Steam drying markedly increases the solubility of feruloylated arabinan-rich pectic polysaccharide in sugar beet pulp

Three sugar beet pulp samples, which were dried by different methods (drum-dried, steam-dried, and shelf-dried), were prepared and hot water extractions (90 °C, 6 h) were performed to compare the pectic polysaccharide yield. The steam-dried pulp yielded 34.1 g of pectic polysaccharides per 100 g of dry matter. This represented about twice the yield of the other techniques, with a recovery of about 60% of the estimated amount contained in the raw material. The pectic polysaccharide obtained from the steam-dried pulp by hot water extraction and dialysis contained larger amount of arabinose (32.4 g/ 100 g solids) as constituent sugars than that of commercial beet pectin. The weight-average molecular mass was 175 kDa, which was lower than that of commercial beet pectin (538 kDa) and most of the extracted feruloyl group were bound to this polysaccharide. These characteristics were similar to those of pectic polysaccharides obtained previously by autoclave extraction from wet beet pulp. It was presumed that the pectic polysaccharides contained in sugar beet pulp were partially hydrolyzed and solubilized under pressurized and high temperature conditions (0.25–0.3 MPa, 150–180 °C) during steam drying, making them easier to extract. Using steam-dried pulp as a raw material, feruloylated arabinan-rich pectic polysaccharides can be efficiently obtained by hot water extraction under non-pressurized conditions without acid addition.