FOOD ENGINEERING

Lesson 48. MICROFLUIDIZATION

Module 6. Recent trends in food processing

Lesson 48

MICROFLUIDIZATION

48.1 Introduction

Micro fluidization technology is a very unique type of high pressure homogenization in order to produce spherical particles that can act as fat substitute. Micro fluidization homogenization results in fat globules with a narrow size distribution and smaller average fat globules sizes than are usually found using traditional valve homogenizers. Micro fluidization is a new type of homogenization process , which gives fat globules with a diameter of 0.1-5.0 µm (av. 0.35 µm), i.e. about half the diameter obtained with conventional homogenization. It works by passing the milk through micro channels into an interaction chamber to produce two fine jets that are directed against each other at right angle at high pressures up to 20,000 psi.. As the two microstreams collide, there is a sudden pressure drop and emulsification occurs as a result of turbulence, cavitation and shear effects that occur on impact. An increase in number of passes through the microfluidizer reduces the mean particle size, but there is little to be gained by having more than three passes.

Micro fluidization can produce of fine emulsion, spherically shaped particles from completed aggregated protein dispersion which will have mimic fat and functionality of fat to produce fat substitute. It is a new alternative to produce fat-substitute, which gives spherically shaped particles from a completed aggregated protein (whey proteins or total milk proteins) dispersion into small spherical shaped to mimic the ball bearing effect of fat particles in food. Micro fluidization can be used to extend shelf-life of products such as cream liqueurs and infant formulae by producing fine emulsions (particle size approx. 0.1 µm). Compared with the high-pressure valve homogenizer, the micro fluidizer produced smaller particles with a narrow size distribution, but the rheological properties of the acid gels were similar to that of produced by high pressure valve homogenization. Micro fluidization in place of homogenization is used as a new technologies for the ice-cream industry and it allows optimal emulsifier concentration around 1% and pressure of 1200 bar. Diameter of the fat globules was changed by varying the micro fluidization pressure from 14 to 35 MPa and the number of passes (2- to 5-times). A decrease in the average hydrodynamic diameter of the fat globules from 390 to 313 nm decreased the rennet coagulation time and the curd firming rate. Consumption of foods containing phytosterols provides health benefits. These nutraceutical compounds have been known to reduce serum total and LDL cholesterol by lowering intestinal cholesterol absorption. However, phytosterols are not suitable in aqueous solution, but micro fluidization process is used as a means of incorporation of phytosterols into fluid milk. Understanding the impact of new micro fluidization processing techniques on the final texture of a cheese helps the food scientist to develop new cheeses like low-fat cheeses with desired texture. Micro fluidization of milk is useful for making cheeses with no or low melting ability or with a crumbly texture. Micro fluidization can cause low-fat and nonfat milk and dairy products, including frozen dairy desserts, to have a body and texture and mouth feel more closely resembling their full-fat counterparts. Micro fluidization produces nonfat and low-fat ice creams that usually had a slower meltdown without affecting sensory properties.

48.2 Operational Principle

Micro fluidics homogenizers contain air-powered intensifier pumps designed to supply the desired pressure at a constant rate to the product stream. As the pump travels through its pressure stroke, it drives the product at constant pressure through precisely defined fixed-geometry microchannels within the interaction chamber.

As a result, the product stream accelerates to high velocities creating shear rates within the product stream that are orders of magnitude greater than any other conventional means. All of the product experiences identical processing conditions, producing the desired results, including: uniform particle and droplet size reduction (often submicron), deagglomeration and high yield cell disruption.

48.3 Technology Overview

The basic principle behind particle-collision technology is the bombardment of a colloid system or fluid stream against itself inside an interaction chamber of fixed geometry and at very high energy. The energy results in the breakup and dispersion of the slurry. None of the energy is wasted. All product components experience the same high force in the same small area, resulting in extremely small particle sizes and a narrow particle size distribution. With particle-collision technology, no grinding media, mixing blade, or homogenizer valve is required because size is reduced by:

• Crushing forces of the particles hitting themselves;
• Shear forces on the particles within the interaction chamber;
• Cavitational forces due to extreme velocity changes in the material stream.

Particle-collision technology pressurizes a fluid stream, develops high-velocity stream(s), and then smashes these against each other within the interaction chamber. The energy applied to the product can be changed by changing the pressure on the fluid stream - to accommodate more viscous liquids, perhaps, or to create a more intense mixing or dispersing action.

The geometry of the jet paths within the interaction chamber remains constant. Therefore, all particles experience the same forces, and the smallest size and the most uniform size distribution of any of the high-performance mixing processes are achieved. Besides the fixed geometry of the interaction chamber, another factor that ensures uniform particle size is the type of pump used, which is called an "intensifier pump." This pump can be driven by air or hydraulic fluid. The intensifier pump's advantage is that it can pump the product, even viscous systems, through the fixed geometry interaction chamber at constant pressure.

The pressure can be incrementally and accurately increased or decreased over a wide range simply by adding or subtracting pneumatic or hydraulic power. Yet, even though intensifier pumps can be set to a broader range of pressures than conventional pumps, once set their pressures stay constant over the entire process stroke.

Another factor that contributes to the range of particle-collision technology is the overall architecture of the process itself. Breaking the stream in two and redirecting the streams to impinge upon themselves doubles the relative velocity with which particles impact each other. Added to the force of this impact are the cavitational forces created by the sudden increase in velocity within the interaction chamber. This sudden increase in velocity results in a sudden decrease of pressure in the channels, creating bubbles that collapse on themselves. This is cavitation. There are also shear forces acting within the passages at very high speeds.

48.3.1 Characteristics of particle-collision technology include

* Smaller particle and droplet sizes;
* More uniform particle size distribution;
* Faster processing times (greater than two orders of magnitude in some applications);
* Better control of the amount of energy applied;
* Much higher energy (up to 40,000 psi sustained);
* Scalability from small batches to continuous production;
* No moving parts in the patented interaction chamber;
* Little or no contamination of product being produced;
* Uniform dispersions and emulsions;
* Highly repeatable process from run to run.

Micro fluidization results fat of globule particle size about 25% smaller than that found with conventional homogenization and there is no major change in fat-globule size over the storage period. Micro fluidization has little effect on the formation of fat-cluster in milk. Micro fluidization can be used for fat substitute production. Micro fluidization can offer better tasting low-fat ingredients since finer emulsions closely imitate the mouth feel of full-fat products.