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Summary: The effect of 4 °C water cooling treatment after extrusion for different time (0 s, 30 s, 1 min, 3 min, and 5 min) on the structure and cooking characteristics of frozen extruded whole buckwheat noodles were investigated. The cooking time and cooking loss of frozen extruded whole buckwheat noodles significantly decreased after water cooling, and the broken rate was kept constant at 0%, indicating that the quality of frozen noodles was significantly improved. When the time for water cooling was 30 s, the noodles had the lowest cooking loss of 4.07% and the highest hardness and springiness of 3993.19 g and 0.96, respectively. X‐ray diffraction results showed that water cooling treatment increased the crystallinity of starch, and the amylose underwent short‐term ageing. It was also observed from a scanning electron microscope that the gel network structure of the noodles treated with 30 s water cooling was more complete and uniform. Differential scanning calorimetry analysis showed that the water cooling treatment significantly increased the freezable water content. Meanwhile, low‐field nuclear magnetic resonance indicated that the water mobility in the noodles was weakened. The above results showed that 4 °C water cooling treatment for 30 s was beneficial to the formation of starch gel structure and improved the quality of frozen noodles. This study provides a new approach to improve the quality of extruded whole buckwheat noodles. [ABSTRACT FROM AUTHOR]

Summary: The formation of 4‐hydroxy‐hexenal (HHE) and 4‐hydroxy‐nonenal (HNE) in eight vegetable oils was investigated at 180 °C. HHE was only detectable in soybean (SBO), rapeseed (RO) and linseed oils (LO). HNE was measured in all tested oils, but was found mainly in corn (CO), sunflower (SO) and soybean oil (SBO). Oil‐dependent formation of HHE/HNE was remarkably observed. Furthermore, different fatty acid methyl esters in tricaprylin, as model oil systems, were constructed to demonstrate their characteristic contribution to HHE/HNE formation. As expected, HHE and HNE originated from the oxidative degradation of methyl linolenate (MLN) and methyl linoleate (ML) respectively. Whereas low concentrations of MLN (<5.0%) and ML (<1.0%) produced no detectable HHE/HNE. The results suggested MLN/ML could induce both HHE/HNE formation and pro‐oxidation at higher concentrations. Unexpectedly, methyl stearate and methyl oleate slightly promoted HHE/HNE formation, which might be attributed to free radical transfer mechanisms during thermal oxidation. [ABSTRACT FROM AUTHOR]