## 1 Introduction
The Strecker degradation of amino acids mainly occurs in the advanced stage of the Maillard reaction, and is an important source of flavour substances. In this process, amino acids react with \(\alpha\)-dicarbonyl compounds (\(\alpha\)-DCs) to form aldehydes, carbon dioxide and \(\alpha\)-amino ketones through oxidative decarboxylation [13], and the aldehydes and acids produced by the Strecker degradation of amino acids have strong aromatic potential. \(\alpha\)-DCs are intermediate products with high reactivity in the Maillard reaction, and are also the main precursor of flavour substances. The generation of \(\alpha\)-DCs mainly includes a caramelization reaction [14] and the Maillard reaction [15]. The caramelization reaction is the main pathway for the formation of \(\alpha\)-DCs [16; 17], and includes carbohydrate degradation and oxidation reactions, such as glucose degradation to 3-deoxyglucone aldehyde (3-DG), and oxidation to glucose ketoaldehyde (G). [PERSON] et al. [18] detected 3-DG produced by glucose degradation at 37 \({}^{\circ}\)C. In the Maillard reaction pathway, the reaction products of sugars and amino acids form macromolecule \(\alpha\)-DCs, such as G [19], 1-DG and 3-DG [9], through Amadori rearrangement, oxidation, deamination and enolization. [PERSON] et al. [20] detected 3-DG with 1 mmol phenylalanine and 1 mmol glucose heated at 100 \({}^{\circ}\)C for 30 min. When the pH of the Maillard reaction is less than 7, Amadori rearrangement products tend to undergo a 1,2-alcoholization reaction to form 3-DG; when the pH of the reaction is greater than 7, the rearrangement products tend to undergo a 2,3-alkenyl alcoholization reaction to form 1-DG. These long-chain \(\alpha\)-DCs are easily broken into small-molecule \(\alpha\)-DCs, such as glyoxal (GO), acetone aldehyde (MGO), etc. The accurate detection of \(\alpha\)-DCs and their formation routes is the key to study the formation mechanism of flavour substances in the Maillard reaction. [PERSON] et al. [21] reported that \(\alpha\)-DCs such as GO and MGO reacted with L-leucine, respectively, to form isovaleric aldehyde. [PERSON] et al. [22] reported that \(\alpha\)-phenylenediamine (OPD) was added to beer as an inhibitor to prevent the reaction between \(\alpha\)-DCs and amino acids, but no flavour substance for Strecker aldehyde was detected. Currently, the main methods for the detection of \(\alpha\)-DCs include high pressure liquid chromatography-ultraviolet spectrometry (HPLC-UV) [23], HPLC-MS [24], GC-MS [25], etc. HPLC-UV can detect \(\alpha\)-DCs introduced into chromophore by derivation, but an extensive derivation time will affect the accuracy of detection. HPLC-MS is an effective method to separate and analyse complex organic mixtures, but short-chain \(\alpha\)-DCs cannot be detected, and by-products may be produced during the determination of samples with high sugar content, affecting the accuracy of the detection results [26]. GC-MS has the advantages of high sensitivity, wide detection range, etc. It is used to detect volatile compounds, which can make up for the shortcoming of HPLC-MS in detecting short-chain \(\alpha\)-DCs [27]. Compared with fresh CWC, the flavour of CWC becomes more intense after steaming, which may be because the substances contained in CWC crack or react with each other at high temperature to produce flavour substances [2]. The substances involved in the reaction can be preliminarily determined by comparing the content changes before and after steaming. Our team used the detection method in reference [28] to detect the substances contained in fresh CWC and steamed CWC by HPLC-MS/MS. According to the changes in its peak area, the contents of phenylalanine and glucose in steamed CWC were significantly reduced, which may be the possible substrate of the characteristic flavour substance phenylacetaldehyde.