OUM-NESTLE 2008 4
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  • 1. LECTURE NOTES 04/08 “HOMOGENIZATION PROCESS” SAIFUL IRWAN ZUBAIRI PMIFT, Grad B.E.M. B. Eng. (Chemical-Bioprocess) (Hons.), UTM M. Eng. (Bioprocess), UTM ROOM NO.: 2166, CHEMISTRY BUILDING, TEL. (OFF.): 03-89215828, FOOD SCIENCE PROGRAMME, CENTRE OF CHEMICAL SCIENCES AND FOOD TECHNOLOGY, UKM BANGI, SELANGOR 28 MAY 2008
  • 2. SUB-TOPIC: FOOD CONVERSION AND MANUFACTURING
    • Cooling and Freezing process.
    • Concentration & Dehydration: Concentration, Spray Drying & Vacuum Drying process.
    • Industrial Fermentation process.
    • Irradiation Process.
    • Homogenization Process.
    • Wet and Dry Mixing process.
    • Transport and Conveying process.
  • 3. Homogenization/Emulsification
    • Emulsification: “ is the formation of a stable emulsion by the intimate mixing of two or more immiscible liquids”
    • Results: the dispersed phase is formed into very small droplets within the second (continuous phase)
    Homogenization: “A mechanical treatment of the fat globules in the milk brought about by passing milk under high pressure through a tiny orifice” Results: 1) Decrease in the average diameter & increase in number & surface area of fat globules. 2) Reduced tendency for creaming of fat globules. The Homogenization process actually has a little @ no effect on nutritional value @ shelf life e.g: margarine & low-fat spreads, salad cream, mayonnaise, sausage meat, ice-cream & cakes
  • 4. Homogenization/Emulsification
    • Theory-2 types of liquid-liquid emulsion:
    • 1) oil in water (o/w)
    • 2) water in oil (w/o)
    • Milk is an oil-in-water emulsion
    • With fat globules dispersed in a continuous skim milk phase.
    • Stability of emulsions is determined by:
    • 1) The type & quantity of emulsifying agent.
    • 2) The size of the globules in the dispersed phase.
    • 3) The interfacial forces acting at the surfaces of the globules.
    • 4) The viscosity of the continuous phase.
    • 5) The differences between the densities of the dispersed & continous phases.
    • 3 factors contribute to enhanced stability of homogenized milk:
    • Decrease in diameter of the fat globules.
    • Decrease in size distribution of fat globules.
    • An increase in density of the globules (bringing them closer to the continuous phase).
  • 5. Homogenization (cont)
  • 6. 5 main types of homogenizer:
    • High-speed mixers
    • Pressure homogenizers
    • Colloid mills
    • Ultrasonic homogenizers
    • Hydro shear homogenizers & microfluidisers
  • 7.
    • (1) High speed mixers
    • Use turbines @ propellers.
    • To pre-mix emulsions of low viscosity liquid.
    • Operate of shearing action of the food at the edges & tips of the blades.
    • (2) Colloid mills
    • Essentially disc mills with a small clearance between stationary disc & vertical disc rotating.
    • Create high shearing forces & more effective than pressure homogenizers for high viscosity liquids (peanut butter, meat, fish pastes).
    Types of Homogenizer:
  • 8.
    • (3) Ultrasonic homogenizers
    • Use high-frequency sound waves (18-30kHz) to cause alternate cycles of compression & tension in low viscosity liquid & cavitations of air bubbles, to form emulsion with droplet sizes (1-2 µm).
    • Used for the production of salad creams, synthetic creams, baby foods & essential oil emulsions.
    • Also used for dispersing powders in liquids.
    • (4) Hydro shear homogenizers & microfluidisers
    • Is a double-cone shaped chamber which has a tangential feed pipe at the centre & outlet pipes at the end of each cone.
    • Feed liquid enters the chamber at high velocity, reaches the centre & discharged, differences in velocity causes high shearing forces together with cavitations, ultra-high frequency vibration, break droplets in the dispersed phase.
    Types of Homogenizer:
  • 9.
    • (5) PRESSURE HOMOGENIZERS
    • Mechanism, consider a conventional homogenizing valve processing an emulsion such as milk (flow rate: 20,000 l/hr. at 14 MPa (2100 psig).
    • First enters the valve, liquid velocity about 4-6 m/s. It then moves into the gap between the valve & the valve seat & its velocity is increased (to 120 meter/sec in about 0.2 millisec)
    • Liquid then moves across the face of the valve seat (the land) and exits in about 50
    • microsec
    Types of Homogenizer:
  • 10. Homogenization (cont)
    • Homogenization phenomena is completed before the fluid leaves the area between valve & the seat.
    • Therefore emulsification is initiated and completed in < 50 microsec.
    • The whole process occurs between 2 pieces of steel in a steel valve assembly.
    • Product may then pass through a second stage valve similar to the first stage.
  • 11.  
  • 12.
    • Most of the fat globules reduction takes place in 1-stage, there is a tendency for clumping or clustering of the reduced fat globules.
    • 2-stage valve permits the separation of those clusters into individual fat globules.
  • 13. Homogenization: Effect on Foods
    • (1) Viscosity or texture
    • The desire mouth feel (liquid & semi-liquid foods) achieved by careful selection of (1) emulsifying agent, (2) stabilizer (3) homogenization condition.
    • Homogenization giving the milk a creamier texture.
    • Solid food emulsion and texture determined by the composition of the food and homogenization condition.
    • The quality of the emulsion is influenced by:
    • The ratio of meat-ice-water-fat.
    • The use of poly phosphate to bind water content.
    • The time, temperature & speed of homogenization.
  • 14.
    • (2) Colour, aroma, nutritional value & shelf life
    • Homogenization can effect the COLOUR (i.e milk), because the large globules number causes greater reflectance & scattering of light.
    • Flavour & aroma improved in many emulsified foods because volatile components are dispersed throughout the food & greater contact with taste bud.
    • Nutritional value of emulsified foods changed if components separated (i.e: butter making), there is improved digestibility of fats & protein due to the reduction in particle size.
  • 15.
    • In summary, the homogenization variables are:
    • Type of valve
    • Pressure
    • Single @ two-stage
    • Fat content
    • Surfactant type & content
    • Viscosity
    Homogenizer (Lab-scale)
  • 16. Assignment: 1. What is the process of homogenization? 2. Why is it used for milk? 1. Homogenization : One of the oldest applications of homogenization is in milk processing, aim to prevent @ delay the separation of cream from the rest of the emulsion. This is done by forcing the milk at high pressure through small orifices. 2. Milk contains little globs of fat which rise to the surface as what we call cream. Homogenization breaks these little globs of fat into very tiny globs which are so small that the force making them rise to the top doesn't overwhelm random bumps and swirls from the milk around them.
  • 17.
    • The process of reducing the particle size of fluid products such as milk, fruit juice & sauces, under conditions of extreme pressure, sheer, turbulence, acceleration & impact to make them more stable & better texture
    • The effect achieved by forcing product through a special homogenizing valve at high pressure.
    • Particles enter the homogenizer with sizes ranging typically from 0.2 - 20 microns.
    • Large particles are dispersed to produce a product with particles ranging typically from 0.4 to 1 micron depending on the application.
    SUMMARY - Homogenization
  • 18. Food and Dairy Homogenizer Applications
    • Puddings
    • Puree
    • Sauces
    • Soy milk
    • Syrups
    • Tomato juice
    • Tomato paste / concentrate
    • Tomato Products
    • Vegetable oil
    • Whey
    • Yeast
    • Yoghurt
    • Fruit juices
    • Fruit pulps and concentrates
    • Gelatines
    • Gum Arabic
    • Honey
    • Ice cream mix
    • Ketchup
    • Margarine
    • Meat paste
    • Milk and cream-based liqueurs
    • Milk concentrates
    • Milk protein
    • Milk, recombined/sterilized
    • Animal fats
    • Baby foods
    • Butter oil
    • Caseinates
    • Chestnut / hazelnut paste
    • Chocolate
    • Condensed milk and cream
    • Confectionery
    • Cream cheese
    • Cream for coffee
    • Desserts
    • Egg
    • Fish paste
    • Flavors
  • 19. CASE STUDY: ICE CREAM MANUFACTURING
    • (1) Homogenization
    • The mix is also homogenized which forms the fat emulsion by breaking down or reducing the size of the fat globules found in milk or cream to less than 1 µ m.
    • Two stage homogenization is usually preferred for ice cream mix.
    • Clumping or clustering of the fat is reduced thereby producing a thinner, more rapidly whipped mix.
    • Melt-down is also improved.
    • Homogenization provides the following functions in ice cream manufacture:
    • (1) Reduces size of fat globules.
    • (2) Increases surface area.
    • (3) Forms membrane.
    • (4) Makes possible the use of butter, frozen cream, etc.
  • 20.
    • By helping to form the fat structure, it also has the following indirect effects:
    • (1) Makes a smoother ice cream.
    • (2) Gives a greater apparent richness and deliciousness.
    • (3) Better air stability.
    • (4) Increases resistance to melting.
    CASE STUDY: ICE CREAM MANUFACTURING
  • 21.
    • (2) Ageing
    • The mix is then aged for at least four hours and usually overnight.
    • This allows time for the fat to cool down and crystallize, and for the proteins and polysaccharides to fully hydrate.
    • Aging provides the following functions:
    • Improves whipping qualities of mix and body and texture of ice cream
    CASE STUDY: ICE CREAM MANUFACTURING
  • 22.
    • It (ageing) does so by:
    • Providing time for fat crystallization, so the fat can partially unite.
    • Allowing time for full protein and stabilizer hydration and a resulting slight viscosity increase.
    • Allowing time for membrane rearrangement and protein/emulsifier interaction, as emulsifiers displace proteins from the fat globule surface, which allows for a reduction in stabilization of the fat globules and enhanced partial unite.
    • OTHER CONSIDERATION DURING THE PROCESS:
    • Aging is performed in insulated or refrigerated storage tanks, silos, etc.
    • Mix temperature should be maintained as low as possible without freezing, at or below 5 o C.
    • An aging time of overnight is likely to give best results under average plant conditions.
    • A &quot;green&quot; or unaged mix is usually quickly detected at the freezer.
    CASE STUDY: ICE CREAM MANUFACTURING
  • 23.
    • Homogenization of the mix should take place at the pasteurizing temperature.
    • The high temperature produces more efficient breaking up of the fat globules at any given pressure and also reduces fat clumping and the tendency to thick, heavy bodied mixes.
    • No one pressure can be recommended that will give satisfactory results under all conditions.
    • The higher the fat and total solids in the mix, the lower the pressure should be.
    • If a two stage homogenizer is used, a pressure of 2000 - 2500 psi on the first stage and 500 - 1000 psi on the second stage should be satisfactory under most conditions.
    • Two stage homogenization is usually preferred for ice cream mix. Clumping or clustering of the fat is reduced thereby producing a thinner, more rapidly whipped mix.
    • Melt-down is also improved.
    CASE STUDY: ICE CREAM MANUFACTURING