Functional and biological properties of Maillard conjugates and their potential application in medical and food: A review

Dissecting dietary melanoidins: formation mechanisms, gut interactions and functional properties

Dietary melanoidins are late stage Maillard reaction products (MRPs), browning colorants and predominantly high molecular weight (HMW) chemicals. They originate through polycondensation reactions of reducing sugars and proteins or amino acids upon thermal processing. Their presence in several daily food and beverages (i.e. coffee, beer, honey, bakery products, chocolate, grilled meat) contribute to food sensory characters (i.e. color, aroma, and flavor). Additionally, melanoidins exhibit many biological attributes (i.e. antioxidant, anti-obesity, antibacterial activity and impact on gut microbiota as prebiotics). However, dissecting melanoidins specific biological and functional characteristics in relation to their metabolism and gut interaction with link to their chemical structures has yet to be reported in literature. For a better understanding of melanoidins benefits and flavor properties in processed foods, this review represents a state of the art comprehensive insight of its formation mechanism and chemistry in relation to their functionalities and health effects. Further, a compile of the factors affecting melanoidins production to optimize for the best flavor attributes while minimizing hazardous compounds is presented. This study presents the first analysis of melanoidins gut interaction in context to its different action mechanisms.

Maillard conjugates of whey protein isolate-xylooligosaccharides for the microencapsulation of Lactobacillus rhamnosus: protective effects and stability during spray drying, storage and gastrointestinal digestion

The Maillard reaction products (MRPs) of whey protein isolate (WPI) and xylooligosaccharides (XOS) were prepared by a moist heat method for use as protectants to encapsulate Lactobacillus rhamnosus via spray drying. The protective effects of MRPs on bacterial cells during drying, storage, and in vitro digestion were explored. FTIR results indicated that MRPs were successfully prepared. All MRPs showed good thermo-protective effect on the bacteria, and the survival ratio achieved with 1 : 2 XOS-WPI as a wall material reached 99.83 ± 8.44%, which was around 2 times as high as that of the WPI wall material and 1.5 times as high as that of the 1 : 2 XOS-WPI mixture. The dried lactobacilli showed similar growth curves to the fresh culture. After 10 weeks of storage at 4 °C, the decrease in the bacterial activity was less than 1 log CFU g-1 for all types of microcapsules, while the microcapsules composed of all MRPs had better storage stability. MRPs improved the stability of microcapsules during in vitro digestion. The number of viable bacteria in 1 : 2 XOS-WPI MRPs microcapsules was maintained at 4.09 ± 0.59 × 109 CFU g-1 after simulated gastrointestinal digestion for 4 hours, which only decreased by 0.20 log CFU g-1.

Contribution of starch to the flavor of rice-based instant foods

Increased consumption of instant foods has led to research attention, especially rice-based instant foods. Starch, one of the most important components of rice, significantly affects food quality. However, the mechanisms by which starch contributes to rice-based instant foods flavor are poorly understood in many cases. The review aims to describe the common mechanisms by which starch contributes to food flavor, including participating in flavor formation, and affecting flavor release throughout starch multiscale structure: particle morphology, crystal structure, molecular structure. Five specific examples of rice-based instant foods were further analyzed to summarize the specific contribution of starch to flavor, including instant rice, fermented rice cake, rice noodles, fried rice, and rice dumplings. During foods processing, reducing sugars produced by heating or enzymatic hydrolysis of starch participate in Maillard reaction, caramelization and thermal degradation, which directly or indirectly affect the formation of flavor compounds. In addition, adsorption by granules, encapsulation by retrograded V-type crystal, and controlled release by starch gel all contribute to rice-based instant food flavor qualities. These mechanisms jointly contribute to flavor compounds formation and release. Proper theoretical application and improved processing methods are needed to promote the high-quality, mechanization, and automation of rice-based instant foods production.

Utilization of Maillard reaction in moist-dry-heating system to enhance physicochemical and antioxidative properties of dried whole longan fruit

This research aimed to enhance the physicochemical and antioxidant properties of dried whole longan fruit using Maillard reaction or non-enzymatic glycosylation (glycation) in a moist-dry-heating system at 60 °C with approximately 75% relative humidity for 5-50 days. During Maillard reaction, the browning index (BI) of the fruits increased significantly while lightless, redness and yellowness decreased. Interestingly, the rare sugars especially D-psicose and D-allose gradually increased by 2-3 folds when compared to the initial Maillard reaction. The development of D-mannose was additionally established through the glycation. The degree of glycation increased with the decrease of free amino acid, suggesting that conjugation of sugar with amino acids was involved. SDS-PAGE confirmed that the high molecular weight (HMW) of conjugated sugar-amino acid was the Maillard reaction product. The antioxidative properties including DPPH and ABTS radical scavenging activities, also ferric reducing antioxidant power (FRAP) were also increased as Maillard reaction progressed, which showed the activities in the range of 43.2-94.1 mg GAE/100 g dry basis, 0.23-3.09 g TE/100 g dry basis, and 0.35-5.95 g FeSO4/100 g dry basis, respectively. This study demonstrated a practical approach of Maillard reaction for the development of dried longan fruit with high antioxidative properties.

Improvements of plant protein functionalities by Maillard conjugation and Maillard reaction products

Plant-derived protein research has gained attention in recent years due to the rise of health concerns, allergenicity, trends toward vegan diet, food safety, and sustainability; but the lower techno-functional attributes of plant proteins compared to those of animals still remain a challenge for their utilization. Maillard conjugation is a protein side-chain modification reaction which is spontaneous, and do not require additional chemical additive to initiate the reaction. The glycoconjugates formed during the reaction significantly improves the thermal stability and pH sensitivity of proteins. The modification of plant-derived protein using Maillard conjugation requires a comprehensive understanding of the influence of process conditions on the conjugation process. These factors can be used to establish a correlation with different functional and bioactive characteristics, to potentially adapt this approach for selective functionality enhancement and nutraceutical development. This review covers recent advances in plant-derived protein modification using Maillard conjugation, including different pretreatments to modify the functionality and bioactivity of plant proteins and their potential uses in practice. An overview of different properties of conjugates and MRPs, including food safety aspects, is given.

Fermented Maillard Reaction Products by Lactobacillus gasseri 4M13 Alters the Intestinal Microbiota and Improves Dysfunction in Type 2 Diabetic Mice with Colitis

Inflammatory bowel disease is a chronic relapsing disease. Multiple factors can cause inflammatory bowel disease (IBD), including diet, imbalance of the immune system, and impaired intestinal barrier function. Type 2 diabetes mellitus is a complex and chronic metabolic disease caused by a combination of insulin resistance and an ineffective insulin secretory response. The co-occurrence of these two diseases, demonstrating interrelated effects within the gut microbiota, has been frequently reported. This study evaluated the effects of a fermented glycated conjugate of whey protein and galactose with Lactobacillus gasseri 4M13 (FMRP) to prevent type 2 diabetes mellitus with inflammatory bowel disease. C57BLKS/J- db/db mice were orally administered FMRP for 14 consecutive days and 2% dextran sulfate sodium (DSS) in water ad libitum for 5 days to induce colitis. FMRP-fed mice showed improved insulin secretion and symptoms of colitis. Compared to the DSS group, the FMRP group showed a decreased abundance of six bacterial genera and increased abundance of Alistipes and Hungateiclostridium. In cecal contents, the levels of short-chain fatty acids increased in the FMRP group compared to those in the DSS group. Continuous administration of FMRP thus may improve the homeostasis of not only insulin secretion and inflammation, but also the intestinal environment in inflammatory bowel disease and type 2 diabetes mellitus.

Effect of temperature and pH on the gelation, rheology, texture, and structural properties of whey protein and sugar gels based on Maillard reaction

This study aimed to determine the effect of initial pH and temperature on whey protein gel formation via the Maillard reaction, including changes in gel structure, rheological and texture properties. The color changes in the whey protein and glucose gels were not significant with increasing heat temperature. High temperature and alkaline conditions promoted exposure to hydrophobic groups such as -SH, which accelerated protein aggregation and gel formation. Moreover, the increased particle size and additional hydrophobic groups contributed to higher elastic modulus (G') in the whey protein gel. Fluorescence measurements revealed that more tryptophan on the protein surface decreased with increasing temperature, which indicated that exposure to tryptophan could increase the hydrophobicity of the protein gels. Whey proteins formed stronger, gummier, more elastic, and more cohesive gels at 70 ℃ under initial pH 9 conditions, which also increased with the addition of fructose.

Extrusion Processing of Pure Chokeberry (Aronia melanocarpa) Pomace: Impact on Dietary Fiber Profile and Bioactive Compounds

The partial substitution of starch with dietary fiber (DF) in extruded ready-to-eat texturized (RTE) cereals has been suggested as a strategy to reduce the high glycemic index of these food products. Here, we study the impact of extrusion processing on pure chokeberry (Aronia melanocarpa) pomace powder (CPP) rich in DF and polyphenols (PP) focusing on the content and profile of the DF fractions, stability of PP, and techno-functional properties of the extrudates. Using a co-rotating twin-screw extruder, different screw speeds were applied to CPP with different water contents (cw), which resulted in specific mechanical energies (SME) in the range of 145-222 Whkg-1 and material temperatures (TM) in the range of 123-155 °C. High molecular weight soluble DF contents slightly increase with increasing thermomechanical stress up to 16.1 ± 0.8 g/100 g dm as compared to CPP (11.5 ± 1.2 g/100 g dm), but total DF (TDF) contents (58.6 ± 0.8 g/100 g dm) did not change. DF structural analysis revealed extrusion-based changes in the portions of pectic polysaccharides (type I rhamnogalacturonan) in the soluble and insoluble DF fractions. Contents of thermolabile anthocyanins decrease linearly with SME and temperature from 1.80 ± 0.09 g/100 g dm in CPP to 0.24 ± 0.06 g/100 g dm (222 Whkg-1, 155 °C), but phenolic acids and flavonoids appear to be largely unaffected. Resulting techno-functional (water absorption and water solubility) and physical properties related to the sensory characteristics (expansion, hardness, and color) of pure CPP extrudates support the expectation that granulated CPP extrudates may be a suitable food ingredient rich in DF and PP.

The impact of caseinate oligochitosan-glycation by transglutaminase on amino acid compositions and immune-promoting activity in BALB/c mice of the tryptic caseinate hydrolysate

Caseinate was glycated with oligochitosan via transglutaminase (TGase) action and then hydrolyzed by trypsin to generate glycated caseinate hydrolysate (GCNH) that was investigated for in vivo immune-promoting activity. Caseinate hydrolysate (CNH) containing glucosamine of 5.7 g/kg had amino acid compositions similar to GCNH. In normal BALB/c mice, GCNH at 100-400 mg/(kg d) showed higher immune-promoting activity than CNH via increasing serum IgM, IgA, and IgG by 1.5-24.5%, enhancing spleen and thymus indices by 9.7-26.2%, or increasing splenocyte lymphocyte proliferation and natural killer (NK) cell activity by 1.2-11.5%. GCNH also exerted higher activity than CNH in the suppressed BALB/c mice through increasing serum IgM, IgA, and IgG by 2.6-10.5%, enhancing spleen and thymus indices by 0.4-50.1%, or increasing splenocyte lymphocyte proliferation and NK cell activity by 3.4-18.9%. The results highlight that this TGase-type oligochitosan-glycation is potential to generate functional protein ingredients that possess improved immune-promoting activity once hydrolyzed by trypsin.

Effect of glycation degree on the in vitro simulated gastrointestinal digestion: A promising formulation for egg white gel with controlled digestibility

The mechanism between food gelation and its digestibility has attracted increasing attention over the past few decades. This study aimed to evaluate the effect of glycation degree on the gelation and digestibility of egg white gel (EWG) using an in vitro model and a multi-scale characterization of gel structure. Results showed that EWG glycated with increasing d-ribose by covalent bonds exhibited better gelling properties and lower in vitro digestibility according to the appearance of soluble proteins and peptides. Besides, glycation preference for ovotransferrin at lysine might be important for regulating gel structure and proteolysis accessibility via the ratio of fibrous and granular aggregates. Moreover, gel structure was predominant over amino acids modification for digestibility. Binding disorder and steric hindrance could ascribe to the lower digestibility of gels. These findings are enlightening for the formulation and production of food matrix with controlled digestibility through glycation in food and related pharmaceutical fields.

Physicochemical stability and gastrointestinal fate of β-carotene-loaded oil-in-water emulsions stabilized by whey protein isolate-low acyl gellan gum conjugates

This study aimed to examine the effect of whey protein isolate-low acyl gellan gum (WPI-GG) conjugate on the physicochemical properties and digestibility of β-carotene-loaded oil-in-water emulsions. The WPI-GG conjugate-stabilized emulsions had lower droplet sizes with more homogenous distribution, more negative surface charge, and higher interfacial protein concentration and viscosity, compared to those stabilized by WPI-GG mixture and WPI. The emulsion droplets coated by the conjugate were also generally more stable to environmental stresses (i.e., storage, pH changes, ionic strength, freeze-thaw cycles, and thermal treatment) along with higher β-carotene retention than other systems. The stability to droplet aggregation during in vitro digestion was remarkably increased for the conjugate-stabilized emulsion. However, the β-carotene bioaccessibility was significantly affected when the conjugate was used to stabilize the emulsions, likely due to the thick interfacial layer, high viscosity, and negative charge of the corresponding emulsions that could inhibit droplet digestion and mixed micelle formation.

Glycation sites and bioactivity of lactose-glycated caseinate hydrolysate in lipopolysaccharide-injured IEC-6 cells

During the thermal processing of milk, Maillard reactions occur between proteins and lactose to generate glycated proteins. In this study, a lactose-glycated caseinate was hydrolyzed by trypsin. The obtained glycated caseinate (GCN) hydrolysate had a lactose content of 10.8 g/kg of protein. We identified its glycation sites and then assessed it for its protective effect against lipopolysaccharide-induced barrier injury using a rat intestinal epithelial cell line (IEC-6 cells) as a cell model and unglycated caseinate (CN) hydrolysate as a reference. Results from our liquid chromatography-mass spectrometry analysis of the GCN hydrolysate verified that lactose glycation occurred at the Lys residues in 3 casein components (α_S1-casein, β-casein, and κ-casein), and this resulted in the formation of 5 peptides with the following amino acid sequences: EMPFPKYPKYPVEPF, HIQKEDVPSE, GSENSEKTTMPL, NQDKTEIPT, and EGIHAQQKEPM. The results from cell experiments showed that the 2 hydrolysates could promote cell growth and decrease lactate dehydrogenase release in the lipopolysaccharide-injured cells; more importantly, they could partially protect the damaged barrier function of the cells by increasing trans-epithelial electrical resistance, decreasing epithelial permeability, and upregulating the expression of the 3 tight junction proteins zonula occludens-1, occludin, and claudin-1. However, compared with CN hydrolysate, GCN hydrolysate showed lower efficacy in protecting against cellular barrier dysfunction. We propose that the different chemical characteristics of the CN hydrolysate and the GCN hydrolysate (i.e., amino acid loss and lactose conjugation) contributed to the lower barrier-protective efficacy of the GCN hydrolysate. During dairy processing, protein glycation of the Maillard type might have a non-negligible, unfavorable effect on dairy proteins, in view of the resulting protein glycation we found and the critical function of proteins for maintaining the integrity of the intestinal barrier.

Novel methods for the rapid detection of trace tetracyclines based on the fluorescence behaviours of Maillard reaction fluorescent nanoparticles

The Maillard reaction and its fluorescent products have attracted widespread attention in the field of food safety and biology. Herein, the novel Maillard reaction fluorescent nanoparticles (MRFNs) as a fluorescent probe were synthesized via a “green” method with simple technical processes. In addition, the effects of tetracycline (TC) and chlorotetracycline (CTC) representing certain properties of tetracyclines (TCs) on the fluorescence behaviour of MRFNs were studied, respectively. The present study showed that the fluorescence intensity of MRFNs greatly enhanced with a linear increase in the CTC concentration. However, with the gradual increase in the TC concentration, the intensity of MRFNs tended to significantly decrease linearly. Based on this, novel fluorescence analysis methods for the simple and rapid detection of TC and CTC in water bodies were established, respectively. Significantly, the proposed detection methods were successfully adopted for detecting TC and CTC in some environmental water samples. Besides, the possible mechanisms for TC-induced fluorescence quenching and CTC-induced fluorescence enhancement of MRFNs were also discussed, respectively.

The Maillard reaction and its fluorescent products have attracted widespread attention in the field of food safety and biology.

Encapsulation of resveratrol using Maillard conjugates and membrane emulsification

Resveratrol is a stilbene phenolic associated with health-promoting properties such as antioxidant, anti-inflammatory and chemoprevention. Due to its chemical instability and low water solubility, microencapsulation represents a good alternative to provide better results when employing resveratrol as a nutraceutical ingredient. The main purpose of our work was to use low shear membrane emulsification to produce resveratrol-loaded emulsions of low polydispersity and integrate this process to spray drying to produce a powdered product. Resveratrol was dispersed with palm oil in a continuous phase obtained via Maillard reaction. We evaluated the influence of process conditions and phases composition on emulsions properties and performed the characterization of the spray-dried powder. Emulsions droplet size and span decreased as shear stress was increased. Higher dispersed phase fluxes provided increased droplet size polydispersity. Process conditions were set on 60.0 Pa shear stress and 70 L m^-2h^-1 of dispersed phase flux, obtaining emulsions with mean diameter around 30 μm and span of 0.76. Despite this relatively high droplet size of the infeed emulsions, the spray drying process resulted in particles with high encapsulation efficiency (97.97 ± 0.01%), and water content (~3.6%) and diameter (~10.2 μm) similar to particles obtained from fine emulsions in previously reported works.

Cytotoxicity study of bakery product melanoidins on intestinal and endothelial cell lines

Melanoidins contribute to organoleptic properties of processed foods and exert benefits in health. The aim of this study was to isolate and characterize melanoidins from baked products (common bread, soft bread and biscuits), evaluate their cytotoxicity and determine their suitability as functional additives. Extraction yield, spectrophotometric characteristics, colorimetric properties, antioxidant capacity, and cytotoxicity of melanoidins were assessed. Among the studied products, soft bread had the highest extraction throughput. Melanoidins from biscuit showed the highest antioxidant capacity, closely followed by those of soft bread. Melanoidins did not exert cytotoxic effects on Caco-2 and HUVEC cells (viability was >80%). Nevertheless, incubation of HUVEC cells with melanoidins from common bread and biscuit slightly decreased viability, whereas gastrointestinal digestion of such melanoidins softened the decrease in cell viability. This study point to soft bread as a safe and efficient source of melanoidins, that could be potentially used in the future as functional ingredient.

Characterization of Volatile Profiles and Marker Substances by HS-SPME/GC-MS during the Concentration of Coconut Jam

Characteristic aromas are usually key labels for food products. In this study, the volatile profiles and marker substances of coconut jam during concentration were characterized via sensory evaluation combined with headspace solid phase microextraction-gas chromatography-tandem mass spectrometry (HSPME/GC-MS). A total of 33 aroma compounds were detected by HSPME/GC-MS. Principal component analysis revealed the concentration process of coconut jam can be divided into three stages. In the first stage, esters and alcohols were the two main contributors to the aroma of the coconut jam. Next, a caramel smell was gradually formed during the second stage, which was mainly derived from aldehydes, ketones and alcohols. The concentration of aldehydes increased gradually at this stage, which may be the result of a combination of the Maillard reaction and the caramelization reaction. In the final sterilization stage, the 'odor intensity' of caramel reached the maximum level and a variety of aroma compounds were produced, thereby forming a unique flavor for the coconut jam. Finally, furfural fit a logistic model with a regression coefficient (r2) of 0.97034. Therefore, furfural can be used as a marker substance for monitoring the concentration of coconut jam.