Pentosan extraction from rye bran on pilot scale for application in gluten-free products

Arabinoxylan, a pentosan, is the most important thickening agent and key component in rye for bread making. The idea of the study was to use pentosans for future application in gluten-free bread. Arabinoxylans were extracted in laboratory and pilot scale. For pilot scale experiments three protease combinations and different pH levels of the solvent (neutral and alkaline conditions) were tested. The extract was cleared by centrifugation, protein and starch degradation with enzymes, heat and bentonit treatment. Finally, pentosans were separated with alcoholic precipitation or ultra-dia-filtration. Rye bran was used as raw material, because it is a low-cost by-product and contains high amounts of pentosans. The purity of pentosan isolates was more than 65% mass and the yield of pentosan reached values up to 2.5 g out of 100 g bran. These results were higher than any yield achieved in previous studies with rye flour as raw material. Alkaline conditions showed better performance for extraction than pure water. Compared to precipitation with 65% ethanol ultra-dia-filtration with a cut-off-level of 8 kD proved to be a better method for purification, because loss of arabinoxylans was much lower. The applied procedure was not able to remove proteins completely. But gluten was no longer detectable in significant concentrations (below 5 ppm) by the applied screening test, except for extraction at high pH and increased temperature. Subsequent analyses by RP-HPLC showed that amounts of secalins were below 20 ppm in all isolates. Thus isolates are suitable for future application in glutenfree products. (C) 2013 Elsevier Ltd. All rights reserved.