3.4. Protein extractability during steaming. High temperature conditions cause wheat protein disulfide crosslinking, leading to large protein aggregates (Lagrain, Brijs Veraverbeke, & Delcour, 2005). Fig. 4 shows the protein extractability in SDS buffer for three different noodles with the increase of steaming time. Steaming significantly (P <0.05) reduced SDSEP which can be ascribed to protein aggregation (Lagrain et al, 2005) This was similar to the results reported by Buggenhout, Brijs, and Delcour (2013) for parboiled brown rice, who reported that more severe steaming conditions caused greater reductions in protein extractability, indicating a denser protein network. With the in crease of steaming time from 1 to 3 min, SDSEP of control noodles decreased dramatically, and then decreased slowly with further steaming. The level of SDSEP in white salted noodles followed the same tendency, but it was higher than that of control noodles under the same condition. The reason may be that the addition of salt increased non-covalent interactions, increasing protein extractability in SDS (Tuhumury et al., 2014). However, as for yellow alkaline noodles, reduction in SDSEP was found to be 62.2%, when noodles were steamed for 1 min, while no differences were observed from 2 to 8 min. The results indicated that the gluten protein polymerization in yellow alkaline noodles was already complete after steaming 2 min, which accounted for the changes in noodle quality and differences in steamed noodles microstructure. Compared to control and white salted noodles, yellow alkaline noodle were lower in SDSEP, which was due to the formation of disulfide linkages through mild oxidation of the gluten proteins promoted by alkaline salt(Shiau & Yeh,2001).
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