Brown Precursor Research Articles

Integrated HS-SPME-GC–MS and UHPLC-O-TOF-MS-based metabolomics revealed the characteristics flavor and nonvolatile metabolites during the hydrolysis process of Boletus edulis

This research aimed to investigate the flavor characteristic, metabolites and bioactivities of Boletus edulis hydrolysates via HS-SPME-GC-MS and UHPLC-MS/MS. The Maillard reaction (MR) significantly enhanced the sensory qualities of Boletus edulis, including like-meat, caramel, continuity, and complete acceptance. The accumulation of browning precursors during MR was verified through spectral analysis. We also found that the MR enhanced the antioxidant and hypoglycemic activities of Boletus edulis hydrolysates. Furthermore, 11 VOCs were also identified as key aromatic compounds and had important impact on the flavor characteristics of Maillard reaction products (MRPs). Non-targeted metabolomics analyses revealed that the formation of MRPs was affected through amino acid metabolism, lipid metabolism and plant secondary metabolism. Briefly, the flavor and biological activity of Boletus edulis were improved through enzymolysis and MR. The results provided a theoretical foundation for deep processing and resource utilization of Boletus edulis.

Inhibitory effect of thiol compounds on browning precursors and intermediates in sorbitol/glycine system.

Sorbitol as a sweetener is often thought to be unable to participate in the Maillard reaction causing browning. However, browning of a system was found to be significant when sorbitol was mixed with glycine and heated. The thiol compounds glutathione and cysteine were added to the system, and the inhibition mechanism of the two on the browning of the system was studied by combining the changes of precursor substances, intermediate products and browning degree. When the concentration of thiol compounds reached 25 mg mL-1, both could make the browning inhibition of the system more than 80%, and the accumulated glucose concentration was reduced to <35% of the control. The production of 3-deoxyglucosone, a precursor of melanoidin, was significantly reduced. Glutathione and cysteine directly inhibited the production of substrates in the sorbitol/glycine system, reduced glucose accumulation through competitive consumption and captured highly active intermediates through sulfhydryl groups. This has implications for the browning control of food systems containing sugar alcohols. © 2024 Society of Chemical Industry.

Light-Colored Maillard Peptides: Formation from Reduced Fluorescent Precursors of Browning and Enhancement of Saltiness Perception.

The browning formation and taste enhancement of peptides derived from soybean, peanut, and corn were studied in the light-colored Maillard reaction compared with the deep-colored reaction. The fluorescent compounds, as the browning precursors, were accumulated during the early Maillard reaction of peptides and subsequently degraded into dark substances, which resulted in a higher browning degree of deep-colored Maillard peptides (MPs), especially for the MPs derived from corn peptide. However, the addition of l-cysteine in light-colored Maillard reaction reduced the formation of deoxyosones and short-chain reactive α-dicarbonyls, thereby weakening the generation of fluorescent compounds and inhibited the browning of MPs. Synchronously, the peptides were thermally degraded into small peptides and amino acids, which were consumed less during light-colored thermal reaction due to its shorter reaction time at high temperature compared with deep-colored ones, thus contributing to a stronger saltiness perception of light-colored MPs than deep-colored MPs. Besides, the Maillard reaction products derived from soybean and peanut peptides possessed an obvious "kokumi" taste, making them suitable for enhancing the soup flavors.

Formation of fluorescent substances and correlation with process flavor changes of dehydrated Maillard reaction intermediates of peanut protein hydrolysates

Maillard reaction intermediates (MRIs) derived from peanut protein hydrolysates (PPH) and xylose (Xyl) were prepared using the water bath combined with spray drying and vacuum drying. The monitoring of free amino content, browning precursors, and taste characteristics was carried out throughout the thermal treatment at low temperature, where the Maillard reaction process was slowed down, and the formation and degradation of MRIs were dynamically balanced at low conversion rates. The reaction between amino compounds and the reducing sugars contributed to the increased taste characteristics during the early phase of Maillard reaction. Fluorescence intensity was reduced after reaching its maximum value and browning intensity was significantly increased during vacuum drying, which confirmed that the Maillard reaction entered into an advanced stage. Vacuum drying also led to a significant increase in the total amount of volatile compounds in the subsequent thermal processing reaction (from 212.93 ng/g to 564.91 ng/g), which demonstrated that the higher fluorescence intensities resulted in the more accumulation of MRIs and better capabilities of flavor formation.

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

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

Variation of moisture state and taste characteristics during vacuum drying of Maillard reaction intermediates of hydrolyzed soybean protein and characterization of browning precursors via fluorescence spectroscopy

Maillard reaction intermediates (MRIs) derived from enzymatic hydrolysates of soybean protein were prepared by combining dehydration method with spray drying and vacuum drying. Taste characteristics, browning precursors, water activity, and moisture state were monitored during the process of vacuum drying. The water activity was significantly reduced and the proportion of bound water was increased, which could promote the large accumulation of MRIs. The saltiness, umami, and bitterness responses of MRIs were all reduced and the reduction of taste intensity during vacuum drying was probably caused by the reaction of small peptides of taste-active amino acids with glucose. The continuous accumulation of browning precursors during vacuum drying was confirmed by fluorescence spectroscopic analysis and by quantitative analysis of α-dicarbonyl compounds. Subsequent browning reactions further demonstrated that the MRI with the highest fluorescence intensity also had the greatest browning potential.

Glycine-Xylose Amadori Compound Formation Tracing through Maillard Browning Inhibition by 2-Threityl-thiazolidine-4-carboxylic Acid Formation from Deoxyosone and Exogenous Cysteine

The browning inhibition of cysteine on the Maillard reaction of glycine-xylose performed under stepwise increased temperature was investigated. The browning degrees of the final products prepared with cysteine addition at different time points were found dissimilar, and the addition time point of cysteine yielding the lightest browning products was consistent with the time when the glycine-xylose Amadori rearrangement product (GX-ARP) reached its maximum yield. To clarify the reason for browning inhibition caused by cysteine, the evolution of key browning precursors formed in the GX-ARP model with cysteine involved was investigated by HPLC with a diode array detector. The results on the browning degree of the thermal reaction products of GX-ARP with cysteine addition showed great inhibition of α-dicarbonyl generation, which resulted in a significant increase in the activation energy of GX-ARP conversion to browning formation during heat treatment. Strong evidence suggested that the additional cysteine got involved in GX-ARP degradation and reacted with the deoxyosones derived from GX-ARP to yield cyclic 2-threityl-thiazolidine-4-carboxylic acid (TTCA). TTCA formation shunted the degradation of deoxyosones into short-chain α-dicarbonyls, which were important browning precursors, and consequently inhibited the Maillard browning.

Autophagy-mediated NCOR1 degradation is required for brown fat maturation and thermogenesis

Brown adipose tissue (BAT) thermogenesis affects energy balance, and thereby it has the potential to induce weight loss and to prevent obesity. Here we document a macroautophagic/autophagic-dependent mechanism of PPARG activity regulation that induces brown adipose differentiation and thermogenesis, and that is mediated by TP53INP2. Disruption of TP53INP2-dependent autophagy reduced brown adipogenesis in cultured cells. In vivo specific-tp53inp2 ablation in brown precursor cells or in adult mice decreased the expression of thermogenic and mature adipocytes genes in BAT. As a result, TP53INP2-deficient mice had reduced UCP1 content in BAT and impaired maximal thermogenic capacity, leading to lipid accumulation and to positive energy balance. Mechanistically, TP53INP2 stimulates PPARG activity and adipogenesis in brown adipose cells by promoting the autophagic degradation of NCOR1, a PPARG co-repressor. Moreover, the modulation of TP53INP2 expression in BAT and in human brown adipocytes suggest that this protein increases PPARG activity during metabolic activation of brown fat. In all, we have identified a novel molecular explanation to the contribution of autophagy to BAT energy metabolism that could facilitate the design of therapeutic strategies against obesity and its metabolic complications.

Investigation of thermo-chemical properties of mechanochemically generated glucose–histidine Maillard reaction mixtures

Mechanochemistry is gaining increasing interest as an efficient tool for solvent-free organic transformations. Recently, it was applied to perform the Maillard reaction of glucose with various amino acids that lead to the selective formation of Schiff bases and their Amadori rearrangement products. In this study, we report the thermal properties of the mechanochemically generated glucose–histidine reaction mixtures. Direct video recordings of their melting behavior show that the browning of the ball-milled mixtures starts at lower temperatures and proceed more slowly compared to the non-milled mixtures. Furthermore, pyrolysis of ball-milled mixtures generated more pyrazines and fewer furan derivatives compared to the non-milled mixtures. The chemical composition of the ball-milled glucose–histidine was also investigated in depth by high-resolution mass spectrometry. The decarboxylation and C2–C3 sugar chain cleavage reactions were identified as the most important transformations during ball milling. These findings further support the utility of mechanochemically generated mixtures as potential Maillard flavor and browning precursors.

Insulin-induced serine 22 phosphorylation of retinoid X receptor alpha is dispensable for adipogenesis in brown adipocytes

ABSTRACT Insulin action initiates a series of phosphorylation events regulating cellular differentiation, growth and metabolism. We have previously discovered, in a mass spectrometry-based phosphoproteomic study, that insulin/IGF-1 signalling induces phosphorylation of retinoid x receptor alpha (RXRα) at S22 in mouse brown pre-adipocytes. Here, we show that insulin induces the phosphorylation of RXRα at S22 in both brown precursor and mature adipocytes through a pathway involving ERK, downstream of IRS-1 and −2. We also found that RXRα S22 phosphorylation is promoted by insulin and upon re-feeding in brown adipose tissue in vivo, and that insulin-stimulated S22 phosphorylation of RXRα is dampened by diet-induced obesity. We used Rxra knockout cells re-expressing wild type (WT) or S22A non-phosphorylatable forms of RXRα to further characterize the role of S22 in brown adipocytes. Knockout of Rxra in brown pre-adipocytes resulted in decreased lipid accumulation and adipogenic gene expression during differentiation, and re-expression of RxraWT alleviated these effects. However, we observed no significant difference in cells re-expressing the RxraS22A mutant as compared with the cells re-expressing RxraWT. Furthermore, comparison of gene expression during adipogenesis in the WT and S22A re-expressing cells by RNA sequencing revealed similar transcriptomic profiles. Thus, our data propose a dispensable role for RXRα S22 phosphorylation in adipogenesis and transcription in differentiating brown pre-adipocytes.

The monofunctional cobalamin biosynthesis enzyme precorrin-3B synthase (CobZRR) is essential for anaerobic photosynthesis in Rhodospirillum rubrum but not for aerobic dark metabolism.

The in vivo physiological role of the gene cobZ, which encodes precorrin-3B synthase, which catalyzes the initial porphyrin ring contraction step of cobalamin biosynthesis via the cob pathway, has been demonstrated here for the first time. Cobalamin is known to be essential for an early step of bacteriochlorophyll biosynthesis in anoxygenic purple bacteria. The cobZ (cobZRR) gene of the purple bacterium Rhodospirillum rubrum was localized to a 23.5 kb insert of chromosomal DNA contained on the cosmid pSC4. pSC4 complemented several mutants of bacteriochlorophyll and carotenoid biosynthesis, due to the presence of the bchCX and crtCDEF genes at one end of the cosmid insert, flanking cobZRR. A second gene, citB/tcuB, immediately downstream of cobZRR, shows homologies to both a tricarballylate oxidoreductase (tcuB) and a gene (citB) involved in signal transduction during citrate uptake. CobZRR shows extensive homology to the N-terminal domain of the bifunctional CobZ from Rhodobacter capsulatus, and the R. rubrum citB/tcuB gene is homologous to the CobZ C-terminal domain. A mutant, SERGK25, containing a terminatorless kanamycin interposon inserted into cobZRR, could not grow by anaerobic photosynthesis, but grew normally under dark, aerobic and microaerophilic conditions with succinate and fructose as carbon sources. The anaerobic in vivo activity of CobZ indicates that it does not require oxygen as a substrate. The mutant excreted large amounts of protoporphyrin IX-monomethylester, a brown precursor of bacteriochlorophyll biosynthesis. The mutant was complemented either by the cobZRR gene in trans, or when exogenous cobalamin was added to the medium. A deletion mutant of tcuB/citB did not exhibit the cob phenotype. Thus, a role for tcuB/citB in cobalamin biosynthesis could not be confirmed.

Eicosapentaenoic acid (EPA) promotes differentiation of human brown precursor cells into metabolically active classical brown adipocytes via Gq/11 signaling

Eicosapentaenoic acid (EPA) supplementation exerts a plethora of health benefits. Previously, we demonstrated that EPA promotes brown adipogenesis by mediating G‐coupled protein receptor 120 (GPR120) activation in rodent brown precursor cells. The aim of this study is to establish the role of EPA in regulating brown adipogenesis in human classical brown precursor cells. The immortalized human brown precursor cells were employed to induce differentiation in the presence of oleic acid, palmitic acid, and EPA. EPA treatment significantly increased brown‐specific gene expressions including Ucp1, Prdm16, Cidea, DiO2, UCP1 protein expressions and oxygen consumption rate. To further investigate the role of GPR120, a receptor family involved in Gq/11 subtype, human brown precursor cells were treated with either GPR120‐specific agonist cdpA or a potent Gq/11 inhibitor (YM‐254890) during differentiation. GPR120 agonism significantly promoted EPA‐mediated brown adipogenesis, while inhibition of Gq/11 signaling completely abrogated brown adipogenesis. Consistently, the genetic deletion of GRR120 by CRISPR/Cas9 abrogated EPA‐mediated brown adipogenic effects. Collectively, these results demonstrate that EPA supplementation mediates Gq/11 signaling of GPR120 leading to augmentation of brown adipogenesis in human brown precursor cells.Support or Funding InformationNIH 1P20GM104320

Prior exposure of angiogenic factors promote cell‐autonomous brown adipogenesis of human classical brown precursor cells

Humans contain substantial amount of classical brown fat in the neck area. In contrast to beige fat that requires stimulatory signal, classical brown fat constitutively expresses uncoupling protein 1 (UCP1), thereby significantly contributing to energy balance. Despite metabolic significance, environmental factors that alter brown fat development in humans have not been clearly established. Given the intimate relationship between brown adipogenesis and capillary network in vivo, we hypothesize that angiogenic factors such as vascular endothelial growth factor (VEGF) and fibroblast growth factor 2 (FGF2) modulate brown adipogenic potential. Immortalized classical brown precursors established from human, were pre‐exposed with or without endothelial growth medium (EGM) containing VEGF and FGF2 before the induction to adipogenic differentiation. Pre‐exposure of anigoenic medium resulted in &gt;10‐fold increases of brown signature gene expressions including UCP1, Cidea and DIO2, as well as oxygen consumption rate. In addition, exposure to angiogenic media significantly modulated brown adipogenesis via epigenetic mechanisms: 1) downregulation of histone deacetylase (HDAC) expression specifically HDAC1 and HDAC9, and 2) biogenesis of functional cluster of brown‐specific microRNAs, i.e., miR‐378, miR‐30b and miR‐193b/365. Collectively, we demonstrated that prior exposure of anigogenic environment promotes cell‐autonomous potential to convert brown precursor cells into metabolically active human brown adipocytes via epigenetic mechanisms.Support or Funding InformationSupported by NIH 1P20GM104320

Sugar-Conjugated Bis(glycinato)copper(II) Complexes and Their Modulating Influence on the Maillard Reaction.

Transition metal ions are known to play an important role in the Maillard reaction in catalyzing redox reactions. They can also form strong binary complexes with amino acids with increased reactivity toward smaller aldehydes. To take advantage of this enhanced reactivity and to demonstrate the ability of glucose to conjugate with glycine copper complexes, model systems containing (Gly)2Cu and glucose or their isotopically enriched counterparts were heated in aqueous solutions in the presence and absence of paraformaldehyde at 110 °C for 2 h and the residues were analyzed by electrospray ionization/quadrupole time-of-flight/mass spectrometry (ESI/qTOF/MS). Isotope-labeling studies have indicated the ability of (Gly)2Cu complexes to act as molecular scaffolds and undergo multiple reactions with glucose to generate various complexes of sugar conjugates. These relatively stable intermediates allowed for the slower release of aroma and browning precursors, such as Amadori products, during heating, as assessed by the extent of browning and total volatile release.

Double SET point: G9a makes its mark in adipogenesis

EMBO J (2013) 32 1, 45–59 doi:10.1038/emboj.2012.306; published online November232012 Sequence-specific DNA-binding transcription factors (TFs) bind throughout the genome to orchestrate the process of adipocyte differentiation in an exquisitely timed and precise manner. TF binding recruits histone-modifying enzymes, resulting in dynamic epigenomic modifications that correlate with extensive gene expression changes. In this issue of The EMBO Journal, Wang et al (2012) demonstrate a critical role for the SET-containing histone methyltransferase G9a in generating repressive chromatin marks that are lost in the process of adipogenesis.

Distribution and Development of Brown Adipocytes in the Murine and Human Adipose Organ

Murine white and brown adipocytes are found together in dissectible visceral and subcutaneous fat depots supplied by specific vessels and nerves, forming a multi-depot organ with plastic properties. Many of the anatomo-physiological features of murine fat depots apply to humans.

Preparation of nanosized alumina using a low cost precursor

Alpha alumina powders have been prepared by the pyrolysis of sucrose, aluminium nitrate and ammonium nitrate. After spray pyrolysis at 400°C the mixture yields fluffy light brown precursor mass. After grinding followed by heat-treatment at 900°C and 1000°C it produced the alpha-alumina having particle sizes of 42 nm and 55 nm with surface area 12 m 2 /gm and 16 m 2 /gm respectively .The yield per unit time from precursor with ammonium nitrate is 3-4 times that of simple thermal spray pyrolysis without ammonium nitrate. The particle size and crystallite size have been decreased with increase of sucrose commensurated with ammonium nitrate in the reaction mixture. The crystallite sizes are comparable with particle sizes due to poor agglomeration due to excess addition of sucrose and ammonium nitrate.

The presence of UCP1 demonstrates that metabolically active adipose tissue in the neck of adult humans truly represents brown adipose tissue

Classically, adult humans have been considered not to possess active brown adipose tissue (BAT). However, positron-emission-tomography has shown fluorodeoxyglucose uptake that is distributed in such a way (e.g., in the neck) that it would seem to be BAT. Until now this has not been supported by direct evidence that these areas truly represented BAT, that is, the presence of the BAT-unique uncoupling protein-1 (UCP1). Samples of adipose tissue from the neck of 35 patients undergoing surgery for thyroid diseases were obtained and analyzed. In 1/3 of the subjects (the younger and leaner), distinct islands composed of UCP1 immunoreactive brown adipocytes could clearly be discerned, accounting for up to 1/3 of all adipocytes. The brown-adipose islands were richly sympathetically innervated (indicating acute central control); adjacent white adipose areas were not. The capillary density was high, implying a high capacity for oxygen delivery. Cells with features of brown adipocyte precursors were found in pericapillary areas. These data demonstrate that human adults indeed possess BAT and thus imply possibilities of future therapeutic strategies for the treatment of obesity, including maintenance of brown adipocytes and stimulation of the growth of preexisting brown precursors.

ACRYLAMIDE IN FOOD : AN OVERVIEW

The risk of acrylamide has only come to the attention of scientists recently, as its discovery in foods was accidental. Acrylamide is formed in many types of food cooked at high temperatures, presence of acrylamide in many foods has been recently reported. Four main theories have been proposed to explain the mechanisms by which acrylamide is formed in food: Theory 1 : Direct formation from amino acids; Theory 2 : Pathways based on acrolein intermediates; Theory 3 : Pathways based on an acrylic acid intermediate and Theory 4 : Pathways based on Maillard browning precursors .A hypothesis that acrylamide is formed by/upon cooking was confirmed in experimental animals by verification of the identity of the acrylamide adduct in haemoglobin (Hb). This was comprehensively approved by GC/MS analysis and the demonstration that the increased adduct levels were compatible with expectation from the contents of acrylamide determined in fried feeds. A significant dependence of acrylamide formation on temperature was demonstrated. Extensive efforts have been made to assess human exposure to acrylamide by monitoring several metabolites excreted in the urine as well as products resulting from biological alkylation by acrylamide. Results from in vivo studies conducted on rats explored that dermal absorption ranged from approximately 14 to 61% of the applied dose. Meanwhile, it was obvious that acrylamide is widely distributed in all tissues of the body. The major metabolite formed from acrylamide via the cytochrome P450 pathway is glycidamide. Conjugation to reduced glutathione (GSH) catalyzed by glutathione S-transferase (GST) and excretion as mercapturic acid is a major pathway for the metabolism of acrylamide. Experiments revealed neuro and reproductive toxicity of acrylamide. Notwithstanding, the International Agency of Research on Cancer (IARC) has classified acrylamide as “probably carcinogenic to humans”. Acrylamide in foods can be determined by GC/MS, HPLC and liquid chromatography-mass spectrometry (LC-MS) using the MS/MS mode. For the GC/MS and HPLC methods, the achieved detection level of acrylamide was 5 µg/kg while for LC-MS/MS method was 10 µg/kg. The latter method is simple and preferable for routine analysis.

Determination of the shape, size and porosity of fine α-Al2O3 powders prepared by emulsion evaporation

Stable water in oil emulsions were prepared from Al(NO 3 ) 3 solutions of different molarities. Dark brown precursors were obtained from these emulsions which were evaporated by adding them dropwise into hot mineral oil. The precursors containing diaspore as raw alumina were calcined at 1000 °C and fine α-Al 2 O 3 powders were obtained. The photographs of the powders were taken by the use of an electron microscope and their particle size distributions were determined. The shapes and sizes of the powders were discussed. Their mesopore size distributions were obtained from the data of the desorption of nitrogen at 77 K. The relation between the obtained results and the concentrations of the Al(NO 3 ) 3 solutions were discussed.