterants that make milk appear to be higher in fat (vegetable oil) Adulterants that make milk to be higher in protein (melamine) Adulterants can significantly reduce the quality, safety, and usability of milk = loss of profit