Direct evidence for the role of Maillard reaction products in protein cross-linking in milk powder during storage

Reduction of maillard browning in spray dried low-lactose milk powders due to protein polysaccharide interactions

Lactose hydrolysed concentrated milk was prepared using β-galactosidase enzyme (4.76U/mL) with a reaction period of 12 h at 4 °C. Addition of polysaccharides (5 % maltodextrin/β-cyclodextrin) to concentrated milk either before or after lactose hydrolysis did not result in significant differences (p > 0.05) in degree of hydrolysis (% DH) of lactose and residual lactose content (%). Three different inlet temperatures (165 °C, 175 °C and 185 °C) were used for the preparation of powders which were later characterised based on physico-chemical and maillard browning characteristics. Moisture content, solubility and available lysine content of the powders decreased significantly, whereas, browning parameters i.e., browning index, 5-hydroxymethylfurfural, furosine content increased significantly (p < 0.05) with an increase in inlet air temperature. The powder was finally prepared with 5 % polysaccharide and an inlet air temperature of 185 °C which reduced maillard browning. Protein-polysaccharide interactions were identified using Fourier Transform infrared spectroscopy, fluorescence spectroscopy and determination of free amino groups in the powder samples. Maltodextrin and β-cyclodextrin containing powder samples exhibited lower free amino groups and higher degree of graft value as compared to control sample which indicated protein-polysaccharide interactions. Results obtained from Fourier Transform infrared spectroscopy also confirmed strong protein-polysaccharide interactions, moreover a significant decrease in fluorescence intensity was also observed in the powder samples. These interactions between the proteins and polysaccharides reduced the maillard browning in powders.

Protein interactions during dry and wet heat pre-treatment of skim milk powder (dispersions) and their effect on the heat stability of recombined filled evaporated milk

Skim milk powder (SMP) as well as aqueous dispersions were subjected to dry and wet heat pre-treatment, respectively, to improve the heat stability of recombined filled evaporated milk (RFEM) derived therefrom. However, microrheological analysis revealed that prolonged incubation caused detrimental effects on the heat stability of RFEM, which were thought to be due to protein interactions. SDS-PAGE results indicated that protein aggregation via non-disulfide covalent bonds occurred upon long-time dry or wet heat incubation. This was probably related to some Maillard reaction products, which is sustained by the increase in lactulose and protein carbonyl content. Considerable protein aggregation via disulfide bonds in the serum was found upon wet heat incubation at temperatures of at least 80 °C. Principal component analysis (PCA) revealed that the negative effects of overprocessing on the heat stability of RFEM were predominantly related to protein cross-linking via non-disulfide covalent bonds related to protein carbonylation.

Influence mechanism of polysaccharides induced Maillard reaction on plant proteins structure and functional properties: A review

Plant proteins have high nutritional value, a wide range of sources and low cost. However, it is easily affected by the environmental factors of processing and lead the problem of poor functionality. These problems of plant proteins can be improved by the polysaccharides induced Maillard reaction. The interaction between proteins and polysaccharides through Maillard reaction can change the structure of proteins as well as improve the functional properties and biological activity. The products of Maillard reaction, such as reductone intermediates, heterocyclic compounds and melanoidins have certain antioxidant, antibacterial and other biological activities. However, heterocyclic amines, acrylamide, and products generated in the advanced stage of the Maillard reaction also have a negative impact, which may increase cytotoxicity and be associated with chronic diseases. Therefore, it is necessary to effectively control the process of Maillard reaction. This review focuses on the modification of plant proteins by polysaccharide-induced Maillard reaction and the effects of Maillard reaction on protein structure, functional properties and biological activity. It also points out how to accurately reflect the changes of protein structure in Maillard reaction. In addition, it also points out the application ways of plant protein-polysaccharide complexes in the food industry, for example, emulsifiers, delivery carriers of functional substances, and natural antioxidants due to their improved solubility, emulsifying, gelling and antioxidant properties. This review provides theoretical support for controlling Maillard reaction based on protein structure.

Changes in partial properties of glycosylated egg white powder during storage

BACKGROUND

Glycosylation is an effective method to modify protein. However, there is a lack of research on the property changes of glycosylated protein during storage. In the present study, the changes in the physicochemical, functional, and structural properties of xylo-oligosaccharide (XOS) glycosylated egg white powder (EWP) (XOS-EWP conjugates) prepared with different glycosylation conditions (XOS/EWP ratio and reaction time) were investigated when stored at 25 °C and 60% relative humidity.

RESULTS

In the 12 weeks of storage, the degree of grafting, browning, and the formation of Maillard reaction products of XOS-EWP conjugates increased. The increase in XOS/EWP ratio and reaction time led to an increase in protein aggregation, though a decrease in solubility, due to increased degree of glycosylation and structural changes. Furthermore, improved gel hardness of XOS-EWP conjugates deteriorated, while improved emulsification ability was kept stable during storage. For the sample with a lower XOS/EWP ratio and reaction time, the gel hardness and emulsifying properties underwent little or no deterioration even improving during storage. The results could be attributed to the limited degree of glycosylation, further unfolding of the protein structure, increased surface hydrophobicity of protein, and improved thermal characteristics.

CONCLUSION

During storage, the Maillard reaction would continue to occur in the glycosylated EWP, further affecting the performance of modified EWP. Modified EWP prepared under different glycosylation conditions performed differently during storage. Modified EWP with a larger XOS/EWP ratio and reaction time meant it was harder to maintain good performance. Modified EWP with a smaller XOS/EWP ratio and reaction time changed significantly to better performances. © 2022 Society of Chemical Industry.

Cross-linking reactions in food proteins and proteomic approaches for their detection

Various protein cross-linking reactions leading to molecular polymerization and covalent aggregates have been described in processed foods. They are an undesired side effect of processes designed to reduce bacterial load, extend shelf life, and modify technological properties, as well as being an expected result of treatments designed to modify raw material texture and function. Although the formation of these products is known to affect the sensory and technological properties of foods, the corresponding cross-linking reactions and resulting protein polymers have not yet undergone detailed molecular characterization. This is essential for describing how their generation can be related to food processing conditions and quality parameters. Due to the complex structure of cross-linked species, bottom-up proteomic procedures developed to characterize various amino acid modifications associated with food processing conditions currently offer a limited molecular description of bridged peptide structures. Recent progress in cross-linking mass spectrometry for the topological characterization of protein complexes has facilitated the development of various proteomic methods and bioinformatic tools for unveiling bridged species, which can now also be used for the detailed molecular characterization of polymeric cross-linked products in processed foods. We here examine their benefits and limitations in terms of evaluating cross-linked food proteins and propose future scenarios for application in foodomics. They offer potential for understanding the protein cross-linking formation mechanisms in processed foods, and how the inherent beneficial properties of treated foodstuffs can be preserved or enhanced.

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.

What Is the Color of Milk and Dairy Products and How Is It Measured?

Exactly six-hundred (600) scientific articles that report milk and milk products’ color results in scientific journals in the last couple of decades were reviewed. Thereof, the greatest part of the articles derived from Europe (36.3%) and Asia (29.5%). The greatest share of researchers used Minolta colorimeters (58.8%), while 26.3% of them used Hunter devices. Most reports were on cheese (31.0%) followed by fermented products (21.2%). Moreover, the highest number of papers reported color data of milk and milk products made from cow’s milk (44.81%). As expected, goat’s cheese was the brightest (L* = 87.1), while cow’s cheese was the yellowest (b* = 17.4). Most importantly, it appeared that color research results reported were often impossible to replicate or to interpret properly because of incomplete description of the methodology. In some of the manuscripts reviewed, illuminant source (61.0%), aperture size (93.8%), observer angle, and number of readings (over 70% of all cases) were not reported. It is therefore critical to set rules regarding the description of the methodology for (milk) color research articles in order to ensure replicability and/or comparison of studies.

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

Protein and peptides are usually sensitive to environmental stresses, such as pH changes, high temperature, ionic strength, and digestive enzymes amongst other, which limit their food and medicinal applications. Maillard reaction (also called Maillard conjugation or glycation) occurs naturally without the addition of chemical agents and has been vastly applied to boost protein/peptide/amino acid functionalities and biological properties. Protein/peptide-saccharide conjugates are currently used as emulsifiers, antioxidants, antimicrobials, gelling agents, and anti-browning compounds in food model systems and products. The conjugates also possess the excellent stabilizing ability as a potent delivery system to enhance the stability and bioaccessibility of many bioactive compounds. Carbonyl scavengers such as polyphenols are able to significantly inhibit the formation of advanced glycation end products without a significant effect on early Maillard reaction products (MRPs) and melanoidins, which are currently applied as functional ingredients. This review paper highlights the technological functionality and biological properties of glycoconjugates in food model systems and products. Recent applications of MRPs in medical sciences are also presented.

Isolation and Characterization of Melanoidins from Dulce de Leche, A Confectionary Dairy Product

Melanoidins, the brown-colored compounds formed through the Maillard reaction, are responsible for color development in dulce de leche (DL), a popular confectionary dairy product in the Río de la Plata region, particularly in Uruguay and Argentina. Color is a critical quality parameter that strongly influences consumer preference. This work aimed to develop a method to perform preliminary structural characterization of the chromophores produced by the Maillard reaction. Melanoidins are present in a water-insoluble fraction, linked to a protein backbone, conforming melanoproteins of high molecular weight. The insoluble melanoprotein fraction (10% total solids) was isolated, and the chromophores released by proteolysis and isolated by gel-permeation chromatography. The analysis of the products revealed that they present a high degree of molecular weight (MW) polydispersity, in a range of 300 to 2000 Da, where the compounds of higher molecular weight contributed the most to the color of the product. The isolated fractions were further analyzed by RP-HPLC using a diode array detector (DAD) detector. These results, together with H-NMR data, suggested that the chromophores isolated belonged to a relatively simple mixture of aromatic products with higher hydrophobic character relative to other products of the melanoprotein digestion.

Time effect on structural and functional properties of whey protein isolate-gum acacia conjugates prepared via Maillard reaction

BACKGROUND

The functional properties of whey protein isolate (WPI) are sensitive to pH, ionic strength, and temperature. This prevents its application in various food systems and processing technologies. The conjugation of proteins with polysaccharides via the Maillard reaction is an efficient method to improve the functionality of proteins. The purpose of this work was to conjugate gum acacia (GA) with WPI via the dry-heating Maillard reaction and to investigate the effect of reaction time on the physicochemical and functional properties of WPI-GA conjugates.

RESULTS

Sodium dodecyl sulfate-polyacrylamide gel electrophoresis and high-performance size exclusion chromatography confirmed the formation of higher molecular weight conjugates. The degrees of glycation for WPI-GA conjugates incubated for 1, 3, 5, and 7 days were 28.14%, 44.98%, 49.50%, and 51.20%, respectively. The glycation reaction reduced the surface hydrophobicity and fluorescence intensity of WPI significantly (P < 0.05). Functional properties of the conjugates, such as solubility, stability against heat-induced insolubility, and emulsion properties were all superior to the control WPI. However, a reaction time longer than a day resulted in a high degree of browning and decreased the functionality of the conjugate significantly (P < 0.05).

CONCLUSION

The results indicated that conjugation of WPI with GA can be a promising way to enhance its functional properties. However, the reaction time suitable for producing conjugates with superior functional properties was not necessarily the highest glycation degree that could be reached. © 2019 Society of Chemical Industry.

Acid-Induced Gelation of Caseins Glycated with Lactose: Impact of Maillard Reaction-Based Glycoconjugation and Protein Cross-Linking

During food processing or storage, milk proteins can react with reducing sugars via the Maillard reaction (glycation), which may alter their techno-functional properties. The aim of this study was to investigate the relationship between molecular changes of casein occurring during different stages of the Maillard reaction and its acid-induced gelling properties. Therefore, sodium caseinate was heated in a dry state at 60 °C in the presence of lactose and analyzed for structural modifications by determining Amadori compounds (glycoconjugation) indirectly as furosine, the total lysine modification, and the extent of protein cross-linking. For techno-functional characterization, acid-induced gels were prepared by the addition of glucono-δ-lactone and evaluated by measuring pH kinetics during gel formation, gel strength, and water holding capacity. The time to reach pH 4.6 during the gelation process was significantly delayed with increasing extent of the Maillard reaction. Glycation with lactose also led to a significant increase in gel strength and water holding capacity. The increase in gel stability was rather independent from the amount of sugars covalently bound to the proteins during the early phase of the Maillard reaction but strongly correlated to the degree of protein polymerization. Small- and medium-sized casein oligomers, formed during advanced stages of the Maillard reaction, contributed considerably to the formation of stronger gels with higher water holding capacity, whereas a sharp increase in the relative amount of the polymer fraction observed during prolonged cross-linking processes caused a spontaneous destabilization of the gel network. Knowledge about structure-function relationships on a molecular level can provide useful information to control food texture by raw material quality.

Storage of Micellar Casein Powders with and without Lactose: Consequences on Color, Solubility, and Chemical Modifications

During storage, a series of changes occur for dairy powders, such as protein lactosylation and the formation of Maillard reaction products (MRPs), leading to powder browning and an increase of insoluble matter. The kinetics of protein lactosylation and MRP formation are influenced by the lactose content of the dairy powder. However, the influence of lactose in the formation of insoluble matter and its role in the underlying mechanisms is still a subject of speculation. In this study, we aim to investigate the role of lactose in the formation of insoluble matter in a more comprehensive way than the existing literature. For that, two casein powders with radically different lactose contents, standard micellar casein (MC) powder (MC1) and a lactose-free (less than 10 ppm) MC powder (MC2), were prepared and stored under controlled conditions for different periods of time. Powder browning index measurements and solubility tests on reconstituted powders were performed to study the evolution of the functional properties of MC powders during aging. Proteomic approaches [one-dimensional electrophoresis and liquid chromatography-mass spectrometry (LC-MS)] and innovative label-free quantification methods were used to track and quantify the chemical modifications occurring during the storage of the powders. Reducing the amount of lactose limited the browning of MC powders but had no effect on the loss of solubility of proteins after storage, suggesting that the action of lactose, leading to the production of MRC, does not promotes the formation of insoluble matter. Electrophoresis analysis did not reveal any links between the formation of covalent bonds between caseins and loss in solubility, regardless of the lactose content. However, LC-MS analyses have shown that different levels of chemical modifications occur during the MC powder storage, depending upon the presence of lactose. An increase of protein lactosylation and acetylation was observed for the powder with a higher lactose content, while an increase of protein deamidation and dephosphorylation was observed for that containing lower lactose. The decrease of pH in the presence of lactose as a result of Maillard reaction (MR) may explain the difference in the chemical modifications of the two powders. In view of the present results, it is clear that lactose is not a key factor promoting insolubility and for the formation of cross-links between caseins during storage. This suggests that lactosylation is not the core reaction giving rise to loss in solubility.

Analysis of carbohydrates and glycoconjugates by matrix-assisted laser desorption/ionization mass spectrometry: An update for 2013-2014

This review is the eighth update of the original article published in 1999 on the application of Matrix-assisted laser desorption/ionization mass spectrometry (MALDI) mass spectrometry to the analysis of carbohydrates and glycoconjugates and brings coverage of the literature to the end of 2014. Topics covered in the first part of the review include general aspects such as theory of the MALDI process, matrices, derivatization, MALDI imaging, fragmentation, and arrays. The second part of the review is devoted to applications to various structural types such as oligo- and poly- saccharides, glycoproteins, glycolipids, glycosides, and biopharmaceuticals. Much of this material is presented in tabular form. The third part of the review covers medical and industrial applications of the technique, studies of enzyme reactions, and applications to chemical synthesis. © 2018 Wiley Periodicals, Inc. Mass Spec Rev 37:353-491, 2018.

Protein cross-linking and the Maillard reaction decrease the solubility of milk protein concentrates

Milk protein concentrate (MPC) is a widely used material in the food industry. However, despite its widespread use, the mechanism underlying the decreased solubility of MPC that occurs during storage has not yet been clarified. In this study, the solubility changes, protein cross-linking, and Maillard reaction and the relationships between them were investigated in modified MPC powders (MMPC) containing different concentrations of protein and/or lactose stored at 50°C for 15-45 days. The results demonstrated that both the protein and lactose contents affected solubility. The proteins interacted through hydrogen bonding, disulfide bonding, hydrophobic interactions, and nondisulphide covalent bonding, which led to cross-linking. The Maillard reaction promoted protein cross-linking and was in turn influenced by protein cross-linking. The Maillard reaction was slower when the degree of protein cross-linking was greater. These results improve our understanding of the mechanism leading to poor solubility of MPC powders during storage.

Extrusion modifies some physicochemical properties of milk protein concentrate for improved performance in high-protein nutrition bars

BACKGROUND

Extruded and ground milk protein concentrate powders, specifically those with 800 g kg^-1 protein (i.e. MPC80), imparted softness, cohesion and textural stability to high-protein nutrition (HPN) bars. The present study evaluated some physicochemical properties of extruded and conventionally produced (i.e. spray-dried) MPC80 to explain these improvements. Protein chemical changes and aggregations within MPC80-formulated HPN bars during storage were characterized.

RESULTS

Extruded MPC80 powders had broader particle size distribution (P < 0.05) and smaller volume-weighted mean diameter (P < 0.05) than the spray-dried control. Loose, tapped and particle densities increased (P < 0.05) and correspondingly occluded and interstitial air volumes decreased (P < 0.05) after extruding and milling MPC80. Extrusion decreased water holding capacity (P < 0.05) and solubility (P < 0.05), yet improved the wettability (P < 0.05) of MPC80. MPC80 free sulfhydryl (P < 0.05) and free amine (P < 0.05) concentrations decreased after extrusion. Sulfhydryl and amine concentrations changed (P < 0.05) and disulfide-linked and, more prominently, Maillard-induced aggregates developed during HPN bar storage.

CONCLUSION

Extrusion and milling together changed the physicochemical properties of MPC80. Chemical changes and protein aggregations occurred in HPN bars prepared with either type of MPC80. Thus, the physicochemical properties of the formulating powder require consideration for desired HPN bar texture and stability. © 2017 Society of Chemical Industry.