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BACKGROUND: During vegetable cooking, one of the most notable and common chemical reactions is the Maillard reaction, which occurs as a result of thermal treatment and dehydration. Amadori compound determination provides a very sensitive indicator for early detection of quality changes caused by the Maillard reaction, as well as to retrospectively assess the heat treatment or storage conditions to which the product has been subjected. In this paper, a hydrophilic interaction liquid chromatographic-electrospray ionization-tandem mass spectrometric method was developed for the analysis of eight Amadori compounds, and the initial steps of the Maillard reaction during cooking (steaming, frying and baking) bell pepper, red pepper, yellow onion, purple onion, tomato and carrot were also assessed by quantitative determination of these Amadori compounds.

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Amadori compounds (ACs; N-(1-deoxy-d-fructos-1-yl)-amino acid) are superior flavor precursors and potential functional ingredients in food processing. In this study, vacuum dehydration as an excellent and universal method for the formation of ACs in both simulation systems and food processing was revealed. In total, 12 amino acids referring to all six categories were selected to conduct simulated reactions with glucose in aqueous models. At 90 °C, yields of 11 ACs were significantly increased by vacuum dehydration, reaching 4–198 times compared to a heat sealing reaction in aqueous systems, and formation of 5-hydroxymethyl-2-furaldehyde (5-HMF) and browning were slower than that by a dry powder reaction. In particular, the yields of Fru-Arg, Fru-His, and Fru-Glu reached 87.03, 90.73, and 89.88 mol %, respectively. The order of promotion effect was acid ACs > basic ACs > unique ACs > polar neutral ACs > aliphatic ACs > aromatic ACs. The excellent effect was mainly attributed to the control of water activity (Aw) and pH, which enabled the models to reach the optimal reaction state quickly by adjusting the vacuum degree at mild temperatures. The method was also applied to AC enrichment in tomato sauce processing; the AC content could rise to 30.72 mg/g, which was more than 17 times than those in samples without vacuum dehydration and two commercial tomato sauces.

In order to establish an efficient detection method to evaluate the formation of Amadori compounds (ACs) in food products and study the potential health effects, an ultra-high performance liquid chromatography-tandem mass spectrometric (UPLC-MS/MS) method using caffeine as internal standard was developed to determine eight ACs. The detection limits ranged from 0.0179 to 0.0887 mg/L for the ACs. The accuracy of the method was tested through measuring recovery of the spiked samples that varied from 81.90 ± 2.98% to 108.74 ± 2.34%. This method was further applied to detect ACs in 10 food products. Results showed that dry fruits and vegetables were rich in ACs, the total content of ACs varied from 1.36 ± 0.26 to 3415.91 ± 147.96 mg/100 g. The total amount of ACs in tomato juice heated under vacuum condition showed significant increment (P < 0.05) in 25 min at 80°C comparing with that under atmospheric pressure due to the rapid loss of water. Besides, the amino acid content shows positive correlation with the corresponding AC formation in Maillard reaction during food drying. After heated at fixed water activity (Aw) for 4 hr by sous-vide process, the ACs content in tomato powder increased significantly and the antioxidant activity improved as well.Practical Application: Results of this study provided a valuable tool to evaluate the formation of ACs in complex dry food products, facilitated the quality control of food products. The knowledge obtained will offer useful information to food processors. The synthesized ACs would facilitate further study into the antioxidant activities and potential health effects of specified AC.