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26. Effects of Arabic Gum and Guar Gum, Polysaccharides with Different Viscosity, on the Emulsifying Properties of Myofibrillar Protein

Author

MIAO Yuyan, CAO Yan, LI Jingzhi, WU Mangang, WANG Qingling, GE Qingfeng, YU Hai

Subjects
myofibrillar protein, arabic gum, guar gum, emulsion, interfacial protein, rheological properties, Food processing and manufacture, TP368-456
Abstract

The effects of adding different amounts (0.1%–0.5%) of arabic gum (AG) or guar gum (GG), natural polysaccharides with similar molecular mass but different viscosity, on the emulsifying properties of myofibrillar protein (MP) were investigated. The results showed that both AG and GG could significantly improve the emulsifying properties of MP, and AG was more effective in improving the emulsifying activity, while GG was more conducive to the emulsion stability. Both emulsifying activity index (EAI) and emulsion stability index (ESI) initially increased and then decreased with increasing the amount of added polysaccharides, reaching maximum values when 0.3% AG or 0.2% GG was added. Both polysaccharides, especially GG, resulted in a marked reduction of the interfacial protein content. The droplet size of emulsions gradually decreased with increasing the amount of added polysaccharides, and the droplet size distribution became more uniform. When more than 0.3% GG was added, slight flocculation occurred in the emulsions. At the same concentration, GG reduced the droplet size of the emulsions compared to AG. Rheological analysis confirmed that all emulsions were pseudoplastic fluids, exhibiting weak gel properties. AG at low levels (≤ 0.3%) caused a decrease in the viscosity of the emulsions while remarkably increasing the storage modulus. In contrast, the addition of GG significantly increased the apparent viscosity and storage modulus of the emulsions. Compared with AG, the emulsion prepared with GG, with higher viscosity, exhibited greater apparent viscosity and storage modulus, which was more favorable to the emulsion stability.

Published
2023
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49. Discovery, Structure, and Engineering of a cis‐Geranylfarnesyl Diphosphate Synthase.

Author

Li, Fang‐Ru, Wang, Qingling, Pan, Xingming, Xu, Hui‐Min, and Dong, Liao‐Bin

Subjects
*THIAMIN pyrophosphate, *SITE-specific mutagenesis, *PYROPHOSPHATES, *CRYSTAL structure, *ENGINEERING, *PROTEIN engineering
Abstract

cis‐Prenyltransferases (cis‐PTs) catalyze the sequential head‐to‐tail condensation of isopentenyl diphosphate (IPP) to allylic diphosphates, producing mixed E–Z prenyl diphosphates of varying lengths; however, the specific enzymes synthesizing cis‐C25 prenyl diphosphates have not been identified. Herein, we present the discovery and characterization of a cis‐geranylfarnesyl diphosphate synthase (ScGFPPS) from Streptomyces clavuligerus. This enzyme demonstrates high catalytic proficiency in generating six distinct cis‐polyisoprenoids, including three C25 and three C20 variants. We determined the crystal structure of ScGFPPS. Additionally, we unveil the crystal structure of nerylneryl diphosphate synthase (NNPS), known for synthesizing an all‐cis‐C20 polyisoprenoid. Comparative structural analysis of ScGFPPS and NNPS has identified key differences that influence product specificity. Through site‐directed mutagenesis, we have identified eight single mutations that significantly refine the selectivity of ScGFPPS for cis‐polyisoprenoids. Our findings not only expand the functional spectrum of cis‐PTs but also provide a structural comparison strategy in cis‐PTs engineering. [ABSTRACT FROM AUTHOR]

Published
2024
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50. Characterization of Degraded Konjac Glucomannan from an Isolated Bacillus licheniformis Strain with Multi-Enzyme Synergetic Action.

Author

Zhang, Xueting, Ding, Jieqiong, Liao, Minghong, Meng, Xin, Fu, Yubiao, Huang, Linjuan, Wang, Zhongfu, and Wang, Qingling

Subjects
KONJAK, BACILLUS licheniformis, EXTRACELLULAR enzymes, MICROBIAL contamination, SCANNING electron microscopy, POLYSACCHARIDES
Abstract

The large molecular weight and high viscosity of natural konjac glucomannan (KGM) limit its industrial application. Microbial degradation of low-molecular-weight KGM has health benefits and various biological functions; however, the available KGM strains used in the industry have microbial contamination and low degradation efficiencies. Therefore, exploring novelly adaptable strains is critical for industrial processes. Here, the Bacillus licheniformis Z7-1 strain isolated from decaying konjac showed high efficiency for KGM degradation. The monosaccharide composition of the degradation products had a reduced molar ratio of mannose to glucose, indicating that Z7-1 preferentially degraded glucose in KGM. The degraded component was further characterized by ESI-MS, Fourier-transform infrared spectroscopy (FT-IR), and scanning electron microscopy (SEM), and it also exhibited good antibacterial activity against various food-spoilage bacteria. Genome sequencing and zymolytic analysis revealed that abundant carbohydrate-active enzymes exist in the Z7-1 genome, with at least five types of extracellular enzymes responsible for KGM degradation, manifesting multi-enzyme synergetic action. The extracellular enzymes had significant thermal stability, indicating their potential application in industry. This study provides an alternative method for obtaining low-molecular-weight KGM with antibacterial functions and supports foundational knowledge for its development as a biocatalyst for the direct conversion of biomass polysaccharides into functional components. [ABSTRACT FROM AUTHOR]

Published
2024
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