Sugar beet pectin fractionated using isopropanol differs in galacturonic acid, protein, ferulic acid and surface hydrophobicity

• Sequential isopropanol fractionates sugar beet pectin.
• Protein, ferulic acid, galacturonic acid rich fractions precipitate.
• Surface hydrophobicity was highest in protein and ferulic acid rich fractions.
• FTIR confirmed colorimetric protein analysis, in contrast to UV280 absorbance.
• Low and high methoxyl pectin precipitated at lowest and highest levels of isopropanol.

Isopropanol was used to sequentially precipitate sugar beet pectin (SBP) and generate six fractions that varied in galacturonic acid, protein, ferulic acid and other physic–chemical characteristics. Protein was high in Fractions 1 and 2 at 209 and 154 μg/mg alcohol insoluble solids (AIS), respectively. Fractions 3, 4, and 5 had lower protein values of 77–106 μg/mg AIS; the protein content was 87 μg/mg AIS in unfractionated control. Ferulic acid content in Fraction 1 was 93 μg/mg AIS and at least three times higher than measured in other fractions. The degree of esterification in Fraction 1 was 11% and ranged from 46 to 74% in later precipitating fractions. The relative fluorescence with an external probe for hydrophobicity ranged from 159 to 254 in F1, F2 and F3 compared to negligible values in later fractions. The ζ-potential ranged from −25 to −33 mV and was not different between fractions or control. Molecular weight analysis indicated highly heterogenous pectin (Mw/Mn greater than 2.5) with MW values of 398,630, 543,900, and 442,330 g/mol for F1, F4 and control, respectively. FTIR analysis confirmed that F1 and F2 were richer in protein. SBP that precipitated at the lowest isopropanol addition had the greatest protein, ferulic acid content, particle size, relative fluorescence intensity and lowest uronic acid content and degree of esterification. The type and/or nature of protein in F1 and F4 is likely different. Isopropanol fractionation resulted in SBP fractions with unique physico–chemical properties.

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