Significance of LMW-GS and HMW-GS for dough extensibility: 'Addition' versus 'incorporation' protocols

Low molecular weighs (LMW-GS) and high molecular weight glutenin subunits (HMW-GS) were added to a base flour using both 'addition and 'incorporation' protocols. 'Incorporation of glutenin subunits into the glutenin network of the base flour was performed by partial (reversible) reduction and subsequent reoxidation of the glutenin network in the presence of the added glutenin subunits whereas, in the 'addition' protocol, glutenin subunits were added without reduction/oxidation. The effects of both 'addition and 'incorporation' of alkylated and unalkylated LMW-GS and HMW-C;S on dough extension parameters maximum resistance (MR) and extensibility (EX) were compared and thoroughly discussed. HMW-GS and LMW-GS had totally different effects on dough extensibility. 'Addition' of LMW-GS significantly decreased both MR and EX whereas HMW-GS caused a significant increase in MR. 'Incorporation; of LMW-GS caused a decrease in IIR whereas HMW-GS clearly increased MR. The similarity in effects obtained with 'addition' and 'incorporation of glutenin subunits indicated that, even with 'addition', glutenin subunits can he partially incorporated into the glutenin network in the presence of oxygen. Alkylated and unalkylated glutenin subunits had different effects. This was probably caused by the effect of free sulphydryl groups in unalkylated subunits (possibility of SS/SH exchanges and/or incorporation) and/or the effect induced by introduction of alkylated derived substituents. A protocol for 'incorporation with excess KIO3' was developed to exclude the possible effect of a lowering of the available oxidant concentration by oxidation of free sulphydryl;l groups in glutenin subunits. However, the use of high levels of oxidant in the 'incorporation with excess KIO3' protocol seems to overrule the effects of added glutenin subunits or may force glutenin subunits to incorporate differently from what can be observed under gentle oxidation conditions. Therefore, 'incorporation with excess KIO3' is not suitable for studying the effects of incorporation of glutenin subunits on dough extensibility. (C) 2001 Academic Press.