Effect of hydrothermal processing on changes of insoluble-bound phenolics of lentils

The changes in the insoluble-bound phenolics (IBPs) of lentil cultivars upon hydrothermal (boiling) processing were monitored using HPLC-ESI-MSn analysis and by following different antioxidant capacity measurements. The hydrothermal energy disintegrated or loosened the cell wall matrix, hence the content of insoluble-bound phenolics decreased as shown by HPLC analysis and measurement of phenolics and antioxidant capacity during the boiling process, indicating their possible release from cell wall matrix. However, the released bound phenolics did not remain as soluble/free phenolics (SPs) as their increase was less than the decrease in bound phenolics, indicating loss of phenolic compounds. This loss is speculated to be due to the formation of irreversible covalent bonds to other molecules such as protein, starch, and cellulose, which are not affected by alkali hydrolysis procedure used in this work. Thus, structural and positional changes of bound phenolics and possible alteration of chemical bonding during boiling may be contemplated.