Ball Milling Improves Extractability and Affects Molecular Properties of Psyllium (Plantago ovata Forsk) Seed Husk Arabinoxylan

Psyllium (Plantago ovata Forsk) seed husk (PSH) is very rich in arabinoxylan (AX). However, its high gelling capacity and the complex nature of the AX make it difficult to process. In this study, ball milling was investigated as a tool for enhancing PSH AX water extractability and molecular mass (MM). A 48 h laboratory-scale ball mill treatment under standardized optimal conditions reduced the PSH average particle size from 161 microm for the untreated sample to 6 microm. Concurrently, it increased the water-extractable AX (WE-AX) level from 13 (untreated PSH) to 90% of the total PSH AX. While the WE-AX of the untreated PSH had a peak MM of 216 kDa and an arabinose to xylose (A/X) ratio of 0.20, WE-AX fragments from ball mill-pretreated PSH had a peak MM of 22 kDa and an A/X ratio of 0.31. Ball milling further drastically reduced the intrinsic viscosity of PSH extracts and their water-holding capacity. Prolonged treatment brought almost all AX (98%) in solution and yielded WE-AX fragments with an even higher A/X ratio (0.42) and a lower peak MM (11 kDa). While impact and jet milling of PSH equally led to significant reductions in particle size, these technologies only marginally affected the water extractability of PSH AX. This implies that ball milling affects PSH particles and their constituent molecules differently than impact and jet milling.