Chemical properties and antioxidative activity of glycated α-lactalbumin with a rare sugar, -allose, by Maillard reaction

Characterization of a novel ribose-5-phosphate isomerase B from Curtobacterium flaccumfaciens ZXL1 for D-allose production

Enzymatic preparation of rare sugars as an alternative to traditional sweeteners is an effective strategy to achieve a low-calorie healthy diet. Ribose-5-phosphate isomerase B (RpiB) is a key enzyme in the non-oxidative branch of the catalytic pentose phosphate pathway. Here, we investigated the potential of Curtobacterium flaccumfaciens ZXL1 (C. flaccumfaciens ZXL1) derived RpiB (CfRpiB) in D-allose preparation. The optimal reaction conditions for recombinant CfRpiB were found experimentally to be pH 7.0, 55 °C, and no metal ions. The kinetic parameters Km, kcat, and catalytic efficiency kcat/Km were 320 mM, 4769 s-1, and 14.9 mM-1 s-1 respectively. The conversion of D-allulose by purified enzyme (1 g L-1 ) to D-allose was 13% within 1 h. In addition, homology modeling and molecular docking were used to predict the active site residues: Asp13, Asp14, Cys72, Gly73, Thr74, Gly77, Asn106, and Lys144.

D-allose, a typical rare sugar: properties, applications, and biosynthetic advances and challenges

D-allose, a C-3 epimer of D-glucose and an aldose-ketose isomer of D-allulose, exhibits 80% of sucrose's sweetness while being remarkably low in calories and nontoxic, making it an appealing sucrose substitute. Its diverse physiological functions, particularly potent anticancer and antitumor effects, render it a promising candidate for clinical treatment, garnering sustained attention. However, its limited availability in natural sources and the challenges associated with chemical synthesis necessitate exploring biosynthetic strategies to enhance production. This overview encapsulates recent advancements in D-allose's physicochemical properties, physiological functions, applications, and biosynthesis. It also briefly discusses the crucial role of understanding aldoketose isomerase structure and optimizing its performance in D-allose synthesis. Furthermore, it delves into the challenges and future perspectives in D-allose bioproduction. Early efforts focused on identifying and characterizing enzymes responsible for D-allose production, followed by detailed crystal structure analysis to improve performance through molecular modification. Strategies such as enzyme immobilization and implementing multi-enzyme cascade reactions, utilizing more cost-effective feedstocks, were explored. Despite progress, challenges remain, including the lack of efficient high-throughput screening methods for enzyme modification, the need for food-grade expression systems, the establishment of ordered substrate channels in multi-enzyme cascade reactions, and the development of downstream separation and purification processes.

X-ray structure and characterization of a probiotic Lactobacillus rhamnosus Probio-M9 L-rhamnose isomerase

A recombinant L-rhamnose isomerase (L-RhI) from probiotic Lactobacillus rhamnosus Probio-M9 (L. rhamnosus Probio-M9) was expressed. L. rhamnosus Probio-M9 was isolated from human colostrum and identified as a probiotic lactic acid bacterium, which can grow using L-rhamnose. L-RhI is one of the enzymes involved in L-rhamnose metabolism and catalyzes the reversible isomerization between L-rhamnose and L-rhamnulose. Some L-RhIs were reported to catalyze isomerization not only between L-rhamnose and L-rhamnulose but also between D-allulose and D-allose, which are known as rare sugars. Those L-RhIs are attractive enzymes for rare sugar production and have the potential to be further improved by enzyme engineering; however, the known crystal structures of L-RhIs recognizing rare sugars are limited. In addition, the optimum pH levels of most reported L-RhIs are basic rather than neutral, and such a basic condition causes non-enzymatic aldose-ketose isomerization, resulting in unexpected by-products. Herein, we report the crystal structures of L. rhamnosus Probio-M9 L-RhI (LrL-RhI) in complexes with L-rhamnose, D-allulose, and D-allose, which show enzyme activity toward L-rhamnose, D-allulose, and D-allose in acidic conditions, though the activity toward D-allose was low. In the complex with L-rhamnose, L-rhamnopyranose was found in the catalytic site, showing favorable recognition for catalysis. In the complex with D-allulose, D-allulofuranose and ring-opened D-allulose were observed in the catalytic site. However, bound D-allose in the pyranose form was found in the catalytic site of the complex with D-allose, which was unfavorable for recognition, like an inhibition mode. The structure of the complex may explain the low activity toward D-allose. KEY POINTS: • Crystal structures of LrL-RhI in complexes with substrates were determined. • LrL-RhI exhibits enzyme activity toward L-rhamnose, D-allulose, and D-allose. • The LrL-RhI is active in acidic conditions.

Effect of enzymolysis combined with Maillard reaction treatment on functional and structural properties of gluten protein

In this work, the modified gluten was prepared by enzymolysis combined with Maillard reaction (MEG), and its functional and structural properties were investigated. The result showed that the maximum foamability of MEG was 19.58 m2/g, the foam stability was increased by 1.8 times compared with gluten, and the solubility and degree of graft were increased to 44.4 % and 28.1 % at 100 °C, whereas the content of sulfhydryl group decreased to 0.81 μmol/g. The scavenging ability on ABTS+radical and DPPH radical of MEG was positively correlated with reaction temperature, and the maximum values were 86.57 % and 71.71 % at 140 °C, respectively. Furthermore, the fluorescence quenching effect of tryptophan and tyrosine residues was enhanced, while the fluorescence intensity decreased with the temperature increase. Scanning electron microscopy revealed that the surface of enzymatically hydrolyzed-gluten became smooth and the cross section became straightened, while MEG turned smaller and irregular approaching a circular structure. FT-IR spectroscopy showed that enzymatic hydrolysis promoted the occurrence of more carbonyl ammonia reactions and the formation of precursors of advanced glycosylation end products. These results provide a feasible method for improving the structure and functional properties of gluten protein.

A comprehensive review of recent advances in the characterization of L-rhamnose isomerase for the biocatalytic production of D-allose from D-allulose

D-Allose and D-allulose are two important rare natural monosaccharides found in meager amounts. They are considered to be the ideal substitutes for table sugar (sucrose) for, their significantly lower calorie content with around 80 % and 70 % of the sweetness of sucrose, respectively. Additionally, both monosaccharides have gained much attention due to their remarkable physiological properties and excellent health benefits. Nevertheless, D-allose and D-allulose are rare in nature and difficult to produce by chemical methods. Consequently, scientists are exploring bioconversion methods to convert D-allulose into D-allose, with a key enzyme, L-rhamnose isomerase (L-RhIse), playing a remarkable role in this process. This review provides an in-depth analysis of the extractions, physiological functions and applications of D-allose from D-allulose. Specifically, it provides a detailed description of all documented L-RhIse, encompassing their biochemical properties including, pH, temperature, stabilities, half-lives, metal ion dependence, molecular weight, kinetic parameters, specific activities and specificities of the substrates, conversion ratio, crystal structure, catalytic mechanism as well as their wide-ranging applications across diverse fields. So far, L-RhIses have been discovered and characterized experimentally by numerous mesophilic and thermophilic bacteria. Furthermore, the crystal forms of L-RhIses from E. coli and Stutzerimonas/Pseudomonas stutzeri have been previously cracked, together with their catalytic mechanism. However, there is room for further exploration, particularly the molecular modification of L-RhIse for enhancing its catalytic performance and thermostability through the directed evolution or site-directed mutagenesis.

Enhanced Thermostability of an l-Rhamnose Isomerase for d-Allose Synthesis by Computation-Based Rational Redesign of Flexible Regions

d-Allose is a low-calorie rare sugar with great application potential in the food and pharmaceutical industries. The production of d-allose has been accomplished using l-rhamnose isomerase (L-RI), but concomitantly increasing the enzyme's stability and activity remains challenging. Here, we rationally engineered an L-RI from Clostridium stercorarium to enhance its stability by comprehensive computation-aided redesign of its flexible regions, which were successively identified using molecular dynamics simulations. The resulting combinatorial mutant M2-4 exhibited a 5.7-fold increased half-life at 75 °C while also exhibiting improved catalytic efficiency. Especially, by combining structure modeling and multiple sequence alignment, we identified an α0 region that was universal in the L-RI family and likely acted as a "helix-breaker". Truncating this region is crucial for improving the thermostability of related enzymes. Our work provides a significantly stable biocatalyst with potential for the industrial production of d-allose.

A study of targeted mutation of l-rhamnose isomerase to improve the conversion efficiency of D-allose

D-Allose is a rare cis-caprose with a wide range of physiological functions, which has a wide range of applications in medicine, food, and other industries. L-Rhamnose isomerase (L-Rhi) is the earliest enzyme found to catalyze the production of D-allose from D-psicose. This catalyst has a high conversion rate, but its specificity for substrates is limited; thus, it cannot fulfill the requirements of industrial production of D-allose. In this study, L-Rhi derived from Bacillus subtilis was employed as the research subject, and D-psicose as the conversion substrate. Two mutant libraries were constructed through alanine scanning, saturation mutation, and rational design based on the analysis of the secondary structure, tertiary structure, and interactions with ligands of the enzyme. The yield of D-allose produced by these mutants was assessed; it was found that the conversion rate of mutant D325M to D-allose was increased by 55.73 %, and the D325S improved by 15.34 %, while mutant W184H increased by 10.37 % at 55 °C, respectively. According to modeling analysis, manganese (Mn²⁺) had no significant effect on the production of D-psicose from D-psicose by L-Rhi. The results of molecular dynamics simulation demonstrated that the mutants W184H, D325M, and D325S had more stable protein structures while binding with the substrate D-psicose, as evidenced by its root mean square deviation (RMSD), root mean square fluctuation (RMSF), and binding free energy values. It was more conducive to binding D-psicose and facilitating its conversion to D-allose, providing the basis for the production of D-allose.

Engineering of Escherichia coli for D-allose fermentative synthesis from D-glucose through izumoring cascade epimerization

D-Allose is a potential alternative to sucrose in the food industries and a useful additive for the healthcare products in the future. At present, the methods for large-scale production of D-allose are still under investigation, most of which are based on in vitro enzyme-catalyzed Izumoring epimerization. In contrast, fermentative synthesis of D-allose has never been reported, probably due to the absence of available natural microorganisms. In this work, we co-expressed D-galactose: H+ symporter (GalP), D-glucose isomerase (DGI), D-allulose 3-epimerase (DAE), and ribose-5-phosphate isomerase (RPI) in Escherichia coli, thereby constructing an in vivo Izumoring pathway for yielding D-allose from D-glucose. The carbon fluxes and carbon catabolite repression (CCR) were rationally regulated by knockout of FruA, PtsG, Glk, Mak, PfkA, and PfkB involved in the pathways capable of phosphorylating D-fructose, D-glucose, and fructose-6-phosphate. Moreover, the native D-allose transporter was damaged by inactivation of AlsB, thus driving the reversible Izumoring reactions towards the target product. Fermentation was performed in the M9 medium supplemented with glycerol as a carbon source and D-glucose as a substrate. The results show that the engineered E. coli cell factory was able to produce approximately 127.35 mg/L of D-allose after 84 h. Our achievements in the fermentative production of D-allose in this work may further promote the green manufacturing of rare sugars.

Insight into the mechanism of d-allose in reducing the allergenicity and digestibility of ultrasound-pretreated α-lactalbumin by high-resolution mass spectrometry

The mechanism of d-allose in reducing the allergenicity and digestibility of ultrasound-pretreated α-lactalbumin (α-LA) was studied. The intensity reduction and peak red shift occurred in fluorescence spectra of glycated samples. Enzyme-linked immunosorbent assay and basophil degranulation analysis showed that d-allose significantly reduced the allergenicity of α-LA, and ultrasound-pretreated α-LA showed the lowest allergenicity after glycation. Compared with α-LA, the degree of hydrolysis decreased in glycated samples. Size-exclusion high-performance liquid chromatography showed that the glycated α-LA was resistant to digestive enzymes. The glycated sites and average degree of substitution per peptide molecule were determined using LC Orbitrap MS/MS. These results suggested that the masking of linear allergenic epitopes by glycation could reduce the allergenicity. Therefore, the combination of ultrasound pretreatment and glycation is a potential method to reduce protein allergenicity in food processing and provides a useful approach for the application of rare sugars in food processing.

A review on l-ribose isomerases for the biocatalytic production of l-ribose and l-ribulose

Presently, because of the extraordinary roles and potential applications, rare sugars turn into a focus point for countless researchers in the field of carbohydrates. l-ribose and l-ribulose are rare sugars and isomers of each other. This aldo and ketopentose are expensive but can be utilized as an antecedent for the manufacturing of various rare sugars and l-nucleoside analogue. The bioconversion approach turns into an excellent alternative method to l-ribulose and l-ribose production, as compared to the complex and lengthy chemical methods. The basic purpose of this research was to describe the importance of rare sugars in various fields and their easy production by using enzymatic methods. l-Ribose isomerase (L-RI) is an enzyme discovered by Tsuyoshi Shimonishi and Ken Izumori in 1996 from Acinetobacter sp. strain DL-28. L-RI structure was cupin-type-β-barrel shaped with a catalytic site between two β-sheets surrounded by metal ions. The crystal structures of the L-RI showed that it contains a homotetramer structure. Current review have concentrated on the sources, characteristics, applications, conclusions and future prospects including the potentials of l-ribose isomerase for the commercial production of l-ribose and l-ribulose. The MmL-RIse and CrL-RIse have the potential to produce the l-ribulose up to 32% and 31%, respectively. The CrL-RIse is highly stable as compared to other L-RIs. The results explained that the L-RIs have great potential in the production of rare sugars especially, l-ribose and l-ribulose, while the immobilization technique can enhance its functionality and properties. The present study precises the applications of L-RIs acquired from various sources for l-ribose and l-ribulose 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.

Hermetia illucens Protein Conjugated with Glucose via Maillard Reaction: Antioxidant and Techno-Functional Properties

The food industry is considering novel sources of proteins with enhanced functionalities to meet the increasing demand and population growth. Edible insect proteins have emerged as an alternative that is environmentally friendly and economically viable and thus could make a significant contribution to global food security. This study was aimed to establish the effect of conjugation via the Maillard reaction on the antioxidant and techno-functional properties of black soldier fly larvae protein concentrate. Reaction mixtures containing black soldier fly larvae protein concentrate and glucose (2 : 1 weight ratio) were wet-heated at 50, 70, and 90°C for 2, 4, 6, 8, and 10 h, respectively, with an initial pH of 9. The results showed that the browning indices of the black soldier fly larvae-glucose (BSFL-Glu) model system increased with an increase in reaction time and temperature, with conjugates formed at 90°C exhibiting the highest browning intensity at 420 nm. At 50°C, the DPPH-RS of the conjugates ranged from 15.47 to 32.37%. The ABTS⁺ radical scavenging activity of BSFL-Glu conjugates produced at 90°C exhibited significantly (p < 0.05) higher scavenging activity as a function of reaction time. The foaming capacity of BSFL-Glu conjugates produced at 70°C showed a significant increase (p < 0.05) as a function of reaction time. Principal component analysis was applied to browning and antioxidant indices. Component 1 of the score plot accounted for 89%, while component 2 accounted for 8% of the observed variability and allowed discrimination/differentiation of the samples based on the heating temperature. These findings provide a practical means to improve the functionality of novel edible insect proteins for food application.

Rare Sugars: Recent Advances and Their Potential Role in Sustainable Crop Protection

Rare sugars are monosaccharides with a limited availability in the nature and almost unknown biological functions. The use of industrial enzymatic and microbial processes greatly reduced their production costs, making research on these molecules more accessible. Since then, the number of studies on their medical/clinical applications grew and rare sugars emerged as potential candidates to replace conventional sugars in human nutrition thanks to their beneficial health effects. More recently, the potential use of rare sugars in agriculture was also highlighted. However, overviews and critical evaluations on this topic are missing. This review aims to provide the current knowledge about the effects of rare sugars on the organisms of the farming ecosystem, with an emphasis on their mode of action and practical use as an innovative tool for sustainable agriculture. Some rare sugars can impact the plant growth and immune responses by affecting metabolic homeostasis and the hormonal signaling pathways. These properties could be used for the development of new herbicides, plant growth regulators and resistance inducers. Other rare sugars also showed antinutritional properties on some phytopathogens and biocidal activity against some plant pests, highlighting their promising potential for the development of new sustainable pesticides. Their low risk for human health also makes them safe and ecofriendly alternatives to agrochemicals.

A model system based on glucose-arginine to monitor the properties of Maillard reaction products

An arginine-glucose mixture (1:2 mol ratio) with pH 9 was heated at 53-100 °C for 10-350 min, and the effects of process parameters were determined during the Maillard reaction (MR). The heating temperature and time were selected as process conditions and were studied with central composite design. The model system was tested based on the values obtained from antioxidant capacity, browning intensity, pH, acrylamide (AC), and hydroxymethylfurfural (HMF) concentrations. Higher temperatures and longer time resulted in higher antioxidant capacity and browning intensity while lowering the pH values. HMF concentration of MR products was found higher in lower temperatures with longer processing time, whereas AC concentration was found higher in high temperatures.

Evaluation of the Anti-Proliferative Activity of Rare Aldohexoses against MOLT-4F and DU-145 Human Cancer Cell Line and Structure-Activity Relationship of D-Idose

D-Allose (D-All), a C-3 epimer of D-glucose (D-Glc), is a naturally rare monosaccharide, which shows anti-proliferative activity against several human cancer cell lines. Unlike conventional anticancer drugs, D-All targets glucose metabolism and is non-toxic to normal cells. Therefore, it has attracted attention as a unique “seed” compound for anticancer agents. However, the anti-proliferative activities of the other rare aldohexoses have not been examined yet. In this study, we evaluated the anti-proliferative activity of rare aldohexoses against human leukemia MOLT-4F and human prostate cancer DU-145 cell lines. We found that D-All and D-idose (D-Ido) at 5 mM inhibited cell proliferation of MOLT-4F cells by 46 % and 60 %, respectively. On the other hand, the rare aldohexoses at 5 mM did not show specific anti-proliferative activity against DU-145 cells. To explore the structure–activity relationship of D-Ido, we evaluated the anti-proliferative activity of D-sorbose (D-Sor), 6-deoxy-D-Ido, and L-xylose (L-Xyl) against MOLT-4F cells and found that D-Sor, 6-deoxy-D-Ido, and L-Xyl showed no inhibitory activity at 5 mM, suggesting that the aldose structure and the C-6 hydroxy group of D-Ido are important for its activity. Cellular glucose uptake assay and western blotting analysis of thioredoxin-interacting protein (TXNIP) expression suggested that the anti-proliferative activity of D-Ido is induced by inhibition of glucose uptake via TXNIP-independent pathway.

GC-MS Phytochemical Profiling, Pharmacological Properties, and In Silico Studies of Chukrasia velutina Leaves: A Novel Source for Bioactive Agents

Chukrasia velutina is a local medicinal plant commonly known as chikrassy in Bangladesh, India, China, and other South Asian countries. The leaves, bark, and seeds are vastly used as herbal medicine for fever and diarrhea, and its leaves essential oils are used for antimicrobial purposes. In this study, we discuss the neuropsychiatric properties of C. velutina leaves through several animal models, quantitative and qualitative phytochemical analysis, and computational approaches. Neuropsychiatric effects were performed in rodents on the methanolic extract of C. velutina leaves (MECVL). Antidepressant, anxiolytic, and sedative effects experimented through these rodent models were used such as the force swimming test (FST), tail suspension test (TST), hole board test (HBT), elevated plus maze test (EPMT), light/dark box test (LDBT), open field test (OFT), and hole cross test (HCT). In these rodent models, 200 and 400 mg/kg doses were used which exhibited a significant result in the force swimming and tail suspension test (p < 0.001) for the antidepressant effect. In the anxiolytic study, the results were significant in the hole board, elevated plus maze, and light/dark box test (p < 0.001) for doses of 200 and 400 mg/kg. The result was also significant in the open field and hole cross test (p < 0.001) for sedative action in the sake of similar doses. Moreover, qualitative and quantitative studies were also performed through phytochemical screening and GC-MS analysis, and fifty-seven phytochemical compounds were found. These compounds were analyzed for pharmacokinetics properties using the SwissADME tool and from them, thirty-five compounds were considered for the molecular docking analysis. These phytoconstituents were docking against the human serotonin receptor, potassium channel receptor, and crystal structure of human beta-receptor, where eight of the compounds showed a good binding affinity towards the respective receptors considered to the reference standard drugs. After all of these analyses, it can be said that the secondary metabolite of C. velutina leaves (MECVL) could be a good source for inhibiting the neuropsychiatric disorders which were found on animal models as well as in computational studies.

Insight into the Mechanism of Reduced IgG/IgE Binding Capacity in Ovalbumin as Induced by Glycation with Monose Epimers through Liquid Chromatography and High-Resolution Mass Spectrometry

Ovalbumin (OVA) is one of the major food allergens in hen eggs. In this work, it was demonstrated that glycation with d-glucose and its epimers, including d-mannose, d-allose, d-galactose, and l-idose, could effectively attenuate the IgG/IgE binding of OVA, which was attributed to the covalent masking by sugars and to its structural changes. The glycation sites were determined, and their average degree of substitution was found using liquid chromatography coupled with high-resolution mass spectrometry. Fluctuations in OVA conformation were monitored by conventional spectrometry. Compared to those of OVA-Man and OVA-Glu, OVA-All, OVA-Gal, and OVA-Ido showed a higher glycation extent, and the alterations on their steric layouts were more drastic, suggesting that the configuration of hydroxyl groups at positions C-3, C-4, and C-5 in sugars might be important for the glycation reactivity; as such, their capabilities in binding with IgG/IgE decreased more significantly. Attempts were made to provide valuable information for in-depth understanding of the differences in biochemical functionality among epimeric sugars. These insights would be helpful for designing sweetened food products with a desirable level of safety.

Improving the functional properties of bovine serum albumin-glucose conjugates in natural deep eutectic solvents

Glycation between target proteins and saccharides is time-consuming or requires high temperatures. Here, a promising reaction medium, natural deep eutectic solvents (NADES), for glucose glycation with bovine serum albumin (BSA) was applied to improve the grafting of glucose-glycated BSA by shifting reaction equilibrium. Two types of glucose-glycated BSA products were prepared using NADES and water systems. SDS-PAGE and MALDI-TOF-MS revealed that BSA and glucose were covalently bonded. Compared with in water system, glycated BSA products in NADES system had more -OH groups, more disordered secondary structures, lower intrinsic fluorescence intensity, and higher ultraviolet-visible absorption. Lower surface hydrophobicity (1100 versus 1356), higher emulsifying activity index (66.17 versus 46.49 m²/g), higher emulsion stability index (79.62 versus 63.61%), and lesser free sulfhydryl (8.07 versus 8.98 μmol/g) groups were obtained with NADES system than with water system. The results suggest that NADES is a suitable alternative reaction medium for promoting the glycation of BSA.

Characteristics and antioxidant activity of Maillard reaction products from α-lactalbumin and 2'-fucosyllactose

The characteristics and antioxidant activity of Maillard reaction products (MRPs) from 2'-fucosyllactose (2'-FL), a human milk oligosaccharide, and α-lactalbumin (α-LA) were investigated. MRPs were prepared by reacting 2'-FL with α-LA at 60 °C and 79% relative humidity for up to 72 h. The absorbance and fluorescence intensity of heated α-LA-2'-FL increased as the heating time increased, while the free amino group content decreased, confirming that 2'-FL reacted with α-LA and produced various MRPs at different incubation stages. Conjugates of 2'-FL and α-LA and aggregation of α-LA were observed by SDS-PAGE. The secondary structure of α-LA did not change significantly after reacting with 2'-FL. In terms of antioxidant activity, the 2,2-diphenyl-1-picrylhydrazyl (DPPH) scavenging activity and reducing power of α-LA-2'-FL increased significantly when compared with the protein only sample (p < 0.05). The findings provide a foundation for the characterization and functional analysis of MRPs in dairy products.

Role of 'D-allulose' in a starch based composite gel matrix

Type of sugar and gelling agents used in confectionery formulations have vital importance since they directly influence physicochemical properties during storage. In this study, the effect of a non-caloric rare sugar, D-allulose (formerly called D-psicose) on the starch based confectionery gels were investigated in the presence and absence of soy protein isolate (SPI) using different experimental techniques for 28 days. For characterization of the formulized gel systems, common techniques were used (SEM, DSC, XRD, moisture content, water activity, hardness and color). Time Domain Nuclear Magnetic Resonance (TD-NMR) technique was also employed to explain dynamics in the systems. Sugar type was found to be a very significant factor affecting gel characteristics and retrogradation. Results showed that D-allulose containing formulations were less prone to retrogradation and showed smaller changes upon storage by supporting presence of better gel network. According to X-ray results, sucrose containing formulations were more susceptible to crystallization. T₂ relaxation spectra obtained from NMR experiments showed that number of distinct peaks reduced with the addition of SPI while relaxation times of peaks changed when different type of sugar.

Effect of d-psicose substitution on gelatin based soft candies: A TD-NMR study

Confectionary gels are considered as composite gel systems composed of high amount of sugar and gelling agent such as gelatin or starch. d-Psicose is classified as a type of rare sugar, which is a C-3 epimer of fructose and has 70% of the sweetness of sucrose with a caloric value of 0.39 kcal/g. Utilization of d-psicose in food products is gaining particular interest due to its low caloric value. In this study, gelatin-based soft candies were formulated, and the effect of d-psicose substitution was explored on the quality of the products. For characterization of the soft candies, moisture content, water activity, color, hardness, and glass transition temperature of samples were investigated. X-ray diffraction analysis was also performed to explain the crystallization tendency of jelly candies. Results showed that, the softest sample with the highest moisture content and the smallest crystallization tendency was the sample that included the highest amount of d-psicose. Time domain (TD) NMR relaxometry experiments were also conducted on gel samples, and three distinct proton populations were observed in the relaxation spectrum for all formulations. Spin-lattice relaxation times obtained through monoexponential fitting (T₁ ) were also obtained to explain some quality parameters.

Heat-Induced Interactions between Whey Protein and Inulin and Changes in Physicochemical and Antioxidative Properties of the Complexes

Whey protein and inulin at various weight ratios were dry heated at 60 °C for 5 days under relative humidity of 63%. The heated mixtures were found to have significant changes in browning intensity and zeta-potential compared to untreated mixture. Heated samples showed significantly lower surface hydrophobicity than untreated mixtures. Compared with untreated samples, dry-heated samples showed significantly higher 2,2-Diphenyl-1-Picrylhydrazyl (DPPH) scavenging ability with whey protein to inulin mass ratios of 1:2 and 1:3 and significantly higher 2,2′-Azinobis(2-Ethylbenzothiazoline-6-Sulfonate) (ABTS) scavenging abilities and oxygen radical absorbance capacity (ORAC) at all weight ratios. Dry heat-induced interactions between whey protein and inulin was confirmed by changes in Sodium Dodecyl Sulfate Polyacrylamide Gel Electrophoresis (SDS-PAGE) protein profile, Fourier Transform Infrared Spectroscopy (FT-IR) and Far-ultraviolet Circular Dichroism (Far-UV CD) spectra. Dry heating caused physicochemical and structural changes of whey protein and therefore the complexes can be used to improve the antioxidative properties of the mixture under certain conditions.

Characterization and Antioxidant Activity of Products Derived from Xylose-Bovine Casein Hydrolysate Maillard Reaction: Impact of Reaction Time

The characterization and antioxidant activity on Maillard reaction products (MRPs) derived from xylose and bovine casein hydrolysate (BCH) was investigated at 100 °C and initial pH 8.0 as a function of reaction time. The pH values and free amino groups contents of xylose-BCH MRPs remarkably decreased with the reaction time up to 8 h, whereas their browning intensities significantly increased (p < 0.05). After 4 h of heat treatment, the fluorescence properties of xylose-BCH MRPs reached the maximum. There was a production of higher and smaller molecular substances in xylose-BCH MRPs with an increased reaction time, as analyzed by size exclusion chromatography. The 2,2-diphenyl-1-picryl-hydrazyl (DPPH) free radical scavenging capacity and ferrous reducing activity of xylose-BCH MRPs gradually increased with the reaction time extended from 0 to 8 h.

Investigation of the Mechanism of Conformational Alteration in Ovalbumin as Induced by Glycation with Different Monoses through Conventional Spectrometry and Liquid Chromatography High-Resolution Mass Spectrometry

Glycation between ovalbumin (OVA) and different monoses under mild dry heating at 37 °C was studied. The content of free amino groups decreased dramatically, and the conformational changes based on fluorescence and circular dichroism spectra were evident in glycated OVA. The glycated sites and the average degree of substitution per peptide molecule per site were determined using liquid chromatography high-resolution mass spectrometry. Lysine and arginine were the predominant glyaction sites, in which Lys207 was a relatively reactive site for glycation in all of the conjugates. In general, the extent of glycation of aldose was higher, and its alterations on the steric layouts of protein were more drastic than those of ketose. The configuration of hydroxyl groups at C-4 in sugar epimers might be important for the glycation reactivity and conformational modification in the glycated proteins. These insights would have important implications for the creation of sweetened food products with desirable structures and excellent quality control.

Fish Oil Emulsions Stabilized with Caseinate Glycated by Dextran: Physicochemical Stability and Gastrointestinal Fate

Incorporation of fish oil containing ω-3 polyunsaturated fatty acids (PUFAs) into functional foods remains challenging. In this study, caseinate and glycoconjugates (CD6, CD40, CD70, CD100) of caseinate to dextrans of different molecular weights (D6, D40, D70, D100 kDa) were used to stabilize fish oil emulsions, and the impact on physicochemical stability and gastrointestinal fate was investigated. The glycoconjugate of CD6 exhibited significantly higher conjugation efficiency, lower surface hydrophobicity ( H0), and lower surface activity than other glycoconjugates. The glycoconjugate of CD70 displayed the best emulsifying activity and emulsion stability. Except CD6 stabilized emulsions, all other emulsions showed fine storage stability over 14 d at 22 ± 1 °C. The glycoconjugate stabilized emulsions exhibited significantly lower peroxide value (PV) ( P < 0.05) than that of the caseinate stabilized one. During in vitro gastrointestinal tract digestion, the glycation of caseinate with dextrans changed the ζ-potential, average particle size ( D₃₂), and particle size distribution of the emulsions, which influenced flocculation and coalescence of droplets, as demonstrated by confocal microscopy. Caseinate after glycation with dextrans significantly retarded the release of free fatty acids from emulsions ( P < 0.05) during in vitro lipolysis. These results suggested that the dextrans attached to caseinate by glycation played a vital role in physicochemical stability and gastrointestinal fate of emulsions, mainly by its steric hindrance to effectively prevent flocculation and coalescence of droplets.

Recent research on the physiological functions, applications, and biotechnological production of D-allose

D-Allose is a rare monosaccharide, which rarely appears in the natural environment. D-Allose has an 80% sweetness relative to table sugar but is ultra-low calorie and non-toxic and is thus an ideal candidate to take the place of table sugar in food products. It displays unique health benefits and physiological functions in various fields, including food systems, clinical treatment, and the health care fields. However, it is difficult to produce chemically. The biotechnological production of D-allose has become a research hotspot in recent years. Therefore, an overview of recent studies on the physiological functions, applications, and biotechnological production of D-allose is presented. In this review, the physiological functions of D-allose are introduced in detail. In addition, the different types of D-allose-producing enzymes are compared for their enzymatic properties and for the biotechnological production of D-allose. To date, very little information is available on the molecular modification and food-grade expression of D-allose-producing enzymes, representing a very large research space yet to be explored.

Glycation of whey proteins: Technological and nutritional implications

Whey proteins are globular proteins that have received much attention due to their high nutritional value and characteristic functional properties. In addition to being part of the protein system in milk, they constitute the main proteins in whey and whey protein products. Interaction of whey proteins with reducing sugars and carbohydrates via Maillard reaction have been extensively studied in milk and in model systems. Glycation of individual whey proteins results in variable increases in their solubility, thermal stability, antioxidant activity, and emulsion and foam stabilization. Limited glycation of whey protein products particularly whey protein isolates (WPI) using polysaccharides has been studied with the aim to produce conjugates with modified functional properties and acceptable sensory properties. An overview is presented here on the effect of glycation on individual whey proteins and whey protein products and the potential uses of the glycated whey proteins.

Metabolic engineering pathways for rare sugars biosynthesis, physiological functionalities, and applications-a review

Biomolecules like rare sugars and their derivatives are referred to as monosaccharides particularly uncommon in nature. Remarkably, many of them have various known physiological functions and biotechnological applications in cosmetics, nutrition, and pharmaceutical industries. Also, they can be exploited as starting materials for synthesizing fascinating natural bioproducts with significant biological activities. Regrettably, most of the rare sugars are quite expensive, and their synthetic chemical routes are both limited and economically unfeasible due to expensive raw materials. On the other hand, their production by enzymatic means often suffers from low space-time yields and high catalyst costs due to hasty enzyme denaturation/degradation. In this context, biosynthesis of rare sugars with industrial importance is receiving renowned scientific attention, across the globe. Moreover, the utilization of renewable resources as energy sources via microbial fermentation or microbial metabolic engineering has appeared a new tool. This article presents a comprehensive review of physiological functions and biotechnological applications of rare ketohexoses and aldohexoses, including D-psicose, D-tagatose, L-tagatose, D-sorbose, L-fructose, D-allose, L-glucose, D-gulose, L-talose, L-galactose, and L-fucose. Novel in-vivo recombination pathways based on aldolase and phosphatase for the biosynthesis of rare sugars, particularly D-psicose and D-sorbose using robust microbial strains are also deliberated.

Improved Antioxidant Activity and Glycation of α-Lactalbumin after Ultrasonic Pretreatment Revealed by High-Resolution Mass Spectrometry

High-resolution mass spectrometry was performed to investigate the relationship between bovine α-lactalbumin (α-LA) subjected to ultrasonication and glycation treatment with respect to antioxidant activity. After α-LA was pretreated by ultrasonication combined with glycation, the treated α-LA showed low intrinsic fluorescence emission and high antioxidant activity at increased ultrasonic power levels. Prior to ultrasonic pretreatment, three glycated sites were identified, whereas the number of glycation sites was increased to four, four, five, and six after ultrasonic power at 60, 90, 120, and 150 W/cm², respectively, for 15 min. Thus, no obvious difference was found among the glycation sites at the ultrasonic power of 60 and 90 W/cm². The average degree of substitution per peptide molecule of α-LA was used to evaluate the glycation level per glycation site. All the samples pretreated by ultrasonication exhibited a higher glycation level compared with the untreated samples. Ultrasonic power at 150 W/cm² showed the most highly enhanced glycation extent and antioxidant activity. Therefore, the intensified glycation extent and the conformational changes of protein were responsible for the increase of antioxidant activity of α-LA. Moreover, high-resolution mass spectrometry is an efficient technique to understand the mechanism of the improved antioxidant activity.

Implications of the Maillard reaction on bovine alpha-lactalbumin and its proteolysis during in vitro infant digestion

This study investigated the functionality and digestibility of Maillard reaction products (MRPs) of alpha-lactalbumin (α-la), a major whey protein and component of infant formulas. The impact of different carbohydrates (glucose, galactose or galacto-oligosaccharides (GOS)) and heating duration was studied. SDS-PAGE, UV and color measurements monitored reaction extent, which varied between carbohydrates whereby galactose reacted more readily than glucose. Surface hydrophobicity and antioxidant capacity were found to be significantly (p < 0.05) higher following Maillard conjugation, with GOS-based MRPs elevating antioxidant capacity ∼50-fold compared to α-la. In addition, the digestive proteolysis of MRPs was evaluated using an infant in vitro gastro-duodenal model. SDS-PAGE analyses of digesta revealed Maillard conjugation generally increased α-la's susceptibility to proteolysis. Interestingly, GOS-based MRPs presented an optimization challenge, since heating for 12 h delayed proteolysis, while extended heating resulted in the highest susceptibility to proteolysis. Proteomic analyses further demonstrated the differences in enzymatic cleavage patterns and helped identify bioactive peptides rendered bioaccessible during the digestion of α-la or its MRPs. Bioinformatic mining of the proteomic data using PeptideRanker also gave rise to two potentially novel bioactive peptides, FQINNKIW and GINYWLAHKALCS. Finally, antioxidant capacity of luminal contents, measured by DPPH, revealed Maillard conjugation increased the antioxidant capacity of both gastric and duodenal digesta. Overall, this work draws a link between the Maillard reaction, digestive proteolysis and the bioaccessibility of bioactive peptides and antioxidant species in the infant alimentary canal. This could help rationally process infant formulas towards improved nutritional and extra-nutritional benefits.

Impact of the environmental conditions and substrate pre-treatment on whey protein hydrolysis: A review

Proteins in solution are subject to myriad forces stemming from interactions with each other as well as with the solvent media. The role of the environmental conditions, namely pH, temperature, ionic strength remains under-estimated yet it impacts protein conformations and consequently its interaction with, and susceptibility to, the enzyme. Enzymes, being proteins are also amenable to the environmental conditions because they are either activated or denatured depending on the choice of the conditions. Furthermore, enzyme specificity is restricted to a narrow regime of optimal conditions while opportunities outside the optimum conditions remain untapped. In addition, the composition of protein substrate (whether mixed or single purified) have been underestimated in previous studies. In addition, protein pre-treatment methods like heat denaturation prior to hydrolysis is a complex phenomenon whose progression is influenced by the environmental conditions including the presence or absence of sugars like lactose, ionic strength, purity of the protein, and the molecular structure of the mixed proteins particularly presence of free thiol groups. In this review, we revisit protein hydrolysis with a focus on the impact of the hydrolysis environment and show that preference of peptide bonds and/or one protein over another during hydrolysis is driven by the environmental conditions. Likewise, heat-denaturing is a process which is dependent on not only the environment but the presence or absence of other proteins.

Antioxidant activity of bovine alpha lactalbumin Maillard products and evaluation of their in vitro gastro-duodenal digestive proteolysis

Maillard conjugation alters alpha lactalbumin antioxidant capacity, including during in vitro digestion, with different effect in adults versus infants.