Hello! I would suggest using filtration through a fine-pore filter (0.5-1 µm) under pressure. In laboratory conditions this could be a syringe filter. In addition, sedimentation of the extract for 12-24-48 hours (variations are possible for different extracts) at a temperature of 8-10 degrees centigrade is quite effective in precipitating fine particles.

hi,

Turbidity in natural aqueous extracts, such as those derived from cowpea plant parts, commonly arises from suspended particles, colloids, proteins, and other plant-based constituents that only partially dissolve in water (Rafiq et al., 2021). Recent studies have emphasised that extensive ultrasonication and prolonged maceration steps can disintegrate plant materials into smaller fragments, leading to persistent turbidity even after conventional filtration procedures (Quispe et al., 2022). Vacuum filtration with Whatman No. 3 filter paper is often inadequate in removing the finely dispersed particles present in these extracts (Heinrich, Barnes, Gibbons, & Prieto Garcia, 2018). Conversely, multi-step approaches have been shown to enhance clarity while preserving bioactive compounds responsible for antimicrobial activity (Rafiq, Sharma, Lei, & Zhang, 2021).

A recommended strategy involves subjecting the crude extracts to a preliminary centrifugation at moderate to high speeds (e.g., 4,000–10,000 g for 10–15 minutes) to sediment coarse plant debris, followed by vacuum filtration. The application of vacuum filtration through a paper filter with a smaller pore size (e.g., Whatman No. 1) or even a membrane filter of 0.45 µm is recommended, depending on the viscosity and the intended downstream applications (Quispe et al., 2022). This multi-stage protocol ensures that larger particles are separated before subsequent fine-filtration steps. In certain cases, the employment of clarifying agents such as bentonite or gelatin is recommended, although it should be noted that these may alter the composition of the extract and potentially influence its antimicrobial efficacy (Harborne, 1998). Alternatively, the adjustment of the pH to facilitate protein precipitation or the allowance of longer sedimentation times in a refrigerated environment has been shown to further enhance clarity (Mohamed, Sulaiman, & Sulaiman, 2021). However, it is important to note that extended low-temperature storage can potentially lead to the degradation of heat-sensitive or oxidation-prone phytochemicals (Rafiq et al., 2021). Therefore, selecting a suitable filtration strategy that balances the need for clarity with the preservation of the plant's active constituents is essential. A combination of centrifugation, staged filtration with appropriately sized filter media, and analytical verification (e.g. via spectrophotometry or turbidity measurements) represents a robust, evidence-based approach to achieving clear yet biologically active aqueous extracts (Quispe et al., 2022).

Ref

Harborne, J. B. (1998). Phytochemical Methods: A Guide to Modern Techniques of Plant Analysis (3rd ed.). Chapman & Hall. Heinrich, M., Barnes, J., Gibbons, S., & Prieto Garcia, J. (2018). Fundamentals of Pharmacognosy and Phytotherapy (3rd ed.). Elsevier. Mohamed, A. A., Sulaiman, R. R., & Sulaiman, S. (2021). Plant extracts for antimicrobial applications: Clarification approaches and functional implications. Journal of Food Quality, 2021, Article 9971347. Quispe, Y., Orjuela, A., & Olaya, J. (2022). Evaluation of filtration strategies for the clarification of aqueous plant extracts. Journal of Food Processing and Preservation, 46(5), e16237. Rafiq, S., Sharma, V., Lei, S., & Zhang, H. (2021). Recent advances in membrane-based technologies for plant extract clarification: An overview of process parameters and quality outcomes. Food Chemistry, 346, 128914.