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PRINCIPLES OF FLUID_MILK PROCESSING1.pptx-1[1].pptx
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- 2. Milk reception andstorage • Quality assessment • Characteristic of high quality raw milk • Free from debris and sediment • Free from off flavours • Low in microbial load • Normal composition and acidity • Free from antibiotics and chemical residues • Whitish cream to yellowish in colour
- 3. PLATFORM TESTS Simplemilk quality tests that may be carried out routinely both at the farm and milk collection centre: Examples of platform tests Sight-and-smell (organoleptic)/Sensory evaluationtest Clot-on-boiling test Alcohol test Lactometer test
- 4. Characteristics of platformtests Rapid results Simple to carry out Suitable for field conditions Easy to interpret results Provide accurate and reliable results Does not involve expensive equipment or infrastructure Provide parameter for payment
- 5. Confirmatory tests Resazurinetest Peroxide Test Titratable acidity test Peroxide test Compositional tests/ proximate analysis test Inhibitor tests Antibiotic test
- 6. ADVICING DAIRY FARMERSON MILK QUALITY Abnormal appearance and smell that may cause milk to be rejected could be due to: Type of feed or atmospheric taint (e.g. feeding silage or brewer’s waste too close to milking time) Cows in late lactation or in some cows when on heat or soon after conception (due to hormonal changes) Bacterial taints (from cows with mastitis) Chemical taints or discolouring (may be due to equipment not rinsed properly)
- 7. Cont. Advanced acidificationor souring (milk that is fermenting) Marked separation of fat may be caused by: Milk previously chilled and subjected to excessive shaking during transportation Adulteration with other solids (may also show as sediments or particles) Boiling, if milk fat is hardened
- 8. Factors affecting milkquality Microbial contamination (load). Storage temperatures. Time since milking. Exposure to light. Exposure to air/oxidation. Excessive agitation, Use of unsterilized equipment Prolonged cold storage
- 9. MILK PRESERVATION ANDSTORAGE Milk preservation is ensuring milk quality does not deteriorate during storage prior to delivery processing plant or commencement of processing. Done if the milking is not processed immediately Milk should be cooled within 2 -4 hours if it is not collected immediately. The common method of preservation is cooling of milk to below 100 C. Cooling does not destroy (kill) the microorganisms but makes them dormant (sleep).
- 10. Remove impurities frommilk (i) Filtration Milk filtration is the trapping and removal of suspended particles of dirt and debris from milk. Raw milk as produced on the farm and transported to the collection center or a dairy plant generally contains varying amounts of visible, invisible impurities. This foreign matter includes straw and hair pieces, dust particles, leukocytes (somatic cells or white blood cells), insects, etc.
- 11. Factors determining thechoice of filter to use Resistance to flow Clarity of filtrate required Resistance to wear (mechanical strength) Tendency to blind Cost
- 12. (ii) Clarification Itinvolves the use of a centrifugal machine called ‘clarifier’. Thus, clarification is a process of subjecting milk to a centrifugal force in order to eliminate the finer but heavier particles from milk, somatic cells, dust particles, etc These steps of aesthetic improvement of product are particularly useful for overcoming the problem of sediments in fluid milk and milk products in general, and homogenized milk in particular
- 13. Clarification cont. Althoughpart of bacteria is also removed along with the extraneous matter, clarification cannot be considered an effective means of bacteria removal. Hence, one should be aware that it cannot be a substitute for a suitable heat treatment in order to ensure safety against pathogenic (disease-causing) microorganisms.
- 14. (iii) Bactofugation Thisis removal of sediments and bacteria spores using a centrifugal separator. It operates at about 70°C, however part of the casein is also separated. Typical gram positive bacteria are best known producers of spores This method is applied to milk for some special applications especially products that are low- pasteurized eg removal of spores of Bacillus cereus from beverage milk or of Clostridium tyrobutyricum and related species from cheese milk.
- 15. Cont. Spores arequite small, but the density difference with plasma is larger than that of bacteria, and at separation temperatures of 60 to 70°C, a substantial proportion can be removed, generally 90 to 95%. By using two bactofuges in series, a reduction by over 99% can generally be attained. It should be noted that bactofugation is by no means equivalent to sterilization: the product still contains heat-resistant bacteria and a small number of spores.
- 16. Centrifugation Centrifugal separation isa process used quite often in the dairy industry. Some uses include: • clarification (removal of solid impurities from milk prior to pasteurization) • skimming (separation of cream from skim milk) whey separation (separation of whey cream (fat) from whey) Bactofuge treatment (separation of bacteria from milk)
- 17. Principles ofCentrifugation Centrifugation is based on Stoke's Law. The particle sedimentation velocity increases with: increasing diameter increasing difference in density between the two phases decreasing viscosity of the continuous phase
- 18. Separation Ifraw milk were allowed to stand, the fat globules would begin to rise to the surface in a phenomena called creaming. Raw milk in a rotating container also has centrifugal forces acting on it. This allows rapid separation of milk fat from the skim milk portion and removal of solid impurities from the milk.
- 19. Centrifuges canbe used to separate the cream from the skim milk. The centrifuge consists of up to 120 discs stacked together at a 45 to 60 degree angle and separated by a 0.4 to 2.0 mm gap or separation channel.
- 20. Milk isintroduced at the outer edge of the disc stack. The stack of discs has vertically aligned distribution holes into which the milk is introduced.
- 21. Under theinfluence of centrifugal force the fat globules (cream), which are less dense than the skim milk, move inwards through the separation channels toward the axis of rotation. The skim milk will move outwards and leaves through a separate outlet.
- 22. Standardization Thestreams of skim and cream after separation must be recombined to a specified fat content. This can be done by adjusting the throttling valve of the cream outlet; if the valve is completely closed, all milk will be discharged through the skim milk outlet.
- 23. • Homogenization • Milkis an oil-in-water emulsion, with the fat globules dispersed in a continuous skimmilk phase. If raw milk were left to stand, however, the fat would rise and form a cream layer. Homogenization is a mechanical treatment of the fat globules in milk brought about by passing milk under high pressure through a tiny orifice, which results in a decrease in the average diameter and an increase in number and surface area, of the fat globules.
- 25. Pasteurized milkdoes not necessarily need to be homogenized. However, homogenized milk should be pasteurized to inactivate native enzymes that deteriorate fat (lipases) and cause rancidity, which results in off-flavors and reduced shelf life in milk.
- 26. The purposeof homogenization is to reduce the milk fat globules size to less than 1.0 µm which allows them to stay evenly distributed in milk. Homogenization is a high pressure process that forces milk at a high velocity through a small orifice to break up the globules.
- 27. Pasteurization Process Thereare basically two methods of pasteurization in use today – batch and continuous flow In the batch process a quantity of milk is held in a heated vat at 65oc for 30 minutes followed by quick cooling to 4oc.
- 28. Pasteurization Process CONT,D In the continuous flow process also known as High Temperature Short Time (HTST) method. The milk is forced between metal plates in a plate heat exchanger or through pipes in tubular heat exchangers. While flowing under pressure the milk is held at 72oC for at least 15 seconds and the quickly cooled to 4oc. It flows through a heat exchanger to pre-warm cold milk entering the system.
- 29. Pasteurization Process CONT,D The ultimate goal in heat treatment of milk is the destruction of all pathogenic (disease causing microbes) and to improve the keeping quality by reducing the number of spoilage microbes as much as possible.
- 30. UHT Milk Processing Introduction While pasteurization conditions effectively eliminate potential pathogenic microorganisms, it is not sufficient to inactivate the thermoresistant spores in milk.
- 31. The termsterilization refers to the complete elimination of all microorganisms. The food industry uses the more realistic term "commercial sterilization"; a product is not necessarily free of all microorganisms, but those that survive the sterilization process are unlikely to grow during storage and cause product spoilage.
- 32. Milk canbe made commercially sterile by subjecting it to temperatures in excess of 100° C, and packaging it in air-tight containers. The milk may be packaged either before or after sterilization.
- 33. The basisof UHT, or ultra-high temperature, is the sterilization of food before packaging, then filling into pre-sterilized containers in a sterile atmosphere.
- 34. Milk thatis processed in this way using temperatures exceeding 135° C, permits a decrease in the necessary holding time (to 2-5 s) enabling a continuous flow operation.
- 35. • Long shelflife: • Greater than 6 months, without refrigeration, can be expected.
- 36. Difficulties withUHT Sterility: Complexity of equipment and plant are needed to maintain sterile atmosphere between processing and packaging (packaging materials, pipework, tanks, pumps); higher skilled operators; sterility must be maintained through aseptic packaging
- 37. Particle Size: With larger particulates there is a danger of overcooking of surfaces and need to transport material - both limits particle size Equipment: There is a lack of equipment for particulate sterilization, due especially to settling of solids and thus overprocessing
- 38. Keeping Quality: Heat stable lipases or proteases can lead to flavour deterioration, age gelation of the milk over time - nothing lasts forever! There is also a more pronounced cooked flavour to UHT milk.
- 39. Packaging forAseptic Processing The most important point to remember is that it must be sterile! All handling of product post-process must be within the sterile environment.
- 40. • There are5 basic types of aseptic packaging lines: • Fill and seal: preformed containers made of thermoformed plastic, glass or metal are sterilized, filled in aseptic environment, and sealed • Form, fill and seal: roll of material is sterilized, formed in sterile environment, filled, sealed e.g. tetrapak • Erect, fill and seal: using knocked-down blanks, erected, sterilized, filled, sealed. e.g. gable-top cartons, cambri-bloc
- 41. • Thermoform, fill,sealed roll stock sterilized, thermoformed, filled, sealed aseptically. e.g. creamers, plastic soup cans • Blow mold, fill, seal: • There are several different package forms that are used in aseptic UHT processing: • cans • paperboard/plastic/foil/plastic laminates • flexible pouches
- 42. Thermoformed plasticcontainers Flow molded containers Bag-in-box Bulk totes It is also worth mentioning that many products that are UHT heat treated are not aseptically packaged.
- 43. This givesthem the advantage of a longer shelf life at refrigeration temperatures compared to pasteurization, but it does not produce a shelf-stable product at ambient temperatures, due to the possibility of recontamination post-processing.