Endoxylanases in durum wheat semolina processing: Solubilization of arabinoxylans, action of endogenous inhibitors, and effects on rheological properties

Endoxylanases seriously affect the rheological properties of durum wheat (T riticum durum Desf.) semolina spaghetti doughs prepared with, and as evalua ted, by the farinograph. Under the experimental conditions, control doughs (34.9% moisture content) made from two semolinas (semA and semB) yielded a maximal consistency of 525 and 517 farinograph units (FU), with, respective ly, 19.4 and 16.4% of the total level of arabinoxylans (TOT-AX) being water -extractable (WE-AX). When 75.4 Somogyi units/50 g of semolina of the endox ylanases from Trichoderma viride (XTV), rumen microorganisms (XRM), Bacillu s subtilis (XBS), and Aspergillus niger (XAN) were used, the maximal consis tencies at 34.9% moisture decreased for semA to 467, 436, 448, and 417 FU, respectively. This was accompanied by increased WE-AX contents of 60.8, 71. 2, 70.7, and 73.0%, respectively. Similar results were observed for semB. B y reducing the total water content of doughs, it was possible to recover th e maximal consistency of the original doughs. Both the decrease in maximal consistency and the amount of water to be omitted were significantly relate d to the decrease in molecular weight (MW) of the WE-AX and the percentage of WE-AX solubilized as a result of the enzymic action. At the same time, i t was clear that endogenous endoxylanase inhibitors were present in the dur um wheat semolinas and that they inhibited the endoxylanases used to differ ent degrees. Part of the differences in effects between the different endox ylanases (decrease in maximal consistency, amount of AX solubilized, MWs of the WE-AX, and amount of water that could be omitted) could be ascribed. t o the differences in inhibition of the endoxylanases by endogenous inhibito rs.