“The added Cys reacted with TTCA and prevent it from further Maillard reaction by completely restoring it to sugar and amino acid under heat treatment”
The Maillard reaction is a specific type of chemical reaction that occurs in hot and dry conditions between the nucleophilic amino groups of amino acids and the reactive carbonyl groups of reducing sugars.
Occurring in a range of foods including seared steaks, fried fish, biscuits, and bread, the Maillard reaction is the cause of the browning effect and the characteristic taste of foods that have been grilled, roasted or baked as opposed to being boiled, poached, or steamed.
These food enhancing effects arise due to the formation of a wide range of compounds. As such, these Maillard reaction products are of great interest to the food industry as additives to provide desirable flavoring.
The compounds themselves are not heat-stable and so the beneficial effects on food flavor and appearance are likely to be lost on heating during food preparation. More stable Maillard reaction intermediates are thus being investigated as food enhancers.
These are compounds that are produced during the Maillard reaction but are not the final products that affect food flavor and color. The Amadori rearrangement product is one such intermediate. When heated it generates thermal decomposition products that cause desirable changes in food color and flavor.
However, the isolation of Maillard reaction intermediates from aqueous solution has proved challenging. Since the reaction takes place at a high rate in the aqueous conditions needed for preparation of food additives, it is difficult to determine the critical conditions required for the formation of stable intermediates.
This was recently addressed by conducting the Maillard reaction at varying temperatures and using cysteine as an indicator of the formation of stable intermediates.
The Maillard reaction intermediates 2-threityl-thiazolidine-4-carboxylic acid (TTCA) and Amadori rearrangement product was purified and identified by ultra-high-performance liquid chromatography with mass spectroscopy and nuclear magnetic resonance (NMR) spectrometry.
All NMR experiments were performed on a Bruker DRX 400 MHz spectrometer (now replaced by the Bruker AVANCE series). The greatest accumulation of Maillard reaction intermediates was observed at low temperatures when the intermediates were formed more gradually.
In addition, the decomposition of Maillard reaction intermediates was reduced at low temperatures. During the low-temperature reaction stage of the Maillard reaction, TTCA was the main intermediate generated.
The inhibitory effect of cysteine on Maillard browning was shown to be the result of added cysteine reacting with TTCA to inhibit the formation of visible color by preventing the generation of dicarbonyl compounds.
Cysteine prevented the normal reaction pathway from TTCA to the Amadori rearrangement product by restoring TTCA to sugar and amino acid under heat treatment.
Zhai Y, et al. Interaction of Added L-Cysteine with 2-Threityl-thiazolidine-4-carboxylic Acid derived from Xylose-Cysteine System Affecting its Maillard Browning. J. Agric. Food Chem 2019. DOI: 10.1021/acs.jafc.9b04374.