Characterization of Grape Pomace Extract Microcapsules: The Influence of Carbohydrate Co-Coating on the Stabilization of Goat Whey Protein as a Primary Coating.

Both grape pomace and whey are waste products from the food industry that are rich in valuable ingredients. The utilization of these two by-products is becoming increasingly possible as consumer awareness of upcycling increases. The biological activities of grape pomace extract (GPE) are diverse and depend on its bioavailability, which is influenced by processes in the digestive system. In this work, goat whey protein (GW) was used as the primary coating to protect the phenolic compounds of GPE during the spray drying process. In addition, trehalose (T), sucrose (S), xylose (X), and maltodextrin (MD) were added to the goat whey proteins as co-coatings and protein stabilizers. All spray drying experiments resulted in microcapsules (MC) with a high encapsulation efficiency (77.6-95.5%) and yield (91.5-99.0%) and almost 100% recovery of phenolic compounds during the release test. For o-coumaric acid, the GW-coated microcapsules (MC) showed a bioavailability index of up to 731.23%. A semi-crystalline structure and hydrophilicity were characteristics of the MC coated with 10% T, S, X, or 5% MD. GW alone or in combination with T, S, MD, or X proved to be a promising carrier for polyphenols from grape pomace extract and ensured good bioavailability of these natural antioxidants.

Mining novel gene targets for improving tolerance to furfural and acetic acid in Yarrowia lipolytica using whole-genome CRISPRi library.

Abundant renewable resource lignocellulosic biomass possesses tremendous potential for green biomanufacturing, while its efficient utilization by Yarrowia lipolytica, an attractive biochemical production host, is restricted since the presence of inhibitors furfural and acetic acid in lignocellulosic hydrolysate. Given deficient understanding of inherent interactions between inhibitors and cellular metabolism, sufficiently mining relevant genes is necessary. Herein, 14 novel gene targets were discovered using clustered regularly interspaced short palindromic repeats interference library in Y. lipolytica, achieving tolerance to 0.35 % (v/v) acetic acid (the highest concentration reported in Y. lipolytica), 4.8 mM furfural, or a combination of 2.4 mM furfural and 0.15 % (v/v) acetic acid. The tolerance mechanism might involve improvement of cell division and decrease of reactive oxygen species level. Transcriptional repression of effective gene targets still enabled tolerance when xylose was a carbon source. This work forms a robust foundation for improving microbial tolerance to lignocellulose-derived inhibitors and revealing underlying mechanism.

Genomic and metabolic instability during long-term fermentation of an industrial Saccharomyces cerevisiae strain engineered for C5 sugar utilization.

The genetic stability and metabolic robustness of production strains is one of the key criteria for the production of bio-based products by microbial fermentation on an industrial scale. These criteria were here explored in an industrial ethanol-producer strain of Saccharomyces cerevisiae able to co-ferment D-xylose and L-arabinose with glucose through the chromosomal integration of several copies of pivotal genes for the use of these pentose (C5) sugars. Using batch sequential cultures in a controlled bioreactor that mimics long-term fermentation in an industrial setting, this strain was found to exhibit significant fluctuations in D-xylose and L-arabinose consumption as early as the 50th generation and beyond. These fluctuations seem not related to the few low-consumption C5 sugar clones that appeared throughout the sequential batch cultures at a frequency lower than 1.5% and that were due to the reduction in the number of copies of transgenes coding for C5 sugar assimilation enzymes. Also, subpopulations enriched with low or high RAD52 expression, whose expression level was reported to be proportional to homologous recombination rate did not exhibit defect in C5-sugar assimilation, arguing that other mechanisms may be responsible for copy number variation of transgenes. Overall, this work highlighted the existence of genetic and metabolic instabilities in an industrial yeast which, although modest in our conditions, could be more deleterious in harsher industrial conditions, leading to reduced production performance.

Deficiency of ß-xylosidase activity in Aspergillus luchuensis mut. kawachii IFO 4308.

In this study, we investigated a deleterious mutation in the ß-xylosidase gene, xylA (AkxylA), in Aspergillus luchuensis mut. kawachii IFO 4308 by constructing an AkxylA disruptant and complementation strains of AkxylA and xylA derived from A. luchuensis RIB2604 (AlxylA), which does not harbor the mutation in xylA. Only the AlxylA complementation strain exhibited significantly higher growth and substantial ß-xylosidase activity in medium containing xylan, accompanied by an increase in XylA expression. This resulted in lower xylobiose and higher xylose concentrations in the mash of barley shochu. These findings suggest that the mutation in xylA affects xylose level during the fermentation process. Because the mutation in xylA was identified not only in the genome of strain IFO 4308 but also the genomes of other industrial strains of A. luchuensis and A. luchuensis mut. kawachii, these findings enhance our understanding of the genetic factors that affect the fermentation characteristics.

Establishment of low-cost production platforms of polyhydroxyalkanoate bioplastics from Halomonas cupida J9.

Microbial production of polyhydroxyalkanoate (PHA) is greatly restricted by high production cost arising from high-temperature sterilization and expensive carbon sources. In this study, a low-cost PHA production platform was established from Halomonas cupida J9. First, a marker-less genome-editing system was developed in H. cupida J9. Subsequently, H. cupida J9 was engineered to efficiently utilize xylose for PHA biosynthesis by introducing a new xylose metabolism module and blocking xylonate production. The engineered strain J9UΔxylD-P8xylA has the highest PHA yield (2.81 g/L) obtained by Halomonas with xylose as the sole carbon source so far. This is the first report on the production of short- and medium-chain-length (SCL-co-MCL) PHA from xylose by Halomonas. Interestingly, J9UΔxylD-P8xylA was capable of efficiently utilizing glucose and xylose as co-carbon sources for PHA production. Furthermore, fed-batch fermentation of J9UΔxylD-P8xylA coupled to a glucose/xylose co-feeding strategy reached up to 12.57 g/L PHA in a 5-L bioreactor under open and unsterile condition. Utilization of corn straw hydrolysate as the carbon source by J9UΔxylD-P8xylA reached 7.0 g/L cell dry weight (CDW) and 2.45 g/L PHA in an open fermentation. In summary, unsterile production in combination with inexpensive feedstock highlights the potential of the engineered strain for the low-cost production of PHA from lignocellulose-rich agriculture waste.

Maltose accumulation-induced cell death in Saccharomyces cerevisiae.

Pretreatment of lignocellulose yields a complex sugar mixture that potentially can be converted into bioethanol and other chemicals by engineered yeast. One approach to overcome competition between sugars for uptake and metabolism is the use of a consortium of specialist strains capable of efficient conversion of single sugars. Here, we show that maltose inhibits cell growth of a xylose-fermenting specialist strain IMX730.1 that is unable to utilize glucose because of the deletion of all hexokinase genes. The growth inhibition cannot be attributed to a competition between maltose and xylose for uptake. The inhibition is enhanced in a strain lacking maltase enzymes (dMalX2) and completely eliminated when all maltose transporters are deleted. High-level accumulation of maltose in the dMalX2 strain is accompanied by a hypotonic-like transcriptional response, while cells are rescued from maltose-induced cell death by the inclusion of an extracellular osmolyte such as sorbitol. These data suggest that maltose-induced cell death is due to high levels of maltose uptake causing hypotonic-like stress conditions and can be prevented through engineering of the maltose transporters. Transporter engineering should be included in the development of stable microbial consortia for the efficient conversion of lignocellulosic feedstocks.

Enhancing xylose-fermentation capacity of engineered Saccharomyces cerevisiae by multistep evolutionary engineering in inhibitor-rich lignocellulose hydrolysate.

Major progress in developing Saccharomyces cerevisiae strains that utilize the pentose sugar xylose has been achieved. However, the high inhibitor content of lignocellulose hydrolysates still hinders efficient xylose fermentation, which remains a major obstacle for commercially viable second-generation bioethanol production. Further improvement of xylose utilization in inhibitor-rich lignocellulose hydrolysates remains highly challenging. In this work, we have developed a robust industrial S. cerevisiae strain able to efficiently ferment xylose in concentrated undetoxified lignocellulose hydrolysates. This was accomplished with novel multistep evolutionary engineering. First, a tetraploid strain was generated and evolved in xylose-enriched pretreated spruce biomass. The best evolved strain was sporulated to obtain a genetically diverse diploid population. The diploid strains were then screened in industrially relevant conditions. The best performing strain, MDS130, showed superior fermentation performance in three different lignocellulose hydrolysates. In concentrated corncob hydrolysate, with initial cell density of 1 g DW/l, at 35°C, MDS130 completely coconsumed glucose and xylose, producing ± 7% v/v ethanol with a yield of 91% of the maximum theoretical value and an overall productivity of 1.22 g/l/h. MDS130 has been developed from previous industrial yeast strains without applying external mutagenesis, minimizing the risk of negative side-effects on other commercially important properties and maximizing its potential for industrial application.

Deletion of yghZ in Escherichia coli promotes growth in presence of furfural with xylose as carbon source.

Thermo-acidic pretreatment of lignocellulosic biomass is required to make it amenable to microbial metabolism and results in generation of furfural due to breakdown of pentose sugars. Furfural is toxic to microbial metabolism and results in reduced microbial productivity and increased production costs. This study asks if deletion of yghZ gene which encodes a NADPH-dependent aldehyde reductase enzyme results in improved furfural tolerance in Escherichia coli host. The ∆yghZ strain-SSK201-was tested for tolerance to furfural in presence of 5% xylose as a carbon source in AM1 minimal medium. At 96 h and in presence of 1.0 g/L furfural, the culture harboring strain SSK201 displayed 4.5-fold higher biomass, 2-fold lower furfural concentration and 15.75-fold higher specific growth rate (µ) as compared to the parent strain SSK42. The furfural tolerance advantage of SSK201 was retained when the carbon source was switched to glucose in AM1 medium and was lost in rich LB medium. The findings have potential to be scaled up to a hydrolysate culture medium, which contains furan inhibitors and lack nutritionally rich components, under bioreactor cultivation and observe growth advantage of the ∆yghZ host. It harbors potential to generate robust industrial strains which can convert lignocellulosic carbon into metabolites of interest in a cost-efficient manner.

Sustainable biorefinery approach by utilizing xylose fraction of lignocellulosic biomass.

Lignocellulosic biomass (LCB) has been a lucrative feedstock for developing biochemical products due to its rich organic content, low carbon footprint and abundant accessibility. The recalcitrant nature of this feedstock is a foremost bottleneck. It needs suitable pretreatment techniques to achieve a high yield of sugar fractions such as glucose and xylose with low inhibitory components. Cellulosic sugars are commonly used for the bio-manufacturing process, and the xylose sugar, which is predominant in the hemicellulosic fraction, is rejected as most cell factories lack the five­carbon metabolic pathways. In the present review, more emphasis was placed on the efficient pretreatment techniques developed for disintegrating LCB and enhancing xylose sugars. Further, the transformation of the xylose to value-added products through chemo-catalytic routes was highlighted. In addition, the review also recapitulates the sustainable production of biochemicals by native xylose assimilating microbes and engineering the metabolic pathway to ameliorate biomanufacturing using xylose as the sole carbon source. Overall, this review will give an edge on the bioprocessing of microbial metabolism for the efficient utilization of xylose in the LCB.

Construction of Xylose-Utilizing Cyanobacterial Chassis for Bioproduction Under Photomixotrophic Conditions.

Xylose is a major component of lignocellulose and the second most abundant sugar present in nature after glucose; it, therefore, has been considered to be a promising renewable resource for the production of biofuels and chemicals. However, no natural cyanobacterial strain is known capable of utilizing xylose. Here, we take the fast-growing cyanobacteria Synechococcus elongatus UTEX 2973 as an example to develop the synthetic biology-based methodology of constructing a new xylose-utilizing cyanobacterial chassis with increased acetyl-CoA for bioproduction.

Construction of an alternative NADPH regeneration pathway improves ethanol production in Saccharomyces cerevisiae with xylose metabolic pathway.

Full conversion of glucose and xylose from lignocellulosic hydrolysates is required for obtaining a high ethanol yield. However, glucose and xylose share flux in the pentose phosphate pathway (PPP) and glycolysis pathway (EMP), with glucose having a competitive advantage in the shared metabolic pathways. In this work, we knocked down ZWF1 to preclude glucose from entering the PPP. This reduced the [NADPH] level and disturbed growth on both glucose or xylose, confirming that the oxidative PPP, which begins with Zwf1p and ultimately leads to CO2 production, is the primary source of NADPH in both glucose and xylose. Upon glucose depletion, gluconeogenesis is necessary to generate glucose-6-phosphate, the substrate of Zwf1p. We re-established the NADPH regeneration pathway by replacing the endogenous NAD+-dependent glyceraldehyde-3-phosphate dehydrogenase (GAPDH) gene TDH3 with heterogenous NADP + -GAPDH genes GDH, gapB, and GDP1. Among the resulting strains, the strain BZP1 (zwf1Δ, tdh3::GDP1) exhibited a similar xylose consumption rate before glucose depletion, but a 1.6-fold increased xylose consumption rate following glucose depletion compared to the original strain BSGX001, and the ethanol yield for total consumed sugars of BZP1 was 13.5% higher than BSGX001. This suggested that using the EMP instead of PPP to generate NADPH reduces the wasteful metabolic cycle and excess CO2 release from oxidative PPP. Furthermore, we used a copper-repressing promoter to modulate the expression of ZWF1 and optimize the timing of turning off the ZWF1, therefore, to determine the competitive equilibrium between glucose-xylose co-metabolism. This strategy allowed fast growth in the early stage of fermentation and low waste in the following stages of fermentation.

Polyglycerol polyricinoleate and lecithin stabilized water in oil nanoemulsions for sugaring Beijing roast duck: Preparation, stability mechanisms and color improvement.

Traditional Beijing roast duck often suffers from uneven color and high sugar content after roasting. Water-in-oil (W/O) nanoemulsion is a promising alternative to replace high concentration of sugar solution used in sugaring process according to similarity-intermiscibility theory. Herein, 3% of xylose was embedded in the aqueous phase of W/O emulsion to replace 15% maltose solution. W/O emulsions with different ratios of lecithin (LEC) and polyglycerol polyricinoleate (PGPR) were constructed by high-speed homogenization and high-pressure homogenization. Distribution and penetration extent of solutions and emulsions through the duck skin, as well as the color uniformity of Beijing roast duck were analyzed. Emulsions with LEC:PGPR ratios of 1:3 and 2:2 had better stability. Stable interfacial film and spatial structure were important factors influencing emulsion stabilization. The stable W/O emulsions could more uniformly distribute onto the surface of duck skin and longitudinally penetrate through the skin than solutions.

Multi-step strategies for synergistic treatment of urinary tract infections based on D-xylose-decorated antimicrobial peptide carbon dots.

Urinary tract infections (UTIs) caused by Uropathogenic Escherichia coli (UPEC), often reoccur due to the formation of intracellular bacterial colonies (IBCs) and antibiotic resistance. Given the significance of YadC for UPEC infection in our previous study, we developed D-xylose-decorated ɛ-poly-L-lysine (εPL)-based carbon dots (D-xyl@εPLCDs) that can be traced, and employed multi-step approaches to elucidate the functional roles of D-xyl@εPLCDs in UPEC infection. Compared to undecorated particles, D-xyl@εPLCDs demonstrate YadC-dependent bacterial targeting and exhibit enhanced bactericidal activities both intracellularly and extracellularly. Moreover, pre-treatment of D-xyl@εPLCDs before infection blocked the subsequent adhesion and invasion of UPEC to bladder epithelial cells 5637. Increase of ROS production and innate immune responses were observed in bladder epithelial cells 5637 treated with D-xyl@εPLCDs. In addition, treatment of D-xyl@εPLCDs post-infection facilitated clearance of UPEC in the bladders of the UTI mouse model, and reduced ultimate number of neutrophils, macrophages and inflammatory responses raised by invaded bacteria. Collectively, we presented a comprehensive evaluating system to show that D-xyl@εPLCDs exhibits superior bactericidal effects against UPEC, making them a promising candidate for drug development in clinical UTI therapeutics.

Evaluation of Pyrophosphate-Driven Proton Pumps in Saccharomyces cerevisiae under Stress Conditions.

In Saccharomyces cerevisiae, pH homeostasis is reliant on ATP due to the use of proton-translocating ATPase (H+-ATPase) which constitutes a major drain within cellular ATP supply. Here, an exogenous proton-translocating pyrophosphatase (H+-PPase) from Arabidopsis thaliana, which uses inorganic pyrophosphate (PPi) rather than ATP, was evaluated for its effect on reducing the ATP burden. The H+-Ppase was localized to the vacuolar membrane or to the cell membrane, and their impact was studied under acetate stress at a low pH. Biosensors (pHluorin and mQueen-2m) were used to observe changes in intracellular pH (pHi) and ATP levels during growth on either glucose or xylose. A significant improvement of 35% in the growth rate at a pH of 3.7 and 6 g·L-1 acetic acid stress was observed in the vacuolar membrane H+-PPase strain compared to the parent strain. ATP levels were elevated in the same strain during anaerobic glucose and xylose fermentations. During anaerobic xylose fermentations, co-expression of pHluorin and a vacuolar membrane H+-PPase improved the growth characteristics by means of an improved growth rate (11.4%) and elongated logarithmic growth duration. Our study identified a potential method for improving productivity in the use of S. cerevisiae as a cell factory under the harsh conditions present in industry.

Fermentative processes for the upcycling of xylose to xylitol by immobilized cells of Pichia fermentans WC1507.

Xylitol is a pentose-polyol widely applied in the food and pharmaceutical industry. It can be produced from lignocellulosic biomass, valorizing second-generation feedstocks. Biotechnological production of xylitol requires scalable solutions suitable for industrial scale processes. Immobilized-cells systems offer numerous advantages. Although fungal pellet carriers have gained attention, their application in xylitol production remains unexplored. In this study, the yeast strain P. fermentans WC 1507 was employed for xylitol production. The optimal conditions were observed with free-cell cultures at pH above 3.5, low oxygenation, and medium containing (NH4)2SO4 and yeast extract as nitrogen sources (xylitol titer 79.4 g/L, YP/S 66.3%, and volumetric productivity 1.3 g/L/h). Yeast cells were immobilized using inactive Aspergillus oryzae pellet mycelial carrier (MC) and alginate beads (AB) and were tested in flasks over three consecutive production runs. Additionally, the effect of a 0.2% w/v alginate layer, coating the outer surface of the carriers (cMC and cAB, respectively), was examined. While YP/S values observed with both immobilized and free cells were similar, the immobilized cells exhibited lower final xylitol titer and volumetric productivity, likely due to mass transfer limitations. AB and cAB outperformed MC and cMC. The uncoated AB carriers were tested in a laboratory-scale airlift bioreactor, which demonstrated a progressive increase in xylitol production in a repeated batch process: in the third run, a xylitol titer of 63.0 g/L, YP/S of 61.5%, and volumetric productivity of 0.52 g/L/h were achieved. This study confirmed P. fermentans WC 1507 as a promising strain for xylitol production in both free- and entrapped-cells systems. Considering the performance of the wild strain, a metabolic engineering intervention aiming at further improving the efficiency of xylitol production could be justified. MC and AB proved to be viable supports for cell immobilization, but additional process development is necessary to identify the optimal bioreactor configuration and fermentation conditions.

XylR Overexpression in Escherichia coli Alleviated Transcriptional Repression by Arabinose and Enhanced Xylitol Bioproduction from Xylose Mother Liquor.

Xylitol is a polyol widely used in food, pharmaceuticals, and light industries. It is currently produced through the chemical catalytic hydrogenation of xylose and generates xylose mother liquor as a substantial byproduct in the procedure of xylose extraction. If xylose mother liquor could also be efficiently bioconverted to xylitol, the greenness and atom economy of xylitol production would be largely improved. However, xylose mother liquor contains a mixture of glucose, xylose, and arabinose, raising the issue of carbon catabolic repression in its utilization by microbial conversion. Targeting this challenge, the transcriptional activator XylR was overexpressed in a previously constructed xylitol-producing E. coli strain CPH. The resulting strain CPHR produced 16.61 g/L of xylitol in shake-flask cultures from the mixture of corn cob hydrolysate and xylose mother liquor (1:1, v/v) with a xylose conversion rate of 90.1%, which were 2.23 and 2.15 times higher than the starting strain, respectively. Furthermore, XylR overexpression upregulated the expression levels of xylE, xylF, xylG, and xylH genes by 2.08-2.72 times in arabinose-containing medium, suggesting the alleviation of transcriptional repression of xylose transport genes by arabinose. This work lays the foundation for xylitol bioproduction from xylose mother liquor.

Engineered Saccharomyces cerevisiae harbors xylose isomerase and xylose transporter improves co-fermentation of xylose and glucose for ethanol production.

Saccharomyces cerevisiae cannot assimilate xylose, second to glucose derived from lignocellulosic biomass. Here, the engineered S. cerevisiae strains INVSc-XI and INVSc-XI/XT were constructed using xylA and Xltr1p to co-utilize xylose and glucose, achieving economic viability and sustainable production of fuels. The xylose utilization rate of INVSc-XI/XT was 2.3-fold higher than that of INVSc-XI, indicating that overexpressing Xltr1p could further enhance xylose utilization. In mixed sugar media, a small amount of glucose enhanced the consumption of xylose by INVSc-XI/XT. Transcriptome analysis showed that glucose increased the upregulation of acetate of coenzyme A synthetase (ACS), alcohol dehydrogenase (ADH), and transketolase (TKL) gene expression in INVSc-XI/XT, further promoting xylose utilization and ethanol yield. The highest ethanol titer of 2.91 g/L with a yield of 0.29 g/g at 96 h by INVSc-XI/XT was 56.9% and 63.0% of the theoretical ethanol yield from glucose and xylose, respectively. These results showed overexpression of xylA and Xltr1p is a promising strategy for improving xylose and glucose conversion to ethanol. Although the ability of strain INVSc-XI/XT to produce ethanol was not very satisfactory, glucose was discovered to influence xylose utilization in strain INVSc-XI/XT. Altering the glucose concentration is a promising strategy to improve the xylose and glucose co-utilization.

INVSc-XI and INVSc-XI/XT strains were newly constructed to utilize xylose and glucose.XylA, in combination with xylose transporter Xltr1p, enhances xylose consumption.A small amount of glucose enhanced xylose utilization in INVSc-XI/XT strain.The expression of ACS, ADH, and TKL genes is upregulated in the media containing mixed sugars.The highest ethanol yield of 0.29 g/g was produced in a 2-L scale-up fermenter.

Efficient production of 1,2,4-butanetriol from corn cob hydrolysate by metabolically engineered Escherichia coli.

Corn cob is a major waste mass-produced in corn agriculture. Corn cob hydrolysate containing xylose, arabinose, and glucose is the hydrolysis product of corn cob. Herein, a recombinant Escherichia coli strain BT-10 was constructed to transform corn cob hydrolysate into 1,2,4-butanetriol, a platform substance with diversified applications. To eliminate catabolite repression and enhance NADPH supply for alcohol dehydrogenase YqhD catalyzed 1,2,4-butanetriol generation, ptsG encoding glucose transporter EIICBGlc and pgi encoding phosphoglucose isomerase were deleted. With four heterologous enzymes including xylose dehydrogenase, xylonolactonase, xylonate dehydratase, α-ketoacid decarboxylase and endogenous YqhD, E. coli BT-10 can produce 36.63 g/L 1,2,4-butanetriol with a productivity of 1.14 g/[L·h] using xylose as substrate. When corn cob hydrolysate was used as the substrate, 43.4 g/L 1,2,4-butanetriol was generated with a productivity of 1.09 g/[L·h] and a yield of 0.9 mol/mol. With its desirable characteristics, E. coli BT-10 is a promising strain for commercial 1,2,4-butanetriol production.

Enhancement mechanism of glycation with l-arabinose and xylose on texture properties of silver carp mince gel.

BACKGROUND: Glycation is a green processing technology. Based on our previous studies, glycation with l-arabinose and xylose was beneficial to enhance the texture properties of silver carp mince (SCM) gels. However, the possible enhancement mechanism remained unclear. Therefore, in this study, SCM gels with different types of reducing sugar (glucose, l-arabinose, and xylose) were prepared based on our previous study. The possible mechanism of texture enhancement of SCM gels was analyzed by investigating the changes in water distribution, protein structures, and microstructure in the gel system. RESULTS: The glycation of l-arabinose and xylose enhanced the hardness, cohesiveness, chewiness, and resilience of SCM gels. Hardness increased from 1883.04 (control group) to 3624.54 (l-arabinose group) and 4348.18 (xylose group). Low-field nuclear magnetic resonance (LF-NMR) showed that glycation promoted the tight binding of immobilized water to proteins. Raman spectroscopic analysis showed that glycation increased the surface hydrophobicity and promoted the formation of disulfide bonds. Scanning electron microscopy (SEM) showed that glycation promoted the formation of uniform and dense three-dimensional network structure in SCM gels. CONCLUSION: In summary, glycation enhanced the binding ability of immobilized water to proteins, improved the surface hydrophobicity, promoted the formation of disulfide bonds, and led to a more uniform and dense gel network structure of proteins, thus enhancing the texture properties of SCM gels. This research provided a theoretical basis for a better understanding of the mechanism of the effect of glycation on the quality of gel products and also provided technical support for the application of l-arabinose and xylose in new functional gel foods. © 2024 Society of Chemical Industry.

Effect of carbonyl-amino condensation, non-covalent cross-linking and conformational changes induced by ultrasound-assisted Maillard reaction on lysinoalanine formation in silkworm pupa protein.

The inhibition of cross-linked lysinoalanine (LAL) formation in silkworm pupa protein isolates (SPPI) by Maillard reaction (using varying xylose concentration) and ultrasound treatment was studied. Results showed that sonicated SPPI was effectively grafted with high concentration of xylose (5 %), resulting in the lowest LAL content, which was 48.75 % and 30.64 % lower than the control and ultrasound-treated samples, respectively. Chemical bond analysis showed that the combined treatment destroyed the ionic bonds, intrachain (g-g-t), and interchain (g-g-g) disulfide bonds, but stimulated the polymerization of hydrogen and hydrophobic bonds between SPPI and xylose, and as well enhanced the net negative charge between SPPI/Xylose complexes. The particles of the complexes were more loose, dispersed and rough, and had a stronger hydrophilic microenvironment, accompanied by alterations in microscopic, secondary and tertiary structures. Ultrasound treatment induced the breakdown of the oxidative cross-linking in SPPI, and promoted the sulfhydryl group-dehydroalanine binding and the carbonyl-amino condensation of the protein and xylose, and thus inhibited the formation of cross-linked LAL. Furthermore, the physicochemical and structural parameters were highly interrelated with cross-linked LAL content (|r| > 0.9). The outcomes provided a novel avenue and theoretical basis for minimizing LAL formation in SPPI and improving the nutrition and safety of SPPI.