Ceramic Membrane for Fruit Pomace Extract Purification

A large amount of fruit pomace is generated every year during fruit juicing. Most pomace used to be discarded or made into low-value feed, which not only causes waste of bioactive resources, but also brings pressure on environmental treatment. In recent years, many beverage and bio-extraction enterprises have begun to recover functional components from apple pomace, grape pomace, blueberry pomace and citrus pomace. After water extraction or ethanol extraction, the crude extract is mixed with fruit residue particles, denatured protein, coarse pectin and wax, making the liquid turbid, easy to stratify and difficult to be further concentrated and dried.

Traditional purification methods include plate-and-frame filter press, vacuum drum filtration and flocculation sedimentation. These methods have obvious defects: the filtration precision is unstable, a large amount of filter aid needs to be added, the active ingredients are easily lost, and the filter cloth is frequently replaced. Organic polymer membranes such as PVDF and PES are also limited in pomace extract treatment. The extract often contains organic solvents, acid and alkali, and the feed liquid is easy to be mixed with hard fine particles, which may cause organic membrane swelling, chemical corrosion and scratch damage, shortening the service life.

Ceramic membrane is made of inorganic materials such as alumina, zirconia and titanium oxide. It adopts cross-flow filtration mode. The commonly used pore size ranges from 0.05 μm to 1.4 μm. The crude pomace extract is pumped into the membrane channel at a certain flow rate. Under transmembrane pressure, clear permeate liquid containing flavonoids and polyphenols passes through the membrane pores, while solid particles, large colloids and insoluble impurities are intercepted and circulated back to the feed tank. The high-speed tangential flow continuously scours the membrane surface, slowing down the formation of filter cake.

The standard ceramic membrane purification system includes raw liquid tank, pre-filter, sanitary feed pump, heat exchanger, ceramic membrane module rack, permeate collection tank, concentrate tank, CIP cleaning system and automatic control cabinet. The pre-filter is designed to intercept large pomace fragments to prevent scratching the inner surface of the ceramic tube. The operating temperature can reach 60–80°C, which helps reduce the viscosity of the extract and improve filtration efficiency. It is also compatible with ethanol aqueous extraction liquid, which is a prominent advantage over organic membranes.

Membrane fouling is still the main factor affecting continuous operation. Protein and polyphenol polymers are easy to adsorb on the membrane surface. The industrial cleaning scheme is mature: hot water backwashing online during operation; regular CIP circulation cleaning with alkaline solution, acid solution and oxidant. The inorganic ceramic structure will not be degraded by strong chemical cleaning agents. After cleaning, the flux can be restored steadily, and the service life of ceramic membrane can reach 3–5 years, far longer than most organic membranes.

Compared with other separation technologies, ceramic membrane purification has multiple core advantages. First, it has strong chemical stability and can adapt to water phase and dilute alcohol extract. Second, high temperature resistance supports hot filtration, reducing the risk of microbial reproduction. Third, no filter aid is added, and the obtained clear liquid is convenient for subsequent nanofiltration concentration, vacuum drying or spray drying. Fourth, the concentrate after interception can be further processed to recover dietary fiber, realizing the full utilization of pomace.

This technology has been successfully applied in grape pomace proanthocyanidin extraction, apple pomace polyphenol purification, citrus pomace flavonoid separation and other projects. It helps enterprises turn waste pomace into high-value plant extracts, improve the economic benefit of the whole juice production line, and realize cleaner production.

In conclusion, ceramic membrane cross-flow filtration is a reliable purification solution for fruit pomace extracts. With the development of circular economy, this technology will become an important supporting process for the resource recycling of agricultural and sideline products.