![Principles of Homogenizer
• Mechanically increases the number and reduces the size of
the fat globules (from 2-6μm down to < 0.5 μm)
• Milk pumps under high pressure [2000-2500lbs/sq.in(psi)]
through small mesh orifices of a homogenizer .
• There are single and double stage homogenizers
• The homogenization process: Emulsifies the fine fat globules
and as the surfaces of many new fat globules are formed.](https://image.slidesharecdn.com/dairyprocessingtechnologypart1-240329125751-7e9c9726/85/Dairy-processing-technology-part-one-pdf-37-320.jpg)
Dairy processing technology part one.pdf
- 1. FOOD PROCESSING TECHNOLOGY Lecture Four By: Shewarega Habtamu (PhD candidate)
- 2. Chapter 3 Animal products processing Dairy processing technology (1/2) 2
- 3. Learning Objectives to:- • At the end of this Lecture, students should be able A.Understand the nutritional composition of milk and factors affecting the composition B.Explain the production of clean milk and spoilage indicators. C.Discuss the importance of milk processing. D.Understand the major unit operations involved for the production of pasteurized/sterilized milk. 3
- 4. 1. Introduction WHAT IS MILK?
- 5. Cont’d • Fluid secreted by the female of all mammalian species for primary function of meeting the complete nutritional requirements of the neonate of the species. • Cow, goat, sheep, buffalo and human>>well characterized milks.
- 6. Cont’d • High in protein and essential vitamins and minerals • Our most nearly perfect food. • Per-capita consumption • FINLAND- 375 L/year • ETHIOPIA- 16-25 L/year??? • WHO recommend 200 L/year
- 7. 2. Nutritional content a) Gross compositions of selected species Species Total solids Fat protein lactose Ash Human 12.2 3.8 1.0 7.0 0.2 cow 12.7 3.7 3.4 4.8 0.7 goat 12.3 4.5 2.9 4.1 0.8 sheep 19.3 7.4 4.5 4.8 1.0
- 8. B) Proximate compositions of cow’s milk Major minerals- Calcium, phosphate, magnesium, sodium, potassium…. Vitamins A, B6, B12, C, D, K, E, thiamine, niacin, biotin, riboflavin, folates
- 10. Allergy related to milk • Lactose intolerance • The inability to digest lactose, a sugar found in milk and to a lesser extent dairy products, causing side effects. • Undigested lactose can be converted by the microbial flora in the intestine into lactic acid and gases. • Consumption of larger quantities of milk thus causes flatulence, stomach cramps and diarrhea.
- 11. 2.1 Factors affecting milk composition ✓ Breed differences Components Breeds Ayrshire Brown Swiss Guernsey Holstein Jersey Shorthorn Fat 3.95 3.98 4.72 3.54 5.13 3.5 Lactose 3.48 3.64 3.75 3.29 3.97 3.32 Ash 0.72 0.74 0.76 0.72 0.76 0.75 Total Solids 12.77 13.07 14.04 12.16 14.42 12.27
- 12. Cont’d ✓ Age of animal ✓ Stage of lactation & pregnancy ✓ Condition of animal-Mastitis {inflammation of the udder} ✓ Method of milking- Completeness of milking (Hand and Machine milking) ✓ Season of the year ✓ Other factors–contamination and processing
- 13. 2.2 Production of Clean Milk • Environmental hygiene – water, insects, rodents • Hygienic production of milk • Areas and premises for milk production • Animal Health • General hygienic practices including feeding, pest control, veterinary drugs • Hygienic milking • Handling, storage and transport of milk • Milking equipment • Storage equipment and premises • Collection, transport & delivery procedures and equipment • Documentation and Record Keeping- Weighing
- 14. Cont’d ➢ Growing of microbes influenced by: ⚫ Initial cell count ⚫ Quality and kind of microbes ⚫ Temperature of milk ➢ Milk from healthy animal: 103- 104 bacteria/ml ➢ Milk must be chilled to 𝟒 𝒐C or below as soon as it leaves the cow
- 15. 2.3 Results of Microbial Growth in Milk (Milk spoilage indicators) Souring-Most common, due to transformation of lactose into lactic acid, other volatile acids & compounds, principally by lactic acid bacteria. Souring & gassiness-Caused by E.coli group, indicates contamination of milk and its products. Aroma production-Due to production of flavour compounds such as diacetly.
- 16. Cont’d Proteolysis:- Protein decomposition leading to unpleasant odor. Ropiness:- Long threads of milk are formed while pouring. Sweet curdling:- Due to production of a remain like enzyme curdles milk without souring
- 17. 3. Processing of milk 3.1 WHY PROCESSING? 1.Preservation • Longer shelf life 2.Reduction of health hazard 3.Protection • safer 4.Added value • more appealing or healthier • Improves nutrition
- 18. 3.2 Unitoperations for Pasteurization of milk • Milk receiving • Pre-heating • Separation • Standardization • Homogenization • Pasteurization • Packaging
- 19. 1. Collection and reception of milk • The first thing done at reception is to determine the quantity of the milk. • From weighing-in, the raw milk is pumped to storage tanks to await processing. • The empty churns are conveyed to a cleaning station.
- 20. 1.1 Testing milk for quality i. Taste and smell-deviates in taste and smell from normal milk ii. Cleaning checks- The inside surfaces of farm tanks and churns are carefully inspected. iii.Sediment-This applies only to churns. A sample is taken with a pipette from the bottom of a churn and is then passed through a filter. A quality deduction is made if visible impurities are retained by the filter.
- 21. Cont’d iii.Somatic cell (white blood corpuscles or leucocytes) count • A large number (more than 500,000 cells/ml of milk) of somatic cells in the milk indicates that the cows are suffering from udder diseases. The cell content is determined with specially designed particle counters (Coulter counter, etc.). Iv. Bacteria count • A simplified form of bacteria count can also be used to assess the bacteria content.
- 22. Cont’d v. Freezing point • Many dairies check the freezing point of the milk to determine whether or not it has been diluted with water. Milk of normal composition has a freezing point of -0.54 to -0.59°C.The freezing point will rise if water is added to the milk. vi. Protein content vii.Fat content
- 23. Cont’d • 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
- 24. 2. Balance tank • After the milk is collected from the farm or collection center, it will be stored in refrigerated storage tank until it is needed for processing. • Balance tank is used to weigh and maintain constant flow of liquid milk to the next operation during processing.
- 25. 3.Milk Separation • Newer technologies: Both clarification and separation of milk done together: • Both activities, clarification and de- creaming are combined in one operation with a three-phase separation (Dirt, skim milk and cream)
- 26. Decreaming Process • Separation/Centrifugation: the mechanical separation of milk into cream and skim milk by means of centrifugal force. • De-creaming process controls the efficiency of the fat separation due to specific density differences b/n milk fat (0.93 g/cm3) and skim milk (1.035 g/cm3) • density differences: Related with Temperature • Objective of De-creaming: ✓ Obtain a fat-reduced or fat-free milk ✓ Concentrate milk fat for the production of high fat products ✓ Standardize the fat content of milk. • STOCKS LAW:
- 28. Principles of separation • The centrifuge bowl has baffle inserts in the form of conical discs. This increases the area available for sedimentation. • The discs rest on each other and form a unit known as the disc stack. Radial strips called caulks are welded to the discs and keep them the correct distance apart. • This forms the separation channels. The thickness of the caulks determines the width.
- 29. Cont’d
- 30. Cont’d • The cream, i.e. the fat globules, has a lower density than the skim milk and therefore moves inwards in the channels, towards the axis of rotation. The cream continues to an axial outlet. • The skim milk moves outwards to the space outside the disc stack and from there through a channel between the top of the disc stack and the conical hood of the separator bowl to a concentric skim milk outlet.
- 31. Cont’d
- 32. 4. Standardization • Standardization of fat content involves adjustment of the fat content of milk, or a milk product, by addition of cream or skim milk as appropriate to obtain a given fat content. • Various methods exist for calculating the quantities of products with different fat contents that must be mixed to obtain a given final fat content.
- 33. Pearson’s square • How many kg of cream of 40% fat must be mixed with skim milk of 0.05% fat to make a mixture containing 3% fat? • The answer is obtained from a rectangle, where the given figures for fat contents are placed. • Subtract the fat content values on the diagonals to give C – B = 2.95 and A – C = 37. • 2.95 kg of 40% cream 37 kg of 0.05 % skim milk to obtain 39.95 kg of a standardized product containing 3% fat. • From the equations below it is then possible to calculate the amounts of A and B needed to obtain the desired quantity (X) of C.
- 35. 5.Homogenization • One of the essential unit operation in dairy Industries (can reach 65 0C) • The function of homogenization is to prevent creaming/the rising of fat to the top of the container of milk, Disruption of Fat Globules. • Expected result after homogenization: Milk maintains a more uniform composition.
- 36. Cont’d • At homogenization the milk is forced through a narrow gap where the fat globules are split.
- 37. Principles of Homogenizer • Mechanically increases the number and reduces the size of the fat globules (from 2-6μm down to < 0.5 μm) • Milk pumps under high pressure [2000-2500lbs/sq.in(psi)] through small mesh orifices of a homogenizer . • There are single and double stage homogenizers • The homogenization process: Emulsifies the fine fat globules and as the surfaces of many new fat globules are formed.
- 38. Cont’d • Each fat globule becomes coated with a lipoprotein membrane and additional proteins from casein. These proteins adsorb to the freshly-created oil surface preventing globules from reuniting and the fat remains homogenously distributed throughout milk. • Homogenization process prior to subsequent pasteurization
- 39. Cont’d • Single-stage and Second-stage Homogenization.
- 40. Effect of homogenization • The effect of homogenization on the physical structure of milk has many advantages: • Smaller fat globules leading to no cream-line formation, • Whiter and more appetizing colour, • Reduced sensitivity to fat oxidation, • More full-bodied flavour, better mouth feel, • Better stability of cultured milk products.
- 41. Cont’d • However, homogenisation also has certain disadvantages: • Homogenised milk cannot be efficiently separated. • Somewhat increased sensitivity to light – sunlight and fluorescent tubes –can result in “Sunlight flavour”. Reduced heat stability, especially in case of single-stage homogenization, high fatcontent and other factors contributing to fat clumping. • The milk will not be suitable for production of semi-hard or hard cheeses because the coagulum will be too soft and difficult to dewater.
- 42. 6. Pasteurization • Pasteurization is a process used to kill harmful microorganisms, such as certain pathogenic bacteria, yeasts and moulds, which may be present in the milk after initial collection. This process extends the shelf life of milk. • 63 oC- for 30 min • 72 oC- for 15 sec • 88 oC- for 1 sec • Milk’s keeping quality is improved, but nutrient value is not significantly changed. • pasteurized milk should have a shelf life of 8 – 10 days at 5 – 7°C in an unopened package.
- 43. Pasteurizers: A plate type heat exchangers
- 44. 7. Sterilization • 138-150oC for 2 seconds-UHT processing (sterile, aseptic) • The milk does not require refrigeration until it is opened.