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 34.1g of pectic polysaccharides per 100g 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 (32.4g/100g solids) as constituent sugars than that of commercial beet pectin. The weight-average molecular mass was 175kDa, which was lower than that of commercial beet pectin (538kDa) 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 (0.25–0.3MPa, 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.
The stability of the sucrose molecule and the firmness of the tissue structure in the cossettes are of major concern when optimizing the operating conditions for the extraction system. For a given extraction system the retention time is more or less fixed, but the actual pHvalues and temperatures to be set across the system largely determine the extent to which both sugar gets lost by hydrolysis and the cossette structure deteriorates, particularly by dissolution of pectin. Furthermore, potential sugar loss by microbial infection in the extraction system needs to be controlled too. The influence of the pHvalue and temperature on these undesirable chemical and microbial reactions will be outlined in this paper, including the consequences for the subsequent processing steps. It can be concluded that the recommended optimal pHvalues and temperatures for operating the extraction system are a compromise between good and bad.