Evaluation of air-dried soy protein isolate-rice noodles prepared via combined treatment with microbial transglutaminase and glucono-δ-lactone

In this study, the effects of steaming treatments during the preparation of structurally enhanced air-dried rice noodles were investigated. Soy protein isolate-rice noodles (RNS) were combined (COM) with microbial transglutaminase (MTG) and glucono-delta-lactone (GDL), and steamed for 5 (S5) or 10 (S 10) min followed by air-drying to yield air-dried RNS-COM-55 and RNS-COM-S10, respectively. Control samples were air-dried rice flour noodles (ADRN), steamed for 5 or 10 min before air-drying (ADRN-S5 and ADRN-S10). Compared to other air-dried RNS prepared without steaming, RNS-COM-S5 and RNS-COM-S10 showed a reduction in cooking time (5.35 min) and cooking loss (7.11%) and increased cooking yield (125%), supposedly due to low gelatinisation enthalpy, while retaining textural and mechanical properties, significantly higher (P < 0.05) than the controls. The scanning electron micrographs showed that all steamed air-dried noodles also had larger hollows, which could be responsible for the improved cooking qualities. In general, the relative order of starch crystallinity resulting from steaming treatment decreased in all steamed noodles, and RNS-COM1-S10 showed the highest order. The treatment of RNS with MTG and GDL yielded air-dried noodles with a more compact structure. Steaming is necessary to improve the rehydration characteristics of the air-dried noodles without sacrificing textural and mechanical qualities.