How does protein content affect bread wheat functionality?

Wheat samples and flour quality

Samples of AAC Brandon (No. 2 CWRS or better) were blended into 7 aggregates according to their protein content. Aggregates were divided into groups of 11.5%, 12.6%, 13.6%, 14.5%, 15.6%, 16.6%, and 17.7% protein. We found that test weight decreased gradually with increasing protein (Figure 1a). The test weight for each aggregate was, however, above the minimum requirement for No. 1 CWRS (79 kg/hL). Flour samples were prepared using a Bühler MLU 202 laboratory mill with a constant extraction rate of 74% for comparative analysis. Milling yield increased for aggregates with protein content ranging from 11.5% to 14.5% but decreased for aggregates with higher protein content due to a decrease in kernel size and test weight (Figure 1b).

Dough properties and end-product quality

Dough properties were measured by Farinograph and Extensigraph following AACC International Methods. The results from our tests on the AAC Brandon aggregates are given in Table 1. The mixing requirement, as indicated by dough development time, was found to increase as protein content increased. Dough strength, measured by maximum resistance (Rmax) and stability, was also found to increase with protein content. Dough extensibility showed an upward trend with increased protein content.

Baking quality was determined with the Canadian Short Process (CSP) and the Sponge and Dough (S&D) bake tests. Results from the S&D bake test showed that loaf volume increased with increasing protein content (Figure 2) but no change in volume was observed using the CSP bake test. We analyzed bread crumb texture with a TA.XT2 Texture Analyzer using a Texture Profile Analysis test. Loaves produced by both the CSP and S&D bake tests showed a decrease in crumb hardness as protein content increased (Figure 3).

Flour protein and functional protein fractions

Flour proteins were fractionated into monomeric proteins (MP), soluble glutenins (SG), and insoluble glutenins (IG). The absolute quantity of IG in flour from AAC Brandon aggregates was found to increase linearly with protein content while the percentage of IG in the total amount of protein remained largely unchanged (Figure 4). We also found that the sum amount of SG and MP increased proportionally with IG (Figure 5).

Insoluble glutenins were analyzed using reversed-phase ultra-performance liquid chromatography (RP UPLC). The 45% 1-propanol insoluble glutenin fraction was reduced and alkylated before separation with a BEH C4 300Å column. Our results confirmed that the total amount of IG was directly related to flour protein content and that little change was seen in the proportion of IG in total protein when the results were normalized to a protein content of 13.5%. (Table 2).