Studies on non-phenolic lignans in alkaline cooking

Abstract

AbstractThe stability and chemical reactions of lignans during alkaline cooking is not yet fully clarified although their degradation products may have a considerable effect on the pulp and its bleaching, such as spotting and color contamination. To fill this gap, a phenolic lignan (pinoresinol) and four non-phenolic furofuran lignans (gmelinol, paulownin, eudesmin and sesamin) were submitted to alkaline cooking at various conditions. The effect of cooking duration shows that non-phenolic lignans are more stable during a 3-h reaction time than pinoresinol. After a 24-h reaction, most of the lignans were decomposed or polymerized. The effect of cooking temperature shows that pinoresinol, eudesmin and sesamin are more susceptible to degradation with increasing temperature. The concentration of the alkaline liquors only affect significantly to pinoresinol because of its acidity. It was also observed that pinoresinol, gmelinol and eudesmin give rise to small amounts of vanillin and acetovanillone, while paulownin and sesamin were mainly polymerized or degraded. To confirm the reaction mechanism of the occurrence of acetovanillone in the reaction,13C-labeled pinoresinol was also submitted to alkaline cooking. It was revealed that the cleavage at β-β′ position occurred during alkaline reaction. The stability of these compounds during alkaline cooking are not affected by the hydroxyl group in the C-β′ position.