A lipase based study of wheat endogenous lipid and puroindoline functionality in bread making with flour from near-isogenic wheat lines

Even if they are minor constituents of wheat flour, lipids and puroindolines (PINs) co determine bread quality, although their role is not entirely clear. PINs are small proteins with surface active and lipid binding properties. Two types, PINA and PINB, exist, the functionality of which in bread making depends on the lipid population present. We here used lipases with different hydrolysis selectivity in bread making with flour from near-isogenic wheat lines (NILs) differing in PIN protein type. Lipases selectively modify the flour lipid population without altering other flour constituents whereas the applied NILs are genetically identical except for the chromosome region where PINs are encoded. Lipase impact on loaf volume was evaluated and related to changes in lipid population during fermentation. Two lipases, Lecitase Ultra and Lipolase, were applied in different concentrations in small scale bread making with flour from cultivar Alpowa (wild-type, both PINA and PINB present) and a NIL derived thereof (PINA null, no PINA present). For both flour types, Lecitase Ultra was optimally dosed at 0.5 and Lipolase at 0.2 mg enzyme protein/kg flour. At this optimal concentration, loaf volume increase was more pronounced with Lecitase Ultra than with Lipolase. Furthermore, larger volume increases were reached with wild-type flour than with PINA null flour. Lipase hydrolysis patterns were, however, similar for both flour types. Lecitase Ultra had a broad hydrolysis specificity since neutral, galacto- as well as phospholipids were hydrolysed. Lipolase on the other hand had a more narrow specificity towards neutral lipids but also hydrolysed (to a lower extent than Lecitase Ultra) monogalactosyldiacylglycerols. In spite of its more selective action mechanism, Lipolase released more free fatty acids than did Lecitase Ultra. In conclusion, this study revealed only minor differences in lipase impact when applied in bread making with flour from NILs differing in PIN protein type. Furthermore, in agreement with earlier findings, hydrolysis of phospho- and galactolipids improved loaf volume. However, in contrast to what has been reported in the relevant literature, selective hydrolysis of non-polar lipids also led to significant volume improvement.