International Dietary Fibre Conference 2009 edition:4th location:Vienna, Austria date:1-3 July 2009
The potential of ball milling for in situ production of fermentable AXOS in wheat and rye bran in a dry milling process was investigated. An extensive lab scale ball mill treatment (120 h, 50% jar volume capacity) increased the wheat bran water-extractable arabinoxylan (WE-AX) level from 4% (untreated bran) to 61%. Extractable AX fragments had an arabinose to xylose (A/X) ratio of 0.7 and an average degree of polymerization (avDP) of 70. Ball-milling of rye bran gave rise to similar results, the A/X ratio of the extracted AX being somewhat lower (0.5) compared to wheat bran. Optimization of the ball mill treatment by varying the degree of filling of the milling jar permitted to obtain equally high WE-AX levels (> 65%) in wheat and rye bran within a 24 h ball-milling period. Ball-milling at optimal conditions yielded wheat bran AXOS with an A/X ratio of 0.7 and an avDP of 38. Ball milling (24 h, 50% jar volume capacity) of isolated wheat bran pericarp increased the WE-AX level from 1 (untreated pericarp) to 63%. The extractable material was characterized by a high A/X (0.97) and a low avDP (44). In vitro fermentation of the wheat bran AXOS preparation (A/X 0.7, avDP 38, 42% AXOS) with human fecal inoculum showed that 45% and 65% of the arabinose and xylose residues, respectively, were consumed within 48 h, leaving behind AXOS with a high A/X ratio (1.0). Fermentation gave rise to production of short-chain fatty acids, the largest increase being observed for butyric acid. Surprisingly, in spite of the very high A/X value, the wheat pericarp AXOS preparation (A/X 0.97, avDP 44, 61% AX) was partially fermented (30 and 40%, of the arabinose and xylose residues, respectively). These results show that AXOS can be produced in situ in wheat or rye bran in a single-stage dry milling process, rendering a wet extraction step redundant. It can be assumed that these preparations can exert prebiotic properties similar to what we observed in chickens1-2 and rats3 with isolated wheat bran-derived AXOS.