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Wheat is an important trade commodity, and it is vulnerable to fraud due to its large volumes, complex grading system and wide range of composite and processed end products. Wheat fraud has been a persistent issue since the Middle Ages. It not only causes economic loss but harms the customers’ and stakeholders’ rights. Hence, the authentication of wheat and its derived products is important. Stable isotope ratio analysis has been extensively studied and documented as a means of authenticating wheat. However, applying hydrogen (δ²H) and oxygen (δ¹⁸O) stable isotopes to authenticate the processed wheat-derived foods presents greater complexity. The critical question is: for different wheat-derived products with varying ingredients, how does processing influence the isotopic compositions in wheat-derived noodles, and what are the underlying causes or mechanisms of these isotopic shifts? This thesis, therefore, aims to 1) Explore the effects of formulation (gluten-to-starch ratios) on the δ2 H and δ18O stable isotopic compositions in noodles; 2) Elucidate how the δ2 H and δ18O stable isotopic ratios change in noodles during various processing procedures, such as drying and boiling; 3) Study the interactive effects of formulation and processing on the δ2 H and δ18O stable isotopic ratios in processed wheat-derived noodles; 4) Investigate the underlying causes and mechanism of the δ2 H and δ18O stable isotopic shift.
In Chapter 2, the individual and combined effects of formulation (gluten-to-starch ratios), drying methods and drying time on the isotopic composition of noodles, specifically focusing on δ²H and δ¹⁸O isotopes in noodles, were investigated. It is observed that during drying, formulation (gluten-to-starch ratios) is the main factor that significantly influences δ2 H, followed by drying methods and the interaction between both factors (formulation × drying methods). Regarding δ18O, only formulation and drying methods show a significant effect. Additionally, noodles with a higher gluten protein content (from 55–100%) present a higher isotopic shift despite the drying methods, whereas starch-dominated noodles showed a small shift in both δ2 H and δ18O. Comparing industrial stepwise drying with traditional constant drying, the latter consistently produced noodles with higher δ²H and δ18O values, indicating more intense drying and more significant isotope fractionation under such drying methods. This chapter suggests, in view of product authentication, that in the case of low-temperature dried noodles, the δ²H and δ¹⁸O isotopic ratios can be considered relatively stable, but at higher temperature drying, corrections to compensate for the drying effects are required.
In Chapter 3, the effects of formulation, processing (drying and boiling) and their interaction on δ2 H and δ18O were elucidated, respectively. It is found that boiling significantly influenced the δ2 H and δ18O in noodles. Formulation is the main factor which influenced δ2 H followed by the boiling process and formulation × boiling process. Regarding δ18O, the trend was in the order of boiling process > formulation > formulation × boiling process.