Effect of modified starches on the quality of skins of glutinous rice dumplings.

This study aimed to investigate the influence of modified starches on the quality of skins of glutinous rice dumplings (SGRDs), including changes in textural properties, pasting parameters, microstructure, color, transparency, and sensory quality. The results showed that the addition of a single acetylated-modified cassava or potato starch or composite modified cassava and potato starch in a ratio of 2:1 can improve the quality of SGRDs. The springiness and lightness of SGRDs increased, and the transparency increased from 3.22 % to 6.18 %. The cooked samples had delicate mouth-feel, uniform color and luster, good transparency, no depression, and low weight loss and did not stick to the teeth. Moreover, the total consumer acceptability score increased from 60.67 to 89.33, indicating that these products were widely accepted by consumers. However, the addition of hydroxypropyl-modified cassava starch or its composite with other two modified starches had no apparent effect on the quality of SGRDs. In conclusion, the quality of SGRDs were significantly improved by the addition of single or composite acetylated-modified starches. This study provides a theoretical basis for improving the quality of SGRDs.

Thermally Methanol Oxidation via the Mn1@Co3O4(111) Facet: Non-CO Reaction Pathway.

Co3O4, as the support of single-atom catalysts, is effective in electron-structure modulation to get distinct methanol adsorption behaviors and adjustable reaction pathways for the methanol oxidation reaction. Herein, we considered the facets that constitute a Co vacancy of the Co3O4(111) facet and a foreign metal atom M (M = Fe, Ni, Cu, Ru, Rh, Pd, Ag, Os, Ir, Pt, Au, Mn) leading to single-atom catalysts. The Mn1@Co3O4(111) facet is the facet considered the most favorable among all of the possible terminations. Oxygen adsorption, decomposition, and its co-adsorption with methanol are the vital steps of methanol oxidation at the exposed Mn1@Co3O4(111) facet, giving rise to the stable configuration: two O* and one CH3OH* adsorbates. Then, the Mn1@Co3O4(111) facet activates the O-H and C-H bonds within CH3OH*, advances CH3O* → H2CO* → HCOO* → COO*, and releases the products H2, H2O, and CO2 consecutively.

The effects of an innovative pulping technique of synchronously pulping and gelatinizing treatment on raw materials properties, oenological parameters, fermentation process, and flavor characteristics of glutinous rice wine.

Liquid-state fermentation has been increasingly applied in the industrial glutinous rice wine (GRW) production. However, products brewed by this emerging technique possess some deficiencies in flavor quality. Therefore, this study firstly developed and optimized an innovative pulping technique by the synchronously pulping and gelatinizing treatment (Process I) to improve GRW flavor quality, and then revealed the influences of Process I on raw materials properties, oenological parameters, fermentation process, and flavor characteristics of GRW. Results show that Process I significantly (p < 0.05) enriched the soluble solid and crude protein content of glutinous rice milk by improving gelatinization degree and pulping efficiency, which consequently enhanced the microbial growth, glycolysis, and protein decomposition during the GRW fermentation process. GC-MS analysis shows that Process I sequentially significantly (p < 0.05) enhanced the esterification and Ehrlich or Harrison pathway during the fermentation process. This contributed to a higher content of key ester and alcohol compounds. Supplementary Information: The online version contains supplementary material available at 10.1007/s10068-022-01119-7.

Effects of modernized fermentation on the microbial community succession and ethyl lactate metabolism in Chinese baijiu fermentation.

Modernized mechanization and intelligent transformation are the trends of Chinese baijiu industry development. However, these changes affect the operational environment, which lead to the decreased metabolism of esters during baijiu fermentation, especially for ethyl lactate. Ethyl lactate is an important flavor compound in most types of baijiu, which is mainly produced by esterification of lactic acid and ethanol. However, considerably less is known about the dynamic microbial succession related to ethyl lactate metabolism during the modernized baijiu fermentation process. In this study, we investigated the lactic acid bacteria, yeast and mold community succession and ethyl lactate metabolism during baijiu fermentation. Results showed that fermentation mode had a significant effect on lactic acid and ethyl lactate metabolism (p < 0.001). Specifically, the accumulation of lactic acid in modernized process was 50% lower than that in traditional process (23.22 ± 7.41 g/kg versus 33.92 ± 2.32 g/kg fermented grains). The accumulation of ethyl lactate in the modernized baijiu fermentation process (9.46 ± 1.78 g/kg fermented grains) was significantly lower than that in traditional baijiu fermentation process (37.10 ± 5.86 g/kg fermented grains). Moreover, Illumina Miseq sequencing showed 11 lactic acid bacteria OTUs, 6 yeast OTUs and 4 mold OTUs were abundant during fermentation. Compared with traditional baijiu fermentation process, modernized process led to more Lactobacillus and Candida, but less Pichia, Aspergillus, Rhizomucor and Rhizopus during fermentation. Based on the redundancy analysis and correlation network analysis, our study showed the metabolism of ethyl lactate mainly related to the activities of Pichia, Aspergillus, Rhizomucor and Rhizopus, especially for Rhizomucor and Rhizopus. This study revealed that the regulation of Pichia, Aspergillus, Rhizomucor Rhizopus and Candida might be an effective orientation for adjusting the metabolism of ethyl lactate during modernized baijiu fermentation.

Computational insight into biotransformation of halophenols by cytochrome P450: Mechanism and reactivity for epoxidation.

Halophenols (XPs) have aroused great interests due to their high toxicity and low biodegradability. Previous experimental studies have shown that XPs can be catalytically transformed into epoxides and haloquinones by cytochrome P450 enzymes (CYPs). However, these metabolites have never been detected directly. Moreover, the effects of the reaction site and the type and number of halogen substituents on the biotransformation reactivity of halophenols still remain unknown. In this work, we performed density functional theory (DFT) calculations to simulate the CYP-mediated biotransformation of 36 XPs with mono-, di-, and tri-halogen (F, Cl, and Br) substitutions to unravel the mechanism and relevant kinetics of XPs epoxidation. The whole epoxidation process consists of initial rate-determining O-addition and subsequent ring-closure steps. The simulation results show that the epoxidation in low-spin (LS) state is kinetically preferred over that in high-spin (HS) state, and the formation of epoxide metabolite is strongly exothermic. For all XPs, the epoxidation reactivity follows the order of ortho/para O-addition > meta O-addition. Moreover, the O-addition with higher energy barriers roughly corresponds to chlorophenols and fluorophenols with more halogen atoms. Compared with dichlorophenols, the additional ortho-Cl substitution on trichlorophenols can slightly increase the energy barriers of meta O-addition. By contrast, the additional inclusion of an ortho-Cl to monochlorophenols enhances the meta O-addition reactivity of dichlorophenols. Overall, the present work clarifies the biotransformation routes of XPs to produce epoxides, and identifies the key factors affecting the epoxidation reactivity, which are beneficial in understanding comprehensively the metabolic fate and toxicity of XPs.

Identification of Two Myrosinases from a Leclercia adecarboxylata Strain and Investigation of Its Tolerance Mechanism to Glucosinolate Hydrolysate.

Glucosinolates (GSLs), secondary metabolites synthesized by cruciferous plants, can be hydrolyzed by myrosinase into compounds, such as isothiocyanates (ITCs), with various bioactivities. Thus, myrosinase plays an important role in the utilization of GSLs. We isolated a bacterial strain, which was identified as Leclercia adecarboxylata, from the rhizosphere soil of rape seedlings and identified two myrosinase genes and an ITC hydrolase gene. Both myrosinases are intracellular and have 658 amino acid residues. Via molecular docking and chemical modification assays investigating the active sites of the myrosinases, arginine was found to be essential for their catalytic activity. Transcriptomic analysis of the response to sinigrin revealed significant up-regulation of some genes involved in allyl-ITC detoxification, with metallo-ß-lactamase 3836 having the highest fold change. Thus, we discovered two myrosinases from L. adecarboxylata and demonstrated that the mechanism of tolerance of the bacterium to allyl-ITC likely involved metallo-ß-lactamase activity.

Imidazoline Gemini Surfactants as Corrosion Inhibitors for Carbon Steel X70 in NaCl Solution.

The Gemini imidazoline surfactants were synthesized from a series of saturated fatty acids. Electrochemical impedance spectroscopy (EIS), polarization curve, and quantum chemistry methods were used to study the corrosion inhibition behavior of Gemini imidazoline surfactants for X70 carbon steel in NaCl solution. Results reveal that such kind of surfactants has an outstanding inhibition effect on carbon steel X70 in NaCl solution and that the restrained efficiency of Gemini imidazoline in an alkaline solution is better than that in a neutral solution. The shorter the carbon chain length, the higher the suppressive efficiency. The higher the concentration of Gemini imidazoline surfactant, the better the inhibition effect.

Chloroplast genome sequence of a yellow colored rice (Oryza sativa L.): insight into the genome structure and phylogeny.

Colored rice is gaining popularity due to its use in creative agriculture and the value of healthy consumption. However, the quality and yield characteristics of most rice varieties still need to be improved. Revealing the genetic background of colored rice is of great significance to promote crop improvement. Here, the completed chloroplast (cp) genome sequence of yellow colored Oryza sativa voucher HSAGSDYD1802 was sequenced and reported. It was a 134,502 bp circular DNA with a typical quadripartite structure, consisting of two reverse repeat regions (IRa and IRb, 20,804 bp) separated by a large single-copy region (LSC, 80,547 bp) and a small single-copy region (SSC, 12,347 bp). The total GC content was 39%. The cp genome encoded 146 genes, containing 100 protein-coding genes, 8 rRNAs, and 38 tRNA genes. Phylogenetic analysis indicated that O. sativa voucher HSAGSDYD1802 was closely related to O. sativa L. TN1, RP Bio-226 and IR8. This study enriches the genetic information of colored rice and is helpful for future molecular breeding.

Mechanistic Insights into the Oxidative Rearrangement Catalyzed by the Unprecedented Dioxygenase ChaP Involved in Chartreusin Biosynthesis.

ChaP is a non-heme iron-dependent dioxygenase belonging to the vicinal oxygen chelate (VOC) enzyme superfamily that catalyzes the final α-pyrone ring formation in the biosynthesis of chartreusin. In contrast to other common dioxygenases, for example, 2,3-catechol dioxygenase which uses the dioxygen molecule as the oxidant, ChaP requires the flavin-activated oxygen (O22-) as the equivalent. Previous experiments showed that the ChaP-catalyzed ring rearrangement contains two successive C-C bond cleavages and one lactonization; however, the detailed reaction mechanism is unknown. In this work, on the basis of the recently obtained crystal structure of ChaP, the computational model was constructed and the catalytic mechanism of ChaP was explored by performing quantum mechanical/molecular mechanical (QM/MM) calculations. Our calculation results reveal that ChaP uses the proximal oxygen in iron-coordinated HOO- to attack the carbonyl carbon of the substrate, whereas the previous proposal that Asp49 acts as a base to deprotonate the iron-coordinated HOO- to generate O22- is unlikely. In the first stage reaction, owing to the coordination of the substrate with iron, the substrate is activated by accepting an electron from iron and the resulting oxy-radical intermediate formed by O-O cleavage can easily trigger the ring rearrangement. In the final decarboxylation, the phenolic anion of the substrate cooperatively accepts the proton of iron-coordinated HOO- to facilitate the attack of the distal oxygen, and the proton-coupled electron transfer (PCET) from the substrate to the FeIV═O plays a key role for the decarboxylation. These findings may provide useful information for understanding the ChaP-catalyzed oxidative rearrangement and other flavin-dependent non-heme dioxygenases.

Mechanism of Uncoupled Carbocyclization and Epimerization Catalyzed by Two Non-Heme Iron/α-Ketoglutarate Dependent Enzymes.

The non-heme iron/α-ketoglutarate dependent enzymes SnoK and SnoN from Streptomyces nogalater are involved in the biosynthesis of anthracycline nogalamycin. Although they have similar active sites, SnoK is responsible for carbocyclization whereas SnoN solely catalyzes the hydroxyl epimerization. Herein, we performed docking, molecular simulations, and a series of combined quantum mechanics and molecular mechanics (QM/MM) calculations to illuminate the mechanisms of two enzymes. The catalytic reactions of two enzymes occur on the quintet state surface. For SnoK, the whole reaction includes two separated hydrogen-abstraction steps and one radical addition, and the latter step is calculated to be rate limiting with an energy barrier of 21.7 kcal/mol. Residue D106 is confirmed to participate in the construction of the hydrogen bond network, which plays a crucial role in positioning the bulky substrate in a specific orientation. Moreover, it is found that SnoN is only responsible for the hydrogen abstraction of the intermediate, and no residue was suggested to be suitable for donating a hydrogen atom to the substrate radical, which further confirms the suggestion based on experiments that either a cellular reductant or another enzyme protein could donate a hydrogen atom to the substrate. Our docking results coincide with the previous structural study that the different roles of two enzymes are achieved by minor changes in the alignment of the substrates in front of the reactive ferryl-oxo species. This work highlights the reaction mechanisms catalyzed by SnoK and SnoN, which is helpful for engineering the enzymes for the biosynthesis of anthracycline nogalamycin.

An aerobic detoxification photofermentation by Rhodospirillum rubrum for converting soy sauce residue into feed with moderate pretreatment.

This paper reports an effective process for converting soy sauce residue into feeds by combining moderate acid hydrolysis and ammonization with Rhodospirillum rubrum fermentation. After pretreatment with dilute sulfuric or phosphoric acid (1%, w/w) at 100 °C, materials were subjected to fermentation under several gases (N2, CO2, and air) and different light intensities in a 2-L fermentor. Following sulfuric acid treatment, the true protein increased from 188 to 362 g kg-1 and the crude fiber decreased from 226 to 66 g kg-1 after fermentation at 0.5 L min-1 L-1 of air flow and a light intensity of 750 lx and following phosphoric acid treatment, the true protein increased by 90% and the crude fiber decreased by 67% after fermentation at 0.6 L min-1 L-1 of air flow and a light intensity of 600 lx Other contents, including crude fat, crude ash, phosphorus, sulfur, sulfur-containing amino acids, sodium chloride, and calcium, were also improved for use as feed. Meantime, some toxic substances, including furfural, hydroxymethylfurfural (5-HMF), acetic acid, phenol, and cresol, which were produced by the pretreatments, could be removed by 12-32, 5-8, 49-53, 7-8, and 7-8%, respectively; and total sugars, glucose, and xylose could be utilized by 68-69, 71-72, and 63-67% respectively. The quality of soy sauce residue is improved for use as feed and some toxic substances can be decreased via the R. rubrum fermentation.

QM/MM studies on the calcium-assisted ß-elimination mechanism of pectate lyase from bacillus subtilis.

Pectate lyase utilizes the anti-ß-elimination chemistry to catalyze the cleavage of α-1,4 glycosidic bond between D -galacturonate regions during the degradation of plant polysaccharide pectin. We report here detailed mechanistic studies of the Bacillus subtilis pectate lyase (BsPel) using QM/MM calculations. It was found that the residue Arg279 serves as the catalytic base to abstract the α-proton from C52 atom of substrate Ada2 subsite, forming an unstable carbanion intermediate. The glycosidic bond of this intermediate is scissile to generate the 4,5-unsaturated digalacturonate product and a negatively charged ß-leaving group. Two active site residues (Lys247 and Arg279) and two Ca2+ ions (Ca2 and Ca3) form hydrogen-bonding and coordination interactions with C52 COO- of Ada2, respectively, which facilitate the proton abstraction and stabilize the generated carbanion intermediates. Arg284 is not the potential proton donor to saturate the leaving group. Actually, the proton source of leaving group is the solvent water molecule rather than any active site acidic residues. In addition, the calculation results suggest that careful selections of QM- and Active-regions are essential to accurately explore the enzymatic reactions. Proteins 2016; 84:1606-1615. © 2016 Wiley Periodicals, Inc.

Quantum Mechanics and Molecular Mechanics Study of the Catalytic Mechanism of Human AMSH-LP Domain Deubiquitinating Enzymes.

Deubiquitinating enzymes (DUBs) catalyze the cleavage of the isopeptide bond in polyubiquitin chains to control and regulate the deubiquitination process in all known eukaryotic cells. The human AMSH-LP DUB domain specifically cleaves the isopeptide bonds in the Lys63-linked polyubiquitin chains. In this article, the catalytic mechanism of AMSH-LP has been studied using a combined quantum mechanics and molecular mechanics method. Two possible hydrolysis processes (Path 1 and Path 2) have been considered. Our calculation results reveal that the activation of Zn(2+)-coordinated water molecule is the essential step for the hydrolysis of isopeptide bond. In Path 1, the generated hydroxyl first attacks the carbonyl group of Gly76, and then the amino group of Lys63 is protonated, which is calculated to be the rate limiting step with an energy barrier of 13.1 kcal/mol. The energy barrier of the rate limiting step and the structures of intermediate and product are in agreement with the experimental results. In Path 2, the protonation of amino group of Lys63 is prior to the nucleophilic attack of activated hydroxyl. The two proton transfer processes in Path 2 correspond to comparable overall barriers (33.4 and 36.1 kcal/mol), which are very high for an enzymatic reaction. Thus, Path 2 can be ruled out. During the reaction, Glu292 acts as a proton transfer mediator, and Ser357 mainly plays a role in stabilizing the negative charge of Gly76. Besides acting as a Lewis acid, Zn(2+) also influences the reaction by coordinating to the reaction substrates (W1 and Gly76).

Effects of inoculation of commercial starter cultures on the quality and histamine accumulation in fermented sausages.

To meet the requirements of high-quality safe products, starter cultures are used to produce fermented sausages. The effects of 3 commercial starter cultures, namely SM-194, T-SPX, and SM-181, on histamine accumulation and quality parameters including microbial quality, pH, water activity, and total volatile base nitrogen, as well as the color and texture properties, were evaluated during the fermentation and ripening of fermented sausages. Although initial counts of Escherichia coli, Enterobacteriaceae, and Pseudomonas were similar in the 4 batches, the growth of these microorganisms was significantly inhibited (P < 0.05) in batches SM-194, T-SPX, and SM-181 throughout the fermentation and ripening period. The counts of E. coli, Enterobacteriaceae, and Pseudomonas increased to maximum levels of 3.89, 4.41, and 5.15 log10 colony forming units/g in the control sausages, respectively. At the end of ripening, the levels of histamine were 8.85, 0.32, 7.82, and 3.18 mg/kg for batches C, SM-194, T-SPX, and SM-181, respectively. The results revealed that commercial starter cultures, particularly starter cultures SM-194 and SM-181, made a great contribution to histamine reduction. In addition, batches inoculated with starter cultures showed a stronger acidification and lower level of total volatile base nitrogen than the control sample during production (P < 0.05). In conclusion, it seems that the inoculation of commercial starter cultures, particularly starter cultures SM-194 and SM-181, contributes to improving microbial quality, hygienic quality and food safety of fermented sausages.

A QM/MM study of the reaction mechanism of (R)-hydroxynitrile lyases from Arabidopsis thaliana (AtHNL).

Hydroxynitrile lyases (HNLs) catalyze the conversion of chiral cyanohydrins to hydrocyanic acid (HCN) and aldehyde or ketone. Hydroxynitrile lyase from Arabidopsis thaliana (AtHNL) is the first R-selective HNL enzyme containing an α/ß-hydrolases fold. In this article, the catalytic mechanism of AtHNL was theoretically studied by using QM/MM approach based on the recently obtained crystal structure in 2012. Two computational models were constructed, and two possible reaction pathways were considered. In Path A, the calculation results indicate that the proton transfer from the hydroxyl group of cyanohydrin occurs firstly, and then the cleavage of C1-C2 bond and the rotation of the generated cyanide ion (CN(-)) follow, afterwards, CN(-) abstracts a proton from His236 via Ser81. The C1-C2 bond cleavage and the protonation of CN(-) correspond to comparable free energy barriers (12.1 vs. 12.2 kcal mol(-1)), suggesting that both of the two processes contribute a lot to rate-limiting. In Path B, the deprotonation of the hydroxyl group of cyanohydrin and the cleavage of C1-C2 bond take place in a concerted manner, which corresponds to the highest free energy barrier of 13.2 kcal mol(-1). The free energy barriers of Path A and B are very similar and basically agree well with the experimental value of HbHNL, a similar enzyme of AtHNL. Therefore, both of the two pathways are possible. In the reaction, the catalytic triad (His236, Ser81, and Asp208) acts as the general acid/base, and the generated CN(-) is stabilized by the hydroxyl group of Ser81 and the main-chain NH-groups of Ala13 and Phe82.

H(+) -ATPase-defective variants of Lactobacillus delbrueckii subsp. bulgaricus contribute to inhibition of postacidification of yogurt during chilled storage.

UNLABELLED: Continued acid production by Lactobacillus delbrueckii subsp. bulgaricus during the chilled storage of yogurt is the major cause of postacidification, resulting in a short shelf life. Two H(+) -ATPase defective variants of L. delbrueckii subsp. bulgaricus were successfully isolated and their H(+) -ATPase activities were reduced by 51.3% and 34.3%, respectively. It was shown that growth and acid production of variants were remarkably inhibited. The variants were more sensitive to acidic condition and had a significant rate for inactivation of H(+) -ATPase by N, N-dicyclohexylcarbodiimide (DCCD), along with a low H(+) -extrusion, suggesting that H(+) -ATPase is direct response for H(+) -extrusion. In addition, the variants were also more sensitive to NaCl, while H(+) -ATPase activities of variants and parent strain were significantly enhanced by NaCl stress. Obviously, H(+) -ATPase might be involved in Na(+) transportation. Furthermore, variants were inoculated in fermented milk to ferment yogurt. There was no significant difference in flavor, whereas the postacidification of yogurt during chilled storage was remarkably inhibited. It is suggested that application of L. delbrueckii subsp. bulgaricus with reduced H(+) -ATPase activity in yogurt fermentation is one of effect, economic and simple avenues of inhibiting postacidification of yogurt during refrigerated storage, giving a longer shelf life. PRACTICAL APPLICATION: During yogurt fermentation, continued acid production by Lactobacillus delbrueckii subsp. bulgaricus during the chilled storage of yogurt leads to milk fermentation with high postacidification, resulting in a short shelf life. In this work, 2 acid-sensitive variant strains of L. delbrueckii subsp. bulgaricus were isolated. The characteristics related to H(+) -ATPase were compared and it was observed that milk fermented by the variants had lower postacidification, giving a longer shelf life. Application of L. delbrueckii subsp. bulgaricus with reduced H(+) -ATPase activity in yogurt fermentation might be one of effect, economic and simple avenues of inhibiting yogurt postacidification during chilled storage, giving a longer shelf life.