Evaluating nitrite content changes in some Chinese home cooking with a newely-developed CDs diazotization spectrophotometry.

The research developed a diazo-coupling carbon-dots (CDs) method for determining nitrite and optimized variables of sodium sulfanilate, CDs synthesis, characteristic wavelength, reaction time and temperature. The method can assay 0.025-2.0 mg/L NO2- and has a detection limit of 9.6 µg/L and 95-105% recovery. Subsequently, it was applied in detecting NO2- changes in some Chinese home cooking, the gotten results indicated that if the sautéed vegetables (cabbage, Chinese cabbage, spinach and lettuce) and stir-fry pork, fried peas and pickled vegetable are stored at 4 °C for 72 h, nitrite contents are far lower than the recommended value, but if stored at room temperature for 24 h, the content in pure vegetables and shredded pork with green pepper will exceed the recommended value. Therefore, the staying fresher for the sautéed vegetables at room temperature is 24 h, if stored in a refrigerator at 4 °C, their staying fresher can be extended to 72 h.

Effects of microwave heating on the protein structure, digestion properties and Maillard products of gluten.

As a kind of traditional food, gluten is widely studied for its physical and chemical properties after processing, while little attention is paid to the simulation cooking processing, digestion and safety. In this paper, gluten was heated with microwave to study its structural transformations, nutritional efficiency, and food safety under Chinese home cooking (CHC). After microwave treatment, intermolecular and intramolecular cross-linking of gluten were formed to result in more aggregation. The secondary structure of gluten changed significantly as well as the formation of α-helix and ß-turn promoted under the high power input. Treated with 1000 W for 5 min, cross-linking between amino acids increased, leading the reduction of total amino acids, in vitro protein digestibility and the increase of high molecular weight peptides, while the proportion of essential amino acids kept the same. In the simulation of CHC, the highest content of 5-hydroxymethyl furfural was observed after adding all condiments under 1000 W for 5 min. In addition, sugar played a major role in Maillard reaction to promote the formation of melanoidin and fructosamine while salt and oil did not significantly affect these two Maillard products. Vinegar inhibited the reaction due to the acidic condition but provided some melanoidin and fructosamine itself.