Application of Inorganic Ceramic Membrane in Juice Processing

Juice, as a pure natural green food, is increasingly valued by people for its excellent taste and high vitamin content. As China's fruit juice processing industry started late and people's living standards were relatively low, people in China had not become accustomed to fruit juice consumption. On the other hand, the high cost of processing fruit juice produced by traditional evaporation and vacuum evaporation or freeze concentration was also an important reason to prevent fruit juice, a high nutritional product, from rapidly occupying the beverage consumption market.

Significant progress has been made in the application of inorganic membrane technology in the food processing industry, laying a solid foundation for the industrial application of inorganic membrane technology in food processing.

Inorganic ceramic membranes have the following prominent characteristics:

1. Inorganic ceramic membrane tube is a new type of tubular membrane element made of ceramic material sintered at a high temperature of 1300 ℃ as a support layer, and then covered with a 4um thick dense film of alumina or zirconia. Therefore, it is resistant to high temperature (above 1000 ℃), high pressure (0-16bar), acid and alkali (pH=1-14), and has a long service life (generally over 8 years).

2. Inorganic ceramic membranes have high flux, with an average porosity of 30% to 40% in their membrane components. The theoretical pure water flux of 0.2um inorganic membranes is 1200L/m2.h.bar.

3. High mechanical strength and easy backwashing are another advantage of inorganic ceramic membrane technology applied in the food processing industry. It can be backwashed with gas and liquid, easily achieving high-throughput continuous stable operation during system operation, and has a long operating cycle.

4. The inorganic ceramic membrane system equipment is all assembled with stainless steel materials, and there is no pollution problem to food. It consists of a membrane module, a circulating raw material pump, a backwash system, and some auxiliary pipelines, and is characterized by simple operation and easy cleaning and regeneration. The membrane module is composed of inorganic membrane tubes and is the core part of the system; The circulating raw material pump is the power source of the system; The backwash system is the guarantee for the long-term stable operation of the system. It adopts a cross flow cycle operation mode, which minimizes membrane fouling, extends the service life and operating cycle of the membrane, and reduces operating costs to the greatest extent possible. High degree of automation, pumps, valves, etc. are all controlled by electromagnetic circuits.

5. Inorganic ceramic film itself does not promote the growth of microorganisms, and can also intercept all bacteria in the juice, extending the storage period of the juice.

6. Inorganic ceramic membranes can be divided into microfiltration, ultrafiltration, and nanofiltration based on their pore size, which can adapt to the needs of different juice processing techniques.

Membrane separation technology for juice processing

At present, membrane separation for juice processing has become mature and industrialized. Membrane separation is mainly used for concentration, clarification, and sterilization in juice processing.

1. Apple Juice

High quality concentrated apple juice of 25 Brix can be obtained by membrane method, Vc、 The loss of amino acids and aroma components is much less than that of vacuum distillation concentration. If the multi-stage membrane method is used for concentration, concentrated apple juice of 40-45 Brix can be produced.

The price of apple juice clarification using traditional pressure filtration method is $11.62 per cubic meter, while the cost of clarification using ultrafiltration is only $2.78.

2. Orange Juice

The technology of producing high-quality orange juice through membrane separation has matured. Orange juice can already be concentrated to 55 Brix.

3. Other fruit juices

The production lines for membrane separation and concentration of grape juice, bergamot juice, clarified lemon juice, tomato juice, etc. were also established abroad in the late 1980s.

Application examples of inorganic membranes in juice clarification and filtration:

The application of inorganic membranes in juice clarification is one of the most successful examples. Ceramic film is mainly used for juice clarification to remove bacteria, pectin, and crude protein that can easily cause juice spoilage. The resulting juice has excellent quality and a more fragrant aroma than traditional filtered pasteurized juice. The traditional method of clarifying fruit juice requires multiple steps of filtration and the use of filter aids. The application of membrane technology is very meaningful for improving juice quality and reducing operating costs, and inorganic membranes are gradually showing their superiority in juice filtration. Anon et al. found that carbon zirconia membrane has significant advantages in the filtration and clarification of apple juice. Thomas et al. used SS-ZrO2 membrane for pilot scale apple juice clarification and filtration, and obtained an average flux of 120L/m2. h. Using zirconia ceramic membrane for clarification and filtration of apple juice, with a membrane area of 65m2. a three-stage series filtration method is adopted. The operating conditions are: membrane surface flow rate of 5-6m/s, and operating pressure of 0.5MPa. The operation time is 15 days, and after three membrane washes, each lasting 2 hours, it can be seen that membrane washing can restore the membrane's permeate flux. The transmittance of the permeate is greater than 99%, even up to 99.9%; The refractive index is generally 9%; The color is generally around 70.0. with a minimum value of 54.0 and a maximum value of 88.5.

Progressiveness of Membrane Separation Technology in Food Industry

After using membrane separation in juice processing, it can achieve: ⑴ energy saving; ⑵ Good quality. Most of the aromatic components can be retained, while the total labor productivity of the fat soluble components is higher, so the regenerated concentrated juice is not much different from fresh juice; ⑶ Long shelf life. Due to the bactericidal effect of the membrane and the presence of undecomposed pectin in the filtrate treated by acid free method, long-term storage generally does not result in secondary precipitation.

The comparison of traditional methods applied in energy conservation and food industry is shown in Table 1 and Table 2.

Table 1 Energy consumption comparison of three concentration methods

Table 2 Price Comparison of Various Methods for Food Concentration and Dehydration

3. Simplify processes and operations. Traditional beverage production uses pasteurization and the addition of chemical preservatives to meet food hygiene requirements. Microfiltration technology can replace pasteurization and the addition of chemical preservatives. The effective range of microfiltration is 0.05-2.5um, and the size of microorganisms that need to be killed in food processing is mostly within this range. Therefore, using microfiltration membrane separation for aseptic filtration is the most effective method, as it can intercept all bacteria, yeast, and mold, and the effective ingredients in food can pass through the membrane.

In addition, traditional juice clarification is first treated with enzymes in a reaction tank, and then filtered or centrifuged, which takes a long time, occupies a large area, and is costly. Using ultrafiltration to clarify juice can reduce equipment such as reaction tanks, pumps, compressors, centrifuges, etc., save diatomaceous earth or other filter aids and enzyme preparations, and reduce operating and labor costs. In addition, it can also increase juice production and reduce waste residue.

Therefore, whether compared from an economic or technological perspective, the membrane method (especially inorganic ceramic membrane) has unparalleled advantages over other traditional methods in the food processing and production process, and is the best application technology for the future technological transformation of China's food processing (juice processing) industry.