Formation of α-Dicarbonyls from Dairy Related Carbohydrates with and without Nα-Acetyl-l-Lysine during Incubation at 40 and 50 °C

Insight into the mechanism of Maillard reaction and lipids mutually contribute to the flavor release of squid fillets during the drying process

Dried squid fillet is a popular seafood product with a unique flavor. However, its flavor release mechanism is unclear. In this study, volatile compounds (VOCs) were dynamically monitored in thawed squid (TS), salted squid (SS) and dried squid for 6 h (D6) and 24 h (D24). Subsequently, the Maillard reaction (MR) substrate, lipid oxidation index, free fatty acids and lipid profiles were detected. The results showed that the number of VOCs increased from 11 in TS (114.26 μg/kg) to 19 in D24 (1257.89 μg/kg). Besides, MR between glucose/ribose and amino acids (methionine, arginine, etc.) contributed to 3-methyl-butanal, methional and 2,3-butanedione. Meanwhile, lipid oxidation index, lipidomics and correlation analysis indicated that lipids (phosphatidylcholines and triglycerides) containing polyunsaturated fatty acids (C18:2, C20:4, C20:5 and C22:6) were precursors of 3-methyl-butanal, nonanal, heptanal, dodecane and tetradecane. Briefly, lipid hydrolysis, oxidation and MR mutually contributed to the flavor during the drying process of squid fillets.

Identification of Lactose-Derived α-Dicarbonyl Compounds in Dairy Products and Elucidation of Their Formation Mechanism

α-Dicarbonyl compounds (α-DCs) generated from carbohydrates play a key role in food quality and safety as precursors. Lactose contributes to α-DCs generation in dairy products; however, α-DCs with intact lactose carbons have not been investigated so far. This study aimed to identify lactose-derived α-DCs, clarify the mechanism of its formation using model incubations, and investigate the distribution and contents of α-DCs in dairy products. From the heated lactose and lysine solution, four new α-DCs derivatives were isolated by column chromatography and preparative HPLC and identified as lactosone, 1-deoxylactosone (1-DL) and its epimer, and 1,5-dideoxylactoson-4-ene (1,5-DDLE) by MS and NMR analyses. 1-DL, 1-DL epimer, and 1,5-DDLE were specifically formed from Amadori compounds of lactose and could be indicators of lactose-associated Maillard reaction. These α-DCs were abundantly contained in thermally processed dairy products, especially infant formulas and whey protein, and affected by ingredients and manufacturing process.

Investigation of Maillard reaction products in plant-based milk alternatives

Over the past decade, plant-based milk alternatives (PBMAs) have gained increasing popularity. Several processing technologies, including heat treatment, are usually employed during their production in order to replicate the properties of cow's milk. These processes can trigger the Maillard reaction, producing Maillard reaction products (MRPs) and amino acid cross-links, which may alter the nutritional profile and digestibility of PBMAs. This study investigates PBMAs available in the Scandinavian market to assess their MRP and amino acid cross-link concentrations, aiming to understand the relationship between the formation of these heat-induced compounds and the specific chemical composition of individual PBMAs. Two types of UHT-treated cow's milk and ten UHT-processed PBMAs from different brands were analyzed. Quantitative analyses included early-stage MRPs (Amadori products detected as furosine), intermediate MRPs (α-dicarbonyl compounds and furans), advanced glycation end products (AGEs), acrylamide, and amino acid cross-links (lanthionine and lysinoalanine). Protein, carbohydrate, and amino acid profiles were also assessed using LC-MS and HPLC methods. PBMAs were found to differ substantially in carbohydrate and protein content, with soy-based drinks containing higher protein and rice and oat drinks having more carbohydrates. Essential amino acid (EAA) levels were found lower in all PBMAs, impacting their nutritional quality. MRP levels, such as furosine and AGEs, varied across PBMAs, indicating different heat-processing intensities. Specific α-dicarbonyl compounds, like 3-deoxyglucosone, were more concentrated in PBMAs than in UHT-treated cow's milk, and compounds like HMF, furfural, and acrylamide were also found in some PBMAs. Finally, correlations were observed between sugar content, α-dicarbonyls, and AGEs, which offer insights into possible chemical transformations in PBMAs during processing.

Qualitative and Quantitative Profiling of Fructose Degradation Products Revealed the Formation of Thirteen Reactive Carbonyl Compounds and Higher Reactivity Compared to Glucose

Fructose occurs in foods and as a metabolite in vivo. It can be degraded, leading to the formation of reactive carbonyl compounds, which may influence food properties and have an impact on health. The present study performed an in-depth qualitative and quantitative profiling of fructose degradation products. Thus, the α-dicarbonyl compounds 3-deoxyglucosone, glucosone, methylglyoxal, glyoxal, hydroxypyruvaldehyde, threosone, 3-deoxythreosone, and 1-desoxypentosone and the monocarbonyl compounds formaldehyde, acetaldehyde, glycolaldehyde, glyceraldehyde, and dihydroxyacetone were detected in fructose solutions incubated at 37 °C. Quantitative profiling after 7 days revealed 4.6-271.6-fold higher yields of all degradation products from fructose compared to glucose. Except for 3-deoxyglucosone, the product formation appeared to be metal dependent, indicating oxidative pathways. CaCl2 and MgCl2 partially reduced fructose degradation. Due to its high reactivity compared to glucose, particularly toward metal-catalyzed pathways, fructose may be a strong contributor to sugar degradation and Maillard reaction in foods and in vivo.

Galactooligosaccharides in infant formulas: Maillard reaction characteristics and influence on formation of advanced glycation end products

As prebiotics supplemented in infant formulas (IFs), galactooligosaccharides (GOSs) also have many other biological activities; however, their Maillard reaction characteristics are still unclear. We investigated the Maillard reactivity of GOSs and their effects on advanced glycation end product (AGE) formation during IF processing. The results showed that AGE and HMF formation was temperature-dependent and reached the maximum at pH 9.0 in the Maillard reaction system of GOSs and Nα-acetyl-L-lysine. Acidic conditions accelerated HMF formation; however, protein cross-linking was more likely to occur under alkaline conditions. The degree of polymerization (DP) of GOSs had no significant effect on AGEs formation (except pyrraline); however, the greater the DP, the higher the concentration of HMF and pyrraline. Besides, compared with arginine and casein, lysine and whey protein were more prone to Maillard reaction with GOSs. GOSs promoted AGEs formation in a dose-dependent manner during the processing of IFs. These results provide a reliable theoretical basis for application of GOSs in IFs.

Contents of ɑ-dicarbonyl compounds in commercial black tea and affected by the processing

The species and contents of ɑ-dicarbonyls in commercial black tea were examined, along with the effects of the manufacturing process and drying temperature on the formation of ɑ-dicarbonyls. Ten ɑ-dicarbonyls were quantified in commercial and in-process black tea samples by using UPLC-MS/MS and their derived quinoxalines. The ɑ-dicarbonyls content in commercial black tea decreased significantly (p < 0.05) in the following order: 3-deoxyglucosone > glucosone > 3-deoxypentosone = threosone > galactosone ≥ methylglyoxal = glyoxal ≥ 3-deoxygalactosone = 3-deoxythreosone = diacetyl. Except for 3-deoxyglucosone and 3-deoxygalactosone, a further eight ɑ-dicarbonyls were identified in all manufacturing steps of black tea. Except for the drying step, the rolling and fermenting played important roles in the formation of ɑ-dicarbonyls. The total contents of ɑ-dicarbonyls in black tea infusion ranged from 16.48 to 75.32 μg/g based on our detected ten ɑ-dicarbonyls.

Evaluation of Fructo-, Inulin-, and Galacto-Oligosaccharides on the Maillard Reaction Products in Model Systems with Whey Protein

The present study aimed to investigate the effects of fructo-, inulin-, and galacto-oligosaccharides (FOS, IOS, and GOS) on forming the Maillard reaction products such as browning, α-dicarbonyl compounds, and advanced glycation end products (AGEs). The model solutions at pH 6.8 containing each carbohydrate (mono-, di-, and oligosaccharides) and whey protein were incubated at 50 °C for 8 weeks. In the IOS model, sugars of DP3 or larger were significantly decreased at 4 weeks, whereas at 6 weeks in the FOS model. The residual amount of GOS after 8 weeks was higher than FOS and IOS; however, a large amount of 3-deoxyglucosone was formed compared to the other models. N^ε-Carboxymethyllysine (CML) concentrations in oligosaccharide models were about half of those in monosaccharide and lactose models. The highest concentrations of glyoxal- and methylglyoxal-derived hydroimidazolones 3 (G-H3 and MG-H3) were observed in the IOS model, indicating the involvement of fructose units linked by β-2 → 1 bonds. G-H3 and MG-H3 quantification could be a useful indicator to reflect the modification of an arginine residue by fructose if used acid-hydrolysis for AGE analysis. CML, G-H3, and MG-H3 were considerably formed even in the FOS model, which has no reducing terminal site, suggesting that degradation products of oligosaccharides probably participated in the formation of AGEs.

Effect of pectin oligosaccharides supplementation on infant formulas: The storage stability, formation and intestinal absorption of advanced glycation end products

Pectin oligosaccharides with a molecular weight greater than 700 Da was obtained from the pomace of kiwi (Actinidia arguta). Based on characteristics analysis and inhibitory activity of advanced glycation end products (AGEs) formation in vitro, the target pectin oligosaccharides was added to infant formulas and then subjected to accelerated storage. Results showed that pectin oligosaccharides supplementation inhibited the browning of infant formulas and glassy transition of lactose, and slowed down the increase of water activity under accelerated storage conditions. Pectin oligosaccharides also inhibited the formation of AGEs in infant formulas, such as 5-(hydroxymethyl)furfural, N^ε-carboxymethyl-lysine, N^ε-carboxyethyl-lysine, methylglyoxal hydromidazolones, glyoxal hydromidazolones, glyoxal-lysine dimer, methylglyoxal-lysine dimer and pyrraline. Besides, permeability studies using Caco-2 cell monolayer also showed that pectin oligosaccharides supplementation inhibited the intestinal absorption of AGEs, especially 5-(hydroxymethyl)furfural, Nε-carboxymethyl-lysine, Nε-carboxyethyl-lysine and glyoxal hydromidazolones. These results provide a reliable theoretical basis for the application of pectin oligosaccharides in infant formulas.

Effect of Processing of Whey Protein Ingredient on Maillard Reactions and Protein Structural Changes in Powdered Infant Formula

The most widely used whey protein ingredient in an infant formula (IF) is the whey protein concentrate (WPC). The processing steps used in the manufacturing of both a powdered IF and a WPC introduce protein modifications that may decrease the nutritional quality. A gently processed whey protein ingredient (serum protein concentrate; SPC) was manufactured and used for the production of a powdered IF. The SPC and the SPC-based IF were compared to the WPC and the powdered WPC-based IF. Structural protein modifications were evaluated, and Maillard reaction products, covering furosine, α-dicarbonyls, furans, and advanced glycation end products, were quantified in the IFs and their protein ingredients. IF processing was responsible for higher levels of protein modifications compared to the levels observed in the SPC and WPC. Furosine levels and aggregation were most pronounced in the WPC, but the SPC contained a high level of methylglyoxal, revealing that other processing factors should be considered in addition to thermal processing.

Chemical Stability of Proteins in Foods: Oxidation and the Maillard Reaction

Protein is a major nutrient present in foods along with carbohydrates and lipids. Food proteins undergo a wide range of modifications during food production, processing, and storage. In this review, we discuss two major reactions, oxidation and the Maillard reaction, involved in chemical modifications of food proteins. Protein oxidation in foods is initiated by metal-, enzyme-, or light-induced processes. Food protein oxidation results in the loss of thiol groups and the formation of protein carbonyls and specific oxidation products of cysteine, tyrosine, tryptophan, phenylalanine, and methionine residues, such as disulfides, dityrosine, kynurenine, m-tyrosine, and methionine sulfoxide. The Maillard reaction involves the reaction of nucleophilic amino acid residues with reducing sugars, which yields numerous heterogeneous compounds such as α-dicarbonyls, furans, Strecker aldehydes, advanced glycation end-products, and melanoidins. Both protein oxidation and the Maillard reaction result in the loss of essential amino acids but may positively or negatively impact food structure and flavor. Expected final online publication date for the Annual Review of Food Science and Technology, Volume 13 is March 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Effect of unsaturated fatty acids on glycation product formation pathways

Glycation and lipid oxidation in high-nutrient foods are closely related and exhibit complex interactions. To evaluate the effect of unsaturated fatty acids (UFAs) on glycation pathways, glycation products in glucose-lysine-UFA models were detected by ultra performance liquid chromatography-tandem mass spectrometry and electron spin resonance spectroscopy, together with multivariate data analysis. Results indicated that UFAs inhibited glucose oxidation by decreasing the contents of carbonyl compounds about 73.85-86.19%. UFAs promoted the formation of glycation products mainly via production of active radical. In three models, linoleic acid (LA) exhibits stronger glycation activity than oleic acid and eicosapentaenoic acid. LA significantly promoted radical formation, as well as the formation and degradation of fructosyllysine (FL), the signal intensity of active radical increased 647.45% and FL increased 78.73%. The comparison of E(k₃), E(k₇) and variable importance in projection values of orthogonal projections to latent structures discriminant analysis in three models also proved these conclusions. By studying the characteristics of LA on glycation in three UFA, we hypothesized that unsaturation is not the key factor in evaluating their effects on glycation, the radical activity, UFA solubility, spatial structure and interaction should be considered as potentially important factors.

Limitation of Maillard Reactions in Lactose-Reduced UHT Milk via Enzymatic Conversion of Lactose into Galactooligosaccharides during Production

Lactose-hydrolyzed (LH) ultrahigh temperature (UHT) processed milk is more prone to Maillard reactions and formation of advanced glycation end products (AGEs) during processing and storage than conventional (CON) UHT milk because of the presence of free galactose and glucose. Commercially available β-d-galactosidases with transgalactosylating activity can incorporate galactose into galactooligosaccharides (GOSs) and potentially limit Maillard reactions in this lactose-reduced GOS-containing milk. The aim of this study was to examine the extent of Maillard reactions in a lactose-reduced GOS milk compared to LH and CON milk after UHT processing. The GOS milk had significant lower levels of lysine- and arginine-derived AGEs compared to LH milk, while their concentrations were similar to those found in CON milk. The total concentration of measured Arg-derived AGEs was similar to the total concentration of Lys-derived AGEs in the three types of milk, indicating that Arg is an important source of AGEs in milks. Interestingly, the GOS milk generated threefold higher concentrations (up to 330 ± 6 μM) of 3-deoxyglucosone (3-DG, a C6 α-dicarbonyl). These results demonstrate that GOS milk could be a potential alternative for LH milk for lactose-intolerant individuals, although further studies are needed to understand the increased formation of 3-DG in GOS-containing milk.

Quantitation of α-Dicarbonyls and Advanced Glycation Endproducts in Conventional and Lactose-Hydrolyzed Ultrahigh Temperature Milk during 1 Year of Storage

A comprehensive quantitative characterization of Maillard reaction products was carried out for conventional (CON) and lactose-hydrolyzed (LH) ultrahigh temperature (UHT) milk during storage at 20, 30, and 40 °C for 1 year. The accumulation of 3-deoxyglucosone (3-DG) and 3-deoxygalactosone (3-DGal) in LH-UHT milk ranged from 20-fold (at 20 °C) to 44-fold (at 40 °C) higher than that in CON-UHT milk. High temperature storage (40 °C) significantly accelerated the accumulation of 3-DG, 3-DGal, and 5-hydroxymethyl furfural but not the majority of the analyzed advanced glycation endproducts (AGEs). The concentrations of major AGEs including N-ε-carboxymethyllysine (CML), N-ε-carboxyethyllysine (CEL), methylglyoxal-hydroimidazolone isomers (MG-H1/H3), glyoxal-hydroimidazolone isomers (G-H1/H3), and G-H2 detected in CON milk during storage were in the range 12-700, 1-14, 8-45, 4-13, and 1-30 μM, respectively, while they were 30-570, 2-88, 17-150, 9-20, and 5-34 μM, respectively, in LH milk. Pyrraline, S-(carboxymethyl)cysteine (CMC), and glyoxal-lysine dimer were detected in lower levels, while MG-H2, methylglyoxal-lysine dimer, argpyrimidine, glyoxal-lysine-amide, glycolic acid-lysine-amide, and pentosidine were not detected in any of the milk samples. This work demonstrates for the first time that five of the analyzed AGEs (CML, CEL, MG-H1/H3, G-H1/H3, and G-H2) could be selected as markers for evaluation of the extent of the Maillard reaction in UHT milk. These results contribute to a better understanding of how Maillard reactions progress during storage of UHT milk and can be used to develop strategies to inhibit Maillard reactions in LH milk.

Comparison of Differences of α-Dicarbonyl Compounds between Naturally Matured and Artificially Heated Acacia Honey: Their Application to Determine Honey Quality

α-Dicarbonyl compounds (α-DCs) are a major class of intermediates generated during Maillard reactions. They can serve as chemical markers of thermal processing and storage of sugar-rich foods. To distinguish between naturally matured acacia honey (NMAH) and artificially heated acacia honey (AHAH), we purified 12 major α-DCs quinoxaline derivatives to investigate the effects of temperature during heat treatment and storage on their accumulation in acacia honey. Nine of the 12 α-dicarbonyl compounds were found in acacia honey samples, and their contents varied depending on processing and storage conditions. Among them, the contents of 3-deoxyglucosulose (3-DG), 1,4-dideoxyglucosone (1,4-DDG), and 1-deoxyglucosone (1-DG) increased commensurately with heat. 3-DG content ranged from 103.7 to 146.6 mg/kg in NMAH and 572.4-1371.2 mg/kg in AHAH. Given the abundance and stability of 3-DG following heat treatment and storage, this compound can potentially serve as a reliable marker for distinguishing between NMAH and AHAH.