‘Necessity is the mother of all inventions’ and one of the most classic necessity of all times is the need for high-quality and safe foods. These never-ending needs have motivated industries and research groups to advance the development of new products and technologies.
Read: July 2023 Issue of Food Infotech Magazine.
The consumer demand for minimally and naturally processed, nutritious foods has led food scientists and technologists to work towards addressing the challenges of
1. Minimizing the impact of industrial treatments on the nutritional, organoleptic and technological factors with low-cost processes; and
2. Ensuring quality and safety of the product.
Preservation of Liquid Foods
Liquid foods have high nutritional content and health promoting effects, which are preserved by the concentration technology during liquid food processing. The conventional technology used for concentration of liquid food is thermal-based process like evaporation or distillation. However, these thermal processes have negative impact on the nutritional components and the organoleptic properties of these foods.
Nanofiltration (NF) and Reverse Osmosis (RO)
In order to overcome these negative impacts, different non-thermal techniques like Nanofiltration (NF) and Reverse Osmosis (RO) [hydraulic-pressure driven] are employed. These techniques hold an obvious superiority as compared to thermal methods, when it comes to the following points:
1. Preservation of heat-sensitive compounds in the concentrate;
2. less energy consumption and manpower cost and smaller system footprint as compared to conventional thermal methods.
Limitations of NF & RO
However, the severe membrane fouling caused by intricate organic and inorganic compounds in liquid food restricts the processes efficiency of NF and RO. Additionally, the fouling of pressure-driven membrane processes is mainly irreversible without chemical cleaning. These inherent disadvantage limits these conventional membrane techniques for non-thermal concentration in food industry.
Forward Osmosis
To address all of these limitations, techniques that are driven by osmotic pressure like Forward Osmosis (FO) are being used. FO is recognized as the modern non-thermal concentration technique that is dependent on the difference in osmotic pressure and temperature. In comparison to NF and RO, FO has demonstrated a good performance, while exhibiting distinct variances in governing principle, module configuration, membrane fouling behaviour, fouling mitigation technique and operating cost.
Working of Forward Osmosis
During the FO process, a semi-permeable membrane separates two solutions with different osmotic pressures. Water is transported from the low osmotic pressure feed solution (FS) across the membrane and into the high osmotic pressure draw solution (DS) as a result of the difference in osmotic pressure.
Water can pass into DS while solute in liquid meal may be effectively rejected by the semipermeable FO membrane. Here the driving force of the FO process is the composition and concentration of the draw solution. In actual applications, an appropriate DS can be used to achieve FO driving force, which is significantly higher than RO. As a result, FO is suitable for liquid food concentration.
Advantages of FO
As a whole, the technique is quite promising as it is non-thermal, thereby ensuring that the organoleptic properties of the liquid foods are not altered. Requirement for membrane mechanical properties is less along with lesser membrane fouling.
Disadvantages of FO
Despite those advantages, FO is still compromising several problems that hamper their development in liquid food concentration. The development of the DS is the key factor limiting the use of FO in the food business. While there have been some attempts to create innovative draw solutes with little reverse flow, additional research is necessary to fully grasp their costs and process efficiency. Additionally, considering the salt leakage from DS to FS, liquid food concentration via FO necessitates non-toxicity of DS. The creation of an appropriate food additive as DS may help and support the FO’s liquid food concentration. Additionally, liquid food with higher concentration and more complexity compositions, compared with wastewater may cause more severe membrane fouling and flux decline. Therefore, effort should be taken to fully understand the fouling behaviours and mechanisms during liquid food concentration by Forward Osmosis (FO) and Membrane Distillation (MD).
Conclusion
These limitations that are seen can be mastered by developing favourable membranes for FO in liquid food processing. By incorporating different fouling mechanisms along with developing novel membranes will open a new avenue to the future of liquid food concentration by FO and MD.
The food industry now has more options for applying FO and MD thanks to hybrid membrane technology. The efficiency of the overall system could be increased by incorporating FO or MD with other separation methods, which would also make the liquid food concentration process more practical from an economic standpoint. By combining these processes with low-grade waste and/or alternative energy sources, such as solar, geothermal and waste energy, it may also make FO and MD more practical for large-scale deployment.
And thus, a deep understanding of the operation time, membrane fouling, concentration polarization (FO), reverse solute flux (FO) and DS recovery (FO) is very important for employing Forward Osmosis (FO) in liquid food processing.
