The use of membrane technology as a handling and separation method in food industry is gaining importance day-by-day. Membrane separations can be used as a substitute to conventional techniques especially in dairy, sugar, fruits juice processing, and beverage industries. In many cases, membrane processes are more advantageous than traditional technologies and can be considered as green technologies as it does not causes environmental hazards, Using membrane filtration to remove microorganisms for shelf-life extension of foods instead of using additives and preservatives also create a green image for the processed foods as well as for the processing procedure. For example, using cold pasteurization and sterilization with suitable membranes instead of high temperature treatment for the removal of microorganisms is more economical in terms of energy consumption, quality of products, minimize loss of nutritional value.
Membrane separation is a process of separating food components by using semipermeable membranes, based on the molecular size and molecular weight of the components. The driving force of the separation process is, for example, differences in concentration or pressure between the two sides of the membrane.
The different membrane processing methods are as follows-
Reverse osmosis (RO). Concentration of solution by removal of water
Nanofiltration (NF). Concentration of organic components by removal of part of monovalent ions like sodium and chlorine (partial demineralization).
Ultrafiltration (UF). Concentration of large and macro molecules
Microfiltration (MF). Removal of bacteria, separation of macromolecules
Also abbreviated as MF. The basic unit or the heart of a membrane/microfiltration technology is its membrane which acts as a barrier and separate 2 phases. It is important to note that sieving mechanism or size of the particle is the basis for separation in MF while in others it is the molecular weight cut off. The main purpose of MF is clarification and turbidity removal.
As explained Microfiltration (MF) designates a membrane separation process similar to UF but with even larger membrane pore size allowing particles in the range of 0.2 to 2 micrometers to pass through.
- The pressure used is generally lower than that of UF(Ultrafiltration process) process.
- MF is used in the dairy industry for making low-heat sterile milk.
Membrane: It is semi-permeable in nature i.e. allows some materials to pass through it while restricting others selectively.
Process: Solution or the feed is passed with a driving force or pressure through a membrane that is semi-permeable in nature, which causes it to flow. Depending on the pore size, speed, pressure etc. it allows passage of some particle while retain some component on the other side of the membrane
Thus, the feed stream divides into-
1.Permeate-The component that passes to another side or the membrane is known as permeate.
2.Retentate -The components that could not pass through the membrane and remains on one side of the membrane or on the surface of membrane is known as Retentate
Generally, 2 different flow configurations are employed in Microfiltration:
1.Dead-end-flow: It is the most basic form of filtration. In this the complete feed flow is forced through the membrane and the filtered matter is accumulated on the surface of the membrane. The dead-end filtration is a batch process as accumulated matter on the filter decreases the filtration capacity, due to clogging. The next step in the process is to remove the accumulated matter which is required. Dead-end filtration can be an extremely useful technique for concentrating compounds.
2.Cross Flow Micro-filtration: The process is referred to as “cross-flow”, because the feed flow and filtration flow direction have a 90 degrees angle With cross-flow filtration a constant turbulent flow along the membrane surface prevents the accumulation of matter on the membrane surface. The membranes used in this process are commonly tubes with a membrane layer on the inside wall of the tube. The feed flow through the membrane tube has an elevated pressure as driving force for the filtration process and a high flow speed to create turbulent conditions It is an excellent way to filter liquids with a high concentration of filterable matter
The application of membrane technology in food industry is growing gradually in both international and domestic market since 1960s. For selected applications, microfiltration is superior to other conventional methods owing to its inherent advances such as low energy consumption, fewer and mild processing steps, greater separation efficiency, improved final product quality, eco-friendly and ‘cleaner’ processing i.e., better quality products at lowest cost with highest environment protection through minimum/low waste generation.
Application in Dairy Industry:
- The removal of bacteria and spores from milk to extend its shelf-life by MF is an alternative way to ultra-pasteurization. In this approach, the organoleptic and chemical properties of the milk are unaltered. The first commercial system of this so- called Bactocatch was developed by Alfa Laval and marketed by Tetra Pak under the name Tetra Al cross-Bactocatch. In this process, the raw milk is separated into skim milk and cream. The resulting skim milk is micro filtered using ceramic membranes with a pore size of 1.4 µm at constant Trans membrane pressure (TMP). Thus, the retentate contains nearly all the bacteria and spores, while the bacterial concentration in permeate is less than 0.5 % of the original value in milk. The retentate is then mixed with a standardized quantity of cream. Subsequently, this mix is subjected to a conventional high heat treatment at 130 °C for 4 s and reintroduced into the permeate, and the mixture is then pasteurized. Since less than 10 % of the milk is heat treated at the high temperature, the sensory quality of the milk is significantly improved. MF for the removal of bacteria and spores can be further applied in the production of other dairy products. In the production of cheese, the use of low bacterial milk improves also the keeping quality of cheese due to the removal of spores, thus eliminating the need of additives (e.g., nitrate). While in the production of whey protein concentrates (WPC) and isolates (WPI), this MF concept is used to remove bacteria and spores giving a high-quality product.
- Water industry (drinking water + wastewater processing + water desalination) has the largest commercial market for membranes worldwide.
- In Beverage industry –In the classical beer production process as an alternate, reverse osmosis is used for beer dealcoholisation prior to its clarification by microfiltration before pasteurization and bottling MF now successfully employed for beer clarification i.e., for removal of yeasts, microorganisms and for haze without adversely affecting its sensorial attributes
- Wine Industry- Winemaking is a complex and delicate art process that is part creativity and a part science and must be carefully controlled to produce the best wine possible. The winemaker has to take all of this into consideration when composing the perfect balance between aroma, color and taste of a particular wine. In wine treatment oxidation and browning is reduced in healthy way. Wine clarification (remove suspended material & colloids) done by UF and MF is effective, decrease the turbidity, no need for additives and does not produce solid waste and filtration media.