Influence of ethanol precipitation and ultrafiltration on the viscosity and gelling properties of alkaline-extracted pectin from tea residue.

For an economic and environmentally friendly approach, ultrafiltration has been used to replace ethanol precipitation for pectin purification in the biorefinery process of tea residue from beverage factories. However, the resulting pectin product exhibits poor viscosity and gelling properties. To address this, the composition, molecular weight distribution, and particle size distribution were determined to assess the influence of ethanol precipitation and ultrafiltration on the viscosity and gelling properties of the purified alkaline pectin extract (APE). The results suggested that ethanol precipitation could remove protein, polyphenols, and salts, while protein was not removed by ultrafiltration. The ethanol-purified APE had a high viscosity (350 mPa∙s) and good gelling properties (Gʹ = 4170 Pa, G″ = 870 Pa), which might have been caused by the generation of large molecules with similarly sized particles. Removal of free protein led to the production of self-assembling molecules in the APE, and the varied concentrations of Ca²⁺ and Na⁺ influenced the particle size distribution. As ultrafiltration removed both Ca²⁺ and Na⁺ but retained protein, the APE purified by double ultrafiltration processes had poor viscosity and gelling properties. Combined single ultrafiltration and single ethanol precipitation purification is a better solution for pectin purification, as it reduced 80% of the ethanol consumption to obtain a pectin extract with a purity of 64%, a recovery rate of about 80%, and good viscosity and gelling properties similar to those of ethanol precipitation. [ABSTRACT FROM AUTHOR]