Pigment Isolation Using Tangential Flow Filtration

Pantone, a US based company best known for its Pantone Matching System consisting of a library of more than 20,000 hues, has declared Peach Fuzz as its color of the year for 2024. Described as a warm and cozy hue nestled between orange and pink, this sweet and airy tone will influence concepts in fashion, home decor, beauty, and even packing throughout the year. Transitioning from inspiration to realization, however, requires pigments to be derived in order to color products such as inks and dyes to cosmetics and even food and pharmaceuticals. These pigments can be extracted from naturally occurring sources or chemically synthesized.

Pigment Isolation and Purification
Naturally derived pigments can be extracted from plants and are also produced by microbes, such as bacteria, fungi, yeasts, and algae[1][2]. Large-scale microbe cultures allow for the production of large quantities of pigment to be used for industrial applications[2]. Pigments are extracted from natural sources (e.g., plants, microbes) through several solvent-based extraction methods, including traditional solvent extraction, microwave-assisted extraction, ultrasound-assisted extraction, pressurized liquid extraction, pulsed electric field-assisted extraction, supercritical fluid extraction, and enzyme-assisted extraction[3]. Due to growing restrictions and environmental concerns over the large-scale use of organic solvents for these processes, “greener methods” have been and are being developed, including using eutectic solvents[4][5] or ionic liquids[6]. In addition to naturally derived sources, pigments can be chemically synthesized[7][8][9]. Often, these synthetic compounds mimic naturally derived pigments. Regardless of whether they are extracted from fruits or produced by algae, pigments must be purified for downstream applications and can be separated from other molecules by column chromatography and further purified by gel filtration or membrane filtration.

Tangential Flow Filtration

Tangential flow filtration (TFF), or cross-flow filtration, involves applying a solution to the membrane filter at an angle (i.e., tangentially) rather than “dead-end” filtration where the solution flows perpendicular to the filter's plane[10]. Facilitated by a pressure difference, permeate crosses the filter while the retentate solution is retained. While many applications use single-pass TFF, the retentate can also be passed across the membrane again, significantly decreasing loss. In addition to reduced product loss, another significant benefit of this method for bioprocessing is the reduction in membrane fouling, as material does not accumulate on the membrane due to the application angle. There are several factors to consider when employing tangential flow filtration, including:

  •  Type of membrane (e.g., pore size, material compatibility with feed solution)
  •  Application parameters (e.g., temperature, velocity of feed solution application)
  • ·Maintenance requirements (e.g., frequency of membrane cleaning/replacement, maintenance of instrumentation) 

Type of membrane

Common membrane modules for TFF include ceramic, hollow fiber, or cassettes. Each has advantages and disadvantages. For pigment isolation, hollow fiber is most commonly used. Hollow fiber membranes can accommodate large volumes and are gentler on solvents, but they are appropriate for a more limited range of solvents and have a shorter lifespan than other membrane modules. Hollow fiber membranes can be made of a variety of polymers, including polyimide, polyaniline, polybenzimidazole, polyacrylonitrile, and many others [11-13].

Application Parameters

Exposure to shear stress can damage biomolecules in solution, including pigments. In TFF, shear stress is determined by the membrane selected and the velocity and angle of solution application. Hollow fiber membrane modules can deliver the lowest amount of shear stress. In addition to velocity, pH is another parameter that needs to be monitored and optimized as pH dramatically affects solubility. It can also impact the rate of fouling, or aggregation on the membrane. The solution's viscosity will also need to be considered when selecting the membrane and velocity. A highly viscous solution will require a hollow fiber membrane with a larger diameter.

Maintenance

The rate of membrane fouling will be reduced with TFF, but the filter will still need to be cleaned and/or replaced at regular intervals. The proper means of cleaning will depend on the contaminant fouling the membrane as well as the membrane composition [14]. There are several mechanical and chemical protocols for cleaning a hollow fiber membrane for TFF[14].

Benefits of Tangential Flow Filtration for Pigment Isolation

Pigments are utilized in multiple industrial sectors, requiring sustainable, large-scale pigment production. Purification by gel filtration chromatography is not a feasible option for large-scale applications, as it has a low sample volume capacity [15]. In tangential flow filtration, the feed solution can be continuously applied, allowing for filtration of large volumes. Tangential flow filtration is a highly efficient alternative to gel and other membrane-based filtration methods that can readily be scaled for pigment purification. 


References:

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4. Mesquita LD, Contieri LS, Sosa FHB, Pizani RS, Chaves J, Viganó J, et al. Combining eutectic solvents and pressurized liquid extraction coupled in-line with solid-phase extraction to recover, purify and stabilize anthocyanins from Brazilian berry waste. Green Chem. 2023;25(5):1884-97.

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8. Maruoka K, Suzuki R, Kamishima T, Koseki Y, Dao ATN, Murafuji T, et al. Total Synthesis of Azulene Derivative, a Blue Pigment Isolated from Lactarius indigo, and Colorant Application of Its Aqueous Dispersion. J Agr Food Chem. 2023;71(30):11607-14.

9. Vyhnal CR, Mahoney EHR, Lin Y, Radpour R, Wadsworth H. Pigment Synthesis and Analysis of Color in Art: An Example of Applied Science for High School and College Chemistry Students. J Chem Educ. 2020;97(5):1272-82.

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