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1.
J Agric Food Chem ; 69(40): 12002-12011, 2021 Oct 13.
Artigo em Inglês | MEDLINE | ID: mdl-34590865

RESUMO

Xylitol is a widely used natural sweetener for the reduction of excessive sugar consumption. However, concerns of xylitol consumption existed as it is a highly permeable substance in the colon that could cause diarrhea and other adverse symptoms. To assess the relationship between xylitol dosage and diarrhea, especially the influences of diarrhea on physiological characteristics, the immune system, and gut microbiota in rats, the control, low-dose (L), medium-dose (M), and high-dose (H) groups were fed with 0, 1, 3, and 10% of xylitol, respectively, correspondingly for 15 days, followed by a 7-day recovery. Only medium- and high-dose xylitol would cause diarrhea in rats. Quantitative imaging of colonic tissue and the expression levels of proinflammatory factors revealed a higher degree of immune responses in the rats from H groups but statistically stable in M groups, despite that light diarrhea was observed. A shift of the gut microbiota composition was observed in the rats from H groups, including significant decreases of genera Ruminococcaceae and Prevotella and a notable increase and colonization of Bacteroides, accompanied with changes of short-chain fatty acid production. Tolerance and adaptation to xylitol consumption were observed in a dose-dependent manner. Our findings demonstrate that diarrhea caused by the high dosage of xylitol can exert distinctive changes on gut microbiota and lay the foundation to explore the mechanism underlying the shift in gut microbiota composition.


Assuntos
Microbioma Gastrointestinal , Animais , Diarreia , Ácidos Graxos Voláteis , Intestinos , Ratos , Xilitol
3.
Bioprocess Biosyst Eng ; 44(1): 67-79, 2021 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-32772153

RESUMO

To develop new cellulases for efficient utilization of the lignocellulose, an endoglucanase (CoCel5A) gene from Colletotrichum orchidophilum was synthesized and a recombinant Pichia pastoris GS115/pPIC9K/cocel5A was constructed for secretory expression of CoCel5A. After purification, the protein CoCel5A was biochemically characterized. The endoglucanase CoCel5A exhibited the optimal activity at 55-75 °C and high thermostability (about 85% residual activity) at the temperature of 55 °C after incubation for 3 h. The highest activity of CoCel5A was detected when 100 mM citric acid buffer (pH 4.0-5.0) was used and excellent pH stability (up to 95% residual activity) was observed after incubation in 100 mM citric acid buffer (pH 3.0-6.0) at 4 °C for 24 h. Carboxymethyl cellulose sodium salt (n = approx. 500) (CMC) and ß-D-glucan were the best substrates for CoCel5A among the tested substrates. The kinetic parameters Vmax, Km, and Kcat/Km values against CMC were 290.70 U/mg, 2.65 mg/mL, and 75.67 mL/mg/s, respectively; and 228.31 U/mg, 2.06 mg/mL, and 76.45 mL/mg/s against ß-D-glucan, respectively, suggesting that CoCel5A has high affinity and catalytic efficiency. These properties supported the potential application of CoCel5A in biotechnological and environmental fields.


Assuntos
Celulase/química , Colletotrichum/enzimologia , Proteínas Fúngicas/química , Celulase/genética , Clonagem Molecular , Colletotrichum/genética , Estabilidade Enzimática , Proteínas Fúngicas/genética , Concentração de Íons de Hidrogênio , Pichia/genética , Pichia/metabolismo , Proteínas Recombinantes/química , Proteínas Recombinantes/genética
4.
J Agric Food Chem ; 68(44): 12393-12399, 2020 Nov 04.
Artigo em Inglês | MEDLINE | ID: mdl-33095018

RESUMO

Sugar alcohols are the prominent alternatives of sugars in food, medical, and health industries. The ruthenium supported on multiwalled carbon nanotubes (Ru/MWCNTs) catalysts were prepared based on the Ru valence regulation strategy and applied for selective sugar hydrogenation to prepare various sugar alcohols including xylitol, arabinitol, sorbitol, mannitol, and galactitol for the first time, with high selectivity (>99.0%) and yield (>98.0%) under mild conditions (≤110 °C, 3.0 MPa H2 pressure). The hydrogenation reaction of xylose was further optimized and under mild conditions (100 °C, 3.0 MPa H2 pressure, and 500 rpm), which were lower than ever reported for high efficient synthesis of xylitol, 99.8% xylose conversion and 99.0% xylitol yield were achieved after 120 min of reaction.


Assuntos
Rutênio/química , Álcoois Açúcares/química , Açúcares/química , Catálise , Hidrogenação , Manitol/química , Nanotubos de Carbono/química , Sorbitol/química , Xilitol/química
5.
J Biosci Bioeng ; 126(2): 176-182, 2018 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-29627319

RESUMO

Glucose isomerase (GI) responsible for catalyzing the isomerization from d-glucose to d-fructose, was an important enzyme for producing high fructose corn syrup (HFCS). In a quest to prepare HFCS at elevated temperature and facilitate enzymatic recovery, an effective procedure for whole cell immobilization of refractory Thermus oshimai glucose isomerase (ToGI) onto Celite 545 using tris(hydroxymethyl)phosphine (THP) as crosslinker was established. The immobilized biocatalyst showed an activity of approximate 127.3 U/(g·immobilized product) via optimization in terms of cells loading, crosslinker concentration and crosslinking time. The pH optimum of the immobilized biocatalyst was displaced from pH 8.0 of native enzyme to neutral pH 7.0. Compared with conventional glutaraldehyde (GLU)-immobilized cells, it possessed the enhanced thermostability with 70.1% residual activity retaining after incubation at 90°C for 72 h. Moreover, the THP-immobilized biocatalyst exhibited superior operational stability, in which it retained 85.8% of initial activity after 15 batches of bioconversion at 85°C. This study paved a way for reducing catalysis cost for upscale preparation of HFCS with higher d-fructose concentration.


Assuntos
Aldose-Cetose Isomerases , Enzimas Imobilizadas , Xarope de Milho Rico em Frutose/metabolismo , Temperatura Alta , Fosfinas/química , Aldose-Cetose Isomerases/química , Aldose-Cetose Isomerases/metabolismo , Reagentes para Ligações Cruzadas/química , Reagentes para Ligações Cruzadas/farmacologia , Enzimas Imobilizadas/química , Enzimas Imobilizadas/metabolismo , Frutose/química , Frutose/metabolismo , Glucose/química , Glucose/metabolismo , Xarope de Milho Rico em Frutose/química , Concentração de Íons de Hidrogênio , Fosfinas/metabolismo , Fosfinas/farmacologia
6.
Appl Biochem Biotechnol ; 183(1): 293-306, 2017 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-28285356

RESUMO

Glucose isomerase is the important enzyme for the production of high fructose corn syrup (HFCS). One-step production of HFCS containing more than 55% fructose (HFCS-55) is receiving much attention for its industrial applications. In this work, the Escherichia coli harboring glucose isomerase mutant TEGI-W139F/V186T was immobilized for efficient production of HFCS-55. The immobilization conditions were optimized, and the maximum enzyme activity recovery of 92% was obtained. The immobilized glucose isomerase showed higher pH, temperature, and operational stabilities with a K m value of 272 mM and maximum reaction rate of 23.8 mM min-1. The fructose concentration still retained above 55% after the immobilized glucose isomerase was reused for 10 cycles, and more than 85% of its initial activity was reserved even after 15 recycles of usage at temperature of 90 °C. The results highlighted the immobilized glucose isomerase as a potential biocatalyst for HFCS-55 production.


Assuntos
Aldose-Cetose Isomerases/química , Substituição de Aminoácidos , Enzimas Imobilizadas/química , Proteínas de Escherichia coli/química , Escherichia coli/enzimologia , Xarope de Milho Rico em Frutose/química , Aldose-Cetose Isomerases/genética , Enzimas Imobilizadas/genética , Escherichia coli/genética , Proteínas de Escherichia coli/genética , Mutação de Sentido Incorreto , Proteínas Recombinantes/química , Proteínas Recombinantes/genética
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