Feruloylated sugar beet pulp pectic substances extracted by microwave-assisted process

Sugar beet pulp serves as an emerging pectin source with unique functional properties. This study investigated the ferulic acid (FA), a bioactive substance, present in the pectic extracts isolated from sugar beet pulp by a microwave-assisted (MAE) process. Sugar beet pulp (SB, 10 g) was subjected to a pressurized microwave-autoclave (2.67 Bar, 134.8 °C) at three pH levels (2.5, 3.5, and 4.3). Water extraction (WE) was also performed at all pH levels. Other physicochemical properties of SB pectic extracts, including neutral sugar composition using gas chromatography, and FTIR spectroscopies to estimate the degrees of esterification (DE), degree of acetylation (DA), and thermal degradation using a universal TGA analyzer, were also analysed. The results obtained revealed that MAE and lower pH significantly (p < 0.05) improved the pectic yields (% dry basis) (pH 2.5, 19.9±0.05; pH 3.5, 17.10 ± 0.03; pH 4.3, 15.50 ± 0.06) more than WE pectic extracts (pH 2.5, 11.80 ± 0.49; pH 3.5, 11.30 ± 0.12, pH 4.3, 9.10 ± 0.03). Moreover, MAE significantly improved the FA (%)(pH 2.5, 2.71±0.33; pH 3.5, 2.54 ± 0.11; pH 4.3, 2.44 ± 0.17) compared to WE (pH 2.5, 2.29±0.18; pH 3.5, 2.34±0.17; pH 4.3, 2.27±0.77). FTIR spectroscopies of all pectic extracts revealed high DEs (56.68- 64.55 %). Higher proportions of galactose were observed in the MAE SB pectic extracts compared to those of WE extracts, and generally, a high DA is obtained from all pectic substances (14.32±1.24-17.41±0.76%). The thermal degradation of SB pectic extracts resulted in low ash residues (3.54-4.72%). In conclusion, the microwave-assisted technique promotes the extraction of feruloylated pectic substances from sugar beet pulp.