Nanofiltration for Separation of L-Citrulline From Watermelon Rind Juice.

Area of Science:

• Food Science and Technology
• Separation Processes
• Biotechnology

Background:

• Membrane fouling limits nanofiltration (NF) efficiency in juice valorization.
• Ultrafiltration (UF) is a common pretreatment to mitigate fouling in NF processes.
• Watermelon rind is a by-product rich in L-citrulline, a valuable amino acid.

Purpose of the Study:

• To evaluate the efficacy of UF pretreatment in enhancing NF performance for L-citrulline separation from watermelon rind juice.
• To analyze the impact of UF on membrane fouling and process efficiency.
• To assess the selective recovery of L-citrulline and rejection of D-glucose.

Main Methods:

• Watermelon rind juice was pre-clarified using a 50 kDa UF membrane.
• Subsequent NF was performed using a polyamide membrane at 10-40 bar.
• Membrane performance was assessed via permeate flux, solute rejection (L-citrulline, D-glucose), and fouling analysis using Hermia's models.

Main Results:

• UF pretreatment significantly increased permeate flux (84.7 L·m⁻²·h⁻¹) and concentration factor (VCF 11.56) compared to NF alone.
• L-citrulline showed negative rejection (permeate concentration 1,773 mg·L⁻¹), while D-glucose was highly rejected (>74%).
• The combined UF-NF process reduced total soluble solids (TSS), total dissolved solids (TDS), salinity, and electrical conductivity (EC).

Conclusions:

• Integrating UF as a pretreatment step effectively enhances NF performance for selective L-citrulline recovery from watermelon rind.
• The UF-NF process yields a permeate rich in L-citrulline and low in sugars, suitable for functional beverages and nutraceuticals.
• This membrane-based strategy offers a scalable, clean-label approach for valorizing fruit by-products and promoting sustainable food manufacturing.