The current food industry has come about through generations of cultural and technological developments, involving many aspects from food production to processing to retail before reaching the consumer. In this day and age, the highest level of quality and safety are expected from food products, and the market for value-added foods is ever-increasing. As such, much research has been spent in food processing to ensure maximum benefit and satisfaction for the consumer. Membrane separation technology is a prominent figure in ensuring that food meets those requirements, and is hence a much researched topic, advancements occurring constantly to improve the technology and make it as efficient and economical as possible.
History of membrane filtration
Separation technology is basically the division of different components within a sample. These include distillation and other forms involving heat treatment, but in the food industry, the use of excessive heat may produce undesirable results that compromise the nutritional value, chemical makeup and overall quality of the produce. Hence, filtration is often the best option in such cases and may even used in conjunction with the abovementioned processes to enhance the quality of the product. In the food industry, the use of filters to separate solids from liquids is not a new innovation, and has traditionally been done through diatomaceous earth (Butchermaker 2004). However, its use as a filter medium has proved to have many disadvantages including health and safety issues, as well as waste disposal problems. With membrane filters however, such complications can be overcome.
Membrane technology began in the 1920s as a form of water treatment with microfiltration (Howell et al 1993), and only began to advance significantly in the past 30 or so years since the development of ultrafiltration in the 1970s for the dairy industry. Membrane filtration utilizes a pressure driving force to separate constituents in a colloidal dispersion or solution by passing it through a semi-permeable membrane, and is based mainly on the molecular size of particles, although shape and charge also play a minor role (Grandison & Lewis 1996). Initially, commercial membranes were made of cellulose acetate but due to limitations, they were replaced in the 1970s, with polyamides and polysulphones most widely used in the food industry. The use of membrane filtration covers many different aspects of food processing, with different membrane processes filter out different sizes of molecules, from fat globules (microfiltration) to ions (reverse osmosis). This versatility means that it can be used through a range of areas including the clarification of fruit juice and even the treatment of spent process water in the food industry for re-use (Blocher et al. 2002).
The primary advantages of membrane techology revolve around several properties – the exclusion of chemical additives and heat treatment which allows processes to be performed at ambient temperature and pH, the ability to run at a small scale with simple equipment, as well as its low energy and maintanence requirements (Cai 2005). The former is especially applicable in the food processing industry as consumers can easily tell when the quality of food is compromised when taste or appearance is modified due to preservatives or heat. However, many food items do require treatment of sorts for many different reasons to prolong shelf life or to concentrate for transport and convenience which would make the foods more profitable and cost-effective. Membrane technology allows the fulfillment of the stringent criteria required by both the food industry and the consumer due to the properties of the processes as described above, and has even opened up new options such as its advantages to the increasing demand for functional or value-added foods.
Types of membrane processes
Reverse Osmosis (RO)
RO is mainly used...