Homogenization

all about homogenization and Homogenizer

1. DAIRY SCIENCE COLLEGE HEBBAL ,BENGALURU

2. Homogeniser

3. Homogenization is the process of breaking up the fat globules in cream to such a small size that they remain suspended evenly in milk rather than separating out and floating to the surface. Homogenizer is a machine, which disintegrates the fat globules of milk. DEFINITION OF HOMOGENIZATION

4. It is any of several process used to make a chemical mixture the same throughout. It is intensive mixing of mutually insoluble phase (sometimes with the addition of surfactants) to obtain a suspension/emulsion. The process of homogenization was invented and patented by Auguste Gaulin in 1899. Homogenization primarily cause disruption of fat globules into smaller ones.

5. According to the United States Public Health Services (USPHS ), ‘homogenized milk is one that has been treated in such a manner as to ensure the break-up of the globules to such an extent that after 48 hours of quiescent storage, no visible cream separation occurs in milk and the fat percentage of the milk in the upper 10% portion, i.e., in the top 100 ml of milk in a quart bottle or of proportionate volumes in containers of other sizes, does not differ by > 10% of itself from the fat percentage of the remaining milk, as determined after thorough mixing’. The number of fat globules in homogenized milk is about 10,000 times greater than those in un-homogenized milk. The size of fat globule is reduced to < 1 micron, while normal fat globule size averages 2 – 12 µm in milk. The number of fat globules will be increased, but total volume of fat globules will remain almost same. The surface area of newly formed smaller fat globules is increased by 4-6 folds. HOMOGENISED MILK

6. In raw milk, the diameter of the fat particles varies from 2 to 12 µm, while a diameter of about 2 µm or less is required to keep the fat from rising in stored condition. The milk is forced at high pressure through a narrow slit (spring loaded valve), which is only slightly larger than the diameter of the globules. The velocity of milk in the narrow slit can be 100 - 200 m/s. This can cause high shearing stresses, cavitation and micro-turbulence. The globules becomes deformed, wavy and then breakup. PRINCIPLES OF HOMOGENIZATION

7. Homogenizing valve assembly: The homogenizing valve assembly is essential an adjustable orifice- or series of adjustable orifices. The pressure created by the piston pump forces product through the homogenizing valve , causing a very significant pressure drop across the orifice. The valve design and degree of pressure drop determine the effect on the product. In general, the greater the pressure drop, the greater the effect on the particle size of the product being homogenised. The homogenizing valve assembly has three crucial smaller components: The ‘Valve’, ‘Valve Seat’, and the ‘Impact Ring’. The Valve and Valve Seat are the pieces that actually form the orifice. The Impact Ring is a sacrificial piece that prevents the high pressure annular fan from damaging the chamber that surrounds it . All three components are made from a special wear-resistant hardened alloy.

8. HOMOGENIZER-CONSTRUCTION HOMOGENIZER PISTON PUMP HOMOGENIZING VALVE GENERATE HIGH PRESSURE 5 OR 7 PISTONS POPPET TYPE-BETTER PERFORMANCE BALL TYPE –EXERT GREATER PRESSURE

9. 1)Counteracting creaming: To achieve this, the size of the fat globules should be greatly reduced. A cream layer in the product may be a nuisance for the user, especially if the package is non-transparent. 2)Improving stability toward partial coalescence: The increased stability of homogenized fat globules is caused by the reduced diameter and by the acquired surface layer of the fat globules. Moreover, partial coalescence especially occurs in a cream layer, and such a layer forms much more slowly in homogenized products. Objective/Purpose of Homogenization  

10. 3)Creating desirable rheological properties: Formation of homogenization clusters can greatly increase the viscosity of a product such as cream. Homogenized and subsequently soured milk (e.g., yogurt) has a higher viscosity than un-homogenized milk. This is because the fat globules that are now partly covered with casein micelles in the aggregation of the casein micelles. 4)Recombining milk products: At one stage of the process, butter oil must be emulsified in a liquid such as reconstituted skim milk. A homogenizer, however, is not an emulsifying machine. Therefore, the mixture should first be pre-emulsified, for example, by vigorous stirring; the formed coarse emulsion is subsequently homogenized.

11. 1)  Turbulence :. Sudden, high velocity directional changes cause small, intense turbulent eddies to form in the base liquid. Larger globules are torn apart by these eddies, reducing the overall average globule size. 2) Cavitation: When traveling through the small orifice, the product experiences a considerable increase in velocity, then a sudden decrease in velocity and pressure. The rapid velocity & pressure changes cause the base liquid to suddenly vaporize, then collapse back into a liquid – a process known as cavitation. The imploding vapour bubbles further tear apart the fat globules. Theories of Homogenization

12. 3)Shattering & impact The fat globules are shattered by impinging them on the retaining valve or impact ring. 4)Explosion With the release of high pressure, the fat globules explode. 5) Shearing & grinding The fat globules are subjected to unequal forces as milk flows at different velocities in a fluid stream. As a result of the shearing action between globules, it deforms the fat globules beyond its yield point. 6)Attenuation The fat globule disruption is attributed to violent changes in the velocities of milk as it passes through the unit rendering a fragmentation slight effect on the mean particle size.

13. 1)High pressure homogenizer This type of homogenizer consists of single acting triplex pump with each cylinder having suction and discharges valves. The discharge valve of each pump empties into a common discharge pipe, in which a special valve is placed. The pressure ranges between 35 – 350 bar (500-5000 psi) depending on the type of construction of the valve. 2)Low pressure-rotary type homogenizers Usual operating pressures are below 35 bar (500 psi). The construction is so designed that milk is subjected to grinding and shearing action. 3)Sonic vibrators- milk is subjected to high frequency vibration in a device called sonic vibrator or oscillator. Types of Homogenizer

14. Sonic vibrators Low pressure homogenizer- Operating pressures : below 35 bar(500 psi) High pressure homogenizer- Pressure ranges between 35 -350 bars

15. Homogenization effect is achieved by pushing liquid (milk) under a very high pressure through a very narrow orifice, whose diameter is just slightly larger than the diameter of fat globules. When the liquid passes through the narrow gap the flow velocity increases. The speed will increase until the static pressure is so low that liquid starts to boil. The maximum speed depends on the inlet pressure. When liquid leaves the gap the speed decreases and the pressure increases again. The liquid stops boiling and steam bubbles implode (collapse) Homogenization Process  

16. Homogenization can be done in two ways: 1. Single Stage 2. Two Stage In single stage & two stage homogenization the total homogenization pressure is measured before the first stage P1 & the homogenization pressure in 2nd stage is measured before the 2nd stage P2. The 2 stage method is usually chosen to achieve optimum homogenization/efficiency. Best results are obtained when P2/P1=0.2 In first stage pressure is around 2000-2500psi & 2nd stage 500- 1000psi. Temperature is 120ºF In 1st stage fat globules join together to form clumps and is known as Post clumping . Single stage homogenization may be used for production of high viscosity product.(Cream)

17. 1.Complete Homogenization – E.g. Milk 2. Partial Homogenization – E.g. Cream Homogenization can be :

18. Full stream or total homogenization is the most commonly used form of homogenization of UHT milk and milk intended for cultured milk products. The fat content of the milk is standardized prior to homogenization, as is the solids-non-fat content in certain circumstances, e.g. in yoghurt production. Full stream homogenization

19. Partial homogenization is used to save on energy and machinery. The milk is separated into skim milk and cream, and the cream is homogenized and mixed with the separated milk ( Walstra et al., 2006). Partial stream homogenization means that the main body of skim milk is not homogenized, but only the cream together with a small proportion of skim milk. This form of homogenization is mainly applied to pasteurised market milk. The basic reason is to reduce operating costs. Total power `consumption is cut by some 80% because of the smaller volume passing through the homogenizer ( Bylund , 2003). Partial homogenization

20.  The physical state and concentration of the fat phase at the time of homogenization contribute materially to the size and dispersion of the ensuing fat globules. Cream with higher fat content than 12% cannot be homogenized because it causes clumping & shortage of membrane material (Casein). Therefore, a good homogenization effect requires 0.2g casein per g of fat. Temperature during homogenization range from 55 – 80ºC & homogenization pressure is between 10-25Mpa (100 – 250 bar) depending on the product. Process Requirements

21. Temperature of Milk: Milk should have above 33C temperature at the time of homogenization for fat phase in liquid for proper subdivision. Pressure of homogenization: 10-25Mpa (100 – 250 bar). Stage of homogenization: For milk with more than 6% fat, two stage homogenization is better. If the broken up fat globules have a tendency to agglomerate after the first homogenizing stage (150-200 bar), they can be re-dispersed employing 20-40 bar in the second stag. Fat content: Homogenization becomes less effective with increasing fat content. When the fat content is high, raising the temperature improves homogenization efficiency. When the fat content is high, the newly created total fat globule surface is so large that the material (plasma protein) becomes insufficient to form new membranes on fat. Factors affecting Homogenization

22. Smaller fat globules leading to no cream-line formation. Whiter and more appetizing color. Reduced sensitivity to fat oxidation. More full-boiled flavor & better mouth feel. Better stability of cultured milk products (Soft curd). No formation of cream layer/plug Produces soft curd and is better digested; hence recommended for infant feeding Effects/Advantages of Homogenization

23. Homogenized milk cannot be efficiently separated. Milk will not be suitable for production of semi hard/hard cheese because the coagulum will be too soft. Reduced heat stability in case of single stage homogenizer, high fat content & forms clumping of fat globules. More susceptible to ‘sunshine flavor’ Disadvantages

24. Fresh milk – Creaming of fat is avoided & taste improvement is achieved. Coffee cream, Evaporated Milk – Avoids creaming improves whitening power in coffee. Cheese milk – Reduce the fat content of whey, provides a more uniform fat distribution in the cheese mass, inhibits ‘fat sweating’ of cheese & enhance the biochemical fat degradation. Acidified dairy products – Improvement in consistency, taste, more stable acid gel & reduced whey synergizes in yoghurt & in other coagulated products. Milk mix beverage – Good distribution of additive & fat. Ice-cream mix – Reduced buttering of fat during freezing Application of homogenization

25. Effect of Homogenization on Physico -Chemical Properties of Milk Reduction of fat globules size Reduction of fat globule size to < 2 µ prevents formation of cream layer and increases the surface area of the fat about 6 times. Whiter milk Homogenization of milk increases its whitening power due to an increase in the number and surface area of the fat globules. Adsorption of casein miscelles and serum proteins on newly created fat globules surface increases scattering of light thereby causing whiter appearance. Physiology of nutrition Homogenization has been reported to improve the digestibility of milk due to increase in the number and surface area of the fat globules EFFECT OF HOMOGENIZATION ON MILK PROPERTIES

26. Flavor of milk Homogenized milk has a uniform flavor throughout. It tastes richer, smoother and creamier than un-homogenized milk due to an increase in the surface area of the fat globules which are uniformly distributed in milk. Sensitivity to lipase Homogenized milk is more susceptible to enzymatic activities, especially lipase action, than un-homogenized milk. Lipase can cause rancidity rapidly in homogenized raw milk. Susceptibility to oxidation Homogenized milk is more susceptible to oxidized flavors caused by natural or artificial light than un-homogenized milk. To prevent development of off-flavors, homogenized milk must be packaged in opaque containers, such as cartons, plastic containers or colored bottles. Bacterial count There will be an apparent increase in bacterial count after homogenization due to the break-up of clumps and colonies of organisms.

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