Interaction of Added l-Cysteine with 2-Threityl-thiazolidine-4-carboxylic Acid Derived from the Xylose-Cysteine System Affecting Its Maillard Browning

The Maillard reactions: Pathways, consequences, and control

The century old Maillard reactions continue to draw the interest of researchers in the fields of Food Science and Technology, and Health and Medical Sciences. This chapter seeks to simplify and update this highly complicated, multifaceted topic. The simple nucleophilic attack of an amine onto a carbonyl group gives rise to a series of parallel and subsequent reactions, occurring simultaneously, resulting into a vast array of low and high mass compounds. Recent research has focused on: (1) the formation and transformation of α-dicarbonyl compounds, highly reactive intermediates which are essential in the development of the desired color and flavor of foods, but also lead to the production of the detrimental advanced glycation end products (AGEs); (2) elucidation of the structures of melanoidins in different foods and their beneficial effects on human health; and (3) harmful effects of AGEs on human health. Considering that MRs have both positive and negative consequences, their control to accentuate the former and to mitigate the latter, is also being conscientiously investigated with the use of modern techniques and technology.

Flavor Improvement of Maillard Reaction Intermediates Derived from Enzymatic Hydrolysates of Oudemansiella raphanipes Mushroom

Maillard reaction intermediate (MRI) was prepared by the enzymatic hydrolysate (EH) of Oudemansiella raphanipes and fructose. The optimal preparation condition of MRIs was obtained when the Maillard reaction parameters were as follows: fructose addition of 5%, reaction time of 60 min, and temperature of 60 °C. E-Tongue results indicated that the umami and saltiness of MRIs were greater than those of Maillard reaction products (MRPs) and EH, and the taste-enhancing ability of MRIs was even more prominent than that of MRPs. E-Nose could obviously distinguish EH, MRIs, and MRPs, and there was an obvious difference between MRPs and MRIs regarding volatile aroma compounds. A total of 35 volatile flavor substances were identified among the three samples, including 6 alcohols, 13 aldehydes, 9 ketones, 2 esters, and 5 other compounds. Overall, MRIs could avoid the production of complete reaction products with an inferior flavor, and further enhance the umami taste.

Improving the flavor of tilapia fish head soup by adding lipid oxidation products and cysteine

Deodorization and umami enhancement are important challenges in promoting and consuming fish products. The aim of this study was to establish whether exogenous addition of oxidized lipids and cysteine can improve the fishy, umami and create a characteristic flavor in tilapia fish head soup. The results revealed that adding oxidized lipids and cysteine enhanced the sensory attributes of fish head soup and promoted the production of pleasant-tasting amino acids and fewer bitter amino acids in the Maillard reaction. Additionally, the combination increased the levels of well-flavored aldehydes, esters, heterocyclic compounds and less hydrocarbons in the fish head soup. Among the 13 volatile compounds screened, nine were identified as characteristic aromas of fish head soup, including nonanal, (E,E)-2,4-decadienal, 1-octen-3-ol, (E)-2-decenal, acetic acid, hexanal, heptanal, 2-octenal, and decanal. Exogenous lipid oxidation products, fatty acid oxidation, and Maillard reaction can improve the aroma and umami of tilapia fish head soup.

Intrinsic Molecular Mechanisms of Transformation between Isomeric Intermediates Formed at Different Stages of Cysteine-Xylose Maillard Reaction Model through Dehydration

2-Threityl-thiazolidine-4-carboxylic acid (TTCA) and Amadori rearrangement product (ARP), the isomeric intermediates derived from the cysteine-xylose (Cys-Xyl) Maillard reaction model, possessed the ability to produce similar flavor profile during the thermal process, but the flavor formation or browning rate of heated TTCA was significantly lower than that of ARP. Macroscopically, the yield of TTCA reached the maximum when the moisture content of the reaction system just dropped to nearly 0% during the thermal reaction-vacuum dehydration process. During the subsequent dynamic intramolecular dehydration process, the reaction remained at an early stage of the Maillard reaction, and TTCA was the main intermediate. Thereinto, the water activity of the samples decreased with the increased dehydration time. From a molecular perspective, the dissipation of free water promoted the conversion of combined water to immobilized water and free water, increasing the intramolecular dehydration. Instantaneous high-temperature dehydration during the spray drying process revealed a higher efficiency than the thermal reaction-vacuum dehydration process, which facilitated the specific conversion of substrates to intermediates (TTCA, ARP). The loss of free water and immobilized water was a key driving force for the direct formation of TTCA/ARP, regulating the formation stages of MRIs. The increase of the inlet air temperature could alter the ratio of TTCA and ARP at the equilibrium state.

Regulated Formation of Inhibited Color and Enhanced Flavor Derived from Heated 2-Threityl-Thiazolidine-4-Carboxylic Acid with Additional Cysteine Targeting at Different Degradation Stages

This study explored the addition of cysteine (Cys) affecting the color formation of heated 2-threityl-thiazolidine-4-carboxylic acid (TTCA) models under different reaction conditions and pointed out that temperature was considered to be the key parameter influencing the color inhibition behavior of Cys on TTCA reaction models. Results revealed that additional Cys not only controlled the reaction progress and blocked the formation pathway of browning but also changed the formation rate, intensity, and profile of the flavor generated from the TTCA reaction model. Meanwhile, the mechanism of Cys simultaneously regulating the formation of color and flavor was revealed through monitoring of the characteristic downstream products during TTCA degradation and model reaction systems. At the initial stage, the additional Cys acted as a color inhibitor before the deoxyxylosone degradation, preventing the formation of downstream browning precursors. With the continuous depletion of Cys as well as the generation of furans or α-dicarbonyl compounds, Cys became a flavor enhancer to act on the browning precursors and to provide more sulfur/nitrogen elements for the TTCA thermal reaction system. Therefore, Cys had the potential to act as both color inhibitor and flavor fortifier to match with TTCA for the preparation of a light-colored flavoring base with a desired flavor during thermal processing.

Colorants and Antioxidants Deriving from Methylglyoxal and Heterocyclic Maillard Reaction Intermediates

The Maillard reaction is well known for producing antioxidant compounds alongside colored substances. Low-molecular-weight antioxidant intermediates such as maltol (MAL) or norfuraneol (NF) are well described, but it is still unclear which of these Maillard intermediates are the precursors of antioxidant and colored melanoidins-the so-called late stage Maillard reaction products. This study aimed to provide novel insights into the correlation between browning potential and antioxidant properties of reaction products formed during the heat treatment of prominent Maillard reaction intermediates. It was achieved by the incubation of binary reaction systems composed of methylglyoxal (MGO) or NF in combination with furfural (FF), MAL, and pyrrole-2-carbaldehyde (PA) at pH 5 and 130 °C for up to 120 min. Overall, it could be shown that the formation of colored products in the binary NF reaction systems was more efficient compared to those of MGO. This was reflected in an increased browning intensity of up to 400% and a lower conversion rate of NF compared to MGO. The colorants formed by NF and FF or PA (~0.34 kDa and 10-100 kDa) were also found to exhibit higher molecular weights compared to the analogue products formed in the MGO incubations (<0.34 kDa and 10-100 kDa). The incorporation of NF into these heterogenous products with FF and PA resulted in the preservation of the initial antioxidant properties of NF (p < 0.05), whereas no antioxidant products were formed after the incubation of MGO.

Exogenous Threonine-Induced Conversion of Threonine-Xylose Amadori Compound to Heyns Compound for Efficiently Promoting the Formation of Pyrazines

The involvement of exogenous threonine during the degradation of l-threonine-d-xylose Amadori rearrangement product (Thr-ARP) was found to promote the formation of pyrazines. A model including Thr-ARP and ¹⁵N-labeled l-threonine was applied to reveal the role of free threonine in Thr-ARP conversion to pyrazines. Quantitative analyses of pyrazines in the model of Thr-ARP/¹⁵N-labeled threonine showed a precedence of the endogenous threonine (formed by the degradation of Thr-ARP) over the exogenous threonine in pyrazines formation, and the ratio of ¹⁵N to ¹⁴N content in pyrazines increased significantly over time. According to the observed occurrence of the Heyns rearrangement products (HRP) derived from ¹⁵N-threonine, as well as the sharp decrease of ¹⁵N-threonine content and a rapid increase of ¹⁴N endogenous threonine at the initial stage of heat treatment, it was proposed that aldimine condensation between exogenous threonine and Thr-ARP followed by the hydrolysis led to the endogenous threonine and the generation of HRP. Then, the HRP underwent dehydration followed by hydrolysis to form exogenous threonine and deoxyxyosones, and the dehydration and hydrolysis of deoxyxyosones to form organic acids was inhibited, but the retro-aldolization of deoxyxyosones was promoted, facilitating the generation of reactive α-dicarbonyl compounds. In this way, exogenous threonine accelerated the release of endogenous threonine and α-dicarbonyl compounds and the pH decline was slowed down, which was favorable for the formation of pyrazines.

Competitive Formation of 2,3-Butanedione and Pyrazines through Intervention of Added Cysteine during Thermal Processing of Alanine-Xylose Amadori Compounds

The intervention of cysteine (Cys) on the formation of 2,3-butanedione and pyrazines was evaluated during the thermal processing of the alanine-xylose Amadori compound (AX-ARP). With the involvement of Cys, the competitive formation of 2,3-butanedione and pyrazines was induced. The formation of 2,3-butanedione in the AX-ARP/Cys model was suppressed due to the inhibitory effect of the precursors of 2,3-butanedione like deoxypentosones, while the added Cys in the AX-ARP/Cys model competed with the recovered alanine (Ala) to capture glyoxal and methylglyoxal to make up for the absence of pyrazines in the AX-ARP model at an initial pH value of 7. The content of pyrazines increased from 0 up to 16.48 μg/L (120 °C, 120 min). Exogenous Cys itself showed lower reactivity with 2,3-butanedione through the Strecker degradation reaction; while the pH was increased to 8, the degradative products of Cys were facilitated to consume the residual 2,3-butanedione giving rise to the formation of 2,4,5-trimethylthiazole at 120 °C. It was the degradative products of Cys that accelerated the reaction for consumption of 2,3-butanedione rather than Cys itself. Additionally, the inhibitory effect of Cys on 2,3-butanedione formation was weakened under a basic condition, while the promotional effect on the formation of pyrazines was further boosted. With more Cys participating in the process of AX-ARP thermal degradation, the formation of 2,3-butanedione was further inhibited, while the yields of pyrazines were increased.

Food polyphenols and Maillard reaction: regulation effect and chemical mechanism

Maillard reaction is a non-enzymatic thermal reaction during food processing and storage. It massively contributes to the flavor, color, health benefits and safety of foods and could be briefly segmented into initial, intermediate and final stages with the development of a cascade of chemical reactions. During thermal reaction of food ingredients, sugar, protein and amino acids are usually the main substrates, and polyphenols co-existed in food could also participate in the Maillard reaction as a modulator. Polyphenols including flavan-3-ols, hydroxycinnamic acids, flavonoids, and tannins have shown various effects throughout the process of Maillard reaction, including conjugating amino acids/sugars, trapping α-dicarbonyls, capturing Amadori rearrangement products (ARPs), as well as decreasing acrylamide and 5-hydroxymethylfurfural (5-HMF) levels. These effects significantly influenced the flavor, taste and color of processed foods, and also decreased the hazard products' level. The chemical mechanism of polyphenols-Maillard products involved the scavenging of radicals, as well as nucleophilic addition and substitution reactions. In the present review, we concluded and discussed the interaction of polyphenols and Maillard reaction, and proposed some perspectives for future studies.

Effects of Flash Evaporation Conditions on the Quality of UHT Milk by Changing the Dissolved Oxygen Content in Milk

This study assessed the impact of reducing dissolved oxygen (DO) content on the quality of UHT milk using a flash deoxygenation treatment. Flash deoxygenation was designed based on preheated milk reaching boiling early under low-pressure conditions to remove DO from the milk. Two parameters were designed for flash deoxygenation: preheating temperature 65 °C, -0.08 Mpa, and 70 °C, -0.06 Mpa. The flash conditions were applied to two UHT sterilization conditions (135 °C for 10 s and 145 °C for 5 s). After deoxygenation, the total oxidation (TOTOX) value of UHT milk was reduced by 1.4~1.71, and the protein carbonyl (PC) value was reduced by 1.15~1.52 nmol/mg of protein. The maximum inhibition rates of furusine and 5-HMF were 33.23 ± 1.72% and 25.43 ± 3.14%, respectively. The particle size was reduced by 0.141~0.178 μm. The ketones and stale aldehydes causing oxidized taste in the UHT milk were significantly reduced. This study showed that the oxidation and Maillard reactions of UHT milk were significantly inhibited, stability was improved, and the content of undesirable volatile flavor substances was reduced after flash deoxygenation. Therefore, reducing DO content was beneficial to improving the quality of UHT milk.

Effect of the C-Ring Structure of Flavonoids on the Yield of Adducts Formed by the Linkage of the Active Site at the A-Ring and Amadori Rearrangement Products during the Maillard Intermediate Preparation

Flavonoids (dihydromyricetin, dihydroquercetin, epicatechin, and epigallocatechin) were applied to indicate the critical formation condition of the Amadori rearrangement product (ARP) in Maillard reaction performed under a two-step temperature rising process in the threonine-xylose model system. Threonine-ARP (Thr-ARP) was mixed with dihydromyricetin (DM), dihydroquercetin (DQ), epicatechin (EC), and epigallocatechin (EGC) before the heat treatment; then, the mixture was tested by liquid chromatography-mass spectrometry (LC-MS). The results showed that these flavonoids trapped the ARP and generated adducts. The A-ring of flavonoids (the meta-polyhydroxylated benzene ring) was the functional group to capture the Thr-ARP. The relative contents of the adducts of DM-Thr-ARP, DQ-Thr-ARP, EC-Thr-ARP, and EGC-Thr-ARP were compared with each other, and it was found that the structure of the C-ring of the flavonoids (the carbonyl group on C-4) significantly impeded the formation of adducts with Thr-ARP, while the number of hydroxyl groups on the B-ring had little influence. The formation of adducts delayed the degradation of Thr-ARP, decreased the production of α-dicarbonyl compounds, and suppressed Maillard browning. In this way, the flavonoids might trace the critical formation conditions of ARP during the two-step temperature rising process.

Accelerated Dissipation of Free and Immobilized Water Facilitating the Intramolecular Dehydration of N-Xylosamine and Conversion Improvement of the Amadori Rearrangement Product of Aspartic Acid-Xylose Reaction

Compared to the method of aqueous Maillard reaction at atmospheric pressure tandem vacuum concentration, a coupling dehydration method combining spray drying and vacuum drying was used to increase aspartic acid-xylose conversion to the Amadori rearrangement product (ARP). The water activity and moisture states were found as effective indicators to characterize the degree of dehydration of Maillard reaction intermediates and efficient formation of ARP. During the vacuum drying process, the water activity of the product powder decreased significantly. Because the formation of ARP was accompanied by intramolecular dehydration, combining spray drying and vacuum drying increased the proportion of bound water in the vacuum-dried product. Free water was easily dissipated via dehydration, which then converted the immobilized water continuously to free water, and the decreased immobilized water further converted the bound water to immobilized water. The reduction in bound water contributed to the intramolecular dehydration of N-substituted d-xylosamine, which would further be transformed to be the ARP through an intramolecular rearrangement. The yield of ARP was increased from 1.68 to 21.53% after spray drying. The ARP yield was substantially increased up to 77.9% by subsequent vacuum drying.

Degradation of 2-Threityl-Thiazolidine-4-Carboxylic Acid and Corresponding Browning Accelerated by Trapping Reaction between Extra-Added Xylose and Released Cysteine during Maillard Reaction

2-Threityl-thiazolidine-4-carboxylic acid (TTCA), a nonvolatile precursor of flavor and color, is considered to be more stable than its isomeric Amadori compound (ARP). The degradation behavior of TTCA favors higher temperatures and pH. In order to adjust and control the thermal degradation of TTCA to improve its food processing adaptability, a TTCA-Xyl thermal reaction model was constructed to explore the effect of extra-added Xyl on the thermal degradation behavior of TTCA. The results confirmed that the extra-added Xyl was involved in the degradation pathway of TTCA and accelerated its depletion, thus promoting the formation of characteristic downstream products of TTCA including some α-dicarbonyl compounds, and consequently accelerating the browning formation. The isotope-labeling technique was further applied to confirm that the added Xyl could trap the Cys released from the decomposition of ARP and formed additional TTCA, which could promote the movement of chemical equilibrium and gradually accelerate the degradation rate of TTCA as well as melanoidins formation. The higher pH value could even promote this phenomenon.

Multi-colored shades of betalains: recent advances in betacyanin chemistry

Covering: 2001 to 2021Betacyanins cover a class of remarkable natural red-violet plant pigments with prospective chemical and biological properties for wide-ranging applications in food, pharmaceuticals, and the cosmetic industry. Betacyanins, forming the betalain pigment group together with yellow betaxanthins, have gained much attention due to the increasing social awareness of the positive impact of natural products on human health. Betalains are commercially recognized as natural food colorants with preliminarily ascertained, but to be further investigated, health-promoting properties. In addition, they exhibit a remarkable structural diversity based on glycosylated and acylated varieties. The main research directions for natural plant pigments are focused on their structure elucidation, methods of their separation and analysis, biological activities, bioavailability, factors affecting their stability, industrial applications as a plant-based food, natural colorants, drugs, and cosmetics as well as methods for high-yield production and stabilization. This review covers period of the last two decades of betacyanin research. In the first part of the review, we present an updated classification of all known betacyanins and their derivatives identified by chemical means as well as by mass spectrometric and NMR techniques. In the second part, we review the current research reports focused on the chemical properties of the pigments (decarboxylation, oxidation, conjugation, and chlorination reactions as well as the acyl group migration phenomenon) and describe the semi-synthesis of natural and artificial fluorescent betalamic acid conjugates, showing various prospective research directions.

Maillard Browning Inhibition by Ellagic Acid via Its Adduct Formation with the Amadori Rearrangement Product

The Maillard reaction performed under a stepwise increase of temperature was applied for researching the inhibition of Maillard browning caused by ellagic acid. Ellagic acid was found effective for the inhibition of melanoidin formation in the xylose-glycine Maillard reaction but depended on its dosage and the point of time it was added in the reaction system. The lightest color of the Maillard reaction products was observed when ellagic acid was added at the 90th min, which was the point of time when the Amadori rearrangement product (ARP) developed the most. LC-ESI-MS/MS analysis results showed a significant tendency of the ellagic acid hydrolysis product to react with the predominant intermediate ARP to yield an adduct. The adduct stabilized the ARP and delayed its decomposition and inhibited the downstream reactions toward browning. After the ARP was depleted, ellagic acid also showed an effect on scavenging some short-chain dicarbonyls which contributed to the inhibition of Maillard browning.

Transformation between 2-Threityl-thiazolidine-4-carboxylic Acid and Xylose-Cysteine Amadori Rearrangement Product Regulated by pH Adjustment during High-Temperature Instantaneous Dehydration

2-Threityl-thiazolidine-4-carboxylic acid (TTCA) was found to be the predominant product rather than the Amadori rearrangement product (ARP) during the formation of xylose-cysteine-derived (Xyl-Cys-derived) Maillard reaction intermediates (MRIs) through a thermal reaction coupled with vacuum dehydration. To regulate the existence forms of Xyl-Cys-derived MRIs, an effective method carried out by pH adjustment during high-temperature instantaneous dehydration through spray-drying was proposed in this research to promote the conversion from TTCA to ARP. The increased inlet air temperature of spray-drying could properly facilitate the shift of chemical equilibrium between the MRIs and promote the transformation from TTCA to ARP while raising the total yield of TA (TTCA + ARP). The conversion to ARP was increased to 20.83% at 190 °C of hot blast compared to the product without spray-drying (6.03%). The conversion from TTCA to ARP was further facilitated in the pH range of 7.5-9.5. When the pH of the aqueous reactants was adjusted to 9.5, the equilibrium conversion to ARP was improved to 47.23% after spray-drying, which accounted for 59.48% of the TA formation. Accordingly, MRIs with different TTCA/ARP proportions could be selectively obtained by pH adjustment of the stock solution during high-temperature instantaneous dehydration of spray-drying.

Identification of Novel Low-Weight Sulfhydryl Conjugates of Oxidized 5-O- and 6-O-Substituted Betanidin Pigments

The formation of conjugates of oxidized betacyanin pigments with selected low-weight sulfhydryl scavengers was studied. Short-lived quinonoids, quinone methides, and aminochromes derived from oxidized betacyanins are able to form adducts with different efficiencies. In this report, mass spectrometric and NMR identifications of CS-linked conjugates of cysteine, cysteamine, N-acetylcysteine, and dl-dithiolthreitol with quinonoid forms generated through oxidation of betanidin, betanin, and gomphrenin is presented. An adduct that formed between cysteine and quinonoid generated from betanin by its oxidation and decarboxylation (2-decarboxy-xanbetanin) was detected and reported for the first time. The most stable gomphrenin CS-conjugate, N-acetylcysteinylated gomphrenin, was isolated by semipreparative chromatography and its structure was established by NMR analysis. This enabled to confirm the conjugation position at carbon C-4 and to indicate the presence of a dopachromic intermediate during oxidation of gomphrenin. Conjugation of betacyanins with thiol-bearing moieties may generate new molecules with modified chemical and biological properties. Obtained results confirm that gomphrenin is capable of forming CS-conjugates with higher efficiency than betanin.

Maillard reaction products derived from food protein-derived peptides: insights into flavor and bioactivity

Food protein-derived peptides serve as food ingredients that can influence flavor and bioactivity of foods. The Maillard reaction plays a crucial role in food processing and storage, and generates a wide range of Maillard reaction products (MRPs) that contribute to flavor and bioactivity of foods. Even though the reactions between proteins and carbohydrates have been extensively investigated, the modifications of food protein-derived peptides and the subsequent impacts on flavor and bioactivity of foods have not been fully elucidated. In this review, the flavor and bioactive properties of food-derived peptides are reviewed. The formation mechanisms with respect to MRPs generated from food protein-derived peptides have been discussed. The state-of-the-art studies on impacts of the Maillard reaction on flavor and bioactivity of food protein-derived peptides are also discussed. In addition, some potential negative effects of MRPs are described.